24-21-00
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A
737-300/400/500MAINTENANCE MANUAL
C. The magnetic-latch type circuit breakers are in the right-hand load control center P6 or in the right-hand forward and aft compartments outboard of the nose wheel well. This latter location contains the external power contactors and the engine generator No. 1 and No. 2 circuit breakers. This type of breaker is a three-pole electrically-operated, plunger-style solenoid unit. Input and output cables are connected to the A and B terminals respectively. The auxiliary switches and coils circuit connections are made through the multiple wire connector.
D. The magnetic-latch type circuit breaker has one magnet coil which is used for both the close and trip operations. A coil switch in the breaker determines which way the current flows in the coil, which determines the resulting close or trip operation of the unit. Two diodes across the coil suppress power spikes generated when the coil circuit is opened. Other auxiliary switches provide electrical interlocking and circuit monitoring functions.
10. Current Transformers (Fig. 6)____________________
A. The current transformers in each generator system are so located that inputs for various control and protective functions such as overcurrent, power limiting, generator excitation boost, load differential protection, neutral differential protection, and metering are obtained from the generating and distributing system three-phase current transformer (CT) sense current for different purposes.
(1)
The differential protection neutral side current transformers, near the generator, sense current in the grounded feeders from generator terminals T4, T5, and T6. This arrangement is essentially the same for the three generators.
(2)
The differential protection load side assembly contains two sets of CT's identical to the neutral side. One set functions as the differential protection for the engine generator and the other for the APU generator. Both sets are capable of supplying the main load bus and are identified as T4 and T5. Each set contains six separate current coils. Switching of the outputs from the coils is done inside the generator control units by the differential protection relays.
(3)
The functions of measuring overcurrent, power limiting, boost, and current metering are accomplished by a CT assembly containing twelve coils. Nine of these coils furnish inputs to the generator control unit and three coils are connected to ammeters.
11. Operation_________
A. AC generation is a system of providing power to buses from the ac generators. Operation is provided through manual control and limited by the following.
(1) Battery switch must be set to ON.
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A 737-300/400/500MAINTENANCE MANUAL
G3 GENERATOR 1 CONTROL UNIT 1 (P6)
Differential Protection Simplified Schematic
Figure 6 (Sheet 1)
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A 737-300/400/500MAINTENANCE MANUAL
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A 737-300/400/500MAINTENANCE MANUAL
(2)
No source of power can be paralleled with any other source of power. The APU inflight can energize either load bus 1 or 2 but not both.
(3)
The source of power must be manually switched on and will energize the buses only when it is of proper voltage and frequency.
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