GE 750 Instruction Manual page 262

S7 CONTROL
5.8.7 Transfer Scheme
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TRANSFER
5 - 136
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PATH: SETPOINTS S7 CONTROL
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The Transfer scheme is intended for application to a set of three circuit breakers on a
Main-Tie-Main arrangement, two of which (Incomers 1 and 2) connect sources of electrical
energy to two busses which could be paralleled through the Bus Tie breaker. The normal
system configuration is with both incoming breakers closed and the bus tie breaker open.
The transfer scheme implemented in the 750/760 is known as Open Transfer, with an
"Open before Close" operation sequence; this means that the faulty incomer is removed
from service before the tie breaker is closed. FIGURE 5–66: Transfer Scheme One Line
Diagram on page 5–145 shows this arrangement. The equipment designations on this
drawing will be used in the discussion.
The transfer scheme minimizes the effect of outages on one of the incoming supplies by
opening the incoming breaker connected to that supply, and 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.
After the lost source has been reestablished, the scheme provides three methods to
restore the system to normal configuration. Two methods are manual and one is
automatic.
• Manual Method 1, when the sources cannot be synchronized:
The bus tie breaker must be manually opened before the open incomer can be
manually closed. In this procedure the incomer will only be allowed to close if the
incoming source (Line VT) voltage is above a live threshold and the load (Bus VT)
voltage is below a dead threshold value.
• Manual Method 2, when the sources are synchronized with synchrocheck supervision:
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TRANSFER
TRANSFER FUNCTION:
Disabled
BUS TRANSFER LOGIC:
Scheme 1
TRANSFER DELAY THIS
SOURCE: 1.0 s
TRANSFER DELAY OTHER
SOURCE: 3.0 s
BLOCK TRIP ON DOUBLE
LOSS: Disabled
TRANSFER DELAY SELECT
TO TRIP: 0.0 s
TRANSFER READY
RELAY 3: Disabled
750 FEEDER MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETPOINTS
Range: Disabled, Incomer 1,
Incomer 2, Bus Tie
Range: Scheme1, Scheme 2
Range: 0.0 to 10.0 s in steps
of 0.1
Range: 0.0 to 10.0 s in steps
of 0.1
Range: Disabled, Enabled
Range: 0.0 to 10.0 s in steps
of 0.1
Range: Disabled, Enabled