ABB REX 521, Technical Reference Manual, Standard Configurations

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1MRS751802-MUM Protection Relay
Technical Reference Manual, Standard Configurations
REX 521
11.5.2. Measurements
Following measurements are supported in this application example.
• True RMS measurement of phase currents
• True RMS measurement of neutral current
• True RMS measurement of phase-to-phase voltages
• 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
11.5.3. Protection
All the necessary settings for the protection functions can be set by means of the
Relay Setting Tool or the local HMI. The settings can be found in
Main menu\Protection\
.
11.5.3.1. Phase overcurrent protection
The overcurrent protection can be implemented as described in the second
application example (Section 9.2. Incoming feeder, Basic B01)
11.5.3.2. Earth fault protection
The earth fault protection can be implemented as described in the second application
example (Section 9.2. Incoming feeder, Basic B01)
11.5.3.3. Overvoltage and undervoltage protection
Faults in the network or a faulty tap changer or voltage regulator of a power
transformer may cause abnormal busbar voltages. The overvoltage and undervoltage
protection is used for preventing possible damages to the devices connected to the
network.
In this application the overvoltage and undervoltage protection is included in the
functionality of the protection relay of the incoming feeder. In the overvoltage or
undervoltage situation the circuit breaker of the incoming feeder will be opened.
The overvoltage protection includes two protection stages: a low stage U> and a
high stage U>>. The low stage can be set to the definite-time or inverse-time
operation. The definite-time operation is used with the high-set stage.
Similarly, the undervoltage protection includes two protection stages: a low stage
U< and a high stage U<<. The low stage can be set to the definite-time or inverse-
time operation. The definite-time operation is used with the high set stage.
An operational characteristic example on overvoltage and undervoltage protection
is presented in the picture below (Fig. 11.5.3.-1).