DC circuit breakers are common protective components in DC systems of substations and power plants in power systems. To prevent the occurrence of overstep tripping accidents, it is necessary to test the protection characteristics of each DC circuit breaker in the DC system, determine the tripping time of the circuit breaker under different short-circuit currents, conduct effective analysis on the protection characteristics and protection grade coordination of DC circuit breakers, and verify whether the differential coordination between upper and lower-level circuit breakers in the DC system is reasonable. The following introduces the time-current characteristic test of DC circuit breakers using the BD-500A DC Circuit Breaker Time-Current Characteristic Tester.

01 Test Wiring

Connect the red wire of the positive output terminal of the BD-500A DC Circuit Breaker Time-Current Characteristic Tester to the input terminal of the air circuit breaker, and connect the black wire of the negative output terminal to the output terminal of the air circuit breaker. Keep the air circuit breaker in the open state before the test.

02 Time-Current Characteristic Test Method

Turn on the power supply, start the BD-500A DC Circuit Breaker Time-Current Characteristic Tester, and close the air circuit breaker. Set the parameters in accordance with GB/T 10963.2-2020 Electrical Accessories - Circuit Breakers for Overcurrent Protection for Household and Similar Uses - Part 2: Circuit Breakers for AC and DC. The test points are shown in the table below:

△ Time-Current Operating Characteristic Table

The DC circuit breaker tested this time is a Siemens Type C 6A DC air circuit breaker. Tests were carried out at 1.13 times, 1.45 times, 2.55 times, 7 times and 15 times the rated current respectively, and the tripping status and tripping time of the air circuit breaker were observed.

Note: Cold state refers to cooling the air circuit breaker for a period of time after completing the previous test.

03 Test Result Analysis

△ Raw Test Result Data

Test Result Analysis:

At 1.13 times the rated current: the air circuit breaker did not trip after a continuous test of 1 hour.

At 1.45 times the rated current: the air circuit breaker tripped automatically at the 39th minute.

At 2.55 times the rated current: the air circuit breaker tripped automatically in 22 seconds.

At 7 times the rated current: the air circuit breaker tripped automatically in 3 seconds.

At 15 times the rated current: the air circuit breaker tripped automatically in 36.4 milliseconds.The test results meet the requirements of GB/T 10963.2-2020, and the air circuit breaker is qualified.