CHAPTER-10 DESIGN OF EHVAND UHV SUB-STTAION

Transcription

1 CHAPTER-10 DESIGN OF EHVAND UHV SUB-STTAION 10.1 Introduction Large hydro-electric generating stations at remote feasible sites are being planned. Transmission at EHV/UHV level may be required providing for heavy transmission ties for bulk loads transfer from remote generating stations. Special considerations are involved in designing such substation for selection of single line diagram, switching schemes and busbar arrangements, electrical clearances to be adopted and layout of equipment in the switchyard. Shielding of control cables and other special problems in the design of EHV/UHV substations are also briefly outlined. The discussion covers the step-up substation at generating stations, step-down stations at load ends as well as switching stations sometimes necessary for paralleling long EHV/UHV lines. Discussions are made with special reference to EHV substations of Beas Project Switching Schemes for EHV Substations Types of Substations EHV substations may be sub-divided into three types (Figure 10.1) as given below: i) Step-up substation at generation end ii) Transformer substation at load ends of the system iii) Switching substations located along the lines to parallel them Criteria for the selection Major considerations for the selection of a suitable switching scheme for an EHV and are given below: UHV sub-station i) The scheme should fit in the planning criteria used to design the connected transmission system. System should be stable if a permanent fault occurs on a line. It is, therefore, important to limit as much as possible the system un-stability caused by outage of line, transformer or generators due to sub-station faults. ii) Repair or maintenance of the equipment should be possible without interruption of power supply. iii) iv) Expansion of sub-station should be easily possible. Large clearances are required at EHV and UHV level. Therefore in order to obtain lower structures and facilitate maintenance it is also important to design sub-stations, preferably with not more than two levels of bus bar. v) Practical site consideration at a particular location e.g. lack of adequate flat area for layout of equipment in the sub-station may also sometimes influence the choice of layout. The switching schemes suitable for each type of sub-station are discussed below. Based on paper by Author in 44 th Annual Research Session of Central Board of Irrigation & Power (1975) Step-up Substations: Step-up substations at generation ends may have unit connected transformers or else EHV transformers may be used to step-up the power from bus-bars at lower voltage in the switchyards of generating stations. The later type of substation is similar to the transformer step-down substation at load ends and will be discussed along with that type. For generating units connected directly to their step-up transformers, discussions are made with special reference to Dehar Power Plant of Beas Project where six units each of 165 MW are being installed and 4 units will be directly connected to their step-up 420 kv transformers. The other two units are connected to 245 kv system through unit connected transformer. An interlinking transformer 245/420 kv was proposed. Main single line diagram is shown in figure

2 GEN. INTERLINKUNG TRANSFORMER 1 1 STEU-UP SUB-STATION 2 SWITCHING SUB-STATION 3 TRANSFORMER SUB-STATION 2 3 Figure 10.1: Types of Substation Figure 10.2 to Figure 10.5 show the single line diagram, plan views and elevation (one circuit only) for four different schemes which were considered for this substation for 420 kv portion: i) A double bus single breaker scheme as shown in Figure 10.2 (scheme 1). ii) A single bus (sectionalized) with two generating units and one outgoing transmission line connected to each bus section as shown in figure 10.3 (scheme 2). iii) A double bus one and a half breaker scheme, figure 10.4 (scheme 3). 438

3 iv) Incoming lines from generator transformers, connected to two 420 kv buses by single breakers. The outgoing lines connected by two breakers to both the buses. The scheme corresponds to a single sectionalized bus for incoming lines and a two bus two breaker scheme for outgoing lines, figure 10.5 (scheme 4). v) Other schemes ring bus and double bus double breaker schemes were not considered due to lack of space and costs Discussion for Selection of Bus Scheme for Dehar Step-up Substation Forced Outage of Generator-Transformer Unit: In all the schemes capacity equal to one unit is lost when a generator transformer unit is forced out. Bus Section Fault :Generating capacity to the extent of four units (660 MW) may be forced out under certain conditions in case of a fault on 420 kv bus under scheme (1) Figure Outage of this large bulk of power amounting to about 22 percent of the maximum demand (3000 MW approximately) at that time may cause frequency dips which may trip generating units, loads and inter-regional tie lines by the operation of under frequency relays if installed and may upset system stability and was, therefore, not considered desirable. In schemes (2) Figure 10.3 and (4) Figure10.5 maximum power forced out will be to the extent of 2 units (330 MW) while in case of scheme (3) Figure 10.4 circuit breaker connected with the bus will trip but normally no outage of generating capacity will be caused. Figure 10.2: 420 kv Double Bus Single Breaker Scheme Substation Layout (Source: CBIP Paper by Author) 439

4 Figure 10.3: 420 kv Single Bus Single Breaker Scheme Substation Layout (Source: CBIP Paper by Author) 440

5 Figure 10.4: 400 kv One and a Half Breaker Scheme Substation Layout (Source: CBIP Paper by Author) 441

6 Figure 10.5: 420 kv Two Bus Two Breaker Scheme for outgoing Feeder and Single Breaker for Incoming Two Generators (Source: CBIP Paper by Author) 442

7 Transmission Line Outages: No power generating capacity is required to be shut down in case of a fault on 245 kv line (245 kv Bus) while in case of fault on 420 kv feeder (during the first stage of operation) power generation to the extent of about one unit may have to be shut down so as to achieve stability. In case of a bus section or circuit breaker fault there is a forced outage of 420 kv transmission line under schemes (1) Figure 10.2 and scheme (2) Figure It is possible to re-energise the line through bus coupler in case of scheme (1) but not so in scheme (2) Figure In scheme (2) figure 10.3, for carrying out maintenance of the 420 kv feeder breaker, the transmission line has to be forced out. In scheme (3) figure 10.4 when one of the generators is shut down, the advantage of second breaker for 420 kv line is lost as only one breaker will be controlling the transmission line. In scheme (4) figure 10.5 under first stage of operation when a 420 kv line is out due to line fault, power generation to the extent of one unit (165 MW) is automatically switched off and gives stability to the system even in case of limited rotating reserve available. In view of the above discussions, scheme (1) figure 10.2 and (2) figure 10.3 were found to be unsuitable to our requirements and were left out from further considerations. Other Considerations for Adopting Scheme (4) (figure 10.5) a) Requirement of space for switchyard under scheme (4) figure 10.5 will be much less than that for scheme (3) figure b) Requirement of control cables for relaying and inter-locking will be less for scheme (4) figure c) Switching operations for isolating a breaker or a bus section for maintenance in case of a fault are less under scheme (4) figure d) Two levels of busbars are possible in a substation of this type by placing circuit breakers outside the busbars (figure 10.5). e) Number of breakers required for scheme (4) figure 10.5 are less as compared to scheme (3) figure Transformer Substations: For transformer substations at the generating end or the load end, a single breaker double bus, a double breaker double bus (figure 10.6), a one and a half breaker (figure 10.4) or a ring bus (figure 10.7) schemes can be considered. However, only later three schemes generally meet the service continuity criteria. 443

8 Figure 10.6: 400 kv Double Bus Double Breaker Scheme Substation Layout (Source: CBIP Paper by Author) Figure 10.7: 420 kv Ring Bus Scheme Substation Layout (Source: CBIP Paper by Author) 444

9 Ring bus scheme requires only one breaker per circuit and is most economical. It is quite common in Canada and has been utilized in a slightly modified from for EHV/UHV system of Hydro-Quebec and that of Peace River Systems in USA. In simple ring bus scheme provision of protection becomes more complicated if number of circuits increase to more than six and its scope gets, therefore restricted. From the point of view of future expansion of the sub-station, one and a half breaker scheme and double breaker scheme is more suitable. Former requires lesser number of breakers and isolators and has been Figure 10.8: Main Single Line Diagram (Dehar Power Plant) (As Designed)proposed for the ultimate stage of receiving end transformers substation at Panipat. Initially, i.e. till more than 6 bays are required in the substation, layout shall be that for one and a half breaker scheme but shall be operated in ring bus with omission of some breakers and isolators and jumper connections of two circuits to the bus bars. Single line diagram for Dehar Hydro Power Station is at Figure Switching Station For a switching station all single line diagrams (sophisticated or otherwise) with only one busbar for paralleling two or more lines figure 10.3 must be rejected because a fault on this bus or on any equipment connected to it would put more than one line out of service. Neither ring-bus nor one-and a half breaker scheme meet the criteria for a switching station, because a fault on one circuit breaker can cause two lines to be lost. For a sub-station with incoming and outgoing lines, the double breaker scheme (Figure 10.6) is the only one that ensures the service continuity required by the criteria. To construct this kind of substation with only two levels of busbras, the circuit breakers are placed outside the busbars. 445

10 Single Line Diagram of a typical receiving end 420 kv Substation with shunt reactor installation is at Figure Electrical Clearances for Installing EHV/UHV Equipment In Field Space requirements and layout of electrical equipment in switchyard depends upon various types of air clearances required to be provided for laying the equipment of different rated voltages. Following basic clearances govern the sub-station design. (i) Earth clearance i.e. phase to ground clearance. (ii) Phase clearance i.e. phase to phase clearance. (iii) Safety clearance i.e. (a) Ground clearance. (b) Section clearance. Initial designs of substations are based on the air clearances worked out in accordance with the then recent CIGRE Study Committee Report which provides a correlation between the insulation levels and the minimum air clearances to ground and between phases. Tentative clearances for Dehar and Panipat 420 kv substations were, however, based on the similar test data as available earlier. For transmission systems of nominal system voltage below 300 kv sub-station clearances is governed only by lightning impulse over-voltages or BIL of the equipments and bus bars. For transmission system of 300 kv and above, sub-station clearances is mainly governed by internal over voltage i.e. switching impulse over-voltage and dynamic 420kV 420kV 50MVAR 50MVAR 50MVAR 4x105MVA DETAILS AT A 245kV M-1 M-2 T TRANSFER BUS 4x245kV 420kV SIDE 420kV AUX. BUS 33kV SPARE SINGLE PHASE UNIT 36kV 245kV AUX. BUS 245kV SIDE 4x25MVAR DETAILS 'A' Figure 10.9: Single Line Diagram of a Typical 420 kv Substation (Source: CBIP Manual on Sub-station) 446

11 over voltage. In order to reduce clearances and equipment insulation, internal overvoltage including switching impulse over voltages, have to be limited by using one or two step preinsertion resistors, single pole reclosing, synchronous closing of breakers, shunt reactors etc (Figure 10.9). The ratio of controlled switching impulse over voltages to the peak value of highest phase to ground system voltage varies from 2.5 in EHV system to 1.5 in UHV system. IEC publication 71 defines insulation levels for highest voltages for equipment of 300 kv and above as a combination of two components. The rated switching impulse withstands voltages and the rated lightning impulse withstands voltage. Accordingly the minimum clearances shall be the higher of the following and the section clearance will then be based on it. i) Minimum clearance from the consideration of the lightning insulation levels to be adopted for the sub-station equipment. ii) Minimum clearance computed from switching surge requirements Minimum Phase to Ground Clearances Clearances are discussed with special reference to 420 kv, based on the data available at the time of design. For higher voltage i.e. 525 kv and 765 kv level substation similar considerations can be applied based on the data available at the time of design. Insulation Levels and Withstand phase to ground Air Clearances Standard insulation levels for the highest voltage of 420 kv and above as per IS: and IEC recommendation are given in Table In this voltage range the performance of insulation and ground clearances are based on phase to phase switching impulse unless specifically required otherwise. Phase to ground clearance for switching over-voltages in EHV range may be estimated using the following formula. 0.6 d = U w 500K ( 1 1.3σ ) Where, d is the clearance in meters U w is the switching impulse withstand voltage in kv, K is the gap factor characterizing the shape of electrodes and σ is the standard deviation equal to 0.6 for switching impulse tests. For the types of electrodes existing in sub-station design it is possible to associate a value of phase-toground air clearance to each value of rated switching or lightning impulse withstand voltage. the requisite phase to ground clearance for switching and lightning impulse over voltages can be determined using the above formulae and graphs given in the CIGRE Committee report. It is seen that impulse withstand voltage of an air gap depends also on the shape of the electrodes and has been designated as gap factor K in the committee report. The gap factor K depends upon electrodes configuration and is influenced by geometrical dimensions of the gap, including the grounded surroundings configuration are given in table Minimum Phase to Ground Clearances for various Insulation Levels Sub-stations show mainly three types of phase to ground clearances. i) Distances between conductors and beam. ii) Distances between live parts of apparatus and beams. iii) Distance between conductor and ground. 447

12 The electrode configuration found for the first type of clearances is clearly identified, and can be regarded as being of the conductor structure, type, associated with a value of about 1.30 for the gap factor k. As regards the second type of air clearances, it is very difficult to identify a precise electrode configuration and the value of K is varying between 1.10 and Gap factor k=1.10 is characteristic for a configuration similar to rod-structure, e.g. open disconnecting switches near structures. Gap factor k=1.30 corresponds to the conductor-structure configuration, e.g. closed disconnecting switches near structures. As regards the third type of air clearances, conductor-ground configurations, normally the clearances are sufficiently high because bus-bar conductors are supported by metal supports and post insulators. In every case, this configuration is covered by the gap factor Table 10.3 gives the correlation between the various combinations of insulation levels shown in Table 10.1 and corresponding to k-=1.10 and 1.30 the minimum air clearances which are the highest values for each combination, calculated either for the switching or lightning impulse level. This table does not take into account the possibility/ electrodes getting closer together e.g. because of short circuit or wind. Minimum values of phase to earth clearances as per IS based on switching impulse withstand is given in table These values may be used for first approximation. Highest voltage for equipment Um Base for pu values Um 2 3 Table 10.1 Rated switching impulse withstand voltage (peak) Ratio between lightning and switching impulse withstand voltages kv kv p.u. kv 1.11 kv Rated lightning impulse withstand voltage (peak) Table-10.2 Electrode Configurations Rod Plane 1.00 Rod-Structure (Under) 1.05 Conductor Plane 1.15 Conductor Window 1.25 Conductor Strcuture (Under) 1.30 Rod-rod (h-3 m, under) 1.30 Conductor struicture (over and laterally) 1.35 Rod-rod ( h 6m, under) K

13 Conductor-rope 1.40 Conductor crossarm end 1.65 Conductor rod (h = 3m; under) 1.65 Conductor rod (h = 6m; under) 1.90 Conductor rod (over) 1.90 Insulation Level Rated Switching Impulse withstand voltage (kv) Table-10.3 Rated lightning impulse withstand voltage (kv) Minimum phase-to-ground Air Clearance (m) K=1.30 K= Phase-to-Ground Clearances for Dehar Sub-station Lightning impulse level of 1425 kv with a corresponding basic switching impulse level of 1175 for power transformers for Dehar 420 kv E.H.V. system was proposed for first stage installations. Lightning insulation level for circuit breakers and other apparatus connected to the bus bars with the b us bars themselves was proposed for Beas Project as for insulation class about 10% higher i.e kv. Minimum phase to ground air clearances for Beas Project sub-stations for initial designs based upon test data previously available and according to procedure outlined is given in table Table 10.4 (a) Minimum Phase to Ground Clearance Clearance in meters calculated as per latest data Adopted (Meters) (i) (ii) (iii) Conductors and Beams Line parts of apparatus and beams. Conductor and ground to or more 9.0 (b) Minimum Phase to Phase Clearance (ii) Minimum Rigid Bars Spacing (iii) Minimum strain Bus bars spacing (iv) Phase to Phase Spacing for equipment (v) Minimum spacing between 2 sets of bus bars to SAFETY CLEARANCES Safety clearance consists of ground clearance and section clearance. The ground clearance is the minimum clearance from any point on or about the permanent equipment where a man may be required to stand (measured from the position of feet) to the nearest part not at earth potential of an insulator supporting a line conductor and the same was taken as 2.59 m, which is the dimension for a tall man with arms outstretched below the conductor. 449

14 The section clearance is the minimum clearance from any point on or about the permanent equipment where a man may be required to stand (measured from the position of feet) to the nearest unscreened live conductor in air. The section clearance for 420 kv systems was determined as 6 m by adding 2.5 m to minimum phase-to-ground clearance of 3.5 m Height of bus bars above ground within sub-station premises The minimum conductor clearance from ground was obtained by adding ground clearance, earth clearance (2.59 meters height of a tall man with outstretched hands) and height of bus bar supporting clamps on the post insulator. In consideration to it, minimum height of bus bar was proposed to be 7.0 meters, which may be raised to 9.5 meters to correspond to the terminal height of 420 kv circuit breakers (Air blast circuit breakers). SF6 breakers are now used Conductor clearance from roadways within sub-station premises Minimum clearance between over-head conductors and roadways within sub-station premises was computed to be as Ground Clearance plus 6.25 meters. This dimension provides for a truck with a man standing on its top meters = meters PHASE TO PHASE CLEARANCES Insulation levels Phase to phase faults cause severe system disturbances and are, therefore, least desirable. As such phase spacing adopted should be such as to cause flashover to ground instead of phase-to-phase. For this purpose distance between phases is made to exceed that to ground to the extent that flashover can occur only to ground. The distance between systems e.g. between two bays are not only determined by their electrical strength the but also by necessity to carry out maintenance work. Lightning surge stresses between phases will normally not be higher than the lightning surge stresses to ground. Therefore, minimum phase to phase spacing are governed by switching impulse withstand voltage. Owing to the fact that phase-to-phase over-voltage peak is subjected to considerable variations, depending upon the following: (i) The waves shape (time to crest) of the phase-to ground switching over voltages having opposite polarity on adjacent phases. (ii) The ratio and time delay between these two components. It is possible to determine a ratio P between the maximum overvoltage between phases and the maximum overvoltage to ground only by means of TNA or field measurements. The theoretical maximum value of P is equal to 2, provided that the two-phase-ground components have opposite polarity and synchronous peak values equal to maximum overvoltage to ground. In practice, however, P will be lower because these conditions are not fulfilled. According to a number of TNA and field measurements the control of the over voltages to ground increases the ratio P; the higher the control, the higher the value of P, The ratio P = 1.66 to 1.7 of the rated switching impulse withstand voltage to ground between 1050 and 1175 kv was chosen as this generally leads to conservative values of the clearance. With this factor P and according to the standardized IEC values for the impulse levels, the switching impulse withstand voltage between phases start-over characteristics of ring-ring and rod-rod gaps is shown in table 10.5, for 420 kv voltage system. 450

15 Rated Switching impulse withstand voltage to Ratio between phase-to-phase and phase-to-ground switching impulse withstand voltage Table 10.5 Switching impulse voltage between phases (kv) 50% switching impulse flashover voltage between phases (kv) Minimum phase-tophase air clearance (m) ring-rod-ring rod. ring-ring rod-rod ground Phase to Phase Air Clearances In sub-stations mainly three types of phase to phase air clearances may be present depending upon electrode configuration: (i) (ii) (iii) Clearances between conductors Clearances between conductor and apparatus Clearances between poles of apparatus The first type of air clearances is found between the phases of line entrances and bus-bars. Occasionally, the conductor electrode may be sub substantially modified by hardware. The second type includes the conductor-disconnecting switch air clearances; the third type comprises the between breaker-poles, between disconnecting switch poles and between poles of current transformer kind of air clearance and clearances between line-traps. In general, the second and third type of air clearances presents electrodes configurations that are difficult to define. The rod-rod gap can be assumed to be representative for the practical geometrical conditions in the lower voltage, range, whilst the ring-ring gap with a given geometrical dimensions may be considered to be typical for the higher voltage range and be used for first type of air clearance. Many of the second and third type air clearances (clearances between the poles of apparatus i.e. disconnecting switches, breakers, etc.) might be considered proper to the apparatus, just as in the case of phase-to-ground air insulations, even when the apparatus is essentially single phase. The minimum clearance between phases, assuring a given insulation level, should, in this case, be specified by the manufacturer and checked by a type test. It is, therefore unnecessary to fix the minimum air clearances between the poles of apparatus which have the most widely varied electrode configurations. Table 10.6 gives the recommended minimum clearances between phases for rod-rod and ring-ring configuration in 420 kv in.e.h.v. range. Corona shield ring was assumed to have a diameter of 630 mm. Strain bus spacing were obtained by adding 0.7 meters to the spacing for rigid bus as per American practice. Other spacing adopted is shown in figure ELECTRICAL CLEARANCES FOR INSTALLING EHV/UHV EQUIPMENT AS PER CBI & P RECOMMENDATIONS CBI & P manual Entitled substation layout stipulates that air clearances for 420 kv and higher voltage switching over voltages are the governing factor. For determination of phase-to-ground air clearance, the rod-structure configuration is the worst electrode configuration normally encountered in practice; the conductor-structure configuration covers a large range of normally used configuration. But the necessary inter-phase clearance is more related to the rodconductor and conductor-conductor configuration. The unsymmetrical rod-conductor configuration is the worst configuration normally encountered in service. The conductor-conductor configuration covers all symmetrical configurations with similar electrode shapes on the two phases. 451

16 The phase to earth clearances is the higher value of the clearances determined for the rod structure configuration for the standard lightning impulse and for the standard switching impulse withstands voltages. The phase to phase clearance is the higher value of the clearances determined for the rod structure configuration for the standard lightning impulse and for the standard switching impulse withstands voltages. The CBI & P recommended values of clearance for substation up to 800 kv is as follows: Highest System Voltage (kv) Lightning impulse voltage (kvp) Table 10.6 Switching Minimum Clearances $ Impulse Voltage (kvp) Safety clearances (mm) Between phase & earth (mm) Between phase (mm) 3400* ** 6400* 9400** (Ph-E) 1575 (Ph-Ph) (Ph-E) 2550 (Ph-Ph) * Based on Rod-structure air gap. ** Based on Rod-Conductor air gap. $ This value of air clearances are the minimum values dictated consideration and do not include any addition for construction tolerances, effect of short circuits, wind effects and safety of personnel, etc LAYOUT OF EQUIPMENT IN THE SUB-STATION Layout of equipment for various types of single line diagram is shown in figure 10.2 to figure Due to practical considerations of space etc. the layout tentatively proposed for Dehar Sub-station is shown in Figure The layout of equipment at Panipat was proposed for one and a half breaker scheme SHIELDING OF CONTROL CABLES In the control cables and the secondary wiring passing through E.H.V. Sub-station dangerous high voltages are liable to be induced by opening and closing of E.H.V disconnects which may be especially dangerous for static/numerical relays. Accordingly such cables are required to be properly shielded. One of the power utility of U.S.A is using unarmoured cables and provides shielding by running heavy grounded conductor at the top of each cable trench. The portion of control cables in air (outside trenches) is, however shielded by armouring. Magnetic armouring has been used by C.E.G.B. in U.K. and is being adopted on Beas Project on the advice of supplier of protective equipment although effectiveness of magnetic armouring is reduced under short circuit conditions and may be examined in due course by site measurements. 452

17 REFERENCE 1. Thapar, OD,: Stability EHV system CBI & P Annual Reasearch Session, Publication No. 121, pp ,June R. Prourget Selecting a single line Diagram Hydro Quebec Symposium Extra High Voltage and Ultra High Voltage. October R.H. Hill and J.C. Stevens B.C. Hydro E.H.V. Transmissions System Design and construction Line and Station. Maintoba E.H.V. Symposium September, L. Paris, A. Taschini, K.H. Schneider and K.H. Weck Phase-to-Ground and Phase-to-Phase Air Clearances in Sub-stations CIGRE No. 29, 1973l; PP A.I.E.E. Committee Report Interim Report-Minimum Electrical Clearances based on Switching Surge Requirements AIEE Vol. PAS 1963 PP. 6. I.E.E.E. Committee Report Second Interim Report-Minimum Electrical Clearances Sub-station based on May 1965, PP I.E.C. Publication 71 Insulation Coordination Chapters I & II 5 th Edition. 8. Thapar, OD, and Saksena, RB,: Equipment Insulation Coordination in Developing 400 kv EHV System 1974 Issues of Power Engineer. 9. Thapar, OD and Saksena, RB,: Relaying for 400 kv EHV System Proceeding CBI & P Annual Reasearch Session, Publication No Howard, J. Sutton: Transients Induced in Control Cables Located in EHV Substation. IEEE, PAS-89, July-August Stanlay, H. Horowitz and Harold, T. Seeley: Relaying the AEP 765 System. IEEE, PAS July Central Board of Irrigation & Power Manual on Substations Pub Appendix 1.1 List of Indian Standards, Guides, Codes etc. required for Reference IS: 5 Colour for ready mix paints IS: Method of test for carbon type (PNA) Analysis of Mineral oils by Infrared (1991) Spectrophotometer IS: 375 IS: 1367 Marking & arrangement of swgr. bushbars main connections and auxiliary Wiring. Hot dip galvanized cooling on threaded fasteners. IS: 2147 Degree of protection provided by enclosures for low voltage switchgear And control gear. IS: 3347 Dimensions of porcelain transformer bushings for use in lightly polluted Atmospheres IS: 3637 Gas operated relays IS: 3639 Fitting & accessories for Power Transformers IS: 6272 Industrial cooling fans IS: 6600 Guide for loading of oil immersed transformers IS: 8603 Dimensions for porcelain transformer bushing for use in heavily Polluted atmosphere (36 kv class). Dimensions for oil filled porcelain transformer bushings for use in medium polluted atmospheres. IS: 9434 Guide for sampling and analysis of free and dissolved gas in oil filled Atmosphere. 453

18 IS: Code of practice for selection, installation and maintenance of trans- Former IS: 335 IS:325 IS:398(Pt-1) New insulating oils for transformer (Test procedure) Three-phase induction motors Aluminium conductors for overhead transmission purposes; Pt 1- Aluminium stranded conductors IS: 398(Pt-2) Aluminium conductors for overhead transmission purposes : Pt.2- Aluminium conductors, galvanized steel reinforced IS: 398(Pt-5) Aluminium conductors - galvanized steel reinforced for extra high voltage (400 kv and above) IS: 692 Paper insulated lead sheathed cables for rated voltage up to and including 33 kv - specification IS: 694 PVC insulated cables for working voltages up to and including volts. IS: 731 Porcelain insulators for overhead power lines with a nominal voltage greater than 1000 volts IS: 802 IS: 875 (Pt 1-5) IS:933 IS:934 IS: IS: 1248 IS: 1255 IS:1554(Pt-1) Use of structural steel in overhead transmission line towers - Code of practices. Code of practice for design loads (other than earthquake) for buildings and structures Portable chemical fire extinguisher, foam type Portable chemical fire extinguisher, soda acid type Three-phase distribution transformers up to and including 100 kva, 11 kv, outdoor type Direct acting indicating analogue electrical measuring instruments and their accessories Code of practice for installation and maintenance of paper insulated power cables (Up to and including 33 kv) PVC insulated (heavy duty) electric cables Part-1, for working voltages up to and including volts 18:1 554 (Pt-2) Specification for PVC insulated (heavy duty) electric cables Part-2, for working voltages from 3.3 kv up to and including 1 1 kv IS: 1866 IS: 2026 IS: 2062 IS: 2099 IS: 2121 IS: IS: 2190 IS: 2309 IS: 2486 Code of practice for maintenance and supervision of mineral insulating oil in equipment Power transformer Steel for general structural purposes - Specification Bushings for alternating voltages above volts Conductors and earth wire accessories for overhead power lines Insulation coordination Code of practice for selection, Installation and maintenance of portable first-aid fire extinguishers Code of practice for protection of buildings and allied structure against lightning Insulator fittings for overhead power lines with nominal voltage greater than 1000V 454

19 IS: 2544 IS: 2629 IS: 2633 IS: 2705 IS: 3034 IS:3070(Pt.1) IS: 3070 (Pt.2) IS: IS: 3156 IS: 3716 IS: 4004 IS: 4146 IS: 4201 IS: 5082 IS:5216(Pt.1&2) IS: 5547 IS:5553(Pt.1&2) IS: 5561 IS: 5578 IS: 6005 IS:8437(Pt.1&2) IS: 9921 IS:10028(Pt-1,Pt2&3) Porcelain post insulators for systems with nominal voltages greater than 1000 volts Recommended practice for hot-dip galvanizing of iron and steel Methods for testing uniformity of coating of zinc coated articles Current transformers Code of practice for fire safety of industrial building, electrical generating and distributing stations Lightning arresters for alternating current systems non-linear resistor type lightning arrester Metal oxide surge arresters without gaps for alternating current systems Earthing transformers Voltage transformers Application guide for insulation coordination Application guide for non-linear resister type surge arresters without series gap for AC system Application guide for voltage transformers Application guide for current transformers Wrought aluminium and aluminium alloy bars, rods, tubes and sections for electrical purposes Guide for safety procedures and practices in electrical work Application guide for capacitor voltage transformers Shunt reactors Specifications for electrical power connectors Guide for marking of insulated conductors Code of practice for phosphating of iron and steel Guide on effects of currents passing through human body Alternating current disconnections (isolators) for voltages above 1000 volt Code of practice for selection, installation and maintenance of transformers 15:10118 Code of practice for selection, installation and maintenance of switchgear and control gear 13:10136 Code of practice for selection of disc insulator fittings for highest system voltages of 72.5 kv and above 13:10162 Spacers and spacer dampers for twin horizontal bundle conductors. 15: Application guide for power transformers IS: (Pt-2) Graphical symbols used in electro-technology : conductors and connecting device's IS: 12032(Pt-4) Graphical symbols used in electro-technology : Passive components 455

20 IS: 12032(Pt-6) Graphical symbols used in electro-technology : Production and Conversion of electrical energy 13: (Pt-7) Graphical symbols used in electro-technology : Switchgear, control gear and protective devices IS: Voltage bands for electrical installations including preferred voltages and frequency IS: Classification of degrees of protection provided by enclosures of electrical equipment IS: S:13118/IEC: 56 IS: IS: (Pt.1 to 5) Guide for selection of Insulators in respect of pollution conditions. Specification for high voltage AC circuits breakers Methods of synthetic testing of high voltage AC circuit breakers LV switchgear and control gear Appendix 1.2 List of IEC Standards IEC: Fluids for electromechanical applications Unused mineral insulating oils for transformers and switchgear IEC IEC : (P1 to P9) IEC (Part 1 to Part 5) IEC I EC IEC IEC-1129 Instrument Transformers: Measurement of Partial Discharges Recommendations for Direct Acting indicating-analogue electrical measuring instruments and their accessories. Power Transformers Determination of Transformer and Reactor Sound Levels Metal oxide surge arresters without gaps Alternating Current Disconnectors (Isolators) and Earthing switches Alternating Current Earthing Switches Induced Current switching IEC Insulated bushings for alternating voltages above 1000 V. IEC IEC IEC IEC IEC (Part 1 to part 23) IEC (Part 1 & Part 2) Tests on indoor and outdoor post insulators of ceramic material or glass for Systems with Nominal Voltages Greater than 1000 V Guide to the Selection of High Voltage Cables On-Load Tap-Changers Tests on Hollow Insulators for use in electrical equipment. Electrical relays High Voltage switches 456

21 IEC IEC IEC IEC (Pt to P4) IEC IEC IEC IEC IEC IEC (P1 & P2) IEC IEC IEC IEC IEC IEC IEC I EC IEC IEC I EC IEC I EC IEC IEC Characteristics of indoor and outdoor post insulators for systems with nominal voltages greater than 1000V Reactors Dimensions of mechanical structures of the 482.6mm (19 inches) series Specification and Acceptance of New Sulphur Hexafloride Radio Interference Test on High Voltage Insulators Artificial Pollution Tests on High Voltage Insulators to be used on AC Systems Common Specification for High Voltage Switchgear & Control gear Standards Guide for the Selection of Insulators in respect of Polluted Conditions Short Circuit Current - Calculation of effects Loading Guide for Oil - Immersed power transformers High Voltage Alternating Current Circuit Breakers Synthetic Testing of High Voltage alternating current circuit Breakers Pressurized Hollow Column Insulators Coupling capacitors and capacitor dividers Coupling Devices for power Line Carrier Systems Degree of Protection provided by enclosures Line traps for A.C. power systems Coupling Devices for power line carrier systems Single sideboard power line carrier terminals Planning of (single Side-Band) power line carrier systems Expression of the performance of electrical & electronic measuring equipment Symbols for Alternating-Current Electricity meters Man machine interface (MMI) - Actuating principles Class 0.5, 1 and 2 alternating current watt hour metres 457

22 IEC IEC Modular plug-in Unit and standard 19-inch rack mounting unit based on NIM Standard (for electronic nuclear instruments) Insulators for overhead lines with nominal voltage above 1000 V-ceramic or glass insulator units for a.c. systems Characteristics of String Insulator Units of the cap and pintype IEC-60372(1984) Locking devices for ball and socket couplings of string insulator units: dimensions and tests. IEC (P1 and P2) Insulators for overhead lines with a nominal voltage above 1000 V. IEC IEC IEC (P1 to P7) IEC IEC IEC (P1 to P3) IEC IEC (P1 to P3) IEEE: 32 Characteristics of string insulator units of the long rod type Dimensions of Clevis and tongue couplings of string insulator units Polyvinyl Chloride insulated cables of rated voltages up to and including 450/750V Conductors of insulated cables Impulse tests on cables and their accessories Calculation of the continuous current rating of cables (100% load factor) Standard colours for insulation for low-frequency cables and wires Tests on electric cables under fire conditions IEEE standard requirement terminology and test procedure for neutral Grounding device. 458