Measurement Connections; Protection; 1.Overcurrent Protection - ABB REX 521 Technical Reference Manual, Standard Configurations

REX 521
11.2.2.
11.2.3.
11.2.3.1.
174
Protection Relay
Technical Reference Manual, Standard Configurations

Measurement connections

Following measurements are supported in this application example:
• True RMS measurement of phase currents
• True RMS measurement of phase-to-phase voltages
• True RMS measurement of residual voltage
• Fundamental frequency active power [kW]
• Fundamental frequency reactive power [kvar]
• Fundamental frequency displacement power factor cos (φ)
• Power factor PF including harmonics
• Fundamental frequency active energy [kWh]
• Fundamental frequency reactive energy [kvarh]
• System frequency measurement

Protection

All the necessary settings for the protection functions can be set via the Relay
Setting Tool or the local HMI. The settings can be found in
Main menu\Protection\.
Overcurrent protection
In the example of the incoming feeder application, the stage 3I> of the overcurrent
protection of the incoming feeder operate time selectively as a non-directional
overcurrent back-up protection of the outgoing feeders. The stage 3I>-> is used for
the directional overcurrent protection of the parallel incoming feeders to disconnect
faulty feeder from the network. The stage 3I>> is used for the non-directional short-
circuit protection of the busbar system.
The directional high-set stage 3I>-> is set to look into the protected line. This means
it is set to operate in reverse direction. The definite time or IDMT mode can be used.
The directional stage 3I>-> of the incoming feeder provides blocking signal to the
3I>>> stage of the bus sectionalizer. Also it will provide blocking signal for the 3I>>
stages of the parallel incoming feeders. The current setting of the directional stage
looking in reverse direction can be 50 % of the normal full load of the protected
circuit.
If the fault should occur in the busbar system, the stage 3I>> of the bus sectionalizer
provides blocking signal to the incoming feeders and the 3I>>> stage of the
overcurrent protection of the bus sectionalizer provides a trip signal to the bus
sectionalizer circuit breaker. When the fault is limited to the one busbar sector the
3I>> stage of the overcurrent protection of the incoming feeder provides a trip signal
to the circuit breaker of the incoming feeder.
If a fault occurs in the feeder, the overcurrent protection relay of the outgoing feeder
provides a blocking signal to the overcurrent protection relays of the bus
sectionalizer and incoming feeders. Therefore it is possible to use a minimum
operate time of 100 ms for the overcurrent protection 3I>>> stage of the bus
sectionalizer and for the 3I>> stage of the incoming feeders when a fault in the
busbar system occurs.
1MRS 751802-MUM