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 138 kV Normal current 75 – 150 A (Transmission Line) 75 – 150 A (Transformer) (*) Secondary current 1 A Short-circuit thermal intensity 31.5 kA Characteristics of measurement cores
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. 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. 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 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: Description 220 kV 60 kV Continuous service current 300 - 600 A (L.T) 300 - 600 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. Current transformers shall be suitable for the operation of protective gear, instruments and/or metering equipment, and the design characteristics shall be to the Engineer's approval. Current transformers shall have an output rating adequate to cater for all the burden connected to them. They shall have sufficient rating, terminal voltage and accuracy class for the satisfactory operation of their associated equipment. The Contractor shall be responsible for taking into account lead and all other burdens. The primary windings shall not, without special approval, have a short time current rating less than that specified for the associated circuit - breaker. Windings shall be capable of carrying the rated primary current for a period of one minute with the secondary winding open circuited. Multi ratio current transformers should be tapped on the secondary side and not on the primary side unless otherwise approved by the Engineer. The current transformer particulars, as specified in IEC 61869-2 latest edition 2012 shall be given on an accessible plate mounted external to the current transformer. All connections from secondary windings shall be brought out and taken by means of separate insulated leads to a terminal board mounted in an accessible position . Where multi-ratio secondary windings are required, a durable label shall be provided at the secondary terminal board clearly indicating the connections required for each ratio. The connections and ratios in use shall be shown on all diagrams of connections. Current transformer secondary circuits shall be complete in themselves, and shall be earthed at one point only, through links situated in an accessible position. Each separate circuit shall be earthed through a separate link, suitably labelled. The links shall be of the bolted type , have M6 nuts, and provision for attaching test leads. Magnetisation curves of each type of current transformer shall be submitted for approval. Where current transformers have to be supplied on this Contract for mounting in apparatus provided under other contracts , the Contractor supplying the current transformers shall be responsible for making all necessary arrangements with the other Contractors and for keeping the Engineer informed.
Current transformers. ITEM 11 KV 11 KV 11 KV 220 KV SWITCHGEAR SWITCHYARD GENERATOR SWITCHYARD CT CT CT CT ----------------------------------------------------------------------------------------------------------- Core XXX XXX Iron TBD ----------------------------------------------------------------------------------------------------------- Ratio 600/5, 800/5, 1500/1 800/5 100/1 1500/5 ----------------------------------------------------------------------------------------------------------- Function Control and Protection Metering and Protection Protection ----------------------------------------------------------------------------------------------------------- Manufacturer As per vendors As per vendor list As per vendor list * list * * ----------------------------------------------------------------------------------------------------------- Type Window Bushing mounted in Primary Wound Bushing mounted transformer either in transformer or in the dead tank type circuit breaker ----------------------------------------------------------------------------------------------------------- Rated Voltage (kV) 600V, 10kV BIL 600V, 10kV BIL 15kV 600V, 10kV BIL ----------------------------------------------------------------------------------------------------------- Burden capability (VA) 15VA 15VA Differential 15VA ----------------------------------------------------------------------------------------------------------- Short Time Current XXX XXX Relay T200, 1.5 TBD (As) @ 30 C ----------------------------------------------------------------------------------------------------------- Accuracy and 5P10, 5P20 5P20 87,000 0.2, 5P20 over-current factor (%) ----------------------------------------------------------------------------------------------------------- *Or equivalent / similar
