High current test sets or Primary Current injection testing is a preventive maintenance technique that evaluates the performance of circuit breakers installed in an electrical or automation system by injecting electrical current through them. As the circuit breakers are critical for the overall safety and understanding of the equipment, a variety of tests and surveys are performed on Circuit breakers to identify their problems, of which Current injection is the most common and popular. This test helps to identify and monitor underperforming breakers and their protective relays and devices, to ensure that the efficiency of the electrical system is maintained even at peak loads. Typically, High current tests are used to validate the safety and performance of current transformers (CT), Potential or Voltage Transformers (PT or VT), switchgear, relays, breakers, reclosers, contact resistance, ground grid, step & touch devices.
The current injection test works on injecting electrical current to the primary and secondary side of electrical systems to check protective equipment. The objective of these tests is to test the reliability and efficiency of electrical systems (primarily protective equipment such as breakers) and help identify any defective equipment. Depending on the current amplitude and the direction of injection, current test sets are classified as – Primary and Secondary. Both Primary and Secondary test sets operate on the same principle of simulating the real field current flow to validate if the breakers trip at their designed limit and how long the current needs to be flown before a trip is initiated (activation time).
Both Primary and Secondary Current injection tests are available for industrial usage and are chosen based on the application and objective of the test.
Primary current test sets are used for high current/high voltage applications, typically found at large electrical installations such as substations. These test sets operate by injecting currents ranging from 100A to 20,000A depending on the breaker specifications directly onto the electrical system’s primary side, such as a circuit breaker, to test its load-bearing capacity. As opposed to the Secondary current test sets that test only the electronic breakers, Primary current tests are used for thermal-magnetic and electronic breakers. Modern high current test sets are integrated with cable termination, timers, temperature indicators, contractors, individual phase control, and other accessories. They are equipped to perform complete breaker condition monitoring by determining the health of CTs, wiring conditions from CT to the trip unit, and the performance of the trip unit.
The test sets are accepted as the industry standard for the Acceptance and Maintenance test on electrical equipment. Acceptance tests include Factory acceptance testing, testing upon receipt, installation acceptance, and electrical system testing. Maintenance tests are performed before and after a maintenance activity to log the change in performance. The following are typical applications of the Primary current injection technique:
Although widely used, the secondary current test does not check all electrical system components as the primary current test does. Instead, it works by injecting a test current (typically of low magnitudes) into the trip relay unit on the secondary CT side of the electronic breakers and hence the secondary name test. Unlike the primary current tests, the secondary tests do not simulate actual working conditions and cannot reveal defective CTs, polarity, and CT conditions. Therefore, the secondary testing is quick to complete and requires relatively lesser experience, cost, and time to perform.
The selection of a primary or secondary test kit depends on the project complexity and the test objectives. An incorrect test kit either offers too much or too little for your testing needs. The following criteria can be followed for selection:
Accuracy of Current test sets is critical while testing the circuit breakers and depends on the current loading cycles and the operational skill. The kit’s accuracy can also vary due to the movement caused by shock or vibration while transporting the equipment. Other factors that may affect calibration are contact resistance in the control cable, unusual magnetic fields, insulation leakage, and aging electronic components. Therefore, proper operation and calibration are essential for accurate readings.
In addition to calibrating the Test kit per OEM standards, the following components of the kit should also be regularly calibrated:
Cumulative defects in high current test kits often result in operational uncertainties leading to maintenance losses. Calibration avoids these errors, ensures the test kit’s accuracy. Following a regular and timely calibration schedule ensures the circuit breakers are healthy and trip at designed limits. The national laboratories are responsible for maintaining the national reference standards for accuracy and traceability.
e2b calibration offers industry-leading ISO-certified High current test set calibration services. Our labs are ISO/IEC 17025 accredited and operated by a team of qualified calibration experts to test and calibrate your high current test kits. Our verifiable services are unmatched in the industry. We are registered with ANAB. We are also ANSI/NCSL Z540-1-1994 certified. We have the NIST Traceable Wide scope of ISO/IEC 17025 accreditation. Contact e2b calibration for all your equipment calibration needs.