Inverse Time Overcurrent Protection 51 (Oc); Mode Of Operation; Features - ABB RELION REB500 Technical Manual

Section 5
Bay protection functions
Delay
The delay is used to achieve discrimination of the overcurrent function. It is set according to
the grading table for all the over-current units on the power system. The zone of protection of
the overcurrent function under consideration extends to the location of the next downstream
overcurrent relay.
Should the downstream relay fail to clear a fault, the overcurrent function trips slightly later in
a backup role.
Setting MaxMin
This parameter enables the following operating modes to be selected:
• MIN (3ph): Pick-up when the highest phase current also falls below the setting. This
setting is not permitted for single-phase meas.
• MIN (1ph): Pick-up when the lowest phase current falls be-low the setting.
• MAX (3ph): Pick-up when the lowest phase current also exceeds the setting. This setting is
not permitted for single-phase measurement.
• MAX (1ph): Pick-up when the highest phase current exceeds the setting.
• MAX-Inrush: Blocking of inrush currents when a phase current exceeds the setting.
Operation of the inrush blocking feature (parameter
The inrush detector picks up and blocks operation of the function when the amplitude of the
fundamental component of the current exceeds the current function setting.
The inrush detector is based on the evaluation of the second harmonic component of the
current I
amplitudes).
The output of the function is disabled when the ratio I
when it falls below 8%.
There is no setting for the peak value of I
The function can operate with inrush blocking in both the single and three-phase mode
(parameter
In the three-phase mode, the phase used for evaluation is the one with the highest amplitude
at rated frequency (pick-up and inrush detection).
5.3

Inverse time overcurrent protection 51 (OC)

5.3.1

Mode of operation

Overcurrent function with time delay inversely proportional to the current and definite
minimum tripping time.
5.3.2

Features

• Operating characteristics according to British Standard 142:
•
•
•
• Insensitive to DC component
• Insensitive to harmonics
94
in relation to the fundamental frequency component I
2h
NrOfPhase ).
c = 0.02: normal inverse
c = 1 : very inverse and long time earth fault
c = 2 : extremely inverse
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MaxMin set to MAX-Inrush )
/I exceeds 10% and enabled again
2h 1h
/I .
2h 1h
1MRK 505 406-UEN B
(evaluation of the
1h
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Bay protection functions REB500
Technical manual