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 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.
4.1.7.5
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 ground-fault protection in
solid and low resistance grounded networks.
The negative sequence overcurrent protection provides the back-up ground-fault
protection on the high voltage side of a delta-wye connected power transformer for ground
1MRS240050-IB C
Section 4
Protection functions
REF615R
209
Technical Manual
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