(8)
The primary purpose of the GCB is to apply 115 volt ac, 400 Hz power from the IDG to their individual load buses, or to remove the voltage when directed.
(a)
The GCB operates in conjunction with the GEN CONTROL switch and the GCU. Actuation of this switch to the latched (in) position will close the GCR in the GCU. When generator power is of proper voltage and frequency, the GCU will automatically close the GCB. Actuation of the GEN CONTROL switch to the released (out) position will simultaneously actuate the GCR and trip the GCB.
(b)
The GCB can also be tripped as a result of GCU internal protective circuit operation, or by operation of the IDG DRIVE DISC switch. The GCB can also be operated by power transfer control circuitry to provide power transfer. Momentary actuation of the DRIVE DISC switch decouples applicable GCR and GCB. Reconnection of a disconnected IDG is a ground operation only.
(c)
When the GCB is energized, a nominal 28 volt dc close signal is provided to the GCB close coil circuit. When the GCB is deenergized, a nominal 28 volt dc trip signal is provided to the GCB trip coil. The GCB can also be deenergized directly from the GEN CONTROL switch on the electrical system control module.
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(d)
The GCB contacts will open after a trip signal is applied to the GCR. The system can be reset after a protective function trip by actuating the GEN CONTROL switch to the released (out) position and then returning it to the latched (in) position. This will again close the GCR and GCB as described above. If the fault condition is still present or reoccurred, a second protective trip function will be initiated.
(e)
The OFF indicator light in the GEN CONTROL pushbutton switchlight will be illuminated whenever the GCB is tripped. When the GCB is closed, the indicator light will be extinguished.
(9)
The primary purpose of the BTB is to parallel the 115 volt ac, 400 Hz power from the ac buses to the sync buses for load sharing.
(a)
The BTB operates in conjunction with the BUS TIE switch and the GCU. Switch actuation to the released (out) position will open the BTB. Actuation of the BUS TIE switch to the AUTO, latched (in) position will close the BTB through the internal GCU circuits.
(b)
The BTB trip will be operated as a result of internal GCU or BCU protective circuit operation. A system protection BTB trip (other than during autoland) will be reset by actuating the BUS TIE switch to the released (out) position and then returning it to the latched (in) position. This will close the BTB as described above.
(c)
When the BTB is energized, a nominal 28 volt dc close signal is provided to the BTB close coil circuit. When the BTB is deenergized, a nominal 28 volt dc trip signal is provided to the BTB trip coil. The BTB can also be deenergized directly from the BUS TIE switch on the electrical system control module.
(d)
The ISLN indicator light in the BUS TIE switch will be illuminated whenever the BTB is tripped. When the BTB is closed, the indicator light will be extinguished.
(e)
The ISLN indicator light will not be illuminated by an autoland BTB trip lockout. This function is provided by the GCU.
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MAINTENANCE MANUAL
(f)
When automatic tripping of the BTB in any channel is followed by automatic tripping of the GCB in the same channel, the BTB will receive a re-close signal within 30 milliseconds subsequent to the GCB trip. Reclosure will not occur if the tripping of the BTB is initiated by differential fault protection or negative sequence voltage protection, by manual operation of the BUS TIE switch, or by the auto bus isolation circuit. Manual operation of the GEN CONT switch to trip the GCR and GCB will not cause an open BTB to close.
(10)
The primary purpose of the APB is to provide 115 volt ac, 400 Hz power from the APU generator to the sync bus for ground operation.
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