Measurements; Measurement Connections; Protection; 1.Non-Directional Earth-Fault Protection - ABB REX 521 Technical Reference Manual, Standard Configurations

REX 521
11.4.2.
11.4.3.
11.4.4.
11.4.4.1.
186
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 neutral current
• 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

Measurement connections

The three-phase current, neutral current transformers and residual voltage
transformer are connected to the connector X1.1 on the rear panel. The rated currents
of the measuring input are 1 A and 5 A and additionally, for earth-fault, 0.2 A. The
rated values for voltage are 100 V, 110 V, 115 V and 120 V.
In this application two neutral current measurements are used. The neutral current
I measured by a cable transformer is used for directional earth-fault protection and
0b
the neutral current I measured by the sum connection of the phase current
0
transformers is used for non-directional earth-fault protection.
The technical data of the current transformers and the voltage transformer are set via
the Relay Setting Tool or the local HMI. The settings can be found in
Main menu\Configuration\Meas. devices\.
Please refer to Technical Reference Manual, General (1MRS 751108-MUM) for
further information about how to set the rated currents and voltage.

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\.
The overcurrent, the phase discontinuity and thermal overload protection can be
implemented in the same way as in the first application example (chapter 9.1.) and
the directional earth-fault protection as in the fifth application example
(chapter ).
Non-directional earth-fault protection
A double earth-fault occurs when two phase-conductors get in galvanic connection
with the earth. This can occur in the same line or between two lines when the fault
current has to flow through the earth. This fault type is also known as a cross-country
fault.
1MRS 751802-MUM