Sun, Dec 5, 2021

What is the Primary Current Injection Test?

For high voltage and high current substations or circuits, the primary injection test kit is functional. It simply refers to the flow of rated current across the circuit under test. If the circuit’s rated current is 2000 A, then 2000 A of current must flow through the circuit to guarantee the equipment’s general health and the protection scheme’s functioning.

Power circuit breakers need excellent maintenance to ensure their dependability and safety. Maintenance plans must be tailored to the application, well-planned, and carried out by industry best practices and manufacturer guidelines.

Types of Primary Injection Tests performed.

1. Stability Test 

The CTs may have been connected to the incorrect polarities during commissioning. Under typical circumstances, a flow of net differential current sum of each CT secondary current will pass through the relay. Differential Protection will function to trip the breaker if this value exceeds the preset value. Maybe this is not what you’re expecting. During the primary injection test, this commissioning error may be discovered.

We may verify the differential current in the relay while the primary current passes through the circuit. CT polarities are accurate if the differential current is zero. However, if the differential current equals the total of individual CT secondary currents, the CTs are polarized incorrectly. As a result, we may take remedial action before the system goes live.

2. Loose Connection 

If the rated current flows during the primary injection test, a loose connection may readily be detected if there is sparking in the connection/joint. If just a tiny amount of electricity flows throughout the test, there is unlikely to be a spark. This test verifies that the CT circuits are correctly linked to the appropriate cores and that the circuit is free of errors.

Before beginning this test, single-point grounding for CT circuits must be confirmed. With all linked loads, inject 25% of rated primary current between one phase and earth. Measure secondary current in CT circuits at all locations. It will be done for the other stages as well.

3. Core identification 

When a CT contains several cores, each of which is utilized for a distinct purpose, during the primary injection test, the cores may be identified by shorting one of the cores at the CT terminal and testing for no current only under appropriate load. Other cores may be validated in the same way. With all linked loads, inject 25% of rated primary current from phase to phase. Measure secondary current in CT circuits at all locations. It will be done for the other stages as well.

4. Switchgear Testing  

Both assembly makers and users must evaluate low voltage switchgear and control gear assemblies for high current compliance with applicable product standards. Carelabs uses equipment to evaluate the assembly’s rated short-time current and MCB/MCCB tripping time performance, including thermal and short-circuit trips.

3. Heat Runs 

Carelabs conducts heat runs with the assistance of amplifier-based high current producing devices, keeping the current injection constant during long-term testing and monitoring the corresponding time.

4. Relay Testing 

Primary faults are simulated to ensure that protective relays function properly; trip durations are monitored and recorded with a 1 ms precision by the system. The most sophisticated main primary injection test kit for protection relays features current automated regulation, pre-set current injection, injection time management, and test results storing.

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