As we all know, the inverter has many protection functions, such as overcurrent, overvoltage, overload protection and so on. With the continuous improvement of industrial automation, frequency converters have also been widely used. This article will explain to you how to use a multimeter to measure the quality of the inverter.
It should be noted that, for personal safety, it is necessary to ensure that the machine is powered off, and the input power lines R, S, T and output lines U, V, W of the inverter can be removed before operation! First, turn the multimeter to the "diode" file , and then use the red test leads and black test leads of the multimeter to detect as follows:
The black test lead contacts the negative pole P(+) of the DC bus, the red test lead contacts R, S, and T in turn, and the displayed value on the multimeter is recorded. Then touch the red test lead to N(-), and the black test lead to R, S, and T in turn, and record the display value of the multimeter. If the six displayed values are basically balanced, it means that there is no problem with the diode rectification or soft-start resistance of the inverter. Otherwise, the rectifier module or soft-start resistance at the corresponding position is damaged. Phenomenon: no display.
The red test lead contacts the negative pole P(+) of the DC bus, and the black test lead contacts U, V, and W in turn to record the displayed value on the multimeter. Then touch the black test lead to N(-), and the red test lead to U, V, and W in turn to record the display value of the multimeter. If the six displayed values are basically balanced, it means that there is no problem with the IGBT inverter module of the inverter. Otherwise, the IGBT inverter module at the corresponding position is damaged. Phenomenon: no output or a fault is reported.
Use the frequency converter to drive an asynchronous motor with matching power to run at no-load, and adjust the frequency f, which starts to drop from 50Hz to the lowest frequency. In this process, use an ammeter to detect the no-load current of the motor. If the no-load current is stable during the frequency drop and can remain basically unchanged, it is a good inverter. The minimum frequency can be calculated like this, (synchronous speed - rated speed) × number of pole pairs p÷60. For example, for a 4-pole motor, the rated speed is 1470 rpm, and the minimum frequency = (1500-1470) × 2÷60=1Hz.
There is no problem with the soft-start resistance, otherwise the rectifier module or soft-start resistance at the corresponding position is damaged, phenomenon: no display.
Discrimination of AC and DC solid state relays: Usually, the input end and output end of the DC solid state relay shell are marked with "+" and "-" symbols, and the words "Dc input" and "DC output" are marked. The AC solid state relay can only mark the "+" and "-" symbols on the input end, and the output end has no positive or negative points.
Discrimination of input terminal and output terminal: solid-state relay without identification, multimeter R×10k gear, by measuring the forward and reverse resistance values of each pin respectively to determine the input terminal and output terminal. When it is determined that the forward resistance of two pins is small and the reverse resistance is infinite, these two pins are the input terminals, and the other two pins are the output terminals. In a measurement with a small resistance value, the black test lead is connected to the positive input terminal, and the red test lead is connected to the negative input terminal.
If the forward and reverse resistances of two pins are measured to be 0, it means that the solid state relay has been broken down and damaged. If the measured forward and reverse resistance values of each pin of the solid state relay are infinite, it means that the solid state relay has been damaged by open circuit.
