Voltage Transformer

Product Description

There are following types and Sub types of V.Tr. L.T. Tape insulated varnish impregnated type Voltage Transformer, 1Ph/3PhL.T/H.T Cast Resin type Voltage Transformer, 1Ph/3Ph upto 33KVH.T. Outdoor Oil Cooled type Voltage Transformer upto 66 KVH.T. Cast Resin / Oil Filled type Residual Voltage Transformer for Capacitor Bank protection Function of voltage Transformer The main function of the Voltage Transformer is to reproduce the Primary Voltage on its secondary side. The Voltage Transformer isolates the devices connected to their secondary circuit from the network system. Voltage Transformers are specially designed for measuring and protection applications. Standard Range: The standard range for L.T. applications is generally 415/110,433/110V,\Ph or 3Ph type. Sometimes three single phase modules are connected in star to form a three phase system The standard range for H.T applications is as under 3300/Rt3/110/Rt3 for Single Phase, 3300/110O for Three phase system6600/Rt3/110/Rt3 for Single Phase, 6600/110 for Three phase system11000/Rt3/110/Rt3 for Single Phase, 11000/110 for Three phase system22000/Rt3/110/Rt3 for Single Phase, 22000/110 for Three phase system33000/Rt3/110/Rt3 for Single Phase, 33000/110 for Three phase system66000/Rt3/110/Rt3 for Single Phase, 66000/110 for Three phase system Limits of voltage Error and phase Displacement (Clause 5.1) Class Percentage voltage (ratio) Error Phase Displacement (Minutes) (1) (2) (3) 0.1 +0.1 +5 0.2 +0.2 10 0.5 +0.5 20 1 +1.0 40 3 +3.0 - Measuring Voltage Transformer : A Class Application 0.2 For very accurate power measurement and tariff metering 0.5 For very accurate power measurement and tariff metering 1 For meters measuring voltage and power 3P/6P For protection application like over voltage relay Following are the VA Burdens as per IS 3156: 5 VA;10 VA,15 VA,25 VA,50VA,100VA, 200VA Standard Terminology used for Voltage, Transformers: Rated primary voltage : This is the rated voltage required to be stepped down for measurement and protective purposes. Rated secondary voltage : The voltage at which the meters and protective devices connected to the secondary of the voltage transformer operate. Rated burden : This is the load in terms of volt- amperes (VA) posed by the devices connected in the secondary circuit on the VT. Accuracy class required : The transformation errors that are permissible, including voltage (ratio) error and phase angle error. Phase error is specified in minutes. Typical accuracy classes are Class0.2, 0.5, Class 1 and Class 3. Both metering and protection classes of accuracy are specified. In a metering VT, the VT is required to be within the specified errors from 80% to 120% of the rated voltage. Ina protection VT, the VT is required to be accurate from 5% upto the rated voltage factor times the rated voltage. Rated voltage factor : Depending on the system in which the VT is to be used, the rated voltage factors to be specified are different. The table below is adopted from Indian and International standards. Rated voltage factor Rated time Method of connecting primary winding in system 1.2 Continuous Between phases in any network Between transformer star-point and earth in any network 1.2 Continuous Between phase and earth in an effectively earthed neutral system. 1.5 For 30 seconds 1.2 Continuous Between phase and earth in a non-effectively earthed neutral system with automatic fault tripping 1.9 For 30 seconds 1.2 Continuous Between phase and earth in an isolated neutral system without automatic fault tripping or in a nresonant earthed system without automatic fault tripping 1.9 For 8 hours Temperature class of insulation: The permissible temperature rise over the specified ambient temperature. Typically, classes E, Band F.