Measurements; Protection; 1.Overcurrent Protection; 2.Synchro-Check Function - ABB REX 521 Technical Reference Manual, Standard Configurations

1MRS 751802-MUM
11.1.2.
11.1.3.
11.1.3.1.
11.1.3.2.
Protection Relay
Technical Reference Manual, Standard Configurations

Measurements

Following measurements are supported in this application example:
• True RMS measurement of phase currents
• True RMS measurement of phase-to-earth voltages
• True RMS measurement of residual voltage (calculated value from phase-to-earth
voltages)
• Fundamental frequency active power [kW]
• Fundamental frequency reactive power [kvar]
• Fundamental frequency displacement power factor cos (φ)
• Power factor PF including the 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
The basic overcurrent protection principles presented in the application example
11.2. are applicable, but different overcurrent protection stages have been used.
In the example of the incoming feeder application, the stage 3I>>-> of the
overcurrent protection of the incoming feeder operate time-selectively as a
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.
Synchro-check function
In this application example the synchro-check function is used for checking the
conditions for the closing of incoming feeders circuit-breaker. The synchro-check
function does not allow the circuit breaker to be closed if the criteria are not fulfilled.
The synchro-check function can be used for two different operating conditions. The
most typical case is the one where both sides of the circuit breaker to be closed are
live and thus the synchronism is always checked before the circuit breaker is given
the permission to close. In the other situation one or both sides of the circuit breaker
to be closed are dead and, consequently, the frequency and phase differences cannot
be measured, in which case the relay checks the energizing direction.
Operation criteria of the function are:
• Voltages must be in accordance with the energizing direction.
• In cases "Live-Dead", "Dead-Live" and "Dead-Dead" no other conditions are
checked.
• In the case "Live-Live" also the following must be fulfilled:
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