In the factory test, if the A-phase coil is energized first, adjust the air gap length so that the mechanism can be reliably opened at the current SA, and then adjust the C phase in the same way. In the actual operation of the circuit breaker, three phases have current flowing at the same time.
If the three-phase balancing current flows through the circuit breaker, the current is the tens of thousands of times of the rated primary current value of the transformer. At this time, the two overcurrent releases each generate a tripping force. If the weight of the iron core is not counted, the sum of the tripping forces generated by the two overcurrent releases can just make the mechanism open, which cannot satisfy the "the circuit breaker must not trip when the rated current is 90% or less." Requirements.
In order to meet the requirements of the circuit breaker for overcurrent protection, the overcurrent trip test method of the mechanism must be improved to make the test results meet the operational requirements. Improvement of test method 2 Analysis of the problem The overcurrent trip test method of the mechanism is to apply 90% of the rated current to each overcurrent release for 5 trips without tripping, applying 10% to 110% of the rated The current is opened 5 times and should be reliably opened.
When the circuit breaker manufacturer uses the mechanism to perform the overcurrent trip test, it also tests the two phases of A and C with the rated primary current by the riser. In the actual operation, the circuit breaker has three phases and current flows at the same time, that is, the two overcurrent releases of the mechanism simultaneously generate a tripping force, so that the mechanism has been opened when the rated current is not reached once.
The analysis of the problems existing in the institutional test is as follows.
(l) For a mechanism that has been assembled and adjusted, the off-line torque required for the half shaft is constant. Since the frictional force of each transmission link of the overcurrent trip mechanism is also substantially constant. Therefore, the overcurrent tripping force required for the opening is also constant.
(2) The current in the coil of the mechanism overcurrent release is caused by the current flowing through the circuit breaker during the actual operation. Therefore, when the overcurrent trip test is performed, the test method is equivalent. The two overcurrent trip coils are energized simultaneously. The following two methods can be adopted. One is to connect two overcurrent coils in series at the same time during the test, and adjust the air gap length between the two trip units and the static iron core so that the current is less than 4.
SA does not open, the current can be reliably opened at 5-5. 5A, pay attention to make the air gap of the two trip units as the same when adjusting the air gap length; second, can give each overcurrent release The coils are energized separately and the air gap length is adjusted so that the current is at 6.
When 4A and below, the mechanism does not open, and the current is 7.11-7. 8A, the mechanism is reliably opened.
However, with this test method, the weight of the core will have a certain impact on the test results.
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