Mechanical Lock-Out Function; Contact Reinforcement With Heavy Duty Relays - ABB REB670 Applications Manual

Section 6
Differential protection
6.1.3.16
6.1.3.17
128
contacts are required and only RXMS 1/AR relays when medium duty contacts are
sufficient.
This solution is especially suitable for the station arrangements, which require the
dynamic zone selection logic (that is, so called CT switching).

Mechanical lock-out function

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 setting DiffTripOut which can be set either to SelfReset or Latched. When
Latched is selected the 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.

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.
1MRK 505 337-UUS -
Application manual