Lower Slope Of Pickup Characteristic - Siemens 7UT51 Instruction Manual

7UT51 v3
The 87HS pickup level should be set as low as
possible, but not so low that it will trip in the event of
an external fault causing unequal CT saturation. If Z is
the transfer impedance of the transformer, then a
bolted, through fault will result in a through current of
(1/ Z ) × × × × I
, where I is the rated nominal current of the
n n
transformer. A setting of 75% of this value should
9
8
7
6
5
4
3
2
1
87T Min
(1603)
0
0
Figure 4.9 Differential Protection Trip Characteristic when the Protected Object is a Transformer
4.4.3

Lower Slope of Pickup Characteristic

The lower sloped-segment of the trip characteristic
(Slope 1) deals with a differential current resulting from
transformation errors in the CTs, the current inputs of
the relay, or from the position of the tap changer of the
voltage regulator. The baseline intercept of this
segment is the origin; its slope is entered
PRIM-2330C
I I
2
1
7UT51
I I
I
1 2
diff
I I
I
1 2
rest
Operate Area
1 2 3 4
Restraining Current,
Transformer Differential Protection (87T and 87HS)
enable the 87HS function to trip for a fault on a
transformer terminal. For example, if Z is 10%, then 1/
Z = 1/0.10 = 10, so the suggested setting is 0.75 × × × × 10
= 7.5 (since the unit of this setting is I
should be set higher than the minimum 87T pickup
level (Address 1603).
Through-Fault Restraint Area
( slope = 1/2 of 1606, left edge = 1618,
duration = 1617 )
5 6 7
I ( in multiples of
rest
Address 1606.
1606 87SLOPE 1
Slope of lower sloping segment of 87T
pickup characteristic (Slope 1). This segment
intercepts the horizontal axis at the origin.
Range: 0.10
Default: 0.25
). This setting
n
87HS Pickup
(1604)
Non-Operate Area
8 9 10 11
I )
n
–
0.50 (unitless ratio)
4
57