TM 1-1520-238-T-6
Change 5
9–83
9–7.
SYSTEM DESCRIPTION (cont)
9–7
(o) A deenergized bus tie relay provides a ground through pins 11 and 12 to energize the GCR.
Pins 13 and 14 provide a bus tie path from GCU 2 to ac contactor 2. Pins A2, B2, and C2 are disconnected from
bus 2 pins A1, B1, and C1.
(p) The bus tie relay is energized when the generator contactor is deenergized. The ground path is
through pins 6 and 5 of the GCR, to relay coil B. The voltage is supplied by the dc bus tie contactor. Pins 13 and
14 open the bus tie path to ac contactor 2. Pin A2 mates with A1, B2 mates with B1, and C2 mates with C1
connecting ac essential bus 1 to ac essential bus 2.
8
7
1+
13
12
11
4-
3+
5
2-
6
POWER
EXTERNAL
28 VDC
INTERLOCK
C1
B1
A1
C2
B2
ØA
C3
B3
TO AC CONTACTOR 2
BUS
BUS TIE 28 VDC
M69-351
FM GCU 2 (BUS TIE)
14
BUS TIE RLY
GEN CONT RLY
A
B
PIN 5
GEN SWITCH
(OPEN IN TEST)
10
GCU GROUND
GEN 1
GROUND
9
A2
BUS 1
TO AC
AC BUS 2
FROM
OUTPUTS
GENERATOR
A3
ØB
ØC
ØA
ØB
ØC
ØA
ØB
ØC
Figure 9–75.
AC Contactor Simplified Funtional Block Diagram
(2) DC Electrical Power Generation System.
The dc electrical power generation system (fig. 9–76)
contains two T/Rs which convert 115 VAC from ac essential buses 1 and 2 to 28 VDC. Each T/R supports an
identical and redundant system and supplies one-half of the helicopter T/Rs load. The T/Rs are protected by the
XFMR RECT 1 circuit breaker (CB1) and XFMR RECT 2 circuit breaker (CB2). A heat sensor in each T/R
monitors for an overheat condition. When an overheat condition exists, HOT RECT 1 or HOT RECT 2 indicator on
the pilot’s caution/warning panel is lighted.
(a) The outputs of the T/Rs are connected to dc essential bus 1, dc essential bus 2, dc essential bus 3,
and the emergency dc bus through a dc bus tie contactor. The bus tie contactor contains contactors, switching
relays and a bus tie relay. In event of failure, the dc bus tie contactor connects the buses together and lights the
RECT 1 or RECT 2 indicator on the pilot’s caution/warning panel. The operating T/R then supplies the full dc load.
