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2.3 PROTECTION SETTINGS
501: IT_PICKUP - Trip Supervision Current
502: IB_PICKUP - Block Supervision Current
•
Step Distance, PUTT, POTT1 and POTT2 Schemes
These two overcurrent functions provide supervision for the distance functions. IT is also used in the trip
2
bus seal-in circuit. To obtain maximum sensitivity, the following settings are proposed:
IT_PICKUP = minimum
IB_PICKUP = minimum
•
Blocking and Hybrid Schemes
The IT overcurrent function provides supervision for the tripping-zone distance functions, and is also used
in the trip bus seal-in circuit. The IB overcurrent function provides supervision for the reversed phase and
ground distance functions. For a Blocking or Hybrid scheme, the local IT and remote IB functions must
coordinate. This is accomplished by setting IB more sensitively (with a lower pickup) than IT. To obtain
maximum sensitivity, the following settings are proposed:
IB_PICKUP = minimum
IT_PICKUP = 1.3 x IB_PICKUP
where: IB_PICKUP
I
= positive-sequence line charging current (include effect of any non-switched shunt reactors)
c
503: IPT_PICKUP - GDOC Trip Current
504: IPB_PICKUP - GDOC Block Current
The IPT and IPB functions are placed in service whenever Z2GRDCHAR is set to GDOC or MHOGDOC.
The use of these functions will provide more sensitive protection for high resistance ground faults than can be
obtained with ground distance functions alone.
•
Step Distance Scheme
These functions only work with the pilot channel. Therefore, when this type of scheme is selected, they will
have no effect regardless of what setting is used for Z2GRDCHAR and what setting is made for these
functions. In simple terms, don't worry about IPT and IPB if a Step Distance scheme is selected.
•
PUTT Scheme
The IPT and IPB functions should not be used in this scheme. Therefore, insure that Z2GDCHAR is set to
MHO as proposed under the Z2GDCHAR setting description.
•
POTT1 Scheme
IPT is logically ANDed with the forward looking negative sequence directional function, NT, to form the pilot
tripping. The IPT operating quantity is:
IPT
= 3· I
op
0
It is proposed that IPT_PICKUP be set to its minimum value of 0.25 A.
IPB is not used; therefore, any setting that is made regarding IPB is irrelevant.
•
Hybrid and POTT2 Schemes
IPT is logically ANDed with the forward looking negative-sequence directional function, NT, to form the pilot
tripping. The IPT operating quantity is:
IPT
= 3 I
–
op
0
2-
24
+ I
R
c
= pickup setting of IB function at remote terminal of line
R
0.3 I
1
LPS-D Line Protection System
2 CALCULATION OF SETTINGS
2.3.6 CURSUPVISN
GE Power Management
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