1.Overcurrent Protection; 2.Residual Voltage Protection; Connections; 1.Protection Signal Routing - ABB REX 521 Technical Reference Manual, Standard Configurations

1MRS 751802-MUM
10.2.3.1.
10.2.3.2.
10.2.4.
10.2.4.1.
10.2.4.2.
Protection Relay
Technical Reference Manual, Standard Configurations
Overcurrent protection
The overcurrent protection can be implemented as described in the second
application example (chapter 9.2.).
Residual voltage protection
On the busbar, the residual voltage can be measured with a set of voltage
transformers in an open-delta connection.
In this example, the directional earth-fault functions are configured to operate as
three-stage residual voltage protection. The directional earth-fault functions include
three protection stages: a low stage Io>->, a high stage Io>>-> and
an instantaneous stage Io>>>->. The protection is based on measuring the neutral
current Io, the residual voltage Uo and the phase angle between these. In this
application example the stages are set to residual protection (Uo).
In an isolated network, a three-stage residual overvoltage protection can be used for
the main earth-fault protection of the busbar system and for the back-up protection
of the network. The low stage can be given a sensitive setting and have an alarming
function. Note that in this application example the CBFP signal has to be taken out
of use for this stage. With the default settings, the CBFP is in use.
The high stage can work as back-up for the network and perform trip on the outgoing
feeders. Further, the start signal from the high-set stage can be routed to an output
contact to release the blocking for the non-directional earth-fault protection stages
of the outgoing feeders (see also application example 8.1. for the outgoing feeder).
The instantaneous stage can be configured as busbar protection and provide trip to
the incoming feeder.
The settings for the residual voltage protection are made in the settings for the
directional earth-fault current functions and can be found in
Main menu\Protection\Io>->\ ... \Io>>>->\.
In Main menu\Protection\Io>->\Setting group 1, the operation
criteria is set to "Non.dir.Uo".

Connections

All the necessary settings for the connections and signal routings can be set via the
Relay Setting Tool or the local HMI.
Protection signal routing
The settings for the protection signal routing (except the settings for the earth-fault
protection) can be implemented as described in the second application example
(chapter 9.2.).
Indication and control connections
The connections for the indication and the control signals of the circuit breaker and
the disconnector for the incoming feeder can be set as described in the first
application example on page 117 onwards. Settings are made via the Relay Setting
Tool or the local HMI. The settings can be found in:
REX 521
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