GE G60 Instruction Manual page 389

CHAPTER 5: SETTINGS
The characteristic allows for very sensitive settings when fault current is low and less sensitive settings when fault current
is high and CT performance can produce incorrect operate signals.
STATOR DIFF LINE END SOURCE
closest to the load and farthest from the winding neutral point. Wire both line and neutral-side CTs to measure their
currents in the same direction with respect to the neutral point of the winding.
STATOR DIFF NEUTRAL END SOURCE
from the load and closest to the winding neutral point. Wire both line and neutral-side CTs to measure their currents in the
same direction with respect to the neutral point of the winding.
— Defines the minimum differential current required for operation. This setting is based on the amount
STATOR DIFF PICKUP
of differential current that can be seen under normal operating conditions. A setting of 0.1 to 0.3 pu is generally
recommended.
— This setting is applicable for restraint currents from zero to
STATOR DIFF SLOPE 1
ratio of differential to restraint current above which the element operates. 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.
— Defines the end of the Slope 1 region and the start of the transition region. Set it just above the
STATOR DIFF BREAK 1
maximum normal operating current level of the machine.
— This setting is applicable for restraint currents above the
STATOR DIFF SLOPE 2
element is applied to generator stator windings. This slope is set to ensure stability under heavy external fault conditions
that can lead to high differential currents as a result of CT saturation. A setting of 80 to 100% is recommended. 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
— This setting defines the end of the transition region and the start of the Slope 2 region. Set it to the
STATOR DIFF BREAK 2
level at which any of the protection CTs are expected to begin to saturate.
5.7.5.1 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 can be significant
and can 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 makes an additional check on the
G60 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
— This setting selects the source connected to CTs in the end of the machine stator winding
— Selects the source connected to CTs in the end of the machine stator winding farthest
and
STATOR DIFF SLOPE 2
Figure 5-114: Stator differential logic
STATOR DIFF BREAK 1
setting when the
STATOR DIFF BREAK 2
with no discontinuities.
GROUPED ELEMENTS
, and it defines the
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