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Difference between Primary Current Injection Test and Secondary Current Injection Test

by | Apr 23, 2021 | Industrial Equipements

The Electronic Trip Unit is a multifunction overcurrent safety device powered by a microprocessor and designed for low voltage power circuit breakers. The Electronic Trip Units’ modification tolerance helps users quickly handle load adjustments and other safety conditions while ensuring optimal coordination.

A circuit breaker and its safety relays and components are tested using a primary injection test kit and secondary injection tests. The primary and secondary injection tests are performed simultaneously by passing a measured amount of current through the breaker and measuring the time it takes for the breaker to trip. For each form of operation, you choose to measure, the measured sum of current is different. They must all be completed with each step, each breaker, and each breaker feature. 

Primary Current Injection Tests

The trip device’s proper operation can be checked using the primary injection test kit, one step at a time. The main current injection method is typically the preferred test method since it incorporates the current sensors, wiring, and current conduction direction in the circuit breaker into the test. This approach, however, has one drawback: it does not always identify sensor wiring and polarity issues.

If conducting a three-phase primary injection test is impossible, the circuit breaker’s sensors and wiring should be checked independently to ensure that they are operationally sound. The trip device’s proper operation can be checked using primary current injection, one step at a time. Two adjacent phases can be coupled in series and measured as three pairs to measure current sensor polarity.

Secondary Current Injection

The secondary current injection can monitor solid-state trip units using a test package specially designed for the system. Secondary injection checks are conducted for the same purpose as the primary injection test to ensure that a circuit breaker trip unit works properly during initialization testing or repair inspections.

This testing process, unlike primary injection, does not validate the existing sensors, wiring, or circuit breaker current-carrying parts. This is the key reason that a primary injection test is equivalent to secondary injection testing.

What is the purpose of the Primary & Secondary injection test set?

The primary and secondary injection test sets are designed to test breakers’ trip functions based on whether they are mechanical, thermal magnetic, or digital. The circuit breaker’s various functions are long duration and short time, which are overcurrent safety functions; instantaneous, which is short circuit protection; and ground fault, which is ground-fault current protection.

What is the difference between Primary injection test & Secondary injection test?

primary injection test package injects a multiple of the breaker’s fault-rated current through the breaker when calculating trip time. The secondary injection test injects a percentage of the breaker’s fault-rated current directly into the trip device and timers how long it takes for the breaker to trip. Another way to look at it is that primary injection tests the breaker as closely as possible to a real-world situation. In contrast, secondary injection tests the pacing and operation of the trip device.