Download PDF version

Buried copper grounds are vulnerable

Grid conductors in older stations have questionable integrity. Fault levels can increase over time; while buried conductor size may be uncertain. Bonding practices from the grid to fences often vary significantly.

Designers need accurate soil resistivity data. Surface stone resistivity may have fallen below acceptable levels of 3000 W m.

Overly conservative grounding design studies can lead to unnecessary remedial costs. Frequently, actual field measurements of touch potentials are lower than indicated by original designs. Interference due to switching or lightning may be difficult to quantify. High magnetic fields can be present around isolated phase buses.

Kinectrics delivers economical, proven solutions

Kinectrics’ complete Grounding Reviews can deliver substantial savings. Comprehensive site measurements identify over-designed components and provide full conditional assessments, including safety. Integrity tests can prove the proper bonding of power equipment and structures and, combined with special software, can even resolve the size of individual buried conductors. Surface stone measurements indicate when replacement is necessary. Current injection tests measure correct ground potential rise and touch potentials.

Two-layer soil models enable an accurate estimate of the station electrode resistance. Lightning simulation tests allow coordination of stresses with the specified immunity of electronic equipment. Magnetic field measurements can be compared to international exposure guidelines. A Kinectrics Grounding Review study typically combines a controlled field test with advanced analytical modeling to provide practical corroboration and detailed reporting documentation.

Full-service mobile testing capabilities

• A battery-powered 10-A micro ohmmeter with custom cables allows rapid measurement of resistance between accessible grid connections.
• A digital Megger connected to a sampling box and used with de-ionized water provides a repeatable measure of stone quality.
• A 5 kW, 240 V diesel generator and network analyzer mounted in our test van inject sufficient test current to allow a precise measure of ground potential rise and interconnection station ground impedance, including phase angle.
• Probes to measure touch potentials. Clip-on transformers resolve current splits in distribution neutrals and skywires.
• A digital Megger, a cable set with predetermined connection points and custom software provide a two-layer soil model for use by designers.
• A surge generator and portable digitizer to quantify stresses at vulnerable equipment terminals.
• A magnetic field meter with digital output to provide a three dimensional survey of fields in gauss or microtesla.

Generating client savings   -   Recent projects

Comprehensive recommendations for substation upgrades

• A major grid utility requested conditional assessment of 14 substations within a one-year period. Measurements covered the integrity of bonds to every freestanding device or structure. Individual substation reports detailed fault levels, ground potential rise, ground electrode resistance, interconnected ground impedance and touch stresses relative to safe body withstand. The client gained effective recommendations for specifying upgrades and complete report documentation to support corporate due diligence regarding personnel safety concerns.

Effective mitigation of magnetic fields

• The maintenance department at a hydraulic station required measurements and modeling of magnetic fields present in proximity to the isolated phase bus. Tests and analysis showed that high temperatures recorded in supporting structural steel were due to improper bonding of the bus enclosures, resulting in eddy currents reaching 2 kA. Accurate data compiled by Kinectrics enabled the client to choose effectively from several mitigation solutions.

Practical interference containment

• The design/build contractor for an SF6 insulated 230/115 kV station experienced interference to bay modules (Intelligent Electronic Devices) configured in close proximity to circuit breakers. Measurements indicated that radiated fields in the range of 100 MHz were higher than international immunity standards. As a result of this technical review, the bus flanges were covered with a hoop shield to contain interference within the bus enclosure.

Improved lightning protection performance

• A nuclear station experienced failures of control relays during lightning storms. Measurements showed that lightning strikes could result in stresses on dc control wiring several times higher than the specified withstand of the relays. Kinectrics’ report made direct recommendations for improving the high frequency performance of the grounding system. The client was able to install additional lightning protection based on specific relevant data.

For more information, contact:

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