Test Applications of an Insulation Multimeter
When debugging the AC transmission system, it is necessary to use an insulated multimeter to conduct insulation tests on the main and control circuits of the frequency converter and motor respectively, in order to ensure the safe operation of the system. The Fluke1587 insulated multimeter not only provides rapid measurement of the main circuit, but also offers a 'resistance range' function for insulation testing of the control circuit.
1. The following steps should be followed when using a Fluke1587 insulated multimeter to measure the insulation of the main circuit of a frequency converter (using VACONNXP products as an example):
(1) Disconnect all external wiring of the frequency converter to ensure that the tested circuit is not connected to any power source. Then short-circuit the input terminals L1, L2, L3 and the output terminals U, V, W together, as shown in Figure 2-1.
(2) Insert the test probe of the Fluke insulated multimeter into the '+' input terminal, and then connect the other end to the 'ground point' as shown in Figure 2-2.
(3) Connect the probe to the circuit under test, and the insulation multimeter will automatically detect whether the circuit is powered on. If the voltage in the circuit exceeds 30Vacordcjlj, it will be automatically prohibited.
(4) Select the 'Insulation test' test function on the Fluke 1587 insulation multimeter.
(5) Select the appropriate test voltage (500Vdc) through the 'Range' button.
(6) Press and hold the 'Insulation test' button to read the impedance value displayed on the insulation multimeter. It may take a few seconds for the reading to reach stability. The higher the impedance value, the better. At this point, the reading is 550 megaohms, indicating good insulation. As shown in Figure 2-3.
(7) Continue to leave the probe of the insulation multimeter on the testing point, and then release the 'Insulation test' button. The tested circuit begins to discharge through the instrument until it ends.
2. When measuring the insulation of the frequency converter control circuit (taking VACONNXP products as an example), it should be noted that the 'resistance mode' of the Fluke1587 insulated multimeter strap must be used for continuity testing. Generally, the test value is 1 megaohm, indicating good insulation.
3. When using an insulation multimeter for motor insulation testing, the U, V, and W three-phase winding wires should be tested separately relative to the grounding wire. The general measurement value is>=5 megohms, indicating good insulation.
