6.2.1.1 Soft Charge Fuse Test
This test is used to determine if any of the soft charge
fuses are open.
Use the 12-pin connector on the top of the rectifier
module for testing.
1.
L1 to pins 6, 11, and 12 (red wires).
2.
L2 to pins 4, 9, and 10 (white wires).
3.
L3 to pins 2, 7, and 8 (black wires).
A measurement of 0
Ω
indicates good continuity. Replace
any open fuses (infinite resistance). Note that the rectifier
module must be removed to replace fuses.
1
2
Illustration 6.4 Rectifier Detail
1
Rectifier module
2
12-pin connector
6.2.1.2 Soft Charge and Rectifier Circuit Test
Both the rectifier and soft charge circuits are tested
simultaneously. The soft charge circuit is made up of the
soft charge rectifier, fuses and the soft charge resistor. The
rectifier circuit is made up of the SCR/Diode modules. The
soft charge resistor limits the inrush current when power is
applied to the drive. The soft charge circuit card also
provides snubbing for the SCRs.
It is important to pay close attention to the polarity of the
meter leads to ensure identification of a faulty component
should an incorrect reading appear.
Remove the safety covers to access the unit.
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.
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.
Test Procedures
High Power Service Manual for Modular F Frame Drives
MG90K202 - VLT
®
is a registered Danfoss trademark
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