Electrical Theory of Grounding Module 1

Grounding Isolated Transmission Lines Module 1 Electrical Theory—Manual Name: ____________________________________ Date: ____________________________________ Field Technical Learning Transmission Lines March, 2013 Version 1.5

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro COPYRIGHT ©AltaLink L.P 2012. These training materials and templates are the property of AltaLink, L.P. and have been provided to the recipient for training purposes on the express understanding that the information contained herein is not to be copied, reproduced or used by any other individual without the expressed written consent of AltaLink. By granting the above permission, AltaLink makes no warranties or representations regarding the quality, accuracy, or fitness for purpose of any part of, or whole of, the provided training materials. Responsibility for application of any of the information contained in these materials, by the recipient or any other individual, shall reside wholly with the user. 2 Copyright

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro TABLE OF CONTENTS NOTICE OF COPYRIGHT ............................................................................................................ 2 TABLE OF CONTENTS................................................................................................................ 3 PRE-REQUISITES....................................................................................................................... 5 TARGET ................................................................................................................................... 5 ESTIMATED TIME TO COMPLETE............................................................................................... 5 INTRODUCTION ....................................................................................................................... 5 Module Learning Objectives........................................................................................................... 6 Testing ............................................................................................................................................ 6 Module Scope................................................................................................................................. 6 BASIC ELECTRICAL THEORY ....................................................................................................... 7 Introduction.................................................................................................................................... 7 Learning Objectives ........................................................................................................................ 7 Learning Materials.......................................................................................................................... 7 Reference Materials ....................................................................................................................... 7 Relationship between Voltage, Current, and Resistance (Ohm’s Law) .......................................... 8 Charge and Energy Conservation (Kirchhoff’s Laws)...................................................................... 9 Impact of Grounding in Parallel Circuits....................................................................................... 12 Fault Currents ............................................................................................................................... 17 Ground Potential Rise................................................................................................................... 18 Learning Exercises ........................................................................................................................ 20 STEP AND TOUCH POTENTIAL................................................................................................. 25 Introduction.................................................................................................................................. 25 Learning Objectives ...................................................................................................................... 25 Learning Materials........................................................................................................................ 25 Reference Materials ..................................................................................................................... 25 Effects of Current on the Human Body ........................................................................................ 25 GPR and Step and Touch Potential............................................................................................... 27 Step Potential ............................................................................................................................... 28 Touch Potential............................................................................................................................. 30 Learning Exercises ........................................................................................................................ 31 IDENTIFYING ELECTRICAL HAZARDS ........................................................................................ 34 Learning Objectives ...................................................................................................................... 34 Learning Materials........................................................................................................................ 34 Reference Materials ..................................................................................................................... 34 Table of Contents 3

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Hazards of Induction..................................................................................................................... 35 Capacitive Induction ..................................................................................................................... 35 Magnetic Induction ...................................................................................................................... 38 Static Induction............................................................................................................................. 41 Sources of Accidental Line Energization....................................................................................... 41 Learning Exercises ........................................................................................................................ 45 APPENDIX A...........................................................................ERROR! BOOKMARK NOT DEFINED. LEARNING EXERCISES ANSWER KEY ........................................................................................ 47 Basic Electrical Theory ......................................................................Error! Bookmark not defined. LEARNING EXERCISES ANSWER KEY ........................................................................................ 50 Step and Touch Potential .................................................................Error! Bookmark not defined. LEARNING EXERCISES ANSWER KEY ........................................................................................ 51 Identification of Electrical Hazards............................................................................................... 51 APPENDIX B ........................................................................................................................... 52 CIRCUIT CALCULATIONS ......................................................................................................... 52 Circuit 1 – No Portable Protective Grounds Installed................................................................... 52 Circuit 2 – One Portable Protective Ground Installed .................................................................. 53 Circuit 3 – Two Portable Protective Grounds Installed ................................................................ 53 4 Pre-Requisites

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro PRE-REQUISITES There is no training pre-requisite for this module. TARGET  Second-year apprentice or journeyman power line technician  Electrical engineers and technologists dealing with isolated transmission lines or facilities ESTIMATED TIME TO COMPLETE This module is intended as a self study and should take approximately four hours to complete. INTRODUCTION This course is intended to help you identify and mitigate the risk of electrical hazards when working on isolated transmission lines. Since every situation is unique, it is not possible to define a single hazard mitigation strategy for each scenario. This course gives you the background and tools necessary to evaluate a work site for electrical hazards and determine the appropriate work systems and practices. The course includes the following modules:  Electrical Theory (self-study)  Grounding Practices (instructor-led)  Grounding Tools (instructor-led)  Modified No Bond Zone Work Method (instructor-led)  Grounding Application (instructor-led) After completing this course, you will be able to: 1. Apply the concepts of basic electricity to grounding applications. 2. Recognize situations in which there may be electrical hazards. 3. Identify the electrical hazards. 4. Determine appropriate work methods, techniques, and tools to reduce hazards. Pre-Requisites 5

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Module Learning Objectives This module describes basic electrical theory in relation to grounding. Understanding the concepts related to basic electrical theory will help form a foundation to better learn and comprehend the majority of tasks associated with grounding. If you understand the theory, you will think electrically instead of mechanically when using grounding methods. After completing this module, you will be able to:  Apply the concepts of basic electricity in future learning modules, as well as apply them to grounding applications. Testing After completing this module, you will be tested on your understanding of the content. The test will be given on the first day of the instructor-led portion of the course. Module Scope This manual contains the following sections:  Basic Electrical Theory  Step and Touch Potential  Identifying Electrical Hazards 6 introduction

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro BASIC ELECTRICAL THEORY Introduction In order to understand the theory of equipotential bonding and grounding (EB&G) and how it helps protect you from the hazards of high voltage, it is important to review basic electrical theory and to understand how current divides and voltage differences are created. This is easiest understood through a review of Ohm’s law and Kirchhoff’s Current and Voltage laws. It is important to understand these laws as they relate to electricity and our physical surroundings. Learning Objectives 1. Explain Ohm's Law and its relationship to grounding. 2. Explain Kirchhoff’s Laws and their relationship to grounding. 3. Describe fault currents and the factors that influence their magnitude. 4. Explain ground potential rise. Learning Materials  None required Reference Materials  AL-ALL-90001 Working on Isolated Transmission Facilities  CHANCE® Encyclopedia of Grounding 07-0801 Section 5 Basic Electrical Theory 7

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Relationship between Voltage, Current, and Resistance (Ohm’s Law) For a given value of resistance, a linear relationship exists between the applied voltage and the resulting current. An increase in voltage will produce a proportional increase in current. That is, for any given value of resistance, doubling the voltage applied will double the current. This relationship is known as Ohm’s Law and is represented by the formula I = V/R, where:  V = Voltage in volts (V)  I = Current in amperes (amps)  R = Resistance in ohms (Ω)  E = Electromotive force, which is measured in voltage(E and V are used interchangeably) If any two of these electrical elements are known, the third can be calculated using basic algebra. Depending on which element is unknown, the following calculations can be used:  I=V/R  V= I x R  R=V/I Figure 1 visually represents this relationship and can help you remember the equations. The line dividing the left and right sections represents multiplication, and the line dividing the top and bottom sections represents division. To find the value that is missing, cover the symbol for that value in the diagram and perform the indicated operation between the two remaining symbols. V = Voltage I = Current R = Resistance Figure 1. Voltage, Current and Resistance 8 Basic Electrical Theory

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Example Using Ohm’s Law with reference to the circuit in Figure 2, the current (I) can be determined if the voltage and resistance are known. Figure 2. Current In Figure 2, a 6 volt battery and a 3 ohm resistor are connected in a circuit. Using Ohm’s Law to calculate the current: I = V/R = 6v/3Ω = 2 amps If the current in a circuit is measured at 20 amps and the known resistance is 6 Ω, the voltage drop across the resistor would be: V = I x R = 20 amps x 6 Ω = 120 volts. Charge and Energy Conservation (Kirchhoff’s Laws) Kirchhoff’s laws include the Current Law and the Voltage Law. The Current Law states that the sum of all the currents entering a node equals the sum of all the currents leaving the node. In Figure 3, we see that total current entering the node is equal to the sum of the currents leaving the node. Figure 3. Kirchhoff’s Current Law ITotal = A + B + C Kirchhoff's Voltage Law describes the distribution of voltage within a loop of an electric circuit and states that the sum of the voltage (potential) difference in any loop must equal zero. As the charge travels around a loop and arrives at the starting point, it has the same potential as it did when it began, so any increases and decreases in charge along the loop must cancel out for a total change of zero (0). If it didn’t, the potential at the start/end point would have two different values. See Figure 4. Basic Electrical Theory 9

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Figure 4. Kirchhoff's Voltage Law I tot = 4 amps V R1 R1= 5 Ohms VR1 = 4 x 5 = 20V AC Vgen = 120 Volts V R2 R2= 10 Ohms VR2 = 4 x 10 = 40V V R3 R3= 15 Ohms VR3 = 4 x 15 = 60V VSUM = V R1 + V R2 + V R3 + VGEN = 0V VSUM = (4X5) + (4X10) + (4X15) + (-120) = 0V VSUM = (20V) + (40V) + (60V) + (-120V) = 0V Series and Parallel Circuits Components in a circuit may be connected in two fundamental ways—series circuits and parallel circuits. In the series circuit, the components are joined together end to end so that the same current passes from one to the other around one complete path. In the parallel circuit, the current divides across all circuit branches so the same voltage is applied to each circuit branch. There may be multiple components in one circuit branch. Series Circuits In a series circuit, the current is the same throughout the circuit. As the current flows through each component in the circuit, a voltage is developed across the resistance of each component. The sum of the voltage drop must equal the voltage supplying the series loop (Kirchhoff’s Voltage Law). Every current carrying part of a circuit has some resistance. Current flowing through any resistance creates a drop in voltage spread over the resistive component. The circuit current and the drop in voltage will be automatically adjusted based upon the resistance values of each circuit component. The voltages across individual resistances in a series circuit divide proportionally to the value of resistance. 10 Basic Electrical Theory

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Figure 5. Simple Series Circuit Amps Amp = 1.2 AC V = 120 V RVr 1 = 100 ohms Amp = 1.2 Amps I = V/R I = 120 V/100 ohms I = 1.2 amps As current passes through a resistor, a potential difference or voltage is developed across the resistance. The sum of the voltage drop in the circuit will be equal to the total voltage of the source generator. Vr1 = I x R1 Vr1 = 1.2 X 100 Vr1 = 120 volts Parallel Circuits In a parallel circuit, each branch is like a series circuit when considered individually, but when considered as a whole, they are a parallel circuit (see Figure 6). If the resistance of the two paths is equal, the current divides equally. However, if the resistance of the two parallel paths is not equal, the current divides proportionally between the two paths. If one branch has half the value of resistance than the other branch, twice the value of current will flow through the path with the least resistance. So 2/3 of the current will flow through the path with the least resistance and 1/3 will flow through the path with the most resistance. The total resistance of a set of resistors in parallel is found by adding up the reciprocals of the resistance values and then taking the reciprocal of the total: R =Total 1 1 + 1 + 1 ������1 ������2 ������3 A simpler way of calculating total resistance for a parallel circuit with two resistances is the product-over-sum method: RTotal = ������1 × ������2 ������1+ ������2 Basic Electrical Theory 11

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Example A circuit with a resistance of 2 ohms in one path and a resistance of 3 ohms in another path is shown in Figure 6. Figure 6. Parallel Circuit The current through each resistance (R1 and R2) is: (Ohm’s Law I=V/R) I1 = V/R1 I2 = V/R2 I1 = 120 V /2 ohms I2 = 120 V /3 ohms I1 = 60 amps I2 = 40 amps The total current in the circuit is: (Ohm’s Law I=V/R) ITotal = V/RTotal RTotal = (R1 x R2)/(R1 + R2) = (2 x 3)/(2 + 3) ohms = 6/5 = 1.2 ohms ITotal = 120 V / 1.2 ohms = 100 amps As an alternative, the total current can be determined by (Kirchhoff's Current Law): ITotal = I1 + I2 = 60 amps + 40 amps = 100 amps Impact of Grounding in Parallel Circuits Series and parallel circuits exist whenever you work on isolated lines; when you climb a pole, you become part of a circuit. The current and voltages that could potentially flow through the circuit can be controlled in many ways. Applying portable protective grounds is an effective way of reducing the current that could potentially flow through a worker in a circuit. The examples in this section, illustrate how the introduction of portable protective grounds into a circuit impacts the current and voltages in the circuit. 12 Basic Electrical Theory

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro NOTE: Since these examples are for illustration only, it is assumed there is no downlead on the pole. Circuit 1—No Portable Protective Grounds Installed Figure 7 shows a worker contacting a 138 kV phase conductor while working from a wood pole and the equivalent representation as a circuit. There are no portable protective grounds used. Figure 7. Circuit 1—No Portable Protective Grounds Installed In this scenario, the worker is part of a series connection to ground. Therefore, a large amount of current will flow through the worker. It is likely that serious injury or death would occur at such high amperage. NOTE: To see how the currents are calculated for this example, see “: Circuit Calculations” on page 52. Basic Electrical Theory 13

CCContro Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 The important values related to grounding are: Fault will clear slowly because Line fault current seen by protective 24.84 amps there is no trip ground installed. relays for tripping Current is high enough to cause harm to the worker. Current flowing through worker 24.84 amps High voltage across the worker Not a hazard. Voltage across worker 24,840 volts Ground potential rise 497 volts Circuit 2—One Portable Protective Ground Installed Now a portable protective ground is placed on the conductor to a pole band below the worker’s feet. Let’s see how this affects the total fault current, current through the worker, and voltage drop across the worker. Figure 8. Circuit 2—One Portable Protective Ground Installed In this scenario, the portable protective ground is installed parallel to the worker. Since the jumper has a low resistance, almost all of the fault current will flow through it instead of through the worker. The protective relays will see a higher fault current than in the previous scenario because the total resistance to ground is decreased. However, nearly zero current will flow through the worker. 14 Basic Electrical Theory

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro NOTE: To see how the currents are calculated for this example, see “: Circuit Calculations” on page 52. The important values related to grounding are: Fault current increases slightly, but fault will still clear slowly. Line fault current seen by protective 36.03 amps relays for tripping Current through worker 0.0001802 amps The worker is protected. The current through the worker has been reduced from 24 amps to 0.0001802 amps because the current is now flowing through the portable protective ground. Voltage across worker 0.1802 volts GPR 721 volts GPR increased slightly. Circuit 3—Two Portable Protective Grounds Installed Now let’s say a second portable protective ground is placed between the pole band and a ground rod of 2 ohms, 10 meters (32 feet) away from where people on the ground will be working. Let’s see how this affects the total fault current, current through the worker, voltage drop across the worker, the GPR at the pole and GPR at the ground rod. Figure 9. Circuit 3—Two Portable Protective Grounds Installed Basic Electrical Theory 15

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro In this scenario, portable protective grounds are installed that lead directly to a ground rod. This low-resistance path to ground causes the total fault current to be very high. Although the worker is in parallel with a portable protective ground, there is still approximately 20 mA of current through the worker, which is enough to cause intense pain, and for some people, may be past the “let go” threshold (see Table 1. Effects of AC and DC Current, on page 26). An additional hazard in this scenario is a high ground potential rise (GPR). The current through the portable protective grounds and ground rod is very high, which means a large voltage (79 kV) remains to be dissipated in the ground. The voltage gradient developed is a hazard to any workers on the ground in the vicinity of the ground rod. NOTE: To see how the currents are calculated for this example, see “: Circuit Calculations” on page 52. The important values related to grounding: Fault current 3,653.96 amps Increased significantly. Fault will clear quickly. Current through worker 0.01827 amps Painful shock. Voltage across worker 18.27 volts Ground potential rise at the pole 717 volts Ground potential rise at the ground rod 79,598 kV High GPR. If possible, the trip ground should be installed at a location at least 10 meters (32 feet) away from workers on the ground. Summary Voltage across Current through GPR at Pole GPR at Ground Rod Circuit 1: worker worker – RJ1 + RJ2 not installed Circuit 2: 24.8 kV 24.84 amps 497 volts – RJ1 installed + RJ2 not installed Circuit 3: 0.18 volts 0.0001802 amps 721 volts 79.6 kV RJ1 + RJ2 installed 18.27 volts 0.01827 amps 717 volts 16 Basic Electrical Theory

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Fault Currents Load current is primarily limited by the resistance of the loads connected to the transmission system by customers. In contrast, fault current is primarily limited by the source impedance (that is, the resistance between the generator and the fault location). Fault current is generally several times larger in magnitude than the current that normally flows through a circuit. The following factors influence the magnitude of fault current: Factor Effect Principle Transmission system voltage Greater voltage = greater fault current Increase source capacity Transmission source impedance, (that is, bigger battery) that is, impedance from the Greater resistance = smaller fault current generator to the fault location Ohm’s Law with a series Length of line circuit. Size of conductor Longer line = higher line impedance = smaller Ohm’s Law with a series Type of fault (phase-to-phase, fault current circuit. three-phase or phase-to-ground) Ground resistance For example, the closer to a source substation, Ohm’s Law with a series Portable trip ground the shorter the line, the higher the fault circuit. current. Three-phase AC theory Pole or tower resistance Larger conductor = lower resistance = higher Ohm’s Law and Kirchhoff’s fault current Voltage Law Ohm’s Law Three-phase fault = highest fault current1 Ohm’s Law and Kirchhoff’s Single-phase-to-ground = lowest fault current Voltage Law Higher ground resistance = lower fault current = higher ground potential rise Lower trip ground resistance = higher fault current Result: Relays trip the breaker and clear the fault faster Higher pole/tower resistance = lower fault current = higher ground potential rise Three-phase fault current 1 –Although three-phase fault current results in the highest fault current, the fault current flowing to ground, through a portable ground, may be the least amount of fault current. This is because the fault is a balanced fault and the individual current vector sum towards zero. This is similar to the amount of current that would flow in the neutral of a circuit with balanced three-phase loads. Basic Electrical Theory 17

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Ground Potential Rise Ground potential rise (GPR) occurs when a large current flows to earth. When currents of large magnitude enter the earth from a grounding system, the grounding system and the surrounding soil will rise in electrical potential. The maximum GPR is calculated using Ohm’s Law: current multiplied by the impedance of the ground point. GPR is measured relative to a distant point assumed to be at remote earth potential. GPR voltage diminishes very quickly as it moves away from the point at which the current entered the earth, as shown in Figure 10. Figure 10. GPR Voltage Profile The profile will change depending on the following factors:  Magnitude of the current  Number of ground rods and depth of the ground system  Soil resistivity NOTE: GPR creates a touch and step potential hazard. This is discussed in the section “Step and Touch Potential” on page 25. Substations have a very low GPR in comparison to GPR on a transmission line because a substation ground grid has been designed and built to minimize GPR to a set value. Ground Resistance The ground resistance using a single ground rod is influenced by the following factors:  Resistance of the rod and connection to the downlead: <1%  Contact resistance between the rod and earth: 5- 15%  Resistance of the earth: 85-95% 18 Basic Electrical Theory

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Figure 11. Measuring Ground Resistance The ground resistance of ground rods is a function of the diameter and length of the rod. The ground resistance of people is a function of the circular area under each foot. Basic Electrical Theory 19

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Exercise 1A Complete the following exercise. The answers to the exercise “Error! Reference source not found.” on pageError! Bookmark not defined. of this manual. 1. ____ Which calculation is used to determine current in Ohm’s Law? a. I=R/V b. I=VxR c. I=V/R d. I=V-2R 2. ____ Which calculation is used to determine voltage in Ohm’s Law? a. V=R+I b. V=IxR c. V=R/I d. V= I/R 3. ____ Which statement best describes Kirchhoff’s Current Law? a. The sum of the voltage (potential) difference in any loop is always greater than zero. b. The sum of all the currents entering a node equals the sum of all the currents leaving the node. c. The sum of the voltage (potential) difference in any loop must equal zero. d. The sum of all the currents entering a node is less than the sum of all the currents leaving the node. 4. ____ Using Ohm’s Law, if V=20 V and R=5000 Ω, the current (I) is equal to a. 100 mA b. .25 mA c. 4 mA d. 4 A 20 Basic Electrical Theory

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro 5. ____ Using Ohm’s Law, if V= 10 V and I=4 mA, the resistance (R) is equal to a. 6000 Ω b. 2500 Ω c. .250 Ω d. 4000 Ω 6. ____ Using Ohm’s Law, if R = 10000 Ω and I=10 mA, the voltage is equal to a. 1 V b. 100 V c. 20 V d. 10 V 7. ____ What is the difference between fault current and load current? a. Load current is primarily limited by the resistance of the loads connected to the transmission system by customers, whereas fault current is primarily limited by the resistance between the generator and the fault location. b. Load current is generally much greater than fault current. c. Fault current is dependent on the type of customer load connected to the transmission system. d. Fault current is not affected by the transmission line impedance. 8. ____ What effect does transmission system voltage have on the magnitude of fault current? a. Transmission system voltage does not affect fault current. b. The greater the voltage, the lower the fault current. c. The greater the voltage, the greater the fault current. d. Fault current increases exponentially (I2) with an increase in transmission system voltage. 9. ____ What effect does conductor size have on the magnitude of fault current? a. The larger the conductor, the lower the resistance, the higher the fault current. b. The larger the conductor, the higher the resistance, the smaller the fault current. c. The larger the conductor, the lower the resistance, the lower the fault current. d. Conductor size is not a factor in influencing fault current. Basic Electrical Theory 21

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro 10. ____ Which type of fault has the highest fault current? a. phase to phase b. three phase c. phase to ground d. unbalanced phase to phase fault 11. ____ True/False. GPR voltage diminishes very quickly as it moves away from the point at which the current entered the earth. 12. A voltage increase in the earth due to current flow to earth is called ________________________________. 13. Maximum GPR is calculated by multiplying current by the ________________________________. Use the diagram to complete the following questions. 14. What is the total current in the circuit (IT)? __________ 15. What is the current flowing through the portable protective ground (IJI)? __________ 16. What is the current flowing through the worker (IW)? __________ 17. What is the ground potential rise voltage (VG)? __________ 22 Basic Electrical Theory

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Use the diagram to complete the following questions. 18. ____ What is the effect on the circuit of removing the first portable protective ground (J1)? a. Total fault current goes down, current through the worker goes up to dangerous levels, and ground potential rise goes down b. Total fault current goes down, current through the worker goes down, and ground potential rise goes down c. Total fault current goes up, current through the worker goes up, and ground potential rise goes up d. Total fault current goes down, current through the worker goes up, and ground potential rise remains the same 19. ____ What is the effect on the circuit of removing only the second portable protective ground (J2)? a. Total fault current goes down, current through the worker goes up to dangerous levels, and ground potential rise goes down b. Total fault current goes down, current through the worker goes down, and ground potential rise goes down c. Total fault current goes up, current through the worker goes up, and ground potential rise goes up d. Total fault current goes down, current through the worker goes up, and ground potential rise remains the same Basic Electrical Theory 23

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro 20. ____ What is the effect on the circuit of removing both portable protective grounds (J1 and J2)? a. Total fault current goes down, current through the worker goes up to dangerous levels, and ground potential rise goes down b. Total fault current goes down, current through the worker goes down, and ground potential rise goes down c. Total fault current goes up, current through the worker goes up, and ground potential rise goes up d. Total fault current goes down, current through the worker goes up, and ground potential rise remains the same 24 Basic Electrical Theory

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro STEP AND TOUCH POTENTIAL Introduction Step and touch potential is well understood as safety hazards in many situations involving energized power sources. What is not as well understood is that dangerous step and touch voltages can exist on non-energized lines because of electromagnetic coupling, and this is a daily danger for transmission facilities workers. Electrical faults on the transmission system create unique hazards for people on the ground in the area where the fault current enters the ground. These hazards are termed touch and step potential hazards. Understanding and mitigating the hazards of touch and step potential is a fundamental component of protecting workers and the public who are near power lines. In this section, we will examine the effects of current on the body and how touch and step potential situations cause current to flow through the body. Learning Objectives 1. Explain current versus time effects on the body. 2. Explain how a Ground Potential Rise (GPR) gradient creates step potential and touch potential. 3. Define step potential and provide examples of situations that could create this hazard. 4. Define touch potential and provide examples of situations that could create this hazard. Learning Materials  None required Reference Materials  AL-ALL-90001 Working on Isolated Transmission Facilities  CHANCE® Encyclopedia of Grounding 07-0801 Sections 2 and 6  IEEE 524-2003 Guide to the Installation of Overhead Transmission Line Conductors Annex C Effects of Current on the Human Body Electricity flowing through the body can shock, cause involuntary muscle reaction, paralyze muscles, burn tissues and organs, or kill. Shocks can be either steady-state or transient in nature. Although large charges produced by lightning strikes can cause shock, they may or may not produce direct physiological harm because of the transient nature of the current. The typical effects of various electric currents flowing through the body of an average male and female body are given in Table 1. Step and Touch Potential 25

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Table 1. Effects of AC and DC Current Current (mA) Effects Direct Current Alternating Current 60 Hz rms No sensation on hand Men Women Men Women 1.0 0.6 0.4 0.3 Slight tingling—“threshold- 5.2 3.5 1.1 0.7 of-perception” level Shock; uncomfortable, but 9.0 6.0 1.8 1.2 not painful; muscle control not lost Painful shock; muscle 62.0 41.0 9.0 6.0 control not lost—“safe let- go” level for 99.5% of people tested Possible ventricular No data No data 50 No data fibrillation Ventricular fibrillation: Heart No data No data 50-100 67 stops Let-go Current With increasing shock currents, it becomes more difficult for a person to control the muscles in which the current flows. Let-go current is the value of current at which a human holding an energized conductor cannot control his or her muscles enough to release the conductor. The average let-go current is 9 mA for men and 6 mA for women. The let-go currents are chosen as those corresponding to 99.5% probability of not losing muscular control. Currents above the let-go value could lead to muscle contraction in the chest area and can lead to suffocation (respiratory tetanus). Relationship of Electrical Current and Shock Duration The body can withstand high levels of current for a very short period of time and lower levels of current for a longer period of time before going into fibrillation. This relationship between current and the duration of the shock is illustrated in Figure 12. 26 Step and Touch Potential

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Figure 12. Relationship of Current and Duration of Shock Body Resistance Body resistance varies greatly from 100 ohms through values of several thousand ohms when thick calluses are present on skin surfaces. A generally accepted value for body resistance of 1000 ohms is used in determining the current flow through the body. GPR and Step and Touch Potential If a ground-fault current is initiated by breakdown or flashover of an insulator string on an overhead transmission line, current would enter the earth through the footing of steel towers or through any other object connected to the earth. Assuming the earth is homogenous, the current would spread uniformly in concentric circles away from the initial contact point, and the voltage would decrease gradually to zero. Something similar occurs when you drop a stone into water; the ripples get smaller as they get farther away from the centre point. The current flow produces a substantial voltage gradient (voltage drop) as it flows through the surface of the earth. The potential is highest at the point where the current enters the ground and decreases as it radiates from the source. If the potential gradient (drop of voltage with distance) is high, it can injure a person in proximity to the source. When there is a potential difference between a person’s feet (step potential), or between the ground on which a person is standing and a metal object (touch potential), current will flow through the person. Step and Touch Potential 27

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Step Potential Step potential occurs when your feet are apart and you are near an area where electricity is going to ground. Your feet can be at two different voltages. For example, if one foot is nearer the point of contact where the voltage is strongest and the other foot is farther away from the point of contact, the voltage difference between the two points could cause electric current to flow through your body. Essentially, your feet bridge a portion of this voltage drop and create a parallel path for current flow. See Figure 13. Figure 13. Physical Representation of Step Voltage A commonly noted ground potential rise event is the death of cows in a field during a lightning strike. Imagine lightning striking the centre of an open field. The current injected into the earth radiates from the strike point creating voltage gradients on the surface of the earth. A cow standing in the field and facing the lightning strike would have its front hooves closer to the strike point than its rear hooves. This would result in a difference of potential between its front and rear legs, causing current to flow through its body and killing the cow. The voltage across the person’s feet is called step voltage and is determined by the line integral of the voltage gradient over the person’s step width (S) at a distance (X) from the point at which the fault entered the ground. Another way to understand step potential is to relate it to an electrical circuit. See Figure 14. 28 Step and Touch Potential

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Figure 14. Step Potential and Equivalent Circuit a) Physical step potential b) Equivalent circuit As seen from the equivalent electric circuit, the voltage developed across the body is created by the current entering one leg, going across the body and exiting out the other leg. If this current exceeds 50 mA, the heart could go into fibrillation. At a value lower than 50 mA, you may lose muscle control of your legs. Figure 15. Step Potential As seen in Figure 15, Person A standing with both feet together on a single ring of equal potential is at less risk than Person B standing with his feet apart on two rings of unequal potential. Step and Touch Potential 29

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Touch Potential Touch potential is similar to step potential and occurs when different parts of your body contact objects at different voltages and your body becomes “part of the circuit”. This could happen if you were to touch something that is energized with your hand or arm while standing on something at a different voltage or connected to ground. This difference in voltage between the hand contact points and the foot on the ground causes current to flow through your body. For example, in Figure 16, the person’s hand and feet are at a different potential, so current would flow through the person’s body. Figure 16. Touch Potential and Equivalent Circuit a) Physical touch potential b) Equivalent circuit 30 Step and Touch Potential

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Exercise 1B Read the Princeton Pond Incident and then complete the following exercise. The answers to the exercises are in “Error! Reference source not found.” on page Error! Bookmark not defined. of this manual. The case study will be reviewed in class. Princeton Pond Incident In the early morning of October 22nd, one of the Power Company’s 138 kV transmission lines experienced a number of faults prior to holding in an energized state at approximately 4 am. An insulator string on a transmission structure in the Princeton Pond area was damaged with only 2 of 8 discs intact, most likely by vandalism. The repair crew was dispatched and set up under the structure. The outriggers were deployed and grounding equipment made ready. While the crew waited for the foreman to arrive and the protection guarantee to be put in place, it started to snow. The crew decided to wait in the truck. Two crewmembers got into the vehicle, while the victim placed a hot stick in the back of the truck to keep it dry. While he was still outside the truck, the damaged insulators flashed over. Electrical arcs were observed by the crew through the rear window of the truck and an open passenger door. There were a number of recloses of the line, and the flashovers continued intermittently over a one‐minute period. When the arcing ceased, the crew exited the truck and found the victim on the ground at the rear of the vehicle. Emergency responders were contacted immediately, and an ambulance was on the scene within 23 minutes. Sadly, the employee succumbed to his injuries. 1. What caused this accident? Answer: Step and Touch Potential 31

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro 2. What factors increased the danger? Answer: Next, complete the following questions: 3. ____ What could be the effect of 50 mA of alternating current (60 Hz rms) entering a man’s body? a. slight tingling in the body b. shock; uncomfortable, but not painful c. painful shock; muscular control not lost d. ventricular fibrillation 4. ____ What is the relationship between ground fault current and ground potential rise? a. As fault current increases, ground potential rise increases. b. As fault current decreases, ground potential rise increases. c. As fault current increases, ground potential rise decreases. d. There is no relationship between ground fault current and ground potential rise. 5. ____ What factor creates a gradient of voltages away from the point of injection of the current into the ground, thus creating the hazard for step and touch potential? a. ground potential rise b. line impedance c. transmission source impedance d. transmission voltage level 32 Step and Touch Potential

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro 6. ____ What is step potential? a. When each foot is at a different potential and current flows through the body from one foot to the other. b. When a person’s hands and feet are at a different potential and current flows through the body. c. It is the increase in voltage as you move away from the point of fault current entering the earth. d. It is the difference circulatory currents passing through a person’s two feet. 7. ____ When you do not touch conductive objects in an area where fault current can flow, you eliminate which potential hazard? a. magnetic induction b. touch potential c. step potential d. static induction 8. Let-go current is the value of current at which a human holding an energized conductor cannot _______________________________. Step and Touch Potential 33

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro IDENTIFYING ELECTRICAL HAZARDS When working on isolated transmission lines, you must protect against the line being energized from induction or becoming accidentally re-energized. Electrical charges may appear on isolated lines as a result of a combination of the following factors:  Charges induced by electrical and/or magnetic coupling with energized adjacent lines, especially during fault conditions or lightning strikes  Static charge induced on isolated lines due to atmospheric conditions  Isolated lines that are accidentally energized Learning Objectives 1. Describe capacitors and capacitive induction. 2. Describe inductors and magnetic induction. 3. Describe static Induction. 4. Identify and describe possible sources of accidental energization. Learning Materials  None required Reference Materials  AL-ALL-90001 Working on Isolated Transmission Facilities  CHANCE® Encyclopedia of Grounding 07-0801 sections 5 and 6  IEEE 524 – 2003 Guide to the Insulation of Overhead transmission line conductors, Appendix C6, Appendix C1 to C4  IEEE 1048, Section 4 34 Identifying Electrical Hazards

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Hazards of Induction Induction can be fatal, but is often overlooked and underestimated. The likelihood of accidental energization is remote compared to the possibility of induction. Hazards from induction are always present and must be managed and mitigated to protect workers. There are three types of induction:  Capacitive induction  Magnetic induction  Static induction NOTE: The term electromagnetic induction is used to refer to capacitive and magnetic induction occurring at the same time. Capacitive Induction To understand the hazard of capacitive induction you must first understand the characteristics of a capacitor and the process of capacitive coupling. Capacitors A capacitor stores an electric charge in an electric field. It consists of two conductive plates (or objects) separated by a dielectric (partial insulator). The property which enables a capacitor to accumulate and store electric charge is called capacitance. Capacitance is the property of an electric circuit that opposes any change in the voltage across that circuit (while resistance is the property of an electric circuit that opposes the flow of current through the circuit). In a circuit, capacitance and resistance have opposite characteristics. Capacitors in parallel are added together to create a larger capacitance, similar to resistors in series. Ct = C1 + C2 + C3 Capacitors in series are added inversely to create a capacitance less than the smallest capacitor in the series, similar to resistors in parallel. 1/Ct = 1/C1 + 1/C2 + 1/C3 Capacitive Coupling Capacitive induction (also known as electric field induction) occurs anytime an energized conductive object is separated from a de-energized conductive object by a dielectric medium, such as air. This arrangement of two conductive objects creates a simple capacitor. The electric field generated by the energized conductive object will induce a charge onto the nearby de- energized conductive object through a process called capacitive coupling. Identifying Electrical Hazards 35

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro With transmission lines, capacitive coupling occurs when an energized line that is parallel or close to an isolated line produces a voltage on the isolated line because a capacitance exists between the two objects. In this situation, the two lines are equivalent to the conductive objects of a capacitor and the air between the lines is the dielectric material. The induced voltage is proportional to the voltage of the energized line and the distance between the energized and isolated lines. It will have a magnitude somewhere between zero voltage (to ground) and the voltage of the energized line. In practical circumstances, induced voltage can be as high as 30% of the energized line voltage. The current induced by an electric field is proportional to the length of the isolated line exposed to the electric field. Figure 17 illustrates the source of capacitive coupling between an energized and isolated line. Figure 17. Capacitive Coupling The isolated object will retain this capacitive voltage or trapped charge until it is bled off by grounding the conductive object or normal discharge over time. If an isolated line is solidly grounded, the electrically induced voltage will be zero at the ground locations and will be of a small magnitude at locations between grounds. The ground connections of the isolated line will carry continuous 60 Hz induced current, which may be as high as 60 mA per kilometer of the parallel lines. It only takes 50 mA to cause the heart to go into fibrillation. Currents and associated voltages of this magnitude make it imperative that adequate grounding procedures be used to avoid serious danger to workers. 36 Identifying Electrical Hazards

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Figure 18. Capacitive Coupling with Ground on Line Open-End Voltage With parallel lines and a single ground point, the voltage induced on an isolated line is zero at the ground point and increases as you move away from the ground point. This is called open-end voltage. The farther away the worker is from the ground point, the greater the induced voltage. Figure 19 illustrates the concept of the open-end voltage being developed by capacitive coupling where a single ground has been installed on the isolated line. Figure 19. Open End Voltage Profile along an Isolated Power Line in an Energized Corridor Identifying Electrical Hazards 37

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Summary  Capacitive induction from energized conductors can induce high voltages on isolated lines. In practical terms, these voltages can be as high a 30% of the energized line.  A single ground reduces this voltage to a safe level; however, additional grounds may be required to satisfy other safety aspects.  Ground connections carry a continuous 60 Hz current as high as 60 mA per kilometer of parallel line. Magnetic Induction To understand the hazard of magnetic induction, you must first understand the characteristics of an inductor and the process of magnetic induction coupling. Inductors When a conductor is in a coil in an AC circuit, it creates an inductor. As the electric current produces a concentrated magnetic field around the coil, it creates a store of energy representing the kinetic motion of the electrons through the coil. The more current there is in the coil, the stronger the magnetic field and the more energy the inductor stores. Figure 20. Magnetic Field around Coil Because inductors store the kinetic energy of moving electrons in the form of a magnetic field, they behave quite differently than resistors (which simply dissipate energy in the form of heat) in a circuit. When an inductor stores energy, it tries to maintain current at a constant level. In other words, inductors tend to resist changes in current. When current through an inductor is increased or decreased, the inductor “resists” the change by producing a voltage between its leads in opposing polarity to the change. Magnetic Induction Coupling Magnetic induction across transmission lines is similar to the way in which a transformer works. As current flows through an energized transmission line, the line acts as a primary winding of a transformer. An adjacent de-energized power line acts as a secondary winding of the transformer. When two portable protective grounds are placed on the de-energized transmission line, a closed circuit is created, which through transformer action, a current will flow. This is called magnetic induction coupling and can be very hazardous to workers. See Figure 21. 38 Identifying Electrical Hazards

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Figure 21. Magnetic Induction Coupling The amount of magnetic induction is directly proportional to the current flowing in the energized conductor. If an isolated conductor is ungrounded or grounded at only one point, no current can flow due to magnetic induction; however, dangerous voltages can exist. Open-End Voltage With parallel lines and a single ground point, the voltage induced on an isolated line will be zero at the ground point and will increase as you move from the ground point. This is called open-end voltage. The farther away the worker is from the ground point, the greater the hazard the worker is exposed to if he or she touches the isolated conductor. See Figure 22. Figure 22. Touch Potential Hazard from Open-end Voltage By adding additional grounds, the open circuit voltage is minimized to a safe value, but circulating currents between grounds are created causing additional hazards. The circulating currents create an extreme hazard if the worker becomes in series with the isolated conductor and/or one of the grounding conductors. The application of continuity jumpers is critical to ensuring the worker does not become in series with the circulating current. See Figure 23. Identifying Electrical Hazards 39

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Figure 23. Circulating Current from Magnetic Induction NOTE: - Ensure that the steady-state capability of the ground equipment and conductor is adequate to handle the circulating current. - Contact resistance must be low enough to avoid hazardous step and touch voltages near the ground connections. Removing Grounds Parallel grounds must be removed in sequence by starting at one end and working toward the other end. This minimizes the circulating current, and consequently, reduces the amount of circulating current that is broken when the grounds are removed. If this was not done, the resulting arc may be too high to break and would put the worker at risk. Summary  It may be desirable to use more than two grounds to prevent excessive voltage between grounds.  Magnetic induction will induce circulatory currents in the loops that are created when multiple temporary grounds are attached.  Care must be taken to ensure the worker does not become in series with the circulating current (i.e., use continuity jumpers).  Removing grounds may create a hazard depending on the current magnitude to be interrupted and the resulting hazardous arc. 40 Identifying Electrical Hazards

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Static Induction Static induction may occur from atmospheric conditions such as wind, cloud movement or solar flares. A typical example is in the application of a no bond zone where there is no source of induction or energization; but a hazardous potential exists from static induction. Although the current resulting from static induction is less than other forms of induction, it must still be mitigated. To mitigate static induction, apply a ground that bleeds off the induction. This ground is referred to as a bleed ground. See Figure 24. Figure 24. Static Charge from Wind Dissipated by Bleed Ground Summary  Static induction may occur from atmospheric conditions.  To mitigate static induction, apply a bleed ground. Sources of Accidental Line Energization Equipotential bonding and grounding (EB&G) is primarily intended to mitigate the hazards from accidental energization. There are multiple sources of energy which could cause accidental energization. Each of these sources must be mitigated to ensure the worker is protected. Contact with an Energized Line If the line under construction or maintenance contacts an energized line, the isolated line will be energized by the same voltage as the energized line. Identifying Electrical Hazards 41

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro To reduce the likelihood of an isolated line from being accidentally energized through contact with an energized line: 1. Provide appropriate guarding, such as cover-up or rider poles, to mechanically prevent the energized and de-energized lines from touching. 2. Apply EB&G. If the line becomes energized, you are only protected when inside an EB&G zone. Backfeed On-site customer generation is the primary source of backfeed on a power system. Other sources of backfeed include motors, capacitor banks, and potential transformers. To reduce the likelihood of accidental energization resulting from backfeed: 1. Ensure a proper physical point between the power system and the source of backfeed (that is, open switch point). 2. Apply EB&G. If the line becomes energized, you are only protected when inside an EB&G zone. Lightning Although lightning is transient in nature, it still creates an extreme hazard to workers. To reduce the likelihood of accidental energization resulting from lightning strikes: 1. Apply EB&G. If the line becomes energized, you are only protected when inside an EB&G zone. 2. If lightning is reported in the area, stop all work near overhead lines. WARNING: If lightning is reported in the area, stop all work near overhead lines. This is especially important when working in a no bond zone. Switching Errors Although switching errors that cause lines to be accidentally energized are rare, they are the main reason why we use worker protective grounding. AltaLink’s Control Centre (ACC) controls and directs all switching functions. The ACC follows switching procedures, lock-out and tag-out procedures, and GOIs in order to ensure all switching is done correctly. To reduce the likelihood of accidental energization resulting from a switching error: 1. Follow guarantee of isolation (GOI) procedures. 2. Apply EB&G. If the line becomes energized, you are only protected when inside an EB&G zone. 42 Identifying Electrical Hazards

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Conductor Crossings A power line crossing under or over an isolated line that is being worked on is a source of accidental energization. If the energized line falls into the isolated line or the isolated line falls into the energized line, workers on the isolated line would be at risk. To reduce the likelihood of accidental energization from crossing power lines: 1. Inspect the crossing line to ensure its integrity. 2. Do one of the following: o De-energize the crossing line. o Enable a recloser block on the crossing line. o Install rider poles. For example, rider poles could be used during stringing. o Cut in isolation devices or open jumpers that isolate the energized portion of the crossing line from the isolated line. o If the crossing line is a distribution, install cover-up. 3. Apply EB&G. If the line becomes energized, you are only protected when inside an EB&G zone. Sources of Harmful Energy System Neutrals System neutral on distribution circuits can be hazardous because it may not be at zero potential. To mitigate this hazard:  Physically stay away from the system neutrals.  Bond system neutral into the work zone.  Use cover-up. Transferred A transfer of potential can occur at the work location when there is a voltage rise at a Potential remote location connected to the work location. For example, a transfer potential could occur when a Fortis system neutral is on the transmission pole being worked on and a fault occurs on the Fortis system. As the Fortis system neutral rises in voltage, the Fortis neutral on the pole would also rise, creating a hazard for workers on the pole. By using an EB&G zone at the work site with the OHSW and downlead bonded in, a worker is protected from transfer potential. As the OHSW rises in voltage, anything that is bonded in at the work site also rises in voltages, keeping everything at the work site at the same potential. Fault Conditions A fault condition on the energized line adjacent to an isolated line can create additional hazards. For the duration of the fault, a significantly higher spike of magnetic induction occurs. This results in a spike in the circulating current on the conductor and the amount of current that is entering the earth at the location of the grounds. The current entering at the ground locations may cause a touch and step potential hazard due to GPR. In addition to electrical hazards, cables during fault conditions can move violently and endanger the worker. Identifying Electrical Hazards 43

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Summary of Sources of Energization and Effects Electrical charges can appear on de-energized transmission lines. Table 2 summarizes the conditions under which this can occur and the effects that are produced. Table 2. Summary Energy Sources and Hazardous Effects Energy source Condition main Main hazardous effects Secondary hazardous effects Line voltage on an adjacent Capacitive induction Voltage on ungrounded line Current through ground energized line Magnetic induction connections Line current on an adjacent  Induced voltage on a line Step and touch voltages near energized line Fault on adjacent line grounded at one end grounds Faulted line High voltages and fault  Currents at ground points for lines  Higher than steady-state induced current grounded at two or more points currents in ground connections Accidental contact between energized and de-energized  Induced voltage on line grounded  Higher step and touch voltages at lines at one end points between grounds Wind Lightning discharge  Higher than steady-state induced Movement of the ground cables currents at ground points for lines grounded at two or more points Step and touch voltages at all points on isolated line Atmospheric static charge Voltage when system is ungrounded — Lightning Overvoltage on line Overcurrent in ground connections 44 Identifying Electrical Hazards

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro Exercise 1C Complete the following exercise. The answers to the exercises are in Identification of “Identifying Electrical Hazards” on page 34 of this manual. 1. ____ When a conductor is in a coil in an AC circuit, it creates a. a capacitor in a series b. a resistance c. an inductor d. a capacitance impedance in a circuit (XL) 2. ____ Which one of the following best completes this sentence? The current induced through capacitive induction from an adjacent energized line not carrying any load current is proportional to the a. voltage of energized line and the distance between the energized and isolated lines. b. length of the isolated line exposed to the electric field. c. average amount of current flowing in the energized conductor. d. A and B. 3. ____ How do you mitigate potential hazards from static induction? a. apply a bleed ground b. static induction is not hazardous c. apply a trip ground d. apply open jumpers 4. ____ What is the primary source of backfeed on a power system? a. motors b. capacitor banks c. potential transformers d. onsite customer generation Identifying Electrical Hazards 45

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro 5. ____ How do you protect yourself in case system neutrals on distribution circuits may not be at ground potential? a. inspect the line to ensure its integrity b. bond the system neutral into the work zone c. use rider poles d. install a ground on the downlead 6. ____ How do you reduce the likelihood of accidental energization when working on isolated transmission lines that are crossing under or over another power line? a. install continuity jumpers b. physically stay away from the system neutrals in case they are not at zero potential c. inspect the crossing line to ensure its integrity, and then set up an equipotential zone d. all of the above 7. ____ True/False. Capacitive Induction can induce voltages on isolated lines. The voltage is never more than 10% of the energized line. 8. ____ True/False When electromagnetic induction is present; it is proportional to the amount of current flowing in the adjacent energized line. 9. ____ True/False. The magnitude of magnetically inducted current in an isolated line is proportional to voltage of the adjacent energized line. 10. An isolated line in proximity to an energized line not carrying any load current will have a voltage induced on it through _________________________. 46 Identifying Electrical Hazards

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro ANSWERS EXERCISE 1A 1. __C__ Which calculation is used to determine current in Ohm’s Law? c. I=V/R 2. B Which calculation is used to determine voltage in Ohm’s Law? b. V=IxR 3. __B__Which statement best describes Kirchhoff’s Current Law? b. The sum of all the currents entering a node equals the sum of all the currents leaving the node. 4. C Using Ohm’s Law, if V=20 V and R=5000 Ω, the current (I) is equal to c. 4 mA 5. Using Ohm’s Law, if V= 10 V and I=4 mA, the resistance (R) is equal to b. 2500 Ω 6. Using Ohm’s Law, if R = 10000 Ω and I=10 mA, the voltage is equal to d. 10 V 7. What is the difference between fault current and load current? a. Load current is primarily limited by the resistance of the loads connected to the transmission system by customers, whereas fault current is primarily limited by the resistance between the generator and the fault location. 8. What effect does transmission system voltage have on the magnitude of fault current? c. The greater the voltage, the greater the fault current. 9. What effect does conductor size have on the magnitude of fault current? a. The larger the conductor, the lower the resistance, the higher the fault current. 10. Which type of fault has the highest fault current? b. three phase answers 47

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro 11. _TRUE_. GPR voltage diminishes very quickly as it moves away from the point at which the current entered the earth. 12. A voltage increase in the earth due to current flow to earth is called___ Ground potential rise or GPR__. 13. Maximum GPR is calculated by multiplying current by the___ impedance of the ground point___. 14. What is the total current in the circuit (IT)? RTotal = RC + ((RW x RJ1)/(RW + RJ1)) + RP + RG = 0.1 + (1000 x 0.005/1000 + 0.005)) + 3000 + 30 = 0.1 + .005 + 3000 + 30 = 3030 ITotal = V/R = 80,000/3030 = 26.4 amps 15. What is the current flowing through the portable protective ground (IJI)? VJ1 = ITotal x ((RW x RJ1)/(RW + RJ1)) = 26.4 x ((1000 X .005)/(1000 + .005)) = 26.4 x .005 = 0.132 V IJ1 = VJ1/RJ1 = 0.132/0.005 = 26.4 amps 16. What is the current flowing through the worker (IW)? VW = ITotal x ((RW x RJ1)/(RW + RJ1)) = 26.4 x ((1000 X .005)/(1000 + .005)) = 26.4 x .005 = 0.132 V IW = VW/RW = 0.132/1000 = 0.00013 Amps or 0.13 mA 17. What is the ground potential rise voltage (VG)? VG = ITotal x RG = 26.4 x 30 = 792 V 48 ExercisE 1A

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro 18. What is the effect on the circuit of removing the first portable protective ground (J1)? a. Total fault current goes down, current through the worker goes up to dangerous levels, and ground potential rise goes down 19. What is the effect on the circuit of removing only the second portable protective ground (J2)? b. Total fault current goes down, current through the worker goes down, and ground potential rise goes down 20. What is the effect on the circuit of removing both portable protective grounds (J1 and J2)? b. Total fault current goes down, current through the worker goes up to dangerous levels, and ground potential rise goes down ExercisE 1A 49

Grounding Isolated Transmission Lines FTL-LIN-GDN-001-M, Version 1.0 CCContro EXERCISE 1B Princeton Pond Incident 1. What caused this accident? Employee was fatally injured as a result of contact with ground potential rise resulting from the flashover of two disc insulators on a damaged insulator string. The flashover occurred as a result of the change in weather conditions to wet snow, possibly in combination with contamination on the disc insulators 2. What factors increased the danger? Proximity of the crew to a structure with a damaged string of insulators in an energized transmission line presented a ground potential rise hazard. Change in weather conditions to wet flurries increased the likelihood of insulator flashover. 3. What could be the effect of 50 mA of alternating current (60 Hz rms) entering a man’s body? d. ventricular fibrillation 4. What is the relationship between ground fault current and ground potential rise? a. As fault current increases, ground potential rise increases. 5. __A__What factor creates a gradient of voltages away from the point of injection of the current into the ground, thus creating the hazard for step and touch potential? a. ground potential rise 6. __A__ What is step potential? a. When each foot is at a different potential and current flows through the body from one foot to the other. 7. When you do not touch conductive objects in an area where fault current can flow, you eliminate which potential hazard? b. touch potential 8. Let-go current is the value of current at which a human holding an energized conductor cannot ___control his or her muscles in order to release conductor___. 50 Exercise 1B