Danfoss VLT 3032 Service Manual

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Contents

Danfoss VLT 3032 Service Manual Manual pdf 25 page image

26TESTING THEINVERTER SECTIONThe purpose of statically testing the inverter section is to rule out failures of the IGBT power devicesand the snubber diodes. If a short circuit is discovered during the testing, the particular devices canbe pinpointed by noting the output terminal indicating the short circuit. The output terminals aredesignated with a letter corresponding to the phase that feeds that terminal. When looking in the unit,the "U" phase is on the top, "V" phase in the middle and the "W" phase on the bottom. In each phasethe negative half of the phase in on the right and the positive half is on the left.1. Prior to making the test, it is necessary to disconnect the motorleads from the unit. By not doing so, the low resistance windingsof the motor will make a short circuit on one terminal also appearon the other terminals.2. Connect the positive (+) meter lead to terminal 89 (+VDC).Connect the negative (–) meter lead to terminals 96 (U), 97 (V),and 98 (W) in turn. Each reading should show open.3. Reverse the meter leads connecting the (–) lead to terminal 89(+VDC) and the (+) meter lead to terminals 96 (U), 97 (V), and98 (W) in turn. Each reading should show a diode drop.4. Connect the positive (+) meter lead to terminal 88 (–VDC).Connect the negative (–) meter lead to terminals 96 (U), 97 (V),and 98 (W) in turn. Each reading should show a diode drop.5. Reverse the meter leads connecting the (–) lead to terminal 88(–VDC) and the (+) meter lead to terminals 96 (U), 97 (V), and 98(W) in turn. Each reading should show open. Test is complete.Incorrect readings indicate a faulty IGBT and/or Snubber Diode. Tofurther identify the faulty component the IGBT Snubber Board must beremoved. The Snubber Diodes on the IGBT Snubber Board and theIGBT's can then be tested individually. See Removing and ReplacingGate Card and IGBT on page 32.Once the IGBT Snubber Board is removed the Inverter Section can beretested, using the same tests as above, to verify the condition of theIGBT's.Testing Snubber DiodesTo test the Snubber Diodes connect the positive (+) meter lead to theAnode (+) and the negative (–) meter lead to the Cathode (–) of eachdiode. Each reading should show a diode drop.Reverse the meter leads connecting, the (–) lead to the Anode (+) andthe (+) meter lead to the Cathode (–) of each diode. Each readingshould show open.Incorrect readings indicate a faulty Snubber Diode. Replace the SnubberBoard.96 97 98 89 88AC LINE AND MOTOR WIRINGSNUBBER DIODES D1 - D6Anode (+)Cathode (–)D3 D4D1 D2 D6D5