Directional Ground-Fault Principles - ABB RELION 620 Series Technical Manual

Section 4
Protection functions
4.1.5.5
204
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode, the
trip timer is frozen to the prevailing value, but the TRIP output is not deactivated when
blocking is activated. In the "Block all" mode, the whole function is blocked and the timers
are reset. In the "Block TRIP output" mode, the function operates normally but the TRIP
output is not activated.

Directional ground-fault principles

In many cases it is difficult to achieve selective ground-fault protection based on the
magnitude of zero-sequence current only. To obtain a selective ground-fault protection
scheme, it is necessary to take the phase angle of I
comparing the phase angle of I
Relay characteristic angle
The Characteristic angle setting, also known as Relay Characteristic Angle (RCA), Relay
Base Angle or Maximum Torque Angle (MTA), is used in the "Phase angle" mode to turn
the directional characteristic if the expected fault current angle does not coincide with the
polarizing quantity to produce the maximum torque. That is, RCA is the angle between the
maximum torque line and polarizing quantity. If the polarizing quantity is in phase with
the maximum torque line, RCA is 0 degrees. The angle is positive if the operating current
lags the polarizing quantity and negative if it leads the polarizing quantity.
Example 1
The "Phase angle" mode is selected, compensated network (φRCA = 0 deg)
=> Characteristic angle = 0 deg
into account. This is done by
0
to that of the zero-sequence voltage (-V
0
1MAC504801-IB E
).
0
620 series ANSI
Technical Manual