GE 750 Instruction Manual page 268

S7 CONTROL
Note
NOTE
5 - 142
Practical scheme for overall TRANSFER READY indication can be developed by selecting
the setting "Enabled" from all three 750 relays to operate the aux. output relay # 3, and
wiring the relays in series with a DC source to turn on a single light bulb ("white light"). The
aux. 3 output relay from each 750 relay can be wired to turn on an individual light bulb as
well. Refer to the DC ratings of the aux. output relays before wiring to a DC source.
The TRANSFER READY flag will be high, if all of the following conditions are met:
Incomer 1: 750/760-1 (Incomer 2: 750/760-2) relays:
• The "Incomer 1" setting selected under TRANSFER FUNCTION setpoint
• The transfer scheme is not blocked from "Block Transfer" input
• Bus Tie Breaker is open (52a/b contacts)
• Incomer 1 breaker is connected and closed
• Incomer 2 breaker is connected and closed
• No transformer lockout, or source trip is present
• No undervoltage is detected on any of the two sources
Tie-breaker 750/760 relay:
• The "Bus Tie" setting is selected under TRANSFER FUNCTION setpoint
• The transfer is not blocked from "Block Transfer" input
• Bus Tie Breaker is connected and open (52a/b contacts)
• Incomer 1 breaker is closed
• Incomer 2 breaker is closed
If Undervoltage Restoration is used to restore the system automatically, Line Undervoltage
4 (27-4) must be set to "Trip", instead of "Control" or "Alarm", and the Block Trip on Double
Loss feature will not work properly.
The settings and functions of other elements associated with the transfer scheme are
shown below:
• Output Relays 4-7 Auxiliary (all breakers): These output relays are used to implement
the transfer scheme, and must therefore not be operated by any other feature of the
relay. These relays must be programmed to have a not operated state of 'De-
energized' with the output type as 'Self-reset'. These are the default settings.
• Instantaneous Phase (50P1 or 2) and Neutral (50N-1 or 2) [Incomers 1 and 2 only]:
These fault detectors can be used as an input to transfer scheme logic in this
application, and therefore the function setpoint of elements that are used must be set
to Control. These elements block a transfer while a fault, which can cause a severe
voltage dip, is present on the load side of the breaker. This fault should be cleared by
time overcurrent protection on the incomer or an upstream breaker. If Device 50P is
set properly, during this event it will allow Device 27-4 to time out before the inverse
time phase overcurrent operates, but still prevent transfer initiation. The 50P element
should be set above the maximum current caused by either the bus motor
contribution to an upstream fault, or the maximum current during low voltage
conditions. The 50N element should be set to detect arcing ground faults, but allow
permitted unbalances.
• Line Undervoltage 3 (27-3) [Incomers 1 and 2 only]: Since this element is used as an
input to transfer scheme logic in this application, set
CHAPTER 5: SETPOINTS
LINE UNDERVOLTAGE 3 FUNCTION
750 FEEDER MANAGEMENT RELAY – INSTRUCTION MANUAL