Contents Foreword Preface
SECTION A General SECTION B Specifications for Three Phase 11 kV/433 - 250V Class Distribution Transformers (upto and including 100 kVA)
SECTION B1 Specifications for Single Phase 11 kV / 250V and 11 kV/√3/ 250V Distribution Transformers (10, 15 & 25 kVA Ratings)
SECTION C Specifications for Three Phase Distribution Transformers (above 100 kVA and upto 33 kV class) (v) (vii) 1 65 77 87
SECTION D Specifications for Power Transformers of Voltage Class below 145 kV 99
SECTION E Specifications for 145 kV Class Power Transformers SECTION F Specifications for 245 kV Class Power Transformers
SECTION G Specifications for 420 kV Class Power Transformers SECTION G1 Specifications for 800 kV Class Power Transformers SECTION H Specification for Earthing Transformers SECTION I Specifications for Valves for Transformers
SECTION J Test Requirements for Transformers SECTION K Erection, Commissioning and Maintenance
SECTION K1 Condition Monitoring and Diagnostic Techniques for Power Transformers and Reactors
SECTION L Capitalisation Formula for Transformer Losses
SECTION M Specifications for Protective Schemes for Power and Distribution Transformers
SECTION N Specifications for Voltage Control of Power Transformers
SECTION O Specifications for Fire Protection of Power Transformers (ix) 107 115 123 135 147 157 165 223 295 319 323 337 353
1.0 1.1 GENERAL DESIGN OF APPARATUS
Compliance with Specifications 1.1.1 Except where otherwise specified or implied herein, the transformers shall comply with the latest edition of Indian Standard 2026 (hereinafter referred to as "IS").
1.2 Design and Standardisation 1.2.1 The transformer and accessories shall be designed to facilitate operation, inspection, maintenance and repairs. All apparatus shall also be designed to ensure satisfactory operation under such sudden variations of load and voltage as may be met with under working conditions on the system, including those due to short circuits.
1.2.2 The design shall incorporate every reasonable precaution and provision for the safety of all those concerned in the operation and maintenance of the equipment keeping in view the requirements of Indian Electricity Rules.
1.2.3 All material used shall be of the best quality and of the class most suitable for working under the conditions specified and shall withstand the variations of temperatures and atmospheric conditions arising under working conditions without undue distortion or deterioration or the setting up of undue stresses in any part, and also without affecting the strength and suitability of the various parts for the work which they have to perform.
1.2.4 Corresponding parts liable to be replaced shall be interchangeable.
1.2.5 Cast iron shall not be used for chambers of oil filled apparatus or for any part of the equipment which is in tension or subject to impact stresses. This clause is not intended to prohibit the use of suitable grades of cast iron for parts where service experience has shown it to be satisfactory, e.g., large valve bodies.
1.2.6 All outdoor apparatus, including bushing insulators with their mountings, shall be designed so as to avoid pocket in which water can collect.
1.2.7 Means shall be provided for the easy lubrication of all bearings and where necessary of any mechanism or moving part, that is not oil immersed.
1.2.8 All mechanism shall, where necessary, be constructed of stainless steel, brass or gunmetal to prevent sticking due to rust or corrosion.
1.2.9 All taper pins used in any mechanism shall be of the split type complying with IS: 2393 for these items.
1.2.10 All connections and contacts shall be of ample section and surface for carrying continuously the specified currents without undue heating and fixed connections shall be secured by bolts or set screws of ample size, adequately locked. Lock nuts shall be used on stud connections carrying current. All leads from the winding to the terminal board and bushings shall be adequately supported to prevent injury from vibration including a systematical pull under short circuit conditions. Guide pulls shall be used where practicable.
1.2.11 All apparatus shall be designed to minimise the risk or accidental short-circuit caused by animals, birds or vermin.
1.2.12 Provision shall be made to fix safety fence around top cover of transformers of rating 100 MVA and above, for safe working during installation and servicing for large capacity transformers.
1.2.13 In tank on load tap changers shall be located such that the space above the diverter switch chamber will be free of inter connecting pipes etc. for lifting the diverter switch unit for inspection and maintenance purposes.
1.2.14 Dryness of the insulation may be ensured by measuring the water extraction during vacuum drying. The water extraction per tonne of insulation per hour may be limited to 50 grams maximum. Alternatively dryness can be judged by dew point measurement. 1.3 Galvanising
1.3.1 Galvanising where specified shall be applied by the hot-dipped process or by electrogalvanising process and for all parts other than steel wires shall consist of a thickness of zinc coating equivalent to not less than 610 gm of zinc per square meter of surface. The zinc coating shall be smooth, clean and of uniform thickness and free from defects. The preparation of galvanising and the galvanising itself shall not adversely affect the mechanical properties of the coated material. The quality will be established by tests as per IS: 2633. Alternative to galvanising, zinc spraying or aluminising can also be considered.
1.3.2 All drilling, punching, cutting, bending and welding of parts shall be completed, and all burrs shall be removed before the galvanising process is applied.
1.3.3 Galvanising of wires shall be applied by the hot-dipped process and shall meet the requirements of the relevant Indian Standard. The zinc coating shall be smooth, clean and of uniform thickness and free from defects. The preparation for galvanising itself shall not adversely affect the mechanical properties of the wire.
1.3.4 Surfaces which are in contact with oil shall not be electrogalvanised/cadmium plated.