Table of Contents
Advertisement
5 SETPOINTS
The basic operating principle of the percent differential element can be described by the following diagram and
its associated equations:
Figure 5–6: PERCENT DIFFERENTIAL OPERATING PRINCIPLE
Restraint current calculations have been changed from average to maximum to provide better
security during external faults.
NOTE
Basic Operating Principle (3-winding):
(
I
I
max I
=
=
r
restraint
I
=
I
=
I
d
differential
1
I
d
×
%slope
100%
=
--- -
I
r
where
I
= per-phase maximum of the currents after phase, ratio, and zero-sequence correction
restraint
I
= per-phase vector sum of currents after phase, ratio, and zero-sequence correction
differential
In the above equations, the 180° phase shift due to the wiring connections is taken into account, hence
the + sign to obtain the differential current.
NOTE
PICKUP 0.30
Figure 5–7: PERCENT DIFFERENTIAL – DUAL SLOPE CHARACTERISTIC
GE Power Management
V3
V1
CT1
V2
I
1
Percent
Diff
Element
,
,
)
I
I
1
2
3
+
I
+
I
2
3
I
(x CT)
differential
OPERATE
REGION
SLOPE 1
25%
1.00
0.05
745 Transformer Management Relay
CT3
CT2
I
I
3
2
Basic Operating Principle (2-winding):
(
I
I
max I
=
=
r
restraint
1
I
I
I
I
=
=
+
d
differential
1
I
d
×
%slope
=
--- -
100%
I
r
200%
SLOPE 2
100%
100%
50%
RESTRAINT
REGION
15%
2.0
I
restraint
KNEEPOINT
5.6 S4 ELEMENTS
,
)
I
2
2
(x CT)
5-47
5
Advertisement
Table of Contents
