ईट ड 16/ ट

य पक प रच लन म मस द ल ख षण स पन तकन क स म त ईट ड : 16 ---------------------------------------------------------------------------------------------------------------------------------- षत : 1. ईट ड 16 क सभ सद य 2. व त तकन क वभ ग प रषद क सभ सद य तथ 3. च रखन व ल अ य सभ नक य मह दय, क य न न ल खत मस द क एक त स ल न ह : ल ख न. श ष क ईट ड 16 ) 10797 ( प वर सफ म र क लए फ ट ग तथ उपस धन - व ष ट भ ग 2 र लर, भ -स पक ट म नल, न ए ल उ ड ग बसब र और सप ट इ स ल टर स दभ दन क ईट ड 16/ ट - 13-07-2017 क य इन मस द क अवल कन कर और अपन स म तय यह बत त ह ए भ ज क अ तत य द यह म नक क प म क शत ह ज ए त इस पर : क ठन इय आ सकत ह वस य अथव क र ब र म य अमल करन म आपक य स म तय भ जन क अ तम त र ख: 13-09-2017. स म तय य द क ई ह त क य अगल प ठ पर दए प म अध ह त र क उप र ल खत पत पर भ ज द य द क ई स म त त नह ह त अथव स म त म क वल भ ष स ब ध ट ह ई त उपर त ल ख क यथ वत अ त म प दय ज एग य द क ई स म त तकन क क त क ह ई त वषय स म त क अ य क पर मश स अथव उनक इ छ पर आग क क य व ह क लए वषय स म त क भ ज ज न क ब द ल ख क अ त म प द दय ज एग ध यव द, भवद य, (र ज व शम ) व नक ई एव म ख ( व त तकन क ) स ल न उप र ल खत : 1

DRAFTS IN WIDE CIRCULATION DOCUMENT DESPATCH ADVICE Reference Date ETD 16/ T- 13-07-2017 TECHNICAL COMMITTEE ETD 16 ---------------------------------------------------------------------------------------------------------------- ADDRESSED TO: 1. All Members of Transformers Sectional Committee, ETD 16 2. All Members of Electrotechnical Division Council; and 3. All other Interested. Dear Sir(s), Please find enclosed a copy of the following draft Indian Standard: Sl. No. Doc no. Title 1. ETD 16 ( 10797) SPECIFICATION FOR FITTINGS AND ACCESSORIES FOR POWER TRANSFORMERS PART 2 ROLLERS, EARTHING TERMINALS, NEUTRAL GROUNDING BUSBAR AND SUPPORT INSULATORS Kindly examine the draft standards and forward your views stating any difficulties which you are likely to experience in your business or profession, if these are finally adopted as Indian Standards. Comments, if any, may please be made in the format given overleaf and mailed to the undersigned. Last date for comments: 13-09-2017 In case no comments or only editorial comments are received, it will be presumed that there are no technical comments and the document may be finalized in consultation with the chairman of the sectional committee. However, in case comments of technical nature are received, the chairman of the sectional committee will be consulted. Based on the decision of the chairman, the documents may either be finalized or referred to the sectional committee for further action. Thanking you, Yours faithfully (Rajeev Sharma) Sc E & Head (Electrotechnical) Email: eetd@bis.org.in Encl : See attachment. 2

Date Document No. 13-07-2017 Doc: ETD 16 (10797) Sl. No. Name of the Organization Clause/ Subclause Paragraph/ Figure/Table Type of Comment (General/ Technical/ Editorial Comments Proposed Change 3

Doc: ETD 16 (10797) IS 3639 (Part 2) : 2017 BUREAU OF INDIAN STANDARDS DRAFT FOR COMMENTS ONLY (Not to be reproduced without the permission of BIS or used as a STANDARD) Draft Indian Standard SPECIFICATION FOR FITTINGS AND ACCESSORIES FOR POWER TRANSFORMERS PART X ROLLERS, EARTHING TERMINALS, NEUTRAL GROUNDING BUSBAR AND SUPPORT INSULATORS Last date of receipt of comments: 13-09-2017 CONTENTS FOREWORD 1 Scope 2 Definition 2.1 Roller 2.2 Earthing terminal 2.3 Neutral grounding busbar 2.4 Neutral ground busbar support 3 Roller 3.1 General requirements 3.2 Standard Rollers 4 Earthing Terminal 4.1 General requirements 4.2 Dimensions 4

5 Neutral grounding busbar and support insulators 5.1 General requirements 5.2 Arrangement 5.3 Material and size of neutral grounding busbar 5.4 Support Insulator 5

Transformers Sectional Committee, ETD 16 FOREWORD This Indian Standard (Part 2) Specification for fittings and accessories for power transformers Part 2 Rollers, Earthing terminals, neutral grounding busbar and support insulators is adopted after the draft finalised by the Transformers Sectional Committee ETD 16 has been approved by the Electrotechnical Division Council. The Indian standard IS 3639 on fittings and accessories was first published in 1966 with a view to standardise accessories and fittings used for transformer to facilitate inter changeability and to rationalize use of fittings such as would be commonly acceptable to manufacturers and users. This specification covered only seven fittings as follows: a. Valves & valve flanges b. Flanges for Buchholz relay c. Breather pipe d. Thermometer pockets e. Level indicator f. Rollers and g. Earthing terminals There are separate Indian Standards dealing with some other fittings as under: IS: 6088-1988 Specification Oil-to-water Heat Exchangers for Transformer IS: 3637-1966 Gas Operated Relays IS: 3638-1966 Application Guide for Gas Operated Relays These standards are very old. There has been lot of improvements in the intervening period with technological changes and innovations in fittings and accessories of transformers in the country as well as world over. A need is felt to revise and enlarge the scope of IS: 3639 to suit Indian Transformer Industry and also at par with Global Standards. Since standardisation of fittings and accessories is a major task involving several suppliers, manufacturers, users and taking cognisance of international practices it is decided to issue part standards under IS: 3639 series as is done for IS 2026 or IS 1180 series (standards on Power and Distribution Transformers respectively). 6

Doc ETD 16 (10797) IS 3639 (Part 2) : 2017 Draft Indian Standard SPECIFICATION FOR FITTINGS AND ACCESSORIES FOR POWER TRANSFORMERS PART X ROLLERS, EARTHING TERMINALS, NEUTRAL GROUNDING BUSBAR AND SUPPORT INSULATORS 1.0 SCOPE: This standard covers standard requirements and major dimensions of following fittings used in Transformers/Reactors. (a) Rollers (b) Earthing terminals (c) Neutral grounding busbar and support insulators 2.0 DEFINITIONS For the purpose of this standard, the following definitions apply: 2.1 Roller A circular flat or flanged wheel fitted on transformer for enabling forward, backwards and sideways movement. Often it is known as wheel assembly or under carriage. 2.2 Earthing terminal A terminal placed on the transformer/reactor tank or cooling equipment for connection to an earthing system. 2.3 Neutral grounding busbar Conducting busbar (GI / copper flat)used to connect neutral bushing of star connected winding to earthing system either directly or through neutral grounding impedance. 2.4 Neutral grounding busbar support insulator Supports and insulators used to brace or hold neutral grounding busbar during normal service conditions to facilitate connection to earthing system. NOTE This standard does not cover star formation of single phase transformers. 3.0 ROLLER 3.1 General requirements 7

3.1.1 Rollers are of flat or flanged type, application of which depends upon the weight of transformer, type of installation (viz. with or without rail etc.). Figure 1 shows flat and flanged type rollers. Figure 1 Flat and flanged type rollers 3.1.2 Up to 200 kva 3 phase and single phase distribution transformers, rollers are not recommended by Standard IS 1180 (Part 1) because these are mostly pole mounted type. The same standard recommends flat rollers for distribution transformers beyond 200 kva and up to 2500 kva 3 phase with roller spacings and the same should be followed (Refer figure 7 under Cl. 14.2 of IS 1180 (Part 1) 2014). 3.1.3 More often it is required to change direction of rolling of transformer by 90 which is indicated in the transformer technical specifications. Bi directional rollers are used for such applications. Jacking points are provided to facilitate changing the direction of the rollers. Present clause specifies rollers for liquid immersed transformers with rated power from 250 kva to 500 MVA. 3.1.4 Rollers can be single rollers or twin rollers (roller assembly) generally located at 4 points under tank base. 3.1.5 Transformers can be mounted on rollers with stopper plate or anti-earthquake locking provided. Alternatively, subject to users agreement transformer can be placed directly on the plinth sans rollers. In such a case, one set of rollers per station can be provided for a group of transformers. Shunt Reactors are generally recommended to be placed directly on plinth without rollers to reduce noise and vibrations. 3.2 Standard Rollers 3.2.1 Choice of rollers 8

The diameter and the thickness of the wheel assembly shall be in accordance with table 1. Diameter (mm) Thickness (mm) Table 1 Choice of rollers Maximum load capacity per wheel (tonnes) Type (Flat or flanged) 100 40 2.5 Flat 150 50 3.5 Flat 200 80 6.5 Flat 250 100+20 10 Flanged, 250 100+20 25 Flanged, twin 320 90+20 25 Flanged, 320 90+20 60 Flanged, twin 3.2.2 Distance between wheel centres (a) The distance between the wheel centres for flat rollers shall be in accordance with table 2. Table 2 Distance between wheel centres for flat type rollers Distance between wheel centres Rated Power (mm) (kva) Refer figure 2 250 800 315 800 400 800 500 700 650 700 800 700 1000 800 1600 1000 2500 1200 Figure 2 Distance between wheel centres for flat type rollers (b) In case of flanged rollers, standard track gauge dimensions (preferably 1676 mm standard broad rail gauge) in both longitudinal and transverse directional 9

shall be chosen. In case of large rating transformers, in longitudinal direction ¾ rails with standard rail gauge may be used. 90 lb-ft rail with head dimension 64-66 mm is generally used. (c) Anti-earthquake device means shall be provided for locking the swivel movements in position parallel to and at right angles to the longitudinal axis of the tank. In case of seismic zone, calculations should be submitted for specified g value. 3.2.3 Paint shade The paint shade shall be same as standardised for transformer. i.e. shade 631 to IS 5. Epoxy paint thickness of 150 microns shall be maintained. 3.2.4 Material Material forassemblyshall be of Mild steel, Depending upon the load capacity material of the roller can either be of Cast Iron or Cast Steel. 4.0 EARTHING TERMINAL 4.1 General requirements 4.1.1 All non-current carrying metal parts associated with electrical installations shall be effectively earthed to grounding system. This serves the following purpose. a) To reduce shock hazard to personnel by limiting step and touch potentials to tolerable values. b) To provide adequate current carrying capability to handle ground fault current without fire or hazard. c) To provide a low-impedance return path for ground fault current to ensure operation of overcurrent device. 4.1.2 As far as possible all earth connections should be visible for inspection. Earthing terminal should not be painted. A painted surface gives poor contact. 4.1.3 Material used should not corrode. 4.1.4 Earthing terminals shall be capable of carrying maximum short circuit current for 4 seconds. 4.1.5 Provision of earthing terminal shall be made close to bottom of the tank at diagonally opposite corners. 4.1.6 It is a good practice to earth turret flanges, inspection covers and other flanges separated by gasket joints to positively earth them. Type A earth terminal specified below may be used in such cases. 10

4.1.7 Earthing of terminal to nearest available ground earthing system is in the scope of user. GI flat of adequate size is normally used. 4.2 Dimensions: Minimum recommended earthing terminals, dimensions and materials thereof for transformers up to 500 MVA single phase and three phase are tabulated below as table3. Transformer Rating Table 3 Standard earthing terminals Recommended minimum earthing terminals Type (Refer Figure 3) Cable box and structural supports 1 A Transformer tank up to 31.5 MVA 2 B Transformer tank above 31.5 MVA 2 C Type A Earthing terminal for cable box and structural supports 11

Type B Earthing terminal for transformers up to 31.5 MVA Type C Earthing terminal for transformers above 31.5 MVA Figure 3 Standard earthing terminals 12

Figure 4 Connection of earthing strip with earthing terminal 5.0 NEUTRAL GROUNDING BUSBAR AND SUPPORT INSULATORS 5.1 General requirements 5.1.1 Neutral point of star connected winding is connected to earth which offers stabilityof neutral and carry currents during unbalance.it also facilitates earth protection. 5.1.2 Grounding conductor (connection from transformer neutral to ground) must be extended from neutral bushing and brought to tank bottom supported on post insulators. Its purpose is to maintain very low impedance to ground faults so that relatively high fault currents will flow thus insuring that circuit breakers or fuses will clear the fault quickly and therefore minimize damage. It also greatly reduces the shock hazard to personnel. Also the current passing through the busbar generates a potential across it which is less than the test voltage of Neutral. Following are some typical methods of neutral earthing. a) Solid Neutral Earthed System b) Resistance (Low and high) Neutral Earthing System c) Resonant Neutral Earthing System d) Earthing through an earthing Transformer or neutral grounding reactor (generally in case of shunt reactor) 5.1.3 In India, star connected systems are generally solidly earthed. While in solid neutral earthed system neutral point is connected directly to earth.for resistance neutral earthing system, grounding resistors are connected between ground and neutral of transformer. Figure 5 shows schematic diagram of both types of earthing system. 13

Figure 5 Schematic diagram of earthing system 5.1.4 In case of solidly earthed system BIL of neutral is 95 kvp and 38 kvrms for 1 minute. For other cases of earthing customer has to specify BIL of neutral. 5.2 Arrangement In case of solid neutral earthing system neutral terminal of the star connected winding is brought to the ground level using busbar duly supported from the tank using pin insulators. For resistance neutral earthing system, neutral terminal of the start connected winding is connected to NGR (neutral grounding resistor) mounted on separate structure. Other point of NGR is connected to earth. In case of solid neutral earthing system it is necessary to maintain phase to earth clearance from neutral grounding busbar (230 mm for 95 kvp BIL), for resistance neutral earthing system also it is necessary to maintain phase to earth clearance which depends on BIL of neutral terminal. Figure 6 shows typical arrangements adopted for neutral grounding both for solid and resistance earthing system. 14

Type A Neutral grounding busbar arrangement for solid neutral earthing system 15

Type B Neutral grounding busbar arrangement for resistance neutral earthing system Figure 6 Typical neutral grounding arrangements It is essential to connect flexible tinned copper jumpers between neutral grounding busbar and transformer neutral bushing to facilitate ease of connections. In case of resistance neutral earthing system, similar jumpers are connected between busbar and NGR. Arrangement and pitch of neutral grounding support busbar shall be such that so as to prevent moevement of busbar during earth fault conditions. 5.3 Material and size of neutral grounding busbar: Unless otherwise specified Galvanised Iron (GI)of size 50 x 10 mm shall be used as neutral grounding busbar. Alternatively tinned copper can be used based on request from client (50 x 8 mm). 5.4 Support Insulator Epoxy insulators if used as support insulators for neutral grounding busbar shall conform to its performance against ultraviolet rays and outdoor application. Alternatively porcelain insulators can be used. Rating of the support insulator depends 16

on the insulation level of neutral terminal. 17.5 kv or 24 kv class insulators can be used for solidly earthed system. 17