ABB 615 Series ANSI, Техническое руководство, Страница: 203 / 713

Section 4
1MAC050144-MB C
Protection functions
196 615 series ANSI
Technical Manual
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 timer calculates the pickup duration (PICKUP_DUR) value which indicates the
percentual ratio of the pickup situation and the set trip time. The value is available through
the Monitored data view.
Blocking logic
There are three operation modes in the blocking functionality. The operation modes are
controlled by the
BLOCK
input and the global setting "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 relay 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
trip timer is frozen to the prevailing value. In the "Block all" mode, the whole function is
blocked and the timers are reset. 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
faults taking place on the wye-connected low voltage side. If a ground fault occurs on the
wye-connected side of the power transformer, negative sequence current quantities appear
on the delta-connected side of the power transformer.
Multiple time curves and time multiplier settings are also available for coordinating with
other devices in the system.
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 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 operate time setting. For more information, see the
General function block features section in this manual