(2)
If the VSCF trips because of a failure in the VSCF or in the airplane, the GCCU stores data in two non-volatile memories (NVM's). You can use this data in the shop or on the flight line to do trouble-shooting.
(a) The VSCF has a RS-232 serial port on the main connector. This permits you to use an "IBM compatible Personal Computer (PC)" to get failure data from the NVM in the GCCU
ú (AMM 24-21-00/101).
(b) The VSCF has a Fault History Display Module with NVM and three display lights which can be used to display the reason for any VSCF trip or detected passive fault when the VSCF is installed on the airplane (AMM 24-11-11/501).
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(3)
(4)
(5)
(6)
A
737-300/400/500MAINTENANCE MANUAL
The GCCU has protective functions that are also in the GCU. Thus, the GCU protective functions are back-ups for the GCCU protective functions. These protective functions are:
(a)
Overvoltage (130 | 3 volts)
(b)
Undervoltage (100 | 3 volts)
(c)
Overfrequency (430 | 5 Hz)
(d)
Underfrequency (365 | 5 Hz)
(e)
Overcurrent (180.5 | 13.5 Amps)
(f)
Differential Protection (25 | 5 Amps)If a failure occurs in the VSCF, these things occur:
(a)
A bad VSCF will put a signal into the differential protection circuits. This will cause the GCU to energize the feeder fault (FF) light on the M238 annunciator panel. Then, the GCU will open the GCR and the GB. This disconnects the VSCF from the ac buses.
(b)
The GCCU disconnects the generator field. This will make the VSCF output voltage go to 0 volts.
(c)
After 2 to 3 seconds, the GCCU will try to reset.
1) If the VSCF can operate, it will set the output voltage to 5-10 volts. a) Now, you can push the GEN switch to ON. The VSCF
voltage will go to 115 volts and the GCR and the GB will close.
b) Subsequently, after you push the GEN switch to OFF or do a transfer to a different power source, the VSCF voltage will go to 5-10 volts and stay there.
2) If the VSCF can not operate, the output voltage will stay at 0 volts. When you push the GEN switch to ON, the GCR and the GB will not close.
If the voltage regulator in the GCU has a failure, the VSCF will keep the output voltage between 115 and 125 volts. The VSCF will not disconnect in this case.
(a) When you open the GB by transferring the bus to another source, the output voltage will go to residual volts (Usually, it would stay at 115 volts). The GCU will see an undervoltage condition and energize the "LV" light.
The GCCU also has protection for open phase, overheat, externally generated DC content and internally generated VSCF passive faults (passive faults are faults which do not cause a VSCF trip).
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A 737-300/400/500MAINTENANCE MANUAL
~............................................................................... | VSCF Protective Functions | | Table 2 *[1] | .................................................................................
| Protective | Conditions |VSCF opens |Generator| VSCF BIT |Indication |
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