ABB RED615 Technical Manual page 285

1YHT530004D05 D
4.2.2.5
615 series
Technical Manual
controlled by a binary input, a horizontal communication input or an internal signal
of the IED 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. 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
279