Audits and protection Grading
The objective of substation auditing is to provide customers with a non-intrusive evaluation of all High Voltage (HV) equipment for all their substations. A line audit inspection sheet is completed for each component of the line. This comprehensive review list is adapted for each project and comprises the complete line hardware, the support structure and all related hardware attached to the structure/s. Environmental impacts within the servitude of the line and risk factors outside of the servitude that might have an influence on the integrity of the line are recorded and reported with suggested mitigation measures.
Over-voltage pressure tests
The power system may experience temporary over-voltage conditions due to a sudden cut off of the load from the system, incorrect operation of online tap changer, insufficient shunt compensation in the system, etc. Power frequency over-voltage withstand testing of circuit breakers is performed to verify that the insulation strength of the main circuit is sufficient to withstand these abnormal over voltage conditions. The circuit breaker should also be designed to be capable of withstanding over-voltages due to lightning and switching impulses.
Contact resistance testing, timing and travel trip and closed coil testing
Timing and travel testing is used to determine and validate the performance characteristics of circuit breakers. For example, the changing state of main and resistor contacts (open- close, close-open, etc.) and auxiliary contacts versus time, varying defined distances traveled by the main contacts (e.g., total travel, over travel, rebound, stroke, and contact wipe), velocity (average and instantaneous), dwell-time and dead-time, are primary circuit breaker characteristics measured.
Coil current: this measurement can be performed online or offline and is used to detect potential mechanical and/or electrical problems in actuating coils, well in advance of their emergence as actual faults, and extract information about lubrication and latch operation. The quality of the control voltage supply is also detectable from these tests. This diagnostic is perhaps most effective when it is performed as a “First Trip” activity. First Trip is performed when the circuit breaker is in-service and has not been operated for a long time. Lubrication problems are easiest to identify in this scenario. Comparison to previous results is the best method of analysis.
Static (contact) resistance measurements (SRM);
micro-Ohm measurement of the main contacts. This test is conducted by injecting DC current through the breaker main contact system when the circuit breaker is closed, and measuring the voltage drop so that the resistance can be calculated. The resistance reflects the condition of the conducting parts.
Dynamic (contact) resistance measurements (DRM);
this test is used to determine the length and condition of the current carrying part of the arcing contacts in SF6 puffer type circuit breakers. DRM tests are conducted by injecting DC current through the breaker main contacts while the breaker is operated. The breaker analyser then calculates and plots resistance as a function of time. If contact movement is recorded simultaneously, the resistance can be determined at each contact position. With DRM measurement, the arcing contact length can be reliably estimated. The only other means to do this is by dismantling the circuit breaker. In SF6 breakers, the arcing contact is commonly made of a tungsten/copper alloy and is burned off and becomes shorter for each interruption of current.
The objective of testing is to provide confidence in the real-world performance of a part design. Testing also confirms consistency in the outputs of critical manufacturing processes, confirming that there are no defects that affect the part’s performance or expected lifespan.
Partial discharge testing (PD) The Partial Discharge test is critical for verifying long term part performance and detecting any inefficiencies in power transference. This test is especially important for medium voltage, multi-layer laminated bus bars, inverters, and any critical power conductor applications where electrical insulation is of paramount importance.
Ampacity Testing (Rated Current Test or Heat Rise Test) While ampacity tables provide a good estimate for how a conductor of a certain thickness will behave thermally when subjected to a specific level of electrical current, a physical test is the only way to confirm that a part will perform as expected. This test is performed by initiating a specific amperage through the test specimen and measuring the heat rise with thermo-couples.
HiPot Testing (Dielectric Breakdown Test) HiPot (High Potential) testing is performed to confirm that there is proper electrical isolation between conductors. The test runs a specific electrical voltage (AC or DC) through the conductor while a ground is created on the adjacent conductors to verify that there is no electrical path between them. Generally, the HiPot test is run at an exaggerated voltage level of 2X the operating voltage, plus 1,000 volts to ensure safety and performance even in extreme scenarios.
Large power user metering audits
Metering energy audits are typically done by an independent third party to monitor energy efficiencies and best practices in residential, commercial, and industrial spaces. Typically, they require a consultant or specialist with specialized mobile equipment that can be used to test various equipment, and at times are done in-house to ensure the efficiency of electrical devices and controls.