3
Operation by Front Panel
3.4
Setting The Relay (Example)
3.4.1
Example Defined
This hypothetical example has the following requirements:
Parameter
For Phase
For Ground
Time over-current
4.7A
1 .6A
pickup:
Pickup Range:
High
Low
Curve shape:
Very Inverse
Inverse
Time delay setting:
0.38 sec.
@
6 x 0.90 sec
@
3.1
tap
x tap
Instantaneous
1 8.8 x--
1..
6.4�
1.
.
overcurrent pickup:
..
The following style number describes an appropriate relay for
this hypothetical application.
Model: SCORStyle: H1 E Z5 J B1 NOS.
The second style digit indicates that HIGH range was chosen for
phase monitoring, and LOW range for ground current monitor
ing.
3.4.2
Calculating the Settings
1 . The time overcurrent characteristic must be selected such
that it will coordinate with the other relays in the system to
meet the protective needs of the application. Assume that
a Very Inverse function is suitable for phase protection, and
Inverse for ground protection. From
Table 1
we see that
these two characteristics are designated b6 and b5 re
spectively. The table also provides the figure numbers that
illustrate the desired curve sets.
2. Note that the phase time overcurrent pickup, 4.7 A, falls
between tap C and tap D of the HIGH range (as shown on
the front -panel chart illustrated in
Figure 3).
The phase Tap
Cal value (which interpolates between TAP switch posi
tions) is then calculated as follows:
Given:
Pickup value
Tap C (HIGH)
Tap D {HIGH)
= 4.7 A
= 4.0 A
= 5.0 A
Page
15
Then: Set Phase Tap Switch (Front Panel) on C
Span
=Tap D - Tap C
=1 .00
Difference
=Pickup value - Tap C
=0.70
Tap Cal value (phase)
= Difference/Span x 1 00
0.70 /1 .00
X
1 00 = 70
3. The ground time overcurrent pickup, 1 .6 A, falls between tap
C and tap D of the LOW range
(Figure 3).
The ground Tap
Cal value is:
Pickup value
Tap C (LOW)
Tap D (LOW)
= 1 .6 A
= 1 .5 A
= 2.0 A
Then: Set Ground Tap Switch (Front Panel) onC
Span
= Tap D - Tap C
= 0.5
Difference
= Pickup value - Tap C
=
0. 1
Tap Cal value (ground)
= Difference/Span x 100
0 . 1 0/0.50
X
1 00
= 20
4. The ratio oft he phase Instantaneous Overcurrent pickup to
the phase Time Overcurrent Tap is calculated as follows:
Phase Instantaneous Overcurrent
Phase Time Overcurrent Tap
Ratio
= 1 8.8/4.0
Set Pin1 to 4.7
= 1
�
= 4.0
= 4.7
5. The ratio of the ground Instantaneous Overcurrent pickup
to the ground Time Overcurrent Tap is calculated as
follows:
Ground Instantaneous Overcurrent
Ground Time Overcurrent Tap
Ratio
= 6.4/1 . 5
Set nin1 to 4.27
=6. 4�
=
1 .5 A
= 4 . 27
6. From Curve b6
Figure A.6,
find the phase TIME DIAL
setting that corresponds to a delay of 0.38 seconds at 6
times the tap setting.
Answer: A TIME DIAL setting of 07.
7. From Curve b5
Figure A.5,
find the ground TIME DIAL
setting that corresponds to a delay of 0.90 seconds at 3.1
times the tap setting.
Answer: A TIME DIAL setting of 05.
3.4.3
Entering the Settings
1.
Set PHASE TAP Switch (Front Panel) on C, and GROUND
TAP Switch (Front Panel) on C.
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