3-28
Malfunctions Not Indicated by a Fault
24V Internal Unregulated Supply (Series A)
The 24V unregulated power supply is used to supply power for SCR gate
firing signals, the 24V ECOAST string, the pre-pilot relay, and the “faulted”
relay. The components include a step-down transformer located under the
top magnetics bracket, the rectifier and filter capacitors that are located on
The PSI Board. A failure will exhibit a drive fault CP-15 “24V Power
Supply Loss”. Follow the procedure below if a 24V power supply
malfunction is suspected.
1.
Measure the +24V supply level on the PSI Board. With the DVM on the
200V DC range, measure the potential from TP5 to TP23. The voltage
should be 24V DC 6.0 V.
2.
Measure the 20V AC source for the 24V supply. With the DVM on the
200V AC range, measure across J2-9 and J2-10 on the PSI Board. The
measured potential should be 20V AC 30%. If no potential is measured,
check fuse F7 on the top panel. Remove all power prior to checking the
condition of the fuse. If the potential is correct, replace the PSI Board.
3.
If after replacing F7, the fuse still opens, replace the stepdown
transformer 1PT. It is located on the back side of the magnetics bracket
that mounts the incoming protection devices.
Magnetics Bracket Assembly Components
The magnetics bracket is located at the top of the drive. It includes TB1,
TB2, F4 through F8, the pilot relay, 24V supply transformer, and 115V
distribution block. The following procedures describe the remaining
components, not already covered, and how to test them.
Disconnect and lock–out ALL incoming voltage sources prior to
performing any of the tests below. Verify that the 3 phase high voltage is
removed from the incoming protection devices, either F1 – F3 or the main
circuit breaker CB1. Also verify that the 115V logic supply and contactor
power is removed from TB2–3,4, and 5. If an external field supply is used,
verify that it is likewise removed by checking TB1–1 and 5.
1.
Fuses F4 through F6 are 25A rectifier type fuses. These fuses are a
rejection style rectifier type fuse and are sensitive to their orientation in
the fuse holders. The keyed end must be inserted downward in the fuse
holder.
2.
Fuse F7 provides protection for the 24V supply transformer. This fuse is
a fragile glass type and caution should be exercised when handling it.
3.
Fuse F8 provides protection for the 115V circuits. This fuse is a fragile
glass type and caution should be exercised when handling it.
4.
The pilot relay is located on the backside of the magnetics panel.
Remove the wire harness at J1 on the PSI Board. With the DVM on the
20k ohm range, measure the resistance of J1–1 and J1–2 in the harness.
It should be 3.5K ohms 10%.
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