The main shortcoming of the secondary current injection test method is that only the solid-state trip unit logic and components are tested. Photo: SwitchserveĬircuit breakers with solid state and microprocessor trip units can be tested by injecting secondary current into the trip unit directly rather than passing primary current through the CT’s using a high current test set. Secondary test sets are designed by trip unit manufacturers to be used with a single style or family of trip unit using a proprietary connection. Depending on the size, this type of test equipment can also used to test ground fault and other current relays by connecting directly to switchgear bus. Integrated timers display the period between current on and current off to indicate how long it takes for a circuit breaker to trip.Ĭircuit breakers may be connected directly to the high current test set via bus or cable. The large reduction in voltage allows for a large increase in available current output (15kA+), especially for a short duration.Ĭurrent output is controlled by a tap changer and variable resistor. 480V) to a very low level, such as 2-15V. The high current or “primary-injection” test set consists of large transformers that step down line voltage (ex. Low voltage, high current outputs are used for primary-injection testing of low voltage circuit breakers. Photo: MeggerĪ high current test set may consist of two pieces known as a “control unit” and an “output unit”, or these functions may be combined in a single package. Primary injection high current test set with circuit breaker attached. Related: Power Cable Testing and Diagnostics Overview Very low frequency (VLF) withstand testing is the application of an AC sinusoidal waveform, generally at 0.01 – 0.1 Hz, to assess the quality of electrical insulation in high capacitive loads, such as cables. Output voltage can range anywhere from 1kV-100kV+ ac at line frequency or dc depending on the device under test. The hipot test is a “go, no go” test, meaning leakage current must not trip the test set but there is no minimum acceptable value. If too much return current flows, the test set internal protection will trip. The high voltage lead is connected to the device under test with all other components grounded and the resulting current is measured through the return. Hipot test sets consist of a high voltage lead, a return lead, and a ground lead. Insulation is stressed above nominal values to ensure minimal current leaks from the insulation to ground. Photo: HV, Inc.ĭielectric withstand (or hipot) testing checks for good insulation in medium and high-voltage apparatus, the opposite of a continuity test. Your resource for answers.Hipot test sets consist of a high voltage lead, a return lead, and a ground lead.
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