GE Multilin 850 Instruction Manual page 488

CONTROL
4–356
The Transfer Scheme minimizes the effect of outages on one of the incoming supplies by
opening the incoming breaker connected to that supply, then re-energizing the dead bus
by closing the bus tie breaker to transfer the dead bus to the live source. To protect against
damage to motors connected to the dead bus, the bus tie breaker is not allowed to close,
after a Transfer has been initiated, until the decaying (residual) voltage on the bus has
been reduced to a safe level.
The Transfer Scheme can be used in conjunction with both non-draw-out and draw-out
switchgear. Draw-out switchgear designs can make use of an auxiliary switch that
confirms that the monitored breaker is racked-in (connected position) and therefore ready
for operation. Fixed (non-draw-out) breaker installations can use contacts on the
associated isolating disconnect switches (if available) for this purpose.
In addition to the relay required for each of the three circuit breakers, the system requires
two manually-operated control switches (or equivalent devices), or custom-made logic
with digital inputs and communication.
1. Device 43/10: Select to Trip Control Switch.
The Trip Control Switch is a three-position switch with at least three contacts, one for
each relay, which obey the following table:
Contact No.
1
2
3
It is required to connect one contact to each relay. This switch selects the breaker that
trips in the eventuality that all three breakers become closed, to prevent the two
incoming systems to remain connected in parallel. The contacts can be either
normally-open or normally-closed, depending on the logic of the corresponding input
used for this purpose. If custom made logic is used, one breaker has to be selected
only.
2. Device 43/83: Block - Enable Transfer.
This is an optional two-position switch or equivalent device, with at least three
contacts (one for each relay) that obeys the following table:
Contact No.
1: Incomer 1
2: Incomer 2
3: Tie Breaker
One contact must be connected to each relay. This switch selects either the Transfer
Scheme in Block position or the Transfer Scheme in Enable position. The contacts are either
normally-open or normally-closed, depending on the logic of the corresponding input
used for this purpose. When Device 43/83 is in the "Block" position, the contact connected
to 850 places the corresponding input in the position for blocking the operation of the Auto
Transfer Scheme. At this point in time, a system condition that might trip one of the
incomers does not initiate the Transfer sequence.
If custom made logic with digital input and communication is used, the Transfer function
has to blocked (or unblocked) simultaneously for all three relays.
Position
1: Incomer 1 2: Incomer 2
X
X
Position
Block
X
X
X
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS
3: Tie Breaker
X
Enable