Directional Ground-Fault Principles - ABB RER620 Technical Manual

Section 4
Protection functions
4.1.4.5
142
The setting parameter Minimum trip time defines the minimum desired trip time for IDMT.
The setting is applicable only when the IDMT curves are used.
The Minimum trip time setting should be used with great care because the
operation time is according to the IDMT curve, but always at least the value
of the Minimum operate time setting. For more information, see the
General function block features section in this manual.
The timer calculates the pickup duration (PICKUP_DUR) value which indicates the
percentage ratio of the pickup situation and the set trip time. The value is available through
the Monitored data view.
Blocking logic
There are three operation modes in the blocking functionality. The operation modes are
controlled by the BLOCK input and the global setting "Configuration/System/Blocking
mode" which selects the blocking mode. The BLOCK input can be controlled by a binary
input, a horizontal communication input or an internal signal of the relay program. The
influence of the BLOCK signal activation is preselected with the global setting Blocking
mode.
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode, the
trip timer is frozen to the prevailing value. 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, 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 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
1MAC309294-MB F
).
0
RER620
Technical Manual