GE 750 Instruction Manual page 207

S7 Control
GE Multilin
5–66: Transfer Scheme One Line Diagram on page 5–115 regardless of
configuration.
3. The connection of AC voltage to the relay on the bus tie does not affect
operation of the scheme, but the connection to the line voltage input
terminals must be a phase-phase voltage.
For the following discussion assume that Source 1 is the failed side. Identical logic
with all 1s and 2s interchanged applies to Relay 2 for a loss of Source 2. A transfer
(trip of Incomer 1 followed by Bus Tie closing) from Relay 1 can be initiated by:
• Operation of transformer 1 lockout relay (Device 86T1).
• Operation of the Source 1 breaker auxiliary trip device (Device 94-1).
• Time out of Relay 1 line voltage inverse time undervoltage element (Device 27-
4) caused by low voltage on Source 1.
A transfer initiation is blocked if:
• Any of the three breakers is not in the connected state.
• Incoming Breaker 2 (which is to become the new source) is presently open.
• Devices 50P-1 or 2, or 50N-1 or 2, detect an overcurrent condition on bus 1, to
prevent a faulted bus from being transferred to a healthy source.
• The line definite time Undervoltage element (Device 27-3) on Source 2 is
operated, indicating low voltage on the other source.
If any one of the above conditions is present, the
will be displayed by the relays.
Once a condition has caused the 750/760 relay on Incomer 1 (Relay 1) to initiate a
transfer, the following sequence of events will take place:
1. Relay 1 trips Incomer 1 breaker (Breaker 1).
2. Relay 1 issues a close signal to the 750/760 on the Bus Tie breaker (Relay 3).
3. The trip command is maintained until Relay 1 determines that Breaker 1 has
opened.
4. When Relay 3 receives the close command from Relay 1, it is captured and
retained until either the Bus Tie breaker (Breaker 3) closes or the Block Transfer
logic input is received.
5. Relay 3 is inhibited from initiating a close command to Breaker 3 by its synchro-
check element.
6. Synchrocheck monitors the voltage on the disconnected bus, and provides the
bus decayed (residual) voltage permission-to-close when the Bus 1 voltage
decays to the preset level.
The three breakers are under prevent-parallel checking whenever the transfer
scheme is operational. If a third breaker is closed when the other two breakers are
already closed, the scheme will automatically trip the breaker selected by Switch
43/10, 'Selected To Trip'.
c) Additional Setpoints for Transfer Scheme
The following settings are required for the proper operation of the Auto Transfer
Scheme:
• Logic inputs definition: Refer to Logic Inputs Setup on page 5–20 for additional
information. In this step, the Logic Inputs are identified and the asserted logic is
defined.
• Logic inputs for breaker functions: Refer to Breaker Functions on page 5–21 for
additional information. Since the scheme monitors the status of the breaker, it
is necessary to set a digital input for that purpose.
• Logic inputs for control functions: Refer to Control Functions on page 5–22 for
additional information. These settings are required to define how the relay will
receive external commands.
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750/760
Feeder Management Relay
message
TRANSFER NOT READY
5–111