Maintenance of the control cabinet of the Chinese University of Hong Kong

The Chinese University of Hong Kong (Shenzhen) is a university approved by the Ministry of education and established in accordance with the regulations on Chinese foreign cooperation in running schools. The university is committed to building a first-class research university based in China and facing the world. It is committed to cultivating innovative high-level talents with international vision, Chinese tradition and social responsibility. The school running characteristics of the university are the international atmosphere, the teaching environment of both Chinese and English, the tradition of the academy system, general education, the setting of new cross disciplines and the student-oriented education concept.

At present, more than 8000 outstanding students from all over the world are studying at CUHK (Shenzhen). Since its establishment in 2014, after eight years of development, the discipline construction of the university has been gradually improved. There are six colleges including school of economics and management, School of science and technology, School of Humanities and Social Sciences, School of data science, School of medicine, School of music and one graduate school. Among them, the school of medicine currently includes clinical medicine and bioinformatics, biomedical engineering, pharmacy and bioscience in the school of life and health sciences. In the future, the school of medicine will also include the school of pharmacy, the school of public health, the school of nursing, and the Chinese Medical College.

Since the campus construction of the Chinese University of Hong Kong (Shenzhen) is built along the mountain, it is necessary to set up a special municipal booster pump room at the foot of the mountain. The pressurized pump house is operated and managed by Shenzhen Longgang water supply company. Huizhou kenfulai Pump Sales Co., Ltd. carries out daily maintenance, repair and technical improvement.

Main equipment and technical parameters of pump house

Exterior view of pump house

Photos of frequency conversion control cabinet in pump room

Fault condition

1. The users of port Zhongda responded that the liquid level in the phase I water tank was low, and the municipal pump house did not supply water to the phase I water tank.

2. After the maintenance personnel arrive at the site, the site conditions are as follows:

The indicator light of power frequency operation of No. 1 pump is on, indicating that the control circuit has given the command of power frequency operation of No. 1 pump. The relay coil of power frequency operation of No. 1 pump is powered on, and the contactor is in the closed state.

However, by observing the water pump, it was found that the No. 1 water pump was stopped and did not operate.

After opening the cabinet door of the electric control cabinet, it was found that the circuit breakers (air switches) corresponding to the power frequency operation of pumps 1 and 2 on the main circuit were all in the open state. After inquiry, no operator opened the two circuit breakers. Circuit breakers 1 and 2 jumped to the open state by themselves.

After checking the frequency converter, it is found that the frequency converter displays fault, and the fault code is 001.

After querying the fault code in the user's Manual of the frequency converter, it is determined that the 001 fault code means overcurrent fault.

Maintenance process of engineers from Huizhou kenfulai company on site

On site maintenance process:

(1) Switch to manual mode and make sure it is in shutdown state. Prevent accidental operation of the motor and damage to maintenance personnel.

(2) The fan cover of the motor was disassembled, and the water pump and motor were turned for inspection. The turning is normal, and no problems such as stagnation and rotor friction are found in the pump. It is preliminarily judged that there is no mechanical failure.

(3) At the end of the electric control cabinet, disconnect the power supply line of the motor, and use an insulated megger and multimeter to test the motor. Check the winding resistance, ground insulation and phase to phase insulation of the motor. Inspection results: the resistance of winding is normal without open circuit; The insulation is normal. Judge whether the motor is in good condition. Restore the power wiring of the motor.

(4) Check the condition of all electrical components and connecting wires in the electric control cabinet, and no scorching or open circuit is found.

(5) Check the status of thermal relay, which is used for overload and overcurrent protection. No thermal relay trip was found. The characteristic of thermal relay is that when overcurrent occurs, the more it exceeds, the faster it jumps, the less it exceeds, and the slower it jumps. And it is possible to ensure that the circuit is disconnected before the motor winding burns out. The inspection result is that the thermal relay does not trip.

(6) Check whether there are dead animals or short circuits caused by small animals. After inspection, no dead animals were found.

(7) After the above inspection, it is preliminarily judged that power can be re transmitted, fault reset and restart can be attempted.

(8) The main circuit breaker is powered off, and the frequency converter fault is reset. Close the two tripped circuit breakers one by one. And set No. 2 pump to operate independently (cut out No. 1 pump).

(9) Turn the change-over switch to the manual position and restart the machine. Manually start the No. 2 pump, start the No. 2 pump with frequency conversion, start working, and restore water supply.

(10) Manual shutdown. The change-over switch is rotated to the automatic position. 2 # pump is started automatically. 2 # pump is started by frequency conversion and operates with frequency conversion. The water supply is normal.

Fault replay and possible cause analysis

1. The thermal relay does not operate. It indicates that the motor is not overloaded or has not been overloaded for a long time.

2. The circuit breaker trips.

The specification of the circuit breaker is ic65n C 50A. It is a miniature circuit breaker with a rated current of 50A.

The circuit breaker is a switching device that can open, close, carry and disconnect the current under normal circuit conditions, and can close, carry and disconnect the current under abnormal circuit conditions (including short circuit conditions) within a specified time. Its protection is:

A. short circuit protection: when the live wire and the neutral wire (ground wire and live wire) contact, the instantaneous current is very large and the circuit breaker trips.

B. overload protection: the circuit breaker trips when the electric current exceeds the rated current of the appliance.

The tripping characteristic of type C circuit breaker is: 5 ~ 10In, that is, 5 ~ 10 times the rated current.

The tripping current of the circuit breaker of this specification is 250A ~ 500A.

The matching motor power of the pump is 22KW. Rated current: 40.5a. It is found that the starting current is 8.1 times of the rated current. That is, when the direct starting method is adopted, the current at the moment of starting is 328a.

It can be seen that the starting current at the moment of starting the motor is within the tripping current range of the circuit breaker, and the circuit breaker trips, that is, trips.

3. The cause of frequency converter skip current fault is unknown. However, based on experience, there may be the following reasons:

(1) the capacity of the frequency converter is 22KW, and the motor is also 22KW. This ACS510 frequency converter belongs to the general light-duty frequency converter. Generally speaking, it needs to be enlarged by one gear for matching (such as 22KW motor and 30kW frequency converter). Otherwise, overcurrent fault and undervoltage fault may be reported (please note that it is only possible). This is metaphysics. If you don't enlarge it by one gear, you may report faults occasionally or never. However, after zooming in by one gear, the fault will not be reported for no reason.

(2) it may also be that water needs to be supplied to phase 1 and phase 2 pools at present. When the PLC program judges that the water supply of one pump is still insufficient to meet the water supply demand of shanshang port Zhongda, the second pump will be automatically started. However, because there is only one frequency converter, the second pump can only be started at power frequency. When starting at power frequency, the starting mode is direct starting. The starting current is large, which lowers the power supply voltage and triggers the overcurrent protection of the frequency converter.

4. Fault replay

It is necessary to supply water to phase 1 and phase 2 pools. When the PLC program judges that the water supply of one pump is still insufficient to meet the water supply needs of shanshang port Zhongda, à will automatically start the second pump.

However, since there is only one frequency converter, the second pump can only be started at power frequency.

① 2 # pump is started at power frequency, and the starting mode is direct starting.

② The starting current of No. 2 pump directly starts is large, the power supply voltage is pulled down instantaneously, and the frequency converter reports a fault.

③ The starting current of 2 # pump started directly was large, and the circuit breaker of 2 # pump tripped.

④ PLC gets fault feedback of frequency converter. Try to start No. 1 pump directly. The power frequency operation command of No. 1 pump is given.

⑤ No. 1 pump starts directly; The circuit breaker of No. 1 pump tripped due to large starting current.

⑥ Since then, the power frequency circuit breakers of 1 and 2 pumps have tripped; The frequency converter is in fault alarm state.

⑦ Stop water supply.

(Note: the above fault replay is only a post analysis and cannot guarantee the accuracy of its occurrence.)

Modification suggestions for users

1. If the ACS510 series light load general frequency converter is still used, it is recommended to replace the current 22KW frequency converter with a 30kW frequency converter;

2. Add a 30kW frequency converter (ACS510 series light load general frequency converter). Two pumps on site and two frequency converters can be used for startup and operation. Failure of one frequency converter will not affect the operation of another pump.

3. The circuit breaker shall be replaced in strict accordance with 1.5 times of the rated current of the motor, and type D circuit breaker shall be selected. That is, type D 63A circuit breaker is selected. (however, the space in the cabinet is tight. After replacement, the wiring in the cabinet may be ugly.)

4. Replace the original 4 * 16 + 1 * 10 cable from the on-site metering cabinet to the PLC frequency conversion control cabinet with YJV 3 * 70 + 2 * 35 power cable; Replace the current circuit breaker 63A in the metering cabinet with 160A; The main circuit breaker of the PLC frequency conversion control cabinet was also replaced with 160A.