Handbook of Electric Power Calculations, Third Edition
A powerful calculations tool for electric power engineers and technicians, this book offers essential, step-by-step procedures and examples for solving a wide array of electric power problems.
TABLE OF CONTENTS Handbook of Electric Power Calculations, Third Edition
Section 14: SYSTEM GROUNDING
David R.Stocking
Lyncole XIT Grounding
Elizabeth Robertson
Lyncole XIT Grounding
SELECTION OF GROUNDING SYSTEM
Determine what factors are significant in the selection of a grounding system.
Calculation Procedure
1. Consider Grounding Impedance
The different levels of grounding impedance are:
Solidly grounded: No intentional grounding impedance.
Effectively grounded: R 0 ? X 1, X 0 ?3 X 1, where R is the system fault resistance and X is the system fault reactance. (Subscripts 1, 2, and 0 refer to positive-, negative-, and zero-sequence symmetrical components, respectively.)
Reactance grounded: X 0 ?10 X 1.
Resistance grounded: Intentional insertion of resistance into the system grounding connection; R 0 ?2 X 0 .
High-resistance grounded: The insertion of nearly the highest permissible resistance into the grounding connection; R 0 ? X 0 c/3, where X 0 c is the capacitive zero-sequence reactance.
Grounded for serving line-to-neutral loads: Z ? Z 1, where Z is the system fault impedance.
2. Evaluate Disadvantages and Advantages
a. Solidly grounded: Provides for the highest level of fault current to permit maximum ability for overcurrent protection for isolation of faulted circuit. Fault current may need to be limited if equipment ratings are to be met. Will trip on first fault (it is this factor that occasionally leads to use of ungrounded circuits). Provides greatest ability for protection against arcing faults. Provides maximum protection against system overvoltages because of lightning,...
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