Page 518 - Industrial Power Engineering and Applications Handbook

15/492 Industrial Power Engineering and Applications Handbook
Table 15.12 Summary of specifications of a CT

Sr. no. Specifications Measuring CTs Protection CTs Special-purpose protection
CTs type ‘PS’
1 System voltage As in Table 13.1
2 Insulation level (peak) As in IEC 60044-1 or Tables 13.2 and 14.3 for Series I and Tables 14.1 and 14.2 for Series I1
voltage systems
3 Class of insulation E B B
4 Frequency 50 or 60Hz 50 or 60 Hz SO or 60 Hz
5 Nominal current ratio 600/5 A 2000/5 A 2000/5 A
6 VA burden < 2.5, 5, 7.5, 15 or 30 >
7 Class of accuracy 0.1, 0.2, 0.5,1, 3 or 5 (SP, IOP or 15P)a -
8 Accuracy limit factor (ALF) - (5, 10, 15)b -
9 Short-time current I,, and its 25 kA for 1 second SO kA for 1 second -
duration
10 Dynamic current Minimum 2.5 times I,, Minimum 2.5 times I,, -
(in the above case 62.5 kA) (in the above case 125 kA)
11 Nominal turns ratio 1/400
12 Limiting secondary‘ 3
resistance at 90°C (a)
13 Knee point voltage (V) 950
14 Excitation current at knee 0.05
point voltage (or at any other
required voltage or both) (A)
15 Service conditions Indoors or outdoors Indoor or out-door Indoors or outdoors
Ambient temperature Ambient temperature Ambient temperature
Altitude, if above 2000 m Altitude, if above 2000 m Altitude, if above
for LT and above for LT and above 2000 m for LT and
1000 mm for HT 1000 mm for HT above 1000 mm for HT
Humidity Humidity Humidity
Any other important Any other important Any other important
requirement requirement requirement
16 Making of CTs 600/5 Ad 2000/5 A 6.6 kV, 2000 A, 1/400
IO VA, class 1 15 VA, class 5P10 950 x 0.05 R3.
System voltage and insulation level, class of insulation, frequency, short-time rating and
dynamic current rating etc. for all types of CTs
Notes
“The class of accuracy for protection CTs is recommended to be not more than IOP as far as possible.
bProduct of VA ahd ALF not to exceed 150.
‘The limiting secondary resistance is required to determine the secondary limiting e.m.f. which is = (FS) x rated secondary current x VA
x resistance of secondary windings at 90°C or the highest operating temperature as in Table 14.5, where
FS = Instrument security factor
Rated instrument limit orimarv current
Rated primary current
dWherever two separate secondary windings are provided, say, one for measuring and the other for protection, the markings shall indicate
all such details that are marked against (a) for each secondary winding.

2 Routine tests These will cover the following tests: on the secondary circuit, i.e. the electromagnetic
(i) Verification of terminal marking (refer to Table transformer. The test values and test procedure
15.7 and Figure 15.35, illustrating types of will remain the same as discussed above.
transformer connections).
(ii) Power frequency withstand test on the primary Note
windings. This must be conducted Only On the A repeat power frequency test, if considered necessary, must be
electromagnetic unit of a VT. For example, when performed at 80% of the prescribed test voltage. See also Section
testing a capacitor VT it must be conducted only 14.5.