GE G60 Instruction Manual page 197

5 SETTINGS
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
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
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 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.
SETTING
STATOR DIFF
FUNCTION:
Disabled = 0
Enabled = 1
SETTING
AND
STATOR DIFF BLOCK:
Off = 0
SETTING
STATOR DIFF
LINE END SOURCE:
IA
IB
IC
DC Offset
Removal
D.F.T.
SETTING
STATOR DIFF Differential
NEUTRAL END SOURCE: and Restraint
IA
IB
IC
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.
GE Multilin
STATOR DIFF SLOPE 1
Differential Phasors
Iad
Ibd
Icd
and
Restraint Phasors
Iar
Ibr
Icr
Figure 5–52: STATOR DIFFERENTIAL SCHEME LOGIC
G60 Generator Management Relay
5.5 GROUPED ELEMENTS
STATOR DIFF BREAK 1
STATOR DIFF BREAK 2
and with no discontinuities.
STATOR DIFF SLOPE 2
SETTINGS
STATOR DIFF
PICKUP:
STATOR DIFF
SLOPE 1:
STATOR DIFF
BREAK 1:
STATOR DIFF
SLOPE 2:
STATOR DIFF
BREAK 2:
RUN
Iad
Iar
RUN
Ibd
Ibr
RUN
Icd
Icr
5
, and defines
setting when
FLEXLOGIC OPERANDS
STATOR DIFF PKP A
STATOR DIFF DPO A
FLEXLOGIC OPERANDS
STATOR DIFF PKP B
STATOR DIFF DPO B
FLEXLOGIC OPERANDS
STATOR DIFF PKP C
STATOR DIFF DPO C
5-99