Analysis and treatment of motor trip caused by power supply voltage reduction

1. Fault symptoms

In September 2014, in the process of discharging material in the outer circulation of a coal ash steel plate warehouse project, the dust collecting motor on the top of the warehouse often failed to trip, resulting in the failure of the dust collector on the top of the warehouse. The feedback of field staff is as follows.

(1) Occasionally, fault trip of the dust collecting motor occurs during the starting process of the dust collector.

(2) The material in the steel plate warehouse runs for about 1 ~ 2h in external circulation, and the dust collecting motor fails to trip.

(3) When the dust collecting motor is faulty and tripping, the motor protector displays the action current of 40A.

(4) The field dust collector is PPCS32-6 type, and the main data of its nameplate are as follows: the centrifugal fan is 9-26 8D type, the flow rate is 8792 ~ 11320 m3/h, the full pressure is 3834 ~ 3638 Pa; The dust collecting motor is Y2 180M-4 type, rated power 18.5kW, rated current 36A.

Root cause search and data recording

According to the feedback from the site, our company immediately sent relevant professionals to the site to find the cause of the fault from the following aspects.

2.1 Maintenance part inspection

(1) Whether the installation of the coupling between the motor and the reducer meets the standard;

(2) rotor of disc driven fan, whether the fan has scratch friction phenomenon;

(3) whether the oil level of reducer bearing is normal;

(4) whether the dust collector cloth bag is damaged;

(5) Whether the arriving equipment parameters are consistent with the design parameters.

2.2 Electrical inspection

(1) Use insulation resistance meter to check whether the insulation of cable and motor meets the requirements;

(2) Check whether the cable connection is firm and there is no bad contact;

(3) Check the parameter Settings of the motor protector.

2. 3 Record related running data

After inspection by equipment engineers, there is no problem in the maintenance part, and there is no problem in the insulation and cable connection of electrical cables and motors. In view of the occasional fault trip of the dust collector in the starting process, in order to make the dust collector can start smoothly and record the running data, the electric machine protector action current is changed from the original 36A to 40A(i.e. 1.1 times the motor rated current). Record the data of the dust collector during operation as follows:

(1) Input voltage of the power supply line when the equipment is not in operation :AB phase voltage is 399V, AC phase voltage is 397V, and BC phase voltage is 398V.

(2) Data of the dust collector running for 4 hours without load: phase A current 34.1A, phase B current 34.6A, phase C current 33.9A; AB phase voltage is 388 V, AC phase voltage is 386V, BC phase voltage is 387V; The maximum temperature of the motor body is 73.2 ℃, and the maximum temperature of the motor bearing is 70℃.

(3) When the steel plate library is discharged by external circulation, the data of the dust collector running for 90 min are as follows: phase A current 42.2A, phase B current 39.5A, phase C current 39.8A; AB phase voltage 354V, AC phase voltage 351V, BC phase voltage 356V; The maximum temperature of the motor body is 81.4℃, and the maximum temperature of the motor bearing is 77℃.

3 Cause Analysis

Through the above data analysis and the test with clamp table, it is found that when the steel plate depot is discharged from the external circulation, the three-phase power supply voltage decreases from about 398V when the equipment is not running to about 354V when the equipment is running. At the same time, the current and temperature of the dust collecting motor are slightly higher than those in the no-load condition. According to GB 50052-2009 Specification for Design of Power Supply and Distribution System, under normal operation, the allowable voltage deviation at the motor terminals is ±5% of the rated voltage of the motor. It can be seen from the above that the actual operating voltage of the on-site dust collecting motor is much lower than the rated voltage of the motor, and the voltage deviation is about -11%, which cannot meet the requirement of ± 5% of the rated voltage of the motor in GB 50052-2009. According to the power calculation formula P= √ 3uicosφ, the power supply voltage reduced to 354V will directly lead to the motor current increased to about 40A. Because the actual current of the motor at this time is higher than the set value of the motor protector 36A, so the motor protector overcurrent protection action trip. Note: WHEN THE MATERIAL OF STEEL PLATE WAREHOUSE IS IN EXTERNAL CIRCULATION, THE DUST COLLECTING MOTOR IS CONTROLLED BY MOTOR PROTECTOR, AND THE OTHER EQUIPMENT IS CONTROLLED BY FREQUENCY CONVERTER.

After inspection, it is found that the causes of low power voltage of dust collecting motor are as follows.

(1) The incoming power supply of the electrical room of the steel plate library adopts temporary power supply, and the distance between the source point of the power supply and the electrical room of the steel plate library is about 500m.

(2) If only a single device works, the power supply provided by the electrical room of the steel plate warehouse meets the power consumption requirements of the equipment. However, there are 1 18.5KW dust collecting motor, 1 75kW Roots fan and 2 90kW Roots fans involved in the operation of the steel plate depot during the external circulation discharging. At this time, the power supply provided by the electrical room of the steel plate depot can no longer meet the requirements of the equipment.

(3) This project is under construction, and there are other temporary electrical equipment on site to obtain power from the electrical room of the steel plate warehouse, so it is more likely that the temporary electrical equipment will work with the external circulation of materials at the same time.

4. Countermeasures and effects

Replace the steel plate as soon as possible. Before the new power supply is connected, it is forbidden to work with electrical equipment at the same time.

In November 2014, the newly built transformer and distribution room of this project was officially put into use. The power supply in the electrical room of the steel plate warehouse is replaced by the power supply from the grinding electrical room. The distance from the grinding electrical room to the electrical room of the steel plate warehouse is about 60m. After the formal power supply is connected to the electrical room of the steel plate warehouse with cables of the same model and specifications as the temporary power supply cable, the power supply voltage during the external circulation discharge of the steel plate warehouse is stable between 390 and 399V. The field equipment runs normally, and the dust collector motor does not appear overcurrent tripping phenomenon anymore.