Minimum Acceptable Specification of C.T & P.T for Metering
April 1, 2011 12 Comments
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 | |
JIGNESH PARMAR
dear sir!!
your post are very informative..i request you to please guide us on realy testing for different schemes of cable and OHTL protection..please share us your practical knowledge..
Regards
Waqas Ahmed
It is really informative. Please guide me about the following:
We have a new steel plant coming up in the state of west bengal. The plant is still in installation & commissioning stage. We have erected one 220 KV line from supplying utility to the 220/33 KV Main receiving station of the plant. the CT ratio in the line is 400/1, 0.2 Class. We need about 1.5 MVA at present to keep the MRS charged and for commissioning of few of the equipment. However, supplying utility has told us that they will not be able to supply less than 5 MVA in the 220 KV line, as supply of less than 5 MVA may cause error in metering. Kindly guide us whether the stand of supplying utility is correct or not with reasoning.
Regards,
Rajiv
Very good…. keep it up
in maharastra it is required to put check meter on the consumer side for high MD cosumer. please could u tell me its possible to connect with same core of ct or PT or we have to insatall separate metering temple
Dear sir
Your site is very useful. Please tell me that are thumb rules same at both 50 or 60Hz?
please sir provide ct,pt sizing and selection procedure
sir i am arvind sharma
i am electrician . i am information for basic electrical control connection
so please help me all
Regard
Arvind Sharma
7417201007
We have plain feeders with CT ratio 800-400/1-1 specified at 800/1 with circuit breaker of 400A. Now would specifying the CT at 400/1 or 800/1 have any impact on reducing or increasing the reading of the total consumption read by the meter?
Please explain.
Dear Sir,
we have a 1MVA Transformer having the Voltage ratio is of 11KV/433V and a NGR on LV side to limit the fault current. what should be the CT ratio is to be installed in NGR , that should protect against the earth fault.
what is difference btetwee 220 KV CT & 245 KV CT
what should be the distance between 2 no. of DP- pole for 33KV CT/PT and 33KV Isolator.
Works properly with low voltage LED panorama lighting.