Project Objective

Verify compliance of the existing ground grid at an industrial substation with applicable safety standards.  Provide specific recommendations for improvement where required

Background

A 115 / 34.5 kV substation supplied a number of load feeders at a steel mill.  A consultant designing switchgear replacement had concerns regarding its grounding performance. 

Ground loops to the grid displayed corrosion and mechanical damage and fault levels had increased. Previous trenching in the area could have severed grid conductors and little information was available confirming interconnections to downstream service panels.  The substation included a HV circuit breaker, transformer and LV switchgear

Scope of Work

Kinectrics proposed point-to-point resistance tests of the grid in micro-ohms to assess the ground grid integrity.  Secondly, it was proposed that a current injection test would simulate an actual fault condition.  This would identify the ground potential rise, touch potentials, current splits in overhead ground wires, and the isolated grid resistance.  Thirdly, it was proposed that measurements of the surface stone resistivity and soil resistivity would define safe body withstands and corroborate the grid resistance.  Kinectrics also offered to provide comments on the condition of connectors and the ability of the conductors to withstand fault currents.

After acceptance of the proposal by the client, all field tests were completed during a single day.  Subsequent modeling and conditional assessment included the use of Kinectrics custom software.  The final report followed discussions of specific recommendations with the client. 

Results

The study confirmed that the station was well interconnected to nearby buildings, so awkward pulling of new cables into old ducts would be unnecessary.  Even with increased fault levels, the touch potentials coordinated with the safe body withstand, so the basic design of the grounding system was effective and valid. 

However, the tests identified some local deficiencies. The grid was severed in the northwest corner of the station. The fence was interconnected to the grid in only one location, and it lacked longitudinal continuity on two sides of the station.  Also, insulating panels were needed between the fence and two radial fences running away from the station.  The surface stone required replacement, and some non-qualified bolted connections needed replacement near grade level.

Client Benefits

As a result of this study, the client was able to focus improvements on specific areas needing rehabilitation, and show evidence of due diligence in a safety-related area.  The client also saved substantial sums of money by not going through an entire replacement project unneccessarily.

For more information, contact:

Steve Cress, 416.207.6000 x6557, steve.cress@kinectrics.com

Related link:

Station Grounding Review Services