Current transformers. Current transformers shall be single phase, secondary ratio transformers for outdoors assembly, in vertical position, with oil immersed or SF6 gas insulation and will be hermetically sealed. They shall be able to conduct the primary rated current for one minute, while the secondary circuit is open. The core shall be toroidal and made up of steel magnetic foils with very low specific losses, and the windings shall be made of insulated copper. In the case of the transformers that work in connection with the disconnectors, high frequency currents and voltages transferable to secondary and ground circuits shall be taken into consideration during the switching of adjacent live disconnectors. The manufacturer’s structural design shall be such that it prevents: g1. High current density in certain points of the equipment causing localized overheating. g2) Internal surges of very short duration causing dielectric breakdowns in liquid and solid insulators. Current transformers shall have the following additional characteristics: Normal current 75 – 150 A (Transmission Line) 75 – 150 A (Transformer) Short-circuit thermal intensity 31.5 kA Characteristics of measurement cores
a) Accuracy class
b) Power Characteristics of protection cores
i) Accuracy class
j) Power 0.2 % 15 VA (minimum) (*) Current ratio to be reviewed with proper support by the CONCESSIONAIRE in the POS.
Current transformers. Current transformers shall have at least four secondary cores: • Three 5P20 protection cores. • One Class 0,2 core for measurement.
Current transformers. (A) All CTs for Type 1, 2 and 3 Meters must meet the following criteria: Type of Meter Relevant Standard Minimum Class Accuracy No. of sets Usage
1 IEC 6189-2 0.2s 2 1 set of CTs dedicated to the Main Meter only and 1 set supplying the Check Meters. Check Meter CTs can be used for other purposes provided that such Check Meter CTs comply with the accuracy requirements in paragraph 2.2 of these TSRs.
2 IEC 6189-2 0.2s 1 CTs must be dedicated to the CfD Settlement Activities, supplying both Main Meters and Check Meters. An additional set of CTs may be fitted for the Check Meter which may also be used for other purposes provided that Type of Meter Relevant Standard Minimum Class Accuracy No. of sets Usage such Check Meters comply with the accuracy requirements in paragraph 2.2 of these TSRs.
3 IEC 185 0.5 1 1 set of CTs for Main Meters and Check Meters’ CfD Settlement Activities purposes, but may also have other uses if the overall accuracy requirements in paragraph 2.2 of these TSRs are met.
Current transformers. C/Ts shall confirm to IS 2705 (part -I, II and III) in all respects. All C/Ts used for medium voltage application shall be rated for 1 kV. C/Ts shall have rated primary current, rated burden and class of accuracy as specified in schedule of quantities/drawings. Rated secondary current shall be 5A unless otherwise stated. Minimum acceptable class for measurement shall be class 0.5 to 1 and for protection class SP 10. C/Ts shall be capable of withstanding magnetic and thermal stresses due to short circuit faults of 31 MVA on medium voltage. Terminals of C/Ts shall be paired permanently for easy identification of poles. C/Ts shall be provided with earthing terminals for earthing chassis, frame work and fixed part of metal casing (if any). Each C/T shall be provided with rating plate indicating: CTs shall be mounded such that they are easily accessible for inspection, maintenance and replacement. Wiring for CT shall be with copper conductor PVC insulated wires with proper termination works and wiring shall be bunched with cable straps and fixed to the panel structure in a neat manner.
Current transformers. (A) All CTs for Type 1, 2 and 3 Meters must meet the following criteria: 1 IEC 6189-2 0.2s 2 1 set of CTs dedicated to the Main Meter only and 1 set supplying the Check Meters. Check Meter CTs can be used for other purposes provided that such Check Meter CTs comply with the accuracy requirements in paragraph 2.2 of these TSRs.
Current transformers. Current Transformers shall comply with IEC 61869 in general. All ratios shall be obtained by secondary taps only. Generally, Current Transformers (CT) shall have five cores (four for protection and one for metering) whereas; CT in Tie bays shall have six cores (four for protections & two for metering) suitably distributed on both sides of CB (for 400kV and above voltage class). The burden and knee point voltage shall be in accordance with the requirements of the system including possible feeds for telemetry. Accuracy class for protection core shall be PX and for metering core it shall be 0.2S. The rated burden of cores shall be closer to the maximum burden requirement of metering & protection system for better sensitivity and accuracy.
Current transformers. The term "current transformer" used in section 5 does not preclude the use of other measuring techniques with a performance equal to that specified for such measurement transformers. For each circuit where a current transformer is used, it shall meet the requirements set out below. Where required, one set of current transformers to BS EN 60044-1:1999 with a minimum standard of accuracy to Class 0.5 shall be provided per circuit. Preferably the current transformers shall be dedicated for Allocation purposes, but the current transformers may be used for other purposes provided the overall accuracy requirements in section 5.2.4 are met. The total burden on each current transformer shall not exceed the rated burden of such current transformer.
Current transformers. All CTs for Type 1, 2 and 3 Meters must meet the following criteria: Type of Meter Relevant Standard Minimum Class Accuracy No. of sets Usage 1 IEC 60044-1 0.2s 2 1 set of CTs dedicated to the Main Meter only and 1 set supplying the Check Meters. Check Meter CTs can be used for other purposes providing the overall accuracy requirements in paragraph 2.2 of these TSRs are met 2 IEC 60044-1 0.2s 1 CTs must be dedicated to the CfD Settlement Activities, supplying both Main Meters and Check Meters. An Type of Meter Relevant Standard Minimum Class Accuracy No. of sets Usage additional set of CTs may be fitted for the Check Meter which may also be used for other purposes providing the overall accuracy requirements in paragraph 2.2 of these TSRs are met.
Current transformers. Current transformers shall be single phase, secondary ratio transformers for outdoors assembly, in vertical position, with oil immersed or SF6 gas insulation and will be hermetically sealed. They shall be able to conduct the primary rated current for one minute, while the secondary circuit is open. The core shall be toroidal and made up of steel magnetic foils with very low specific losses, and the windings shall be made of insulated copper. In the case of the transformers that work in connection with the disconnectors, high frequency currents and voltages transferable to secondary and ground circuits shall be taken into consideration during the operation of adjacent live disconnectors. The manufacturer’s structural design shall be such that it prevents: g1. High current density in certain points of the equipment causing localized overheating. g2. Internal surges of very short duration causing dielectric breakdowns in liquid and solid insulators. Current transformers shall have the following additional characteristics: Continuous service current 000 - 000 X (X.X) 000 - 000 A (Transformer) (*) 300 - 600 A (L.T) 400 - 800 A (Transformer) (*) Secondary current 1 A 1 A Short-circuit thermal intensity 40 kA 31.5 kA Characteristics of measurement cores a) Accuracy class b) Power 0,2 % 15 VA (minimum) 0,2 % 15 VA (minimum) Characteristics of protection cores a) Accuracy class b) Power 5P20 15 VA (minimum) 5P20 15 VA (minimum) (*) Current relationship to be supported in the POS.
Current transformers. Rated voltage ______ kV Rated normal primary current ______ KA Rated secondary current ______ A Accuracy Class: - Measuring core (Required = 0.2) ________ - Protection Core ________ Rated transformation ratio ________ Continuous thermal rating ________ A Short time current rating ________ KA Maximum Thermal burden ________ VA Impulse withstand voltage _____kV peak Power frequency withstand voltage of primary winding ________ kV Power frequency withstand voltage of secondary winding ________ kV