GE Industrial Solutions AF-600 FP High Power (460V_575V 150HP and above) - Manual (Page 94)

The initial test can be made with the motor connected and running its load. If suspect readings are recorded then the motor leads may have to be disconnected
to further isolate the problem.
1. Using a voltmeter, measure AC output voltage at frequency converter motor terminals 96 (U), 97 (V), and 98 (W). Measure phase to phase checking U to
V, then U to W, and then V to W.
All three readings should be within 8 VAC of each other. The actual value of the voltage depends on the speed at which the frequency converter is running. The
volts/hertz ratio is relatively linear (except in VT mode) so at 60Hz the voltage should be approximately equal to the mains voltage applied. At 30 Hz, it is about
half of that and so on for any other speed selected. The exact voltage reading is less important than balance between phases.
2. Next, monitor three output phases at frequency converter motor terminals 96 (U), 97 (V), and 98 (W) with the clamp on the ammeter. An analog device
is preferred. To achieve an accurate reading, run the frequency converter above 40Hz as this is normally the frequency limitation of such meters.
The output current should be balanced from phase to phase and no phase should be more than 2 to 3% different from another. If the above tests are successful,
the frequency converter is operating normally.
3. If a greater imbalance exists than described above, disconnect the motor leads and repeat the voltage balance test.
Since the current will follow the voltage, it is necessary to differentiate between a load problem and a frequency converter problem. Should a voltage imbalance
in the output be detected with the motor disconnected, it is necessary to test the gate drive circuits for proper firing. Proceed to the gate drive signals test (6.3.11).
If the voltage was balanced but the current imbalanced when the motor was connected, then the load is suspect. There could be a faulty connection between
the frequency converter and motor or a defect in the motor itself. Look for bad connections at any junctions of the output wires including connections made to
contactors and overloads. Also, check for burned or open contacts in such devices.
6.3.11 IGBT Gate Drive Signals Test
This procedure tests the gate drive signals at the output of the gate drive card just prior to them being delivered to the IGBTs.
A simple test to check for the presence of the gate signals can be performed with a DVM, however, to actually check the waveforms, an oscilloscope is required.
Disable the DC bus when performing this test with Test Cable p/n 6KAF6H8437. Failure to do so could result in damage to the frequency
converter if the probe is inadvertently connected to the wrong pins. Additionally, AC mains bus bars are in close proximity to these test points.
Exercise caution when working close to high voltage components.
Prior to beginning the tests, ensure that power is removed from the unit and that the DC Bus capacitors have been discharged.
Check for the presence of DC bus voltage by measuring power card connector MK105 (A) with respect to MK105 (B). The voltage should be zero (0) before proceeding.
1. For 4x-frame size units, follow the procedure in Section 7 for soft charge card removal and disengage the soft charge card far enough to disconnect
the cable plugged into the MK3.
2. Disconnect the cable from the MK3 connector on the soft charge card and connect one end of the test cable into the MK3.
3. For 4x-frame size units, reinstall the soft charge card.
4. Disconnect connectors MK100 and MK105 on the power card.
5. Connect the free end of test cable into MK105.
6. Connect the SCR gate shorting plug (included with test cable 6KAF6H8437) into the cable that was removed from MK100.
A 3 pin test connector is located on the gate drive card near each gate signal lead. These are labelled MK250, MK350, MK450, MK550, MK650, MK750, and, if the
frequency converter is equipped with a brake option, MK850 (see Illustration 6-17).
For the sake of clarity, refer to the 3 pins as one, two, and three, reading left to right. Pins 1 and 2 of each connector are in parallel with the gate drive signal sent
to the IGBTs. Pin 1 is the signal and pin 2 is common.
7. Reconnect AC power to the frequency converter.
8. In stop mode, apply power to the frequency converter.
AF-650 GP and AF-600 FP High Power Service Manual
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