S&C Vista SD, Программирование

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Table 1. I
2
t Security Characteristic Settings Limits (660:1 CT)
Curve
Affected Settings for
Fault Current ≥ 14.5 kA
Affected Settings for
Fault Current = 10.0 kA
U1
Time Dials > 4 .3 @ 50 A pickup
Time Dials > 3 .2 @ 1200 A pickup Time Dials > 9 .1 @ 50 A pickup
Time Dials > 5 .9 @ 1200 A pickup
U2
Time Dials > 3 .9 @ 50 A pickup
Time Dials > 3 .3 @ 1200 A pickup Time Dials > 8 .3 @ 50 A pickup
Time Dials > 5 .8 @ 1200 A pickup
U3
Time Dials > 7 .3 @ 50 A pickup
Time Dials > 6 .0 @ 1200 A pickup Time Dials > 14 .9 @ 450 A pickup
Time Dials > 10 .2 @ 1200 A pickup
U4
Time Dials > 14 .9 @ 730 A pickup
Time Dials > 10 .0 @ 1200 A pickup Time Dials > 14 .9 @ 1100 A pickup
Time Dials > 13 .2 @ 1200 A pickup
U5
Time Dials > 14 .5 @ 50 A pickup
Time Dials > 10 .6 @ 1200 A pickup
Not applicable
C1
Time Dials > 0 .37 @ 50 A pickup
Time Dials > 0 .27 @ 1200 A pickup Time Dials > 0 .78 @ 50 A pickup
Time Dials > 0 .48 @ 1200 A pickup
C2
Time Dials > 0 .99 @ 760 A pickup
Time Dials > 0 .61 @ 1200 A pickup Time Dials > 0 .99 @ 1040 A pickup
Time Dials > 0 .84 @ 1200 A pickup
C3 Not applicable Not applicable
C4
Time Dials > 0 .17 @ 50 A pickup
Time Dials > 0 .06 @ 1200 A pickup Time Dials > 0 .37 @ 50 A pickup
Time Dials > 0 .09 @ 1200 A pickup
C5 Not applicable Not applicable
For our sample coordination study, with a U4 curve selected to have an 880­
ampere pickup and a 0.8 Time Dial setting, we are well below the limits shown
for the operation of the “I
2
t security characteristic” during fault levels up to 14.5
kA. The
Time Dial
setting is below the threshold of 10.0 at a
Pickup
setting of
1200 amperes.
If the setting was above the limit for the “I
2
t security characteristic,” a warning message
would be displayed with the calculation of the cross over point in primary amperes of the
selected US or IEC curve with the “I
2
t security characteristic” curve. A sample warning
message is shown below.
“Phase overcurrent control will operate on the TOC curve for faults up to 18476 A.
Phase overcurrent control will operate on its maximum I
2
t (thermal) limit curve for
faults above 18476 A. Refer to S&C Instruction Sheet 681­515 Appendix D.”
When this occurs, the user must consider the following:
If the fault level displayed in the warning message is
higher than the maximum
avail able fault current level at the switchgear assembly, the “I
2
t security character­
istic” will not become enabled. If the fault level displayed in the warning message is
lower
than the maximum available fault current level, then the “I
2
t security character­
istic” will become enabled resulting in a faster time to operate. To prevent this from
occurring, new settings selec tions should be considered to prevent miscoordination
between upstream source­side and downstream load­side devices. Contact S&C Electric
Company—Power Systems Solutions for application assistance.
Appendix D
S&C Instruction Sheet 695-515 29