Substation and Equipment Grounding

Mentors:Wayne Wittman (PSEG)David Soyster (PPL)Bob Lally (PPL)

Special Thanks to:Dr. John CoulterShaku Jain-Cocks

Author:Megan McLoughlin

Lehigh University 2011M.Eng Energy Systems Engineering

Sponsor:PPL Electric

Summarize the current measurement equipment and techniques for evaluating the condition of energized substation grounding systems; discuss the advantages, disadvantages, and limitations of each technique. Test substations with available equipment to determine effectiveness and

validate a method for pinpointing the substation grounding issues. Develop recommendations for PPL on the best practice for substation grounding system testing.

Substation Importance• At the heart of the transmission and distribution system• Steps up voltage to carry the electricity across long distances• Steps down voltage to bring the electricity to residential and

commercial customers

Grounding• The ground system is a critical part of a substation• It is a network of copper wires below the ground that is

connected to each piece of equipment• Offers a safe, low resistance path to earth during normal or

fault conditions• Ensures operational performance of the equipment and

safety of personnel on site• Provides reliable and continuous flow of electricity by

preventing damage to equipment

The Problem• Many substations were constructed over 50 years ago and electric companies

do not know what condition the grounding system is currently in• The effects of corrosion through water content, pH value, soluble salt content,

and soil resistivity of the soil at the different sites is unknown• With a degraded grounding systems, the likelihood of transfer, step, or touch

potential rises. This is a dangerous temporary voltage that goes through equipment or personnel

• Traditional testing methods currently used to test grounding systems requires a de-energized substation, which is only practical before it comes online.

• When the substation is energized it is tied in with all equipment, neutral wires, transmission lines, and OHGW, it is impossible to isolate the test procedures from the background noise

• No standards exist for continued safety checks on the grounding system after any substation is in-service

Current Test Procedures• Fall of Potential: most common procedure used for

disconnected substations to measure groundresistance• Three-point method• Lazy Spike• Slope Method• Clamp-On

• Wenner Four Point Method: for soil resistivity

Current Equipment• AEMC Instruments: Ground Resistance Tester Model

6472• Fluke: GEO Earth Ground Testers 1623/1625• Megger: digital Earth Tester DET2/2• EPRI Smart Ground Multimeter

Current Industry Studies• Testing and Evaluating Grounding Systems of High Voltage Energized Substations:

Alternate Approaches (1999)• Conventional Method• Transition Method• 70Hz Method

• Practical Testing of Grounding Systems by Current Injection (2005)• The test injects a unique frequency into the ground to differentiate the

background noise from the test signals• It couples the results with modeling software to understand faults in the ground

grid• EPRI Condition Assessment of Substation Ground Grids: Phase 2 –Concept Testing

(2008)• This study goal is to develop a method and instrumentation to determine integrity

of the grounding grid that is inexpensive, reliable and easy to use• EPRI Lenox Test Grid• Injected currents into subsurface grid can be detected using magnetic pickup coils• The more information known about the grid, the better the test results

Conclusions• Big gap in market for technologies that check the integrity of

energized substations ground grids• The current test protocols and equipment have limited

applications for in-service substations• There has been limited and inconsistent research in this area

until recently• The research currently available points towards a unique (not

60Hz) current injection into the ground as best method, thisallows for the differentiation of the background noise.

• Coupling results of current injection with simulationsoftware may lead to the ability to be able to pinpoint breakpoints in ground system