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3 HARDWARE DESCRIPTION
3 HARDWARE DESCRIPTION 3.1 CASE ASSEMBLY
Power down the relay by removing one of the connection plugs or turn both power switches
to OFF before removng or inserting modules. Failure to do so can permanently damage the
relay.
CAUTION
The case that houses the electronic modules is constructed from an aluminum alloy. It consists of a main frame
with side mounting brackets, a front cover and a rear cover.
The front cover, comprised of a metal frame with plate glass, is pivoted on the top and is opened from the bot-
tom by way of two spring-loaded latches. The door is constrained from coming off by tabs that require the door
to be unlatched and lifted slightly to be removed. A push-button extender installed into the plate glass makes it
possible to clear the display without removing the front cover.
The rear cover supports terminal blocks that are used in making external connections to the case. The mod-
ules are mounted vertically inside the case and are supported by sockets on the motherboard within the case.
In addition to providing this mechanical support, the sockets also offer the means of making the electrical con-
nection to the modules. The modules are further restrained inside the case by the front cover.
Proper alignment of the module with respect to the socket is maintained by slotted guides, one guide above
and one guide beneath each module, with the exception of the magnetics module, MGM and MMI modules,
which require two guides above and two beneath.
As mentioned earlier, electrical connections are made to the case through eight terminal blocks mounted on
the rear cover plate. Each block contains 14 terminal points, which consist of a #6 screw threaded into a flat
contact plate. Each terminal is rated for a maximum of two connections. Exceeding this will violate UL
specifications for two wires per terminal.
Connection to the MGM module is made by means of two connector sockets: an 8-contact current block and a
104-pin signal block. The current block contacts are rated to handle current transformer (CT) secondary cur-
rents. They are shorted upon removal of the MGM module.
The DGP model number label is located on the outside of the front cover and on the right-hand sidesheet
inside the case. A marking strip indicating the name and position of every module in a case is included on the
front center of the case. It is placed to be read when the front cover is removed.
The terminal blocks located on the rear cover plate are uniquely identified by a two-letter code found directly
beneath the outermost edge of each terminal block. Also, the terminal points (1 through 14) are identified by
stamped numbers.
Connector PL1 is used for serial communication between the DGP and the PC/Modem. Connector PL2 is used
to output sequence of events (SOE) to a serial printer or a DEC100 unit for additional auxiliary contacts output.
PL3 is used for IRIG-B signal input to the DGP. Note that the PL2 and PL3 connectors are not included on all
DGP models; see Section 1.1.2: ORDER CODES & SELECTION GUIDE on page 1–2 for details.
GE Power Management
3.1.3 ELECTRICAL CONNECTIONS & INTERNAL WIRING
DGP Digital Generator Protection System
3.1 CASE ASSEMBLY
3.1.1 WARNING
3.1.2 CONSTRUCTION
3.1.4 IDENTIFICATION
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