GE G60 UR Series, Instruction Manual

Page: 274 / 634

5-142 G60 Generator Protection System GE Multilin
5.6 GROUPED ELEMENTS 5 SETTINGS
5
2. CT saturation
The characteristic allows for very sensitive settings when fault current is low and less sensitive settings when fault current is
high and CT performance may produce incorrect operate signals.
• STATOR DIFF LINE END SOURCE: This setting selects the source connected to CTs in the end of the machine stator
winding closest to the load and furthest from the winding neutral point. Both line and neutral-side CTs should be wired
to measure their currents in the same direction with respect to the neutral point of the winding.
• STATOR DIFF NEUTRAL END SOURCE: This setting selects the source connected to CTs in the end of the machine
stator winding furthest from the load and closest to the winding neutral point. Both line and neutral-side CTs should be
wired to measure their currents in the same direction with respect to the neutral point of the winding.
• STATOR DIFF PICKUP: This setting defines the minimum differential current required for operation. This setting is
based on the amount of differential current that might be seen under normal operating conditions. A setting of 0.1 to
0.3 pu is generally recommended.
• STATOR DIFF SLOPE 1: This setting is applicable for restraint currents from zero to
STATOR DIFF BREAK 1
, and defines
the ratio of differential to restraint current above which the element will operate. This slope is set to ensure sensitivity to
internal faults at normal operating current levels. The criteria for setting this slope is to allow for maximum expected CT
mismatch error when operating at the maximum permitted current. This maximum error is generally in the range of 5 to
10% of CT rating.
• STATOR DIFF BREAK 1: This setting defines the end of the Slope 1 region and the start of the transition region. It
should be set just above the maximum normal operating current level of the machine.
• STATOR DIFF SLOPE 2: This setting is applicable for restraint currents above the
STATOR DIFF BREAK 2
setting when
the element is applied to generator stator windings. This slope is set to ensure stability under heavy external fault con-
ditions that could lead to high differential currents as a result of CT saturation. A setting of 80 to 100% is recom-
mended. The transition region (as shown on the characteristic plot) is a cubic spline, automatically calculated by the
relay to result in a smooth transition between
STATOR DIFF SLOPE 1
and
STATOR DIFF SLOPE 2
with no discontinuities.
• STATOR DIFF BREAK 2: This setting defines the end of the transition region and the start of the Slope 2 region. It
should be set to the level at which any of the protection CTs are expected to begin to saturate.
Figure 5–71: STATOR DIFFERENTIAL SCHEME LOGIC
SATURATION DETECTION:
External faults near generators typically result in very large time constants of DC components in the fault currents. Also,
when energizing a step-up transformer, the inrush current being limited only by the machine impedance may be significant
and may last for a very long time. In order to provide additional security against maloperations during these events, the G60
incorporates saturation detection logic. When saturation is detected the element will make an additional check on the angle
between the neutral and output current. If this angle indicates an internal fault then tripping is permitted.
SETTING
SETTINGS
FLEXLOGIC OPERANDS
FLEXLOGIC OPERANDS
FLEXLOGIC OPERANDS
SETTING
SETTING
SETTING
STATOR DIFF
FUNCTION:
STATOR DIFF
SLOPE 2:
STATOR DIFF
BREAK 1:
STATOR DIFF
BREAK 2:
STATOR DIFF
SLOPE 1:
STATOR DIFF
PICKUP:
STATOR DIFF PKP A
STATOR DIFF PKP B
STATOR DIFF PKP C
STATOR DIFF DPO A
STATOR DIFF DPO B
STATOR DIFF DPO C
STATOR DIFF BLOCK:
Disabled = 0
Off = 0
Enabled = 1
STATOR DIFF
LINE END SOURCE:
STATOR DIFF
NEUTRAL END SOURCE:
I A
I A
I B
I B
I C
I C
RUN
RUN
RUN
I ad
I bd
I cd
I ar
I br
I cr
AND
Restraint Phasors
Differential Phasors
DC Offset
Removal
D.F.T.
and
Differential
and Restraint
I ar
I ad
I br
I bd
I cr
I cd