If there is frequent current-limitation or overcurrent alarm during the variable speed drive running, we should check the loads and inverter IGBT module is normal or not, if its good, then the failure is the Hall magnetic compensation current sensor damaged on the control circuit of the variable speed drive. Hall magnetic compensation current sensor is a device to measure the current value of sinusoidal and non-sinusoidal periodic, which can truly reflect the real current waveform, to provide a control and protection signal to the variable speed drive.
Sometimes, lightning or lightning impulse voltage also will cause the variable frequency drive damaged. In addition, if the power supply system with a vacuum circuit breaker, short-circuit on/off will generate higher impact voltage. To avoid surge voltage causes overvoltage damaged, the general method is add varistor absorption on the variable frequency drive input side, and the vacuum circuit breakers should add RC surge absorber.
Variable frequency drive power anomalies can be divided into following three types: phase loss, low voltage and power off, sometimes they maybe appear mixed. The main reasons for these anomalies are transmission line impact by wind, snow and lightning, sometimes it's the power supply system appear ground wire and phase short circuit.
If there are interference sources around the variable frequency drive, they will invade into the VFD by radiation or power cable, to cause the control circuit malfunction, and result in machine not work or shut down, even cause the VFD damaged. The specific method to reduce noise interference: Install anti-surge voltage absorption devices to the wirings of relays and contactors around variable frequency drive, such as RC surge absorber.
Variable frequency drive cooling system mainly includes heat sinks and cooling fans, wherein the cooling fan service life is short. The fan generates vibration, noise increases and finally stops when approaching end-life, then the VFD drive tipped in IPM overheat.
The affection on variable frequency drive life in the control loop circuit is the power part, the buffer capacitor in smoothing capacitor and IPM board. The ripple current pass the capacitor is a fixed value which won't be affected by the main circuit, so its life is mainly determined by the temperature and power-on time. Since the capacitors are soldered to the circuit board, it difficult to determine the capacitor deterioration by measuring the electrostatic capacity. Generally, we calculate its life base on the ambient temperature and service time.
First, we should know it's caused by loads or itself. If it's the variable frequency drive problem, we can check the trip current from the VFD operation history, to see if the current exceeds the VFDs rated current or electronic thermal relay settings value. If three-phase voltages and currents are balanced, we should consider overload or sudden change situations, such as motor stall.
Variable frequency drive includes main circuit, power circuit, IPM drive and protection circuits, cooling fan and other several parts. The structure is mostly unitized or modular. Incorrect or unreasonable setting will cause the VFD malfunction and failure easily, or can't meet anticipated operation effect. As a precaution, careful analysis before the failure is particularly important.
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