Description
W1(3) PHASE TIME OC PICKUP: Enter the phase current level (in units of relay nominal
current) above which the winding 1(3) phase time overcurrent element will pickup and
start timing.
W1(3) PHASE TIME OC SHAPE: Select the time overcurrent curve shape to use for the
winging 1(3) phase time overcurrent. Time Overcurrent Curves on page 5–58 describes
the time overcurrent curve shapes.
W1(3) PHASE TIME OC MULTIPLIER: Enter the multiplier constant by which the
selected time overcurrent curve shape (the base curve) is to be shifted in time.
W1(3) PHASE TIME OC RESET: Select “Linear” reset to coordinate with
electromechanical time overcurrent relays, in which the reset characteristic (when the
current falls below the reset threshold before tripping) is proportional to ratio of
energy accumulated to that required to trip. Select “Instantaneous” reset to
coordinate with relays, such as most static units, with instantaneous reset
characteristics.
W1(3) HARMONIC DERATING CORRECTION: Select “Enabled” to enable automatic
harmonic derating correction of the winding 1(3) phase time overcurrent curve. The
745 calculates the derated transformer capability when supplying non-sinusoidal
load currents (as per ANSI / IEEE C57.110-1986) and, when this feature is enabled,
automatically shifts the phase time overcurrent curve pickup in order to maintain the
required protection margin with respect to the transformer thermal damage curve, as
illustrated below.
W1(3) NEUTRAL TIME OC PICKUP: Enter the level of neutral current (in units of relay
nominal current) above which the winding 1(3) neutral time overcurrent element will
pickup and start timing.
W1(3) NEUTRAL TIME OC SHAPE: Select the time overcurrent curve shape to be used
for the winding 1(3) neutral time overcurrent element. The Time Overcurrent Curves on
page 5–58 describe the time overcurrent curve shapes.
W1(3) NEUTRAL TIME OC MULTIPLIER: Enter the multiplier constant by which the
selected time overcurrent curve shape (the base curve) is to be shifted in time.
W1(3) NEUTRAL TIME OC RESET: Select “Linear” reset to coordinate with
electromechanical time overcurrent relays, in which the reset characteristic (when the
current falls below the reset threshold before tripping) is proportional to ratio of
energy accumulated to that required to trip. Select “Instantaneous” reset to
coordinate with relays, such as most static units, with instantaneous reset
characteristics.
In the 745, “ground” refers to the current measured in a CT in the connection between the
transformer neutral and ground. The 745 has two ground inputs which could be assigned
to any of the three windings, based on the transformer type selected with respect to the
rules in table 3-2.
As the ground overcurrent settings corresponding to the winding-assigned ground inputs,
are displayed and enabled. This section contains the settings to configure the ground
overcurrent elements. Included are ground time overcurrents for each associated winding,
and two levels of ground instantaneous overcurrent for each associated winding.
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