The method of measuring the state of a VFD(Variable frequency drive) by a multimeter

measuring the frequency converter by a multimeter
measuring the frequency converter by a multimeter

The method of measuring the state of a VFD(Variable frequency drive) by a multimeter

The multimeter can measure DC current, AC voltage, DC voltage. The VFD(Variable frequency drive) controls the AC motor by modifying the frequency of the power supply of the motor. This article mainly explains how to use a multimeter to measure the quality of the VFD(Variable frequency drive).

It should be noted that, for personal safety, it must be ensured that the machine is powered off and the VFD(Variable frequency drive)'s input power lines R, S, T and output lines U, V, W are removed. First put the multimeter to the “Dip” file, and then use the red meter of the multimeter and the black pen to check the following steps:

The black pen touches the negative pole P(+) of the DC bus, and the red pencils touch R, S, and T in turn, recording the displayed value on the multimeter. Then touch the red meter pen with N(-) and the black pen with R, S, 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 in the VFD(Variable frequency drive) diode rectification or soft-start resistance, otherwise, the corresponding rectifier module or soft-start resistor in the corresponding position is damaged. Phenomenon: No display.

The red meter pen touches the negative pole P(+) of the DC bus, and the black test leads touch U, V, W in turn, recording the display values ​​on the multimeter. Then touch the black test pen with N(-), and the red test leads touch U, V, W in turn, and record the display value of the multimeter. If the six display values ​​are basically balanced, it indicates that there is no problem in the VFD(Variable frequency drive) IGBT inverter module, otherwise, the IGBT inverter module in the corresponding position is damaged, and the phenomenon: no output or fault is reported.

Using a VFD(Variable frequency drive) to drive a power-matched asynchronous motor at no-load, adjust the frequency f from 50Hz to the lowest frequency.

In this process, an ammeter is used to detect the no-load current of the motor. If the no-load current is stable during the frequency declining process, it can remain basically unchanged, and it is a good VFD(Variable frequency drive).

The lowest frequency can be calculated as (synchronous speed – rated speed) x pole pair p÷60. For example, a 4-pole motor with a rated speed of 1470 rpm and a minimum frequency = (1500-1470) x 2 ÷ 60 = 1 Hz.

There is no problem with the soft-resistance resistor, but the rectifier module or soft-start resistor in the corresponding location is damaged. Symptom: No display.

The red meter pen touches the negative pole P(+) of the DC bus, and the black test leads touch U, V, W in turn, recording the display values ​​on the multimeter. Then touch the black test pen with N(-), and the red test leads touch U, V, W in turn, and record the display value of the multimeter. If the six display values ​​are basically balanced, it indicates that there is no problem in the VFD(Variable frequency drive) IGBT inverter module, otherwise, the IGBT inverter module in the corresponding position is damaged, and the phenomenon: no output or fault is reported.

Using a VFD(Variable frequency drive) to drive a power-matched asynchronous motor at no-load, adjust the frequency f from 50Hz to the lowest frequency.

In this process, an ammeter is used to detect the no-load current of the motor. If the no-load current is stable during the frequency declining process, it can remain basically unchanged, and it is a good VFD(Variable frequency drive).

The lowest frequency can be calculated as (synchronous speed – rated speed) x pole pair p÷60. For example, a 4-pole motor with a rated speed of 1470 rpm and a minimum frequency = (1500-1470) x 2 ÷ 60 = 1 Hz.

Identification of AC and DC solid state relays:

Normally, the “+” and “-” symbols are marked on the input side and output side of the DC solid state relay enclosure, and the words “Dc input” and “DC output” are marked. AC solid state relays can only be marked with "+" and "-" symbols at the input, and there is no positive or negative output at the output.

Input and output of the identification: no identification of solid state relays, multimeter R × 10k file, by measuring the positive and negative resistance of each pin to determine the input and output. When measuring the forward resistance of a certain two pins is small, and the reverse resistance is infinite, these two pins are input terminals, and the other two pins are output terminals. In a small-resistance measurement, the black pen is connected to the positive input, and the red pen is connected to the negative input..

If it is measured that the positive and negative resistances of some two pins are all 0, it indicates that the solid state relay has broken down. If the positive and negative resistance values ​​of the solid state relay pins are all infinite, it indicates that the solid state relay has been damaged by an open circuit

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