GE 869 Instruction Manual page 246

PROTECTION
NOTE:
4–114
OUTPUT RELAY X
For details see Common
EVENTS
Range: Disabled, Enabled
Default: Enabled
TARGETS
Range: Disabled, Self-reset, Latched
Default: Latched
The values of the setpoints for minimum pickup, Break 1 and Break 2 are expressed in
terms of CT reference. Please see the definition of CT reference which is described in the
second paragraph of this chapter.
DC Saturation Detection:
D.C. components of both J1-CT and K1-CT bank currents, in phases A, B and C must be
first calculated. The calculation is performed only if the internal summation method is
selected. The method is described below.
In other words, the d.c. component is an absolute value of the average of current
samples over one last cycle of data.
Operation 2 (Eq. 6) is performed three times for each phase separately.
D is a factory constant of 1/2. A new component of the saturation condition is derived
1
as in the figure below:
Saturation Detection
External faults near rotating machines 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 improper
operations during these events, the 869 incorporates saturation detection logic. When
saturation is detected the element makes an additional check on the angle between the
terminal side CT and differential CT currents. If this angle indicates an internal fault then
tripping is permitted. The latter applies only when the Internal summation method is
used.
The saturation detector is implemented as a state machine (see next figure). "NORMAL"
is the initial state of the machine. When in "NORMAL" state, the saturation flag is not set
(SAT = 0). The algorithm calculates the saturation condition, SC. If SC = 1 while the state
machine is "NORMAL", the saturation detector goes into the "EXTERNAL FAULT" state and
sets the saturation flag (SAT = 1). The algorithm returns to the "NORMAL" state if the
Setpoints.
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS
Eq. 6
Eq. 7
Eq. 8