Current transformers. Current transformers shall have at least four secondary cores: Three 5P20 protection cores. One Class 0,2 core for measurement.
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: Description 220 kV Current in continuous operation 500 - 1000 A (L.T) Coupling (*) Secondary current 1 A Short-circuit thermal intensity 40 kA Characteristics of measuring cores a) Precision class b) Power 0,2 % 15 VA (minimum) Characteristics of protection cores a) Precision class b) Power 5P20 15 VA (minimum)
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: Description 220 kV Normal current 500 - 1000 A (L.T) Coupling (*) Secondary current 1 A Short-circuit thermal intensity 40 kA Characteristics of measurement cores a) Accuracy class b) Power 0,2 % 15 VA (minimum) Characteristics of protection cores a) Accuracy class b) Power 5P20 15 VA (minimum)
Current transformers. Current Transformers shall comply with IEC 61869 in general. All ratios shall be obtained by secondary taps. 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. [Signatures of LTTCs]
Current transformers. Current transformers shall be single-phase, secondary, for outdoor vertical mounting, insulated in an oil bath or in SF6 gas, and they shall be hermetically sealed. They must be able to conduct the primary rated current for one minute, with the secondary circuit open. The core will be toroidal and will consist of magnetic steel sheets with very low losses and the coils will be made of insulated copper. For transformers working in relation to disconnectors, high-frequency currents and voltages transferable to the secondary and ground circuits must be taken into account during the operation of adjacent disconnectors under voltage. The manufacturer constructive design shall be such as to prevent: g1) That the high current density at certain points in the equipment may cause localized overheating. g2) That very short internal overvoltages may cause dielectric ruptures in liquid and solid insulation. “Año del Buen Servicio al Ciudadano” Current transformers shall have the following complementary characteristics: Description 500 kV 220 kV Current in continuous operation 1000 – 2000 A 1250 – 2500 A Secondary current 1 A 1 A Short-Circuit Thermal Intensity 00 xX 00 xX x 00 xX (Xxxxxxxxx SS) Characteristics of measuring cores a) Precision class b) Power 0,2 % 15 VA (*) 0,2 % 15 VA (*) Characteristics of protection cores a) Precision class b) Power 5P20 15 VA (*) 5P20 15 VA (*) (*) Minimum value, to be defined in the Pre-Operative Study.
Current transformers. 3.3.1 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. 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: Name and make Serial number Transformation ratio Rated burden Rated voltage Accuracy class 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. Current transformers for the LV switchgear shall be of the ring type, complying with the requirements of SANS 60044-1:2003. Current transformers for indication circuits shall be Class 1 rated in accordance with SANS 60044-1: 2003 dependent upon primary current. The current transformer ratio shall match the rating of the circuit to which it is connected. Each current transformer shall be provided with a robust mounting bracket and proper terminal studs on the circumference of the coil for the connections A nameplate shall be fixed to each current transformer on the circumference of the coil in such a position that it can be easily read from outside the board after removal of the access panels. The nameplate shall clearly indicate the class, rating, ratio, P1, P2, S1 and S2 connections and the function of the current transformers. The current transformers shall be mounted on rigid supports above or below the relevant switchgear in a manner as to facilitate the threading through of the interconnecting wiring to the relevant switchgear. Current transformers shall only be installed on the load side of feeder circuit breaker. The current transformers shall be insulated for 660 volt between phases and shall be capable of withstanding for the duration of time taken by the circuit breaker to clear the fault (with protective devices set at the maximum settings), the fault currents that could occur at the point in the system where the current transformers are installed.
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
