1. Fault phenomenon

In September 2014, during the external circulation discharging operation of a fly ash steel plate warehouse project, the dust collection motor on the top of the warehouse often failed to trip, causing the dust collector on the top of the warehouse to be unable to work. Feedback from on-site staff is as follows.

(1) Occasionally the dust collection motor fails and trips during the starting process of the dust collector.

(2) The external circulation of materials in the steel plate warehouse runs for about 1 to 2 hours, and the dust collection motor fails and trips.

(3) When the dust collection motor trips due to fault, the operating current displayed by the motor protector is 40A.

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

2 Root cause search and data recording

Based on 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 standards;

(2) Turn the fan rotor to see if there is any scratching or friction in the fan;

(3) Is the oil level of the reducer bearing normal?

(4) Whether the dust collector bag is damaged;

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

2.2 Electrical part inspection

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

(2) Check whether the cable wiring is firm and whether there is any bad contact;

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

2. 3Record relevant operating data

After inspection by the equipment engineer, there were no problems with the mechanical part, and there were no problems with the electrical cables, motor insulation, cable wiring, etc. In view of the occasional fault tripping of the dust collector during the starting process, in order to enable the dust collector to start smoothly and record operating data, the operating current of the motor protector was changed from the original 36A to 40A (i.e. 1.1 times the rated current of the motor) . The data recorded when the dust collector is running is as follows:

(1) The power incoming line voltage when the equipment is not running: AB phase voltage is 399V, AC phase voltage is 397V, and BC phase voltage is 398V.

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

(3) When the steel plate warehouse is discharged from the external circulation, the data of the dust collector operating for 90 minutes: A-phase current 40.2A, B-phase current 39.5A, C-phase current 39.8A; AB phase voltage 354V, AC phase voltage 351V, BC The phase voltage is 356V; the maximum temperature of the motor body is 81.4℃, and the maximum temperature of the motor bearing is 77℃.

3 reasons analysis

Through the above data analysis and clamp meter test, it is found that when the steel plate warehouse is discharged from the external circulation, the three-phase power supply voltage drops from the no-load voltage of about 398V when the equipment is not running to about 354V when the equipment is running with load. At the same time, the dust collection motor The current and motor temperature are slightly higher than when no-load. According to GB 50052-2009 "Code for Design of Power Supply and Distribution Systems", under normal operating conditions, 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 collection motor is much lower than the rated voltage of the motor, and the voltage deviation is about -11%. It can no longer meet the requirements of GB 50052-2009 that the allowable voltage deviation is ± 5% of the rated voltage of the motor. According to the power calculation formula P=√3UIcosφ, reducing the power supply voltage to 354V will directly cause the motor current to increase to about 40A. Since the actual current of the motor at this time is higher than the set value of 36A of the motor protector, the overcurrent protection of the motor protector trips. Note: When the steel plate warehouse materials are circulated externally, the dust collection motor is controlled by a motor protector, and the other equipment is controlled by a frequency converter.

After inspection, it was found that the reasons for the low power supply voltage of the dust collection motor are as follows.

(1) The incoming power supply to the electrical room of the steel plate warehouse is a temporary power supply, and the distance from the power source point to the electrical room of the steel plate warehouse is approximately 500m.

(2) If only a single piece of equipment is working, the power supply provided by the electrical room of the steel plate library meets the power requirements of the equipment. However, the equipment involved in the operation when the steel plate warehouse is discharged from the external circulation includes an 18.5kW dust collection motor, a 75kW Roots blower, and two 90kW Roots blowers. At this time, the power supply provided by the electrical room of the steel plate warehouse can no longer satisfy the equipment. Electricity requirements.

(3) This project is under construction. There are other temporary electrical equipment on site that draw power from the electrical room of the steel plate warehouse. There is a high possibility that the temporary electrical equipment and the external circulation of materials will work at the same time.

4 Countermeasures and effects

Replace the power source point of the main incoming line in the electrical room of the steel plate warehouse as soon as possible. Before the new power supply is connected, electrical equipment is prohibited from working at the same time.

In November 2014, the newly built power transformation and distribution room for this project was officially put into use. The power supply in the electrical room of the steel plate library is replaced by being introduced from the grinding electrical room. The distance from the grinding electrical room to the electrical room of the steel plate library is about 60m. After the official power supply is connected to the electrical room of the steel plate warehouse using a cable of the same type and specification as the temporary power cable, the power supply voltage during the external circulation of the steel plate warehouse is stable between 390 and 399V. The on-site equipment operates normally and the dust collector motor resumes operation. No overcurrent tripping occurred.