ABB RELION 620 Series Technical Manual page 610

Section 4
Protection functions
4.4.1.5
604
The "Inverse reset" selection is only supported with ANSI or user
programmable types of the IDMT operating curves. If another
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.
Application
Since the negative sequence current quantities are not present during normal, balanced
load conditions, the negative sequence overcurrent protection elements can be set for
faster and more sensitive operation than the normal phase-overcurrent protection for
fault conditions occurring between two phases. The negative sequence overcurrent
protection also provides a back-up protection functionality for the feeder earth-fault
protection in solid and low resistance earthed networks.
The negative sequence overcurrent protection provides the back-up earth-fault
protection on the high voltage side of a delta-wye connected power transformer for
earth faults taking place on the wye-connected low voltage side. If an earth fault
IDMT curves for overcurrent protection
1MRS757644 F
section
620 series
Technical Manual