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1 Distribution Transformers Reference Standard: IS 1180 --1989 Types of Distribution Transformers a) Non-Sealed type b) Sealed type 2 Non-Sealed type Distribution Transformers Reference Standard IS 1180 (Part 1) : 1989 This standard specifies the requirements and tests for oil immersed 3-Φ Non- Sealed type Distribution Transformers of ratings up to and including 100KVA and voltage class up to and including 11KV 3 IS 1180 (Part 1) : 1989 This standard covers Ratings No load voltage ratios Winding connections and vectors Tapping ranges Fittings Terminal arrangement Losses and Impedance values Tolerances 4 IS 1180 (Part 1) : 1989 Rating : KVA Rating – 16, 25, 63 and 100 Frequency – 50Hz System Voltage – 3.3, 6.6 and 11KV Secondary Voltage – 433 and 250 5 IS 1180 (Part 1) : 1989 Tapping ±2.5% and ±5% +5% Tappings at 5 2 Number of tappings Primary Secondary Winding tapped Above 25 KVA Up to and Including 25 KVA 6 Fittings Oil level indicator Lifting lugs Breather Drain cum sampling valve Rating and terminal marking plates IS 1180 (Part 1) : 1989 7 IS 1180 (Part 1) : 1989 40 140 Phase to earth 75 255 Phase to phase L.V Side H.V Side Clearances in mm 8 IS 1180 (Part 1) : 1989 Limits of temperature rise : Winding 55°C Top oil 45°C Losses and Impedance values 1760 260 100 1235 180 63 685 100 25 475 80 16 Load loss (W) at 75°C No load loss (W) Rating (KVA) 9 Tests Measurement of winding resistance Measurement Voltage ratio and check of voltage vector relationship Measurement of impedance voltage, short circuit impedance and load loss Measurement of no-load loss and current Measurement of insulation resistance 10 Tests SSVW test IOVW test Lightning impulse test Temperature rise test SC test Air pressure test (35KPa 30min) 11 Permissible flux density and overfluxing Bmax – 1.69 Tesla No load current in terms of %of full load current 5 2.5 100 6 3 63 7 3.5 25 8 4 16 At 112.5% rated voltage At 100% rated voltage KVA Rating 12 Mounting arrangements The under-base of all the transformers shall be provided with two 75x40mm channels 460mm long. 415mm 415±2mm 13 Sealed type Distribution Transformers Reference Standard IS 1180 (Part 2) : 1989 This standard specifies the requirements and tests for oil immersed 3-Φ Sealed type Distribution Transformers of ratings up to and including 100KVA and voltage class up to and including 11KV 14 IS 1180 (Part 2) : 1989 No Taps No conservator Air pressure test is to be conducted at 80KPa for 30minutes. 15 IS 1180 (Part 2) : 1989 40 20 140 76 Phase to earth 75 45 255 127 Phase to phase external Internal external Internal L.V Side H.V Side Clearances in mm 16 Power Transformers Reference Standards IS 2026 Part I 1977– General IS 2026 Part II 1977– Temperature Rise IS 2026 Part III 1981– Insulation Levels and Dielectric Tests IS 2026 Part IV 1977– Terminal markings, Tappings and Connections IS 2026 Part V 1994– Transformer/ Reactor Bushings- Minimum external clearance in air 17 IS 2026 Part I This standard covers Service conditions Rating Requirements to withstand Short Circuit Dimensions of Neutral Connection Tolerances Rating plates Fittings Tests 18 Rating Rated KVA Operation at other than rated voltage: The transformer can be operated at its rated KVA at any voltage with in ±10% Rated frequency: 50Hz ± 1.5 19 TOLERANCES +10% +15% ±0.5% ±10% +30 Total Losses Component Losses Voltage ratio Impedance Voltage No-load current Tolerances Item 20 TESTS Measurement of winding resistance Measurement Voltage ratio and check of voltage vector relationship Measurement of impedance voltage, short circuit impedance and load loss Measurement of no-load loss and current Measurement of insulation resistance 21 TESTS Dielectric tests Temperature rise Measurement of Zero Sequence impedance of three phase transformers Short-circuit test Measurement of acoustic Noise level Measurement of harmonics of no-load currents Measurement of power taken by fans and oil pumps 22 IS 2026 Part II This standard covers temperature rise requirements of Power Transformers Identification according to cooling methods. Ex. ONAN,OFAF Limits of temperature rise Procedure for temperature rise test. 23 Temperature rise limits for Oil Immersed Type Transformers Part Temp. Rise in °C Winding 55 ONAF 60 ONWF Oil 50 (with conservator) 45 (without conservator) Core, Should not damage core Metallic parts itself 24 This standard specifies the requirements relating to insulation levels and Dielectric tests for Power Transformers Insulation requirements Dielectric withstand tests i.e a) Short duration power frequency withstand voltage test b) Lightning impulse withstand voltage test c) Induced Over voltage withstand Test IS 2026 Part III 25 Short duration power frequency withstand voltage -- 20 40 60 75 95 145 250 325 3 10 20 28 38 50 70 95 140 1.1 3.6 7.2 12 17.5 24 36 52 72.5 Lightning impulse withstand voltage (KV) power frequency withstand voltage (KV) Voltage class 26 IS 2026 Part IV This standard covers Terminal markings, Tappings and Connections for power transformers Identifying Terminal and tapping markings a) Character b) End points of phase winding c) Line and Neutral terminals d) Marking of Tappings 27 Connections Connections of phase windings Phase displacement between windings 28 IS 2026 Part V This standard specifies clearances in air between live parts of bushings on oil immersed power transformer and to object at earth potential. 29 Bushing clearance -- -- 60 90 125 170 275 450 630 < 1.1 3.6 7.2 12 17.5 24 36 52 72.5 Minimum clearance (mm) Voltage class (KV)
