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

Section 4
Protection functions
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4.2.2.5
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operating curve type is selected, an immediate reset occurs during the
drop-off situation.
The setting Time multiplier is used for scaling the IDMT operate and reset times.
The setting parameter Minimum operate time defines the minimum desired operate
time for IDMT. The setting is applicable only when the IDMT curves are used.
The Minimum operate 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
in this manual.
The timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operating time. The value is available
in the monitored data view.
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
IDMT curves for overcurrent protection
1MRS757644 F
section
620 series
Technical Manual