13-54
BE1-CDS240 Testing and Maintenance
9365200990 Rev F
Sidebar 13-9. Auto Tap Compensation
Tap adjustment factors for the 87ND function are automatically calculated based on the equation:
TAPN * CTRn = TAPG * CTRG
where CTRn is the CT ratio for the CT designated in the SL-x87ND setting in the active logic. Currents
are tap adjusted based on the CT ratios with the driving tap (CT input with the highest CTR) set at the
minimum setting (2.0 for 5 ampere sensing relays and 0.4 for 1 ampere sensing relays) and the other tap
adjusted to the driving tap based on the equation above. For more information on Auto Tap
Compensation, refer to Section 4,
Protection and Control Functions, Differential Protection, 87ND Neutral
Differential Function.
Step 4:
Apply current to the ground input and slowly ramp up until OUT1 closes.
Step 5:
Accuracy when increasing or decreasing the input current is
4% of setting or 75 milliamperes
(whichever is larger) for 5 ampere sensing inputs and
4% of setting or 25 milliamperes
(whichever is larger) for 1 ampere sensing inputs. Verify that pickup occurred within the
specified accuracy of the relay.
Step 6:
Decrease the current to the ground input until the relay drops out.
Step 7:
Repeat for all other values shown in Table 13-41 by substituting for minpu in the S#-x87ND
command or by navigating to Screen \PROT\SGn\87ND\87ND and editing the MIN PICKUP
value.
Table 13-41. Minimum Pickup Accuracy Limits (87ND)
Sensing Type
MINPU X TAP
Calculated TAPG
Pickup (A)
Low Limit (A)
High Limit (A)
0.10 2.00
0.20
0.125
0.275
0.50 2.00
1.00
0.925
1.075
5 A
1.00 2.00
2.00
1.920
2.080
0.10 0.40
0.04
0.015
0.065
0.50 0.40
0.20
0.175
0.225
1 A
1.00 0.40
0.40
0.375
0.425
Step 8:
(Optional.) Repeat Steps 2 through 8 for Setting Groups 1 through 3, using the CS/CO-
GROUP command to change setting groups.
Step 9:
(Optional.) Repeat for 187 element and selection of associated CT inputs (CT1, CT2, CT3,
CT4).
Restrained Pickup Verification (87ND & 187ND)
Purpose:
To verify the accuracy of the restraint operation of the x87ND elements.
Reference Commands:
SL-x87ND, SL- VO, SG-CT, S(n)-87, S(n)-TAP87.
Step 1:
Connect one current source to terminals A9 and A10 (A-phase Input 2) and a second source
at 180
o
to terminals A1 and A2 (ground input). See Figure 13-18. An ohmmeter or continuity
tester may be used to monitor output contact status.
Summary of Contents for BE1-CDS240
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