Utility Relay Company AC-PRO-II, Instruction Manual

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AC-PRO-II
®
Instruction Manual www.utilityrelay.com
Page 37
A conditional 2-year warranty is offered with each AC-PRO-II
trip unit.
Contact Utility Relay Company for full details.
The TCCs are shown in Figures 18.1, 18.2, 18.3 and 18.4.
AC-PRO-II TCCs are similar to AC-PRO TCCs, except with
improvements.
The AC-PRO-II TCCs offers the following improvements
and/or updates:
- Narrower ST bands now allow coordination between the
0.2, 0.3, and 0.4 ST bands.
- Improved power-up times.
- GF I
2
T ON affects currents up to 0.6xCT instead of 2xCT.
The curves are shown on log-log graph with seconds in the
vertical direction and current in the horizontal direction.
Overload and fault currents are shown as multiples of the LT
pick-up setting. GF current is shown as a percentage of the
CT rating.
Tolerances for the Pick-Up bands are ± 10% in the current
direction. Tolerance for LT, ST I
2
T and GF I
2
T trip times are
+ 23% and -17% in the time direction. Tolerance for GF I
5
T
trip times are +69% and -38% in the time direction.
Instantaneous pick-up tolerance is ± 10% for 1A and 0.5A
CTs. Instantaneous pickup tolerance is ± 20% for 0.4A,
0.25A, and 0.2A CTs.
The curves for the following time bands:
Long Time (LT)
Short Time (ST) with I²T ON
Ground Fault (GF) with I²T ON
Neutral Overload (NOL)
are based on the following equation:
I²T = Constant
Where: I is current in amps
T is time to trip in seconds (center of the band)
When performing trip-timing tests using a primary injection
test set, the trip time at various test currents can be
determined by calculation as explained in Sections 18.1,
18.2, 18.3 and 18.4.
The TCCs are based on a total actuator operating time plus
breaker opening time in the 16ms to 33ms range.
For overload currents, the "I²T = Constant" equation can be
restated as follows:
T = TBC
LT
X²
Where:
T = time to trip in seconds (center of the band)
X = current in multiples of the LT pick-up setting
TBC
LT
= the LT Time Band Constant
= 36 X LT time band setting
**** NOTE ****
The LT Time Band Constant (TBC
LT
) is by definition 36
times the LT Time Band Setting in seconds.
EXAMPLE #1:
CT Rating 1600A
LT pick-up 1200A
LT time band 20.0S
Overload Current 3600A
TBC
LT
= 36 X LT Time Band Setting
= 36 X 20.0
= 720
and X = overload current = 3600A = 3
LT Pick-Up 1200A
therefore:
trip time = T = TBC
LT
or 720 = 720
X² 3² 9
= 80 seconds
**** IN SUMMARY ****
To calculate the LT trip time:
1) Calculate the LT Time Band Constant (TBC
LT
)
2) Calculate "X" where
X = overload current
LT Pick-Up Setting
3) Solve the equation:
trip time(sec) = TBC
LT
X
2
17.0 Warranty
18.0 Time-Current Curves (TCC)
18.1 Long Time (LT) Trip Time