Directional Ground-Fault Principles - ABB 615 series Technical Manual

Section 4
Protection functions
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4.2.2.5
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curve type is selected, an immediate reset occurs during the drop-off
situation.
The setting Time multiplier is used for scaling the IDMT trip and reset times.
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 trip time setting. For more information, see the
IDMT curves for overcurrent protection
The timer calculates the pickup duration value PICKUP_DUR, which indicates the
percentage ratio of the pickup situation and the set trip 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 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 residual current only. To obtain a selective ground-fault protection scheme,
it is necessary to take the phase angle of IG 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
1MAC059074-MB A
section in this manual.
615 series ANSI
Technical Manual