777 AIRCRAFT MAINTENANCE MANUAL
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GENERATOR DRIVE -IDG -FUNCTIONAL DESCRIPTION
General
The GCU and the drive disconnect switch control the IDG. The GCU sends information about the IDG to the systems ARINC 629 buses. The EEC sends oil temperature and oil filter data to the systems ARINC 629 buses. This permits the AIMS to show EICAS messages and maintenance data.
Generator Drive Light
The GCU controls the DRIVE light in the disconnect switch. The GCU sends a signal that causes the DRIVE light to come on when the IDG charge pressure is low. If the engine is running, the low oil pressure also causes the ELEC GEN DRIVE advisory message to show. When you see the ELEC GEN DRIVE message, you should immediately disconnect the IDG. This protects the IDG from damage. The drive disconnect switch on the P5 panel controls the IDG drive disconnect solenoid.
Drive Disconnect
The EEC reset/IDG disconnect relay arms the disconnect switch while the related engine fuel cutoff switch is in the RUN position. If the disconnect switch is in, the IDG disconnect solenoid energizes. This causes the spring-loaded disconnect mechanism to disconnect the IDG from the drive shaft.
The IDG can automatically disconnect if the IDG oil gets too hot. A thermal plug in the disconnect mechanism melts. This causes the spring-loaded disconnect mechanism to disconnect the IDG from the drive shaft.
EFFECTIVITY
BEJ ALL
Oil Level Sensing
The remote oil level sensor sends an oil level signal to the GCU. The sensor sends data only when the IDG charge pressure is low (IDG is shutdown). The electrical maintenance page shows the oil level data of the IDG. The oil level data shows two dashes when the IDG operates.
If oil does not cover the underfill sensor for the related IDG, the IDG oil level is too low. The maintenance page will show SERVICE when the IDG is shutdown.
If oil covers the underfill sensor, but not the overfill sensor, the IDG has sufficient oil. The maintenance page will show NORMAL when the IDG is shutdown.
If oil covers the overfill sensor and the related underfill sensor, the IDG oil level is too high. The maintenance page will show SERVICE when the IDG is shutdown.
Frequency Trim Control
The GCU controls the trim coil to increase or reduce the speed of the IDG drive. The speed change changes the frequency of the power output. The GCU uses the trim coil to match the IDG power frequency to the frequency of an other power source during no-break power transfers.
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GENERATOR DRIVE -IDG -FUNCTIONAL DESCRIPTION
Oil Filter Status
The differential pressure switch monitors the difference between the pressures upstream and downstream of the oil filter. The switch sends a filter status signal through the EEC and the systems ARINC 629 buses to the GCU. The GCU causes the electrical maintenance page to show the status of the oil filter. The usual status on the maintenance page is NORMAL.
When the oil filter is clogged, the differential pressure switch closes. The GCU causes the electrical maintenance page to change the filter status to BLOCKED. The GCU inhibits the filter status signal when the oil out temperature is colder than 145F (62C).
Temperature Data
Oil temperature sensors in the inlet and outlet tubing send data to the EEC. The EEC sends the data to AIMS. The electrical maintenance page shows OUT TEMP, the temperature of the oil at the IDG outlet. And, it shows RISE TEMP, the difference between the inlet and the outlet temperatures. The data are in degrees C.
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GENERATOR DRIVE -IDG -FUNCTIONAL DESCRIPTION
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777 AIRCRAFT MAINTENANCE MANUAL
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GENERATOR DRIVE -IDG -OIL SERVICING
Oil Level Indication
The signal from the remote oil level sensor causes the IDG oil level data to show on the electrical maintenance page. The maintenance page shows the oil level data as NORMAL or SERVICE.
The IDG sightglass shows the oil level. You must open the left thrust reverser cowl to see the sightglass.
If the oil level is in the silver area of the sightglass, the IDG oil level is satisfactory. The black zone at the bottom of the sightglass is the low oil zone. The low oil zone is different for the left and right engine. You must add oil to the IDG if the oil level is in the low oil zone.
Add Oil to the IDG
You can add oil to the IDG through the IDG pressure fill valve. It is above an access door in the thrust reverser at the 6:00 position.
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