Directional Earth-Fault Principles - ABB RELION Series Technical Manual

1MRS758755 A
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4.2.2.5
REC615 and RER615
Technical Manual
Blocking logic
There are three operation modes in the blocking function. The operation modes are
controlled by the BLOCK input and the global setting in 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
protection relay's 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 operation timer is frozen to the prevailing value, but the OPERATE 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 OPERATE output" mode, the function
operates normally but the OPERATE output is not activated.

Directional earth-fault principles

In many cases it is difficult to achieve selective earth-fault protection based on the
magnitude of residual current only. To obtain a selective earth-fault protection
scheme, it is necessary to take the phase angle of Io into account. This is done by
comparing the phase angle of the operating and polarizing quantity.
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
Section 4
Protection functions
285