GE AF-650 GP Operating Instructions Manual page 77

Main rectifier circuit test part I
1. Connect positive (+) meter lead to positive (+) DC bus.
2. Connect negative (–) meter lead to terminals L1, L2, and L3 in turn.
Each reading should show infinity. The meter will start at a low value and slowly climb towards infinity due to capacitance within the drive being charged by the
meter.
Incorrect reading
With the Part I test connection, the SCRs in the SCR/Diode modules are reverse biased so they are blocking current flow. If a short circuit exists, it would be possible
that either the SCRs or the diodes in the soft charge rectifier are shorted. To isolate between SCRs or the soft charge rectifier, internal module testing must be
performed.
Main rectifier circuit test part II
1. Reverse meter leads by connecting negative (–) meter lead to positive (+) DC bus.
2. Connect positive (+) meter lead to L1, L2, and L3 in turn. Each reading should show a diode drop.
Incorrect reading
With the Part II test connection, even though the SCRs in the SCR/Diode modules are forward biased by the meter, current will not flow through the SCRs without
providing a signal to their gates. The upper diodes in the soft charge rectifier are forward biased so the meter reads the voltage drop across those diodes.
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If an open reading were present, it would indicate the upper diodes in the soft charge rectifier are open. It could also indicate that one or more of the soft charge
fuses are open. It could further indicate that the soft charge resistor is open. To isolate between the three possibilities, internal module testing must be performed.
A short circuit reading indicates either one or more of the upper soft charge rectifier diodes are shorted or the SCRs are shorted in the SCR/Diode module. To
isolate between SCRs or the soft charge rectifier, internal module testing must be performed.
Main rectifier circuit test part III
1. Connect positive (+) meter lead to negative (-) DC bus.
2. Connect negative (–) meter lead to terminals L1, L2 and L3 in turn. Each reading should show a diode drop.
Incorrect reading With the Part III test connection, the diodes in the SCR/Diode modules are forward biased as well as the lower diodes in the soft charge rectifier.
The meter reads the diode drops. If a short circuit exists it would be possible that either the diodes in the SCR/Diode modules or the lower diodes in the soft charge
rectifier are shorted. To isolate between SCRs or the soft charge rectifier, internal module testing must be performed.
Although an open reading is possible, it is unlikely since that indicates that
both the diodes in the SCR/diode modules and the lower diodes in the soft
charge rectifier are open. Should that occur, replace both diodes.
Main rectifier circuit test part IV
1. Reverse meter leads by connecting negative (–) meter lead to negative (-) DC bus.
2. Connect positive (+) meter lead to L1, L2 and L3 in turn. Each reading should show infinity.
Each reading should show infinity. The meter will start at a low value and slowly climb toward infinity due to capacitance within the drive being charged by the
meter.
Incorrect reading
With the Part IV test connection, the diodes in the SCR/Diode modules are reversed biased as well as the lower diodes in the soft charge rectifier. If a short circuit
exists it would be possible that either the diodes in the SCR/Diode modules or the lower diodes in the soft charge rectifier are shorted. To isolate between SCRs
or the soft charge rectifier, internal module testing must be performed.
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High Power Service Manual for Unit Sizes 6x