What is the reason for the centrifugal pump trip

In general, the main reasons for the pump trip are: (1), the use of centrifugal pump head less than the head of the pump too much lead to excessive flow after the current rise and over current, the solution control the outlet valve opening flow control and the current Down to allow the current range, or change the impeller diameter to reduce the pump head. (2), the pump motor damps lead to excessive current. (3), pump motor quality problems. (4), the pump voltage is unstable. (5), pump control cabinet system problems.
1: centrifugal pump trip fault phenomenon
    After the unit has been put into operation, the centrifugal pump will work for a period of time after a closing trip. After excluding the switch mechanism failure, according to the conventional method to check the cable, the secondary circuit wiring and the relay and its settings are normal, start again and often successful. After the suspected dcs system caused by a soft fault, but changed in the control panel operation, this phenomenon will still occur.
2: Centrifuge the cause of the pump trip
In order to find out the cause of this phenomenon, observe the change of the meter in the process of closing the switch to confirm what causes it to trip.
Test which the voltmeter monitor microcomputer trip circuit, mA table monitor differential relay 1cj, 2cj action, ammeter monitoring thermal protection circuit. After a good meter, start the pump, after a period of time test, and finally once a pump to start the trip, while observing the milliphe pointer deflection of the pointer, the other monitoring table does not respond, the new put on xjl -0025/31-type integrated block signal relay 1xj also action out of the card, indicating that the differential protection action caused by tripping.
3: Centrifugal Pump Trip Root Cause Analysis
     Differential protection action, first suspected of being protected within the equipment failure. Through routine inspection, centrifugal pump motor and its cable normal, differential relay calibration is normal, the current transformer polarity connection is correct. After troubleshooting the cause of the equipment failure and wiring errors, the differential protection operates during the motor start, indicating that the differential current in the differential circuit exceeds the differential relay setting during this process.
     Under normal circumstances caused by differential circuit differential current causes there are two main points: First, the motor on both sides of the current transformer variable ratio error is different from the existence of a very small difference current, the current difference is less than the motor rated current id 5% The Second, the difference between the secondary load on both sides of the current transformer will also cause the difference between the variable ratio, so there is a differential current. The difference between the current transformer load in the differential protection circuit of the feed pump motor is only about 50 m in the length of the secondary cable, and the power consumption of the differential relay is not more than 3 va at the rated current, and the secondary load is not weight. Inspection found that the pump head motor differential protection with the first and second side of the current transformer models are lmzbj-10, b class 15 times the rated current, variable ratio 600/5, capacity 40 va, fully meet the secondary load requirements.
  The above analysis is based on the normal operation of the conditions, the motor starts, the situation is different. Motor current is very large start, both ends of the current transformer may be saturated, this time due to the current transformer magnetization characteristics are inconsistent, the secondary difference current may be great. According to the sub-relay factory lcd-12 differential relay set instructions, the relay action current setting value izd = △ i1 × kk × in / n = 0.06 × 3 × 356/120 = 0.534a (where: △ i1- First and the end of the current transformer normal operation of the maximum error, 0.04 ~ 0.06; kk-reliable coefficient, 2 ~ 3; in-motor rated current; n-current transformer ratio). Should be set at 1.0a position. In the case of the use of b-class transformer, the differential relay operating current is set at 1.5a and the braking coefficient is 0.4, the differential protection is occasionally operated at the time of starting the motor due to the saturation characteristic of the b-type current transformer Lower, low resistance to saturation, can not meet the requirements of differential relays. Usually require differential protection circuit current transformer using d-class, d-class transformer saturation point higher, not so easy to saturation, can reduce the motor when the differential flow through the differential circuit current. In the replacement of the d-level current transformer, while the differential relay operating current set at 1.0a, the braking coefficient of 0.4, there has been no switch off the trip that is the fault.