2.13.2.3
Current Transformers for Metal-Clad Switchgear
Single-ratio units, used for metering and relaying, shall have a metering
accuracy class rating of [_____] [B_____]. Single-ratio units, used only
for relaying, shall have a relaying accuracy class rating of [_____] for
[either] a C [or T] classification.
2.13.2.4
Current Transformers for kW Hour and Demand Metering (Low Voltage)
**************************************************************************
NOTE: Use the following guidelines for specifying
current transformers.
a. Select the standard current transformer (CT)
primary rating which is just below the full load
current of the serving power transformer i.e., for
500 kVA transformer with a full load of 1387 amps at
208 volts - select a 1200/5 CT ratio; for a 750 kVA
transformer with a full load of 902 amps at 480
volts - select a 800/5 CT ratio.
b. Select a continuous-thermal-current rating
factor (RF) in accordance with the following table:
RATIO
RF at 30 degrees C
200/5
4.0
300/5
3.0
400/5
4.0
600/5
3.0
800/5
2.0
1200/5
1.5
1500/5
1.5
2000/5
1.5
3000/5
1.33
c. Select ANSI Metering Accuracy Class in
accordance with the following table:
Primary Amp Rating (of CT)
Accuracy Class
200
0.3 thru B-0.1
300-400
0.3 thru B-0.2
600-1200
0.3 thru B-0.5
1500
0.3 thru B-0.9
2000-3000
0.3 thru B-1.8
**************************************************************************
Current transformers shall conform to IEEE C57.13. Current transformers
with a metering accuracy Class of 0.3 through [_____], with a minimum RF of
[_____] at 30 degrees C, 86 degrees F, with 600-volt insulation, and 10 kV
BIL shall be provided. Butyl-molded, window-type current transformers
mounted [on the transformer low-voltage bushings shall be provided. Route
current transformer leads in a location as remote as possible from the
power transformer secondary cables to permit current measurements to be
taken with hook-on-ammeters.] [in the current transformer cabinet shall be
provided.]
SECTION 16475A
Page 26
Previous Page
