ABB RELION 670 Series Applications Manual page 121

1MRK 505 337-UUS A
It is sometimes required to use lock-out relays for busbar protection operation.
The IED has built-in feature to provide either self-reset or latched tripping in case of busbar
protection operation. Which type of trip signal each zone will issue is determined by a parameter
DiffTripOut which can be set either to SelfReset or Latched . When Latched is selected the
setting
trip output from the IED will only reset if:
1. Manual reset command is given to the IED
2. DC power auxiliary supply to the IED is interrupted (that is, switched-off)
However, if it is required to have mechanically latched tripping and lock-out in the circuit breaker
closing circuit, then it is recommended to use one dedicated lockout IED for each bay. Such
mechanical lock-out trip IEDs are available in the COMBIFLEX range (for example RXMVB2 or
RXMVB4 bistable IEDs alternatively MG6 (hand reset contact) IEDs).
From the application point of view lock-out trip IEDs might have the following drawbacks:
• The trip contacts will remain closed. If the breaker would fail to open the tripping coil will be
burnt and the DC supply short-circuited.
• The trip circuit supervision (TCS) IEDs will reset and give alarm for a failure in the trip circuit if
the alarm is not opened by the lock-out IED or a double trip circuit supervision is
recommended where the trip circuit is supervised with two alternatively, TCS IEDs.
6.1.3.17 Contact reinforcement with heavy duty relays
There is sometimes a request for heavy duty trip relays. Normally the circuit breaker trip coils, with
a power consumption of 200 to 300 W, are provided with an auxiliary contact opening the trip
circuit immediately at breaker tripping. Therefore, no heavy duty breaking capacity is required for
the tripping relays. Nevertheless heavy duty trip relays are still often specified to ensure trip circuit
opening also if the circuit breaker fails due to a mechanical failure or a lack of energy for
operation. This can particularly occur during site testing. In this case it is recommended to use
COMBIFLEX RXMH 2 or RXMVB 2 or MG6 heavy duty relays.
6.1.3.18 Trip circuit supervision for busbar protection
Trip circuit supervision is mostly required to supervise the trip circuit from the individual bay IED
panel to the circuit breaker. It can be arranged also for the tripping circuits from the busbar
protection.
However, it can be stated that the circuit from a busbar protection trip relay located in the busbar
protection panel is not so essential to supervise as busbar faults are very rare compared to faults
in bays, especially on overhead power lines. Also it is normally a small risk for faults in the tripping
circuit and if there is a fault it affects only one bay and all other bays are thus correctly tripped
meaning that the fault current disappears or is limited to a low value.
6.1.4 Different busbar arrangements
6.1.4.1 General
Busbar differential protection application principles for typical busbar arrangements are shown
and described in this chapter.
Application manual
Section 6
Differential protection
M12119-4 v3
M12120-3 v1
M12120-4 v3
M12121-3 v2
M12121-4 v2
SEMOD127495-1 v1
M6640-3 v1
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