Measuring an IGBT in a VFD

Power Off: Ensure that the VFD is completely powered off and disconnected from the power source. Disconnect any external power supplies or inputs.

Discharge Capacitors: Check the VFD's manual for procedures to discharge any high-voltage capacitors. IGBTs can store voltage even when the VFD is turned off, and this can be dangerous.

Safety Gear: Wear appropriate safety gear, including insulated gloves and eye protection, if necessary.

Locate the IGBT: In most VFDs, IGBTs are usually mounted on heat sinks. They are large semiconductor devices and can often be visually identified. Consult the VFD's manual or schematic diagrams for IGBT locations.

Visual Inspection: Visually inspect the IGBT for any visible signs of damage, such as burn marks, cracks, or unusual discoloration.

Multimeter Measurement: Set your digital multimeter to diode test mode. If the IGBT is a module, you might see markings such as "L1", "L2" and "L3" for the input phases as well as "U," "V," and "W" for the different phases for the output. These markings may change depending on which brand or model of a VFD you have. Use the following steps to measure the IGBT:

Locate the large BUS capacitors. This is located either on your terminal strip or on the main power board. With your Meter in Diode mode, place your positive lead on negative side of the BUS capacitor and place the negative lead on L1. There should be a reading of 0.4-0.6. Repeat with L2, L3 and U, V and W. Any OL or shorts indicate a bad IGBT.

Next, we will switch our leads and place the Negative lead on the positive side of the BUS capacitor. With your negative lead, you will test each input and output as we did before. If all readings are correct, then the IGBT is most likely fine.

Reassembly: If you had to remove any covers or components to access the IGBT, ensure they are properly reassembled before reapplying power.