Several methods for troubleshooting the tripping o

2022-09-21
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Several methods for troubleshooting the tripping of water pump

1: fault phenomenon:

since the 125 MW unit of a power plant was put into operation, the feed pump occasionally tripped as soon as it was switched on, and there was no loss of any signal relay. After troubleshooting the switch mechanism, check the cables, secondary circuit wiring, relays and their settings according to the conventional method, and the restart is often successful. Later, it was suspected that it was caused by the software failure of DCS system, but this phenomenon still occurred when the operation was changed on the control panel

2: test to find out the cause:

to find out the cause of this phenomenon, observe the changes of each meter during the closing process of the switch to confirm what caused it to trip

in the test, the voltmeter monitors the microcomputer trip circuit, the milliammeter monitors the action of differential relays 1cj and 2cj, and the ammeter monitors the thermal protection circuit. After connecting the meter, start the feed water pump. After a period of test, there was finally a trip when the feed water pump was started. At the same time, it was observed that the pointer of the milliammeter was actively introduced into the upstream and downstream supporting enterprises of the industrial chain, and other monitoring meters did not respond. The newly replaced xjl-0025/31 integrated block signal relay 1xj also acted and dropped, indicating that the trip was caused by the action of differential protection

3: analysis of the lithium iron phosphate series and three yuan series batteries under the national energy battery:

differential protection action. First of all, it is suspected that these verification regulations in the protected equipment are also an important basis for selecting environmental and reliability experimental equipment. There is a failure. Through routine inspection, the feed pump motor and its cable are normal, the differential relay is verified to be normal, and the polarity of the current transformer is correctly connected. After eliminating the causes of equipment faults and wiring errors, the differential protection acts during the motor starting process, indicating that the differential current of the differential circuit exceeds the setting value of the differential relay in this process

under normal circumstances, there are two main reasons for the differential current of the differential circuit: first, the transformation ratio error of the current transformers on both sides of the motor is different, and there is a small differential current, which is less than 5% of the rated current ID of the motor. Second, the difference between the secondary loads of the current transformers on both sides of the head and tail will also cause the difference of their transformation ratio, so there is a differential current. The load difference of the current transformer in the differential protection circuit of the feed pump motor is only the difference in the length of the secondary cable, which is about 50 m. under the rated current, the power consumption of the differential relay is not more than 3 VA, and the secondary load is not heavy. Through inspection, it is found that the models of current transformers at the head and tail sides for differential protection of feed pump motor are lmzbj-10, class B, 15 times the rated current, the transformation ratio is 600/5, and the capacity is 40 VA, which can fully meet the requirements of secondary load

the above analysis is based on the normal operation conditions. When the motor is started, the situation is different. When the motor starts, the current is large, and the current transformers on both sides of the head and tail may be saturated. At this time, due to the inconsistent magnetization characteristics of each current transformer, the secondary differential current may be large. According to the setting instructions of lcd-12 differential relay of Acheng relay factory, the setting value of relay action current izd= △ I1 × kk × in/n=0.06 × three × 356/120=0.534a (where: △ I1 - the maximum error of the head and tail current transformers during normal operation, 0.04 ~ 0.06; KK - the reliability coefficient, 2 ~ 3; in - the rated current of the motor; N - the transformation ratio of the current transformer). It should be set at the position of 1.0A. When using class B current transformer, when the action current of the differential relay is set at 1.5A and the braking coefficient is 0.4, the differential protection still occasionally acts when the motor is started, because the saturation point of the magnetization characteristics of class B current transformer is low and the anti saturation ability is low, which can not meet the requirements of the visual electrical appliances for differential relay inspection. Generally, the current transformer of differential protection circuit is required to adopt level D. the saturation point of level D transformer is higher, which is not so easy to be saturated, and can reduce the differential current flowing through the differential circuit when the motor is started. After replacing the current transformer with level D current transformer and setting the action current of the differential relay at 1.0A and the braking coefficient at 0.4, there was no fault of tripping as soon as the switch was closed. (end)

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