This article shares two case studies of inverters failing to start, illustrating the causes and solutions for inverters failing to start due to defects in control circuit design and inverter parameter settings that do not meet application requirements, as well as the lessons learned from these troubleshooting experiences.
Troubleshooting Case 1 for Inverter Failure to Start
Faulty device: JP6C-T9 frequency converter.
Fault phenomenon: This frequency converter is used to regulate the speed of a water pump motor , but the frequency converter sometimes starts and sometimes fails to start.
Diagnostic analysis:
① The frequency converter and motor were inspected and found to be in good working order.
② The control circuit of the frequency converter is shown in Figure 1A. The start-up of the frequency converter is controlled by terminal FWD. Analysis suggests that the main circuit of the frequency converter should receive the power supply voltage in advance. However, the auxiliary normally open contact of the main contactor KM is connected between FWD and CM. The main circuit of the frequency converter can only receive the power supply voltage at the same time as the auxiliary contact closes and terminal FWD receives the start signal. This indicates that the time for the main circuit to receive the power supply voltage is delayed, resulting in difficulty in starting the frequency converter.
Figure 1A Figure 1B
Troubleshooting: Improve according to Figure 1B by adding a time relay KT and replacing the auxiliary normally open contact of KM in Figure 1A with its delayed-closing normally open contact. This ensures that the main circuit receives the power supply voltage earlier, and the FWD terminal receives the start signal after a delay of 2-3 seconds, guaranteeing reliable start-up of the frequency converter.
[Experience Summary] Variable frequency drives (VFDs) are electrical devices integrating electrical and electronic technologies. When asynchronous motors use VFD speed control technology, speed adjustment is convenient, energy is saved, and operation is stable and reliable, hence their increasingly wide application. However, familiarity with their performance and control circuits is essential for effective use. When designing the electrical diagram for the VFD starting circuit, the following should be noted: If the VFD main circuit incoming power switch is a contactor, a time relay should be added to delay the start signal before sending it to the VFD starting terminal (FWD). If the VFD main circuit incoming power switch is a circuit breaker, the circuit breaker should be closed first, and then the start signal should be sent to the VFD starting terminal (FWD). This circuit design can prevent the VFD from failing to start normally.
Troubleshooting Case 2 for Inverter Failure to Start
Faulty equipment: ABB AC8510-01 frequency converter (15kW).
Fault Description: This frequency converter is used to control the chilled water circulating pump (14kW) in the refrigeration system. After a shutdown, the frequency converter fails to start when the chilled water circulating pump is restarted.
Diagnostic analysis:
① Observe the inverter display: frequency 13Hz, torque 45%, current slowly rises from 15A to 32A, exceeding the motor's rated current (28.8A). Then these numbers start to jump, the motor stops turning and makes a "humming" sound.
②After several tests, the motor became hot, and the casing was slightly hot to the touch. The frequency converter displayed fault code "1".
③ Consult the instruction manual. Alarm code "1" indicates faults such as motor overload and short acceleration time.
④ Check the main circuit power supply; there is no phase loss and the voltage is normal.
⑤ Manually rotating the circulating pump felt easy, indicating no overload issue. There are two circulating pumps in total, one in operation and one on standby, both controlled by the same frequency converter. Switching to the other circulating pump for testing also failed to start. This indicates the fault lies not with the circulating pump, but with the frequency converter.
⑥ Adjusting the acceleration time parameters (2202#, 2205#) to appropriately extend the start-up acceleration time did not resolve the problem.
⑦ Upon further inspection of the frequency converter, it was found that the output voltage was only about 30V after startup, which resulted in a small output torque and an inability to drive the circulating pump motor.
⑧ Check the original output torque parameters, which were set according to the load of fans and water pumps, and are consistent with the actual load on site.
Troubleshooting: Following the instructions in the manual, adjust some parameters controlling the output torque to increase the output torque. The parameters to be adjusted are:
①2101# (Startup method selection), originally set to "1", now changed to "4".
②2110# (torque boosting current), originally set to 100%, now changed to 150%.
③2603# (1R compensation voltage), originally set to "one", now changed to "12".
④2605# (Voltage/frequency ratio in the case of weak magnetic field), originally set to "2", now changed to "1".
After this adjustment, the frequency converter returned to normal operation.
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