Minimum Acceptable Specification of C.T & P.T for Metering

 

Min. Acceptable Specification of Current Transformer for Metering:

Sr. No	Particulars	11 kV	33 kV	132 kV	220 kV
1	Highest System Voltage (kV rms)	12	36	145	245
2	CT ratio.	2000-1000/1-1	800-400/1-1	400/1-1	800/1-1
		1600-800/1-1	600-300/1-1
		1200-600/1-1	400-200/1-1
		800-400/1-1	300-150/1-1
		600-300/1-1	100-50/1-1
		400-200/1-1
		300-150/1-1
		150-75/1-1
3	Number of metering cores	Two Nos	Two Nos	Two Nos	Two Nos
4	Rated continuous thermal current.	120% of rated primary  current	120% of rated primary  current	120% of rated primary  current	120% of rated primary  current
5	Rated short time thermal current of primary for 1 sec. (kA)	25	25	31.5	40
6	CT characteristics :a) Rated primary current (Amps.)	2000-1000	800-400	400	800
		1600-800	600-300
		1200-600	400-200
		800-400	300-150
		600-300	100-50
		400-200
		300-150
		150-75
	(b) Rated Secondary current (Amps.)	1	1	1	1
	(c) Class of accuracy.	0.2	0.2	0.2	0.2
	(d) Max. instrument security factor	5	5	5	5
	(e) Rated burden (VA).	30	30	30	40
7	IS to which CT conforms.
8	IS to which insulating oil conforms.

 Min. Acceptable Specification of Voltage Transformer for Metering:

Sr. No	Particulars	245 kV CVTs	145 kV CVTs
1	Highest SystemVoltage (kV)	245 kV	145 kV
2	Rated Capacitance (pF)	4400 pf with tolerance + 10% and – 5%
3	For low voltage terminal over entire carrier frequency range.
	(a) Stray capacitance	Shall not exceed 200 pf
	(b) Stray conductance	Shall not exceed 20 us
4	(a) High frequency            capacitance for entirecarrier frequency range	within 80% to 150% of rated capacitance
	(b) Equivalent series resistance over the entire frequency range.	less than 40 Ohms
5	No. of secondary windings for potential device.	Two	Two
6	Transformation ratio:
	(i) Winding –I	20 kV- \/3/110 -\/3V
	(ii) Winding –II	20 kV- \/3/110 -\/3V
7	Rated secondary burden
	(i)Winding –I   (VA)	50 VA	50 VA
	(ii) Winding –II  (VA)	50 VA	50 VA
8	Accuracy Class :
	(i)Winding –I   (VA)	0.2 for metering
	(ii) Winding –II  (VA)	0.2 for metering
9	Voltage factor for winding – IVoltage factor for winding – II	1.2 Cont. & 1.5 for 30 secs.1.2 Cont. & 1.5 for 30 secs.
10	IS to which CVTs conform.	IS 3156 with latest amendment
11	IS to which Insulating Oil conform.	IS 335 with latest amendment

Minimum Acceptable Specification of Single Phase PT for Metering:

Sr.No	Particulars	33 kV	11 kV
1	Highest System Voltage (kV rms)	36	12
2	Transformation ratio.	33kV/ V3/     110/ V3	11 kV/110 V
3	Number of windings.	Two	Two
4	Rated output/ burden (VA) per winding /phase.	50	50
5	Accuracy class. (At 10 to 100% of VA burden)	0.2	0.2
6	Rated voltage factor and duration.	1.2 continuous & 1.5 for 30 secs.
7	IS to which PT conforms.	3156 with latest amendment