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


Min. Acceptable Specification of Current Transformer for Metering:

Sr. NoParticulars11 kV33 kV132 kV220 kV 
1Highest System Voltage (kV rms)1236145245
2CT ratio.2000-1000/1-1800-400/1-1400/1-1800/1-1
3Number of metering coresTwo NosTwo NosTwo NosTwo Nos
4Rated continuous thermal current.120% of rated primary  current120% of rated primary  current120% of rated primary  current120% of rated primary  current
5Rated short time thermal current of primary for 1 sec. (kA)252531.540
6CT characteristics :a) Rated primary current (Amps.) 2000-1000 800-400 400 800
(b) Rated Secondary current (Amps.)1111
(c) Class of accuracy.
(d) Max. instrument security factor5555
(e) Rated burden (VA).30303040
7IS to which CT conforms.    
8IS to which insulating oil conforms.    

 Min. Acceptable Specification of Voltage Transformer for Metering:

Sr. NoParticulars    245 kV CVTs     145 kV CVTs 
1Highest SystemVoltage (kV)         245 kV             145 kV
2Rated Capacitance (pF) 4400 pf with tolerance + 10% and – 5%
3For low voltage terminal over entire carrier frequency range.  
 (a) Stray capacitance Shall not exceed 200 pf
 (b) Stray conductanceShall not exceed 20 us
4(a) High frequency            capacitance for entirecarrier frequency rangewithin 80% to 150% of rated capacitance
 (b) Equivalent series resistance over the entire frequency range.less than 40 Ohms
5No. of secondary windings for potential device.            Two             Two
6Transformation ratio: 
 (i) Winding –I  20 kV- \/3/110 -\/3V
 (ii) Winding –II  20 kV- \/3/110 -\/3V
7Rated secondary burden  
 (i)Winding –I   (VA)50 VA50 VA
 (ii) Winding –II  (VA)50 VA50 VA
8Accuracy Class :  
 (i)Winding –I   (VA)                       0.2 for metering
 (ii) Winding –II  (VA)                       0.2 for metering
9Voltage factor for winding – IVoltage factor for winding – II1.2 Cont. & 1.5 for 30 secs.1.2 Cont. & 1.5 for 30 secs.
10IS to which CVTs conform.IS 3156 with latest amendment
11IS to which Insulating Oil conform.IS 335 with latest amendment

Minimum Acceptable Specification of Single Phase PT for Metering:

Sr.NoParticulars       33 kV        11 kV 
1Highest System Voltage (kV rms)          36            12
2Transformation ratio.  33kV/ V3/     110/ V3  11 kV/110 V
3Number of windings.         Two          Two
4Rated output/ burden (VA) per winding /phase.          50            50
5Accuracy class. (At 10 to 100% of VA burden)         0.2            0.2
6Rated voltage factor and duration.1.2 continuous & 1.5 for 30 secs.
7IS to which PT conforms.  3156 with latest amendment