1、BRITISH STANDARD BS5611:1978 IEC542:1976 Application guide for on-load tap-changers UDC 621.314.214.332BS5611:1978 This BritishStandard, having been prepared under the directionof the Power Electrical Engineering Standards Committee, waspublished underthe authorityofthe Executive Boardon 31October19
2、78 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference PEL/113 Draft for comment 77/22263 DC ISBN 0 580 10383 8 Cooperating organizations The Power Electrical Engineering Standards Committee, under whose direction this BritishStandard was prepared, consi
3、sts of representatives from the following Government departments and scientific and industrial organizations: Associated Offices Technical Committee Association of Short Circuit Testing Authorities British Electrical and Allied Manufacturers Association(BEAMA) British Railways Board* British Steel C
4、orporation Department of Energy Electricity Electrical Contractors Association Electrical Contractors Association of Scotland Electrical Research Association Electricity Supply Industry in England and Wales* Engineering Equipment Users Association* Institution of Electrical Engineers Ministry of Def
5、ence National Coal Board* Trades Union Congress The organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this BritishStandard: Association of Consulting Engineers Engineer Surveyors Associat
6、ion London Transport Executive The Transmission these are as listed below: A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer
7、 immunity from legal obligations. International Standard Corresponding BritishStandard IEC76 BS171 Power transformers IEC76-1:1976 BS171-1:1978 General (Identical) IEC76-4:1976 BS171-4:1978 Specification for tappings and connections (Identical) IEC76-5:1976 BS171-5:1978 Specification for ability to
8、withstand short circuit (Identical) IEC214:1976 BS4571:1978 Specification for on-load tap changers (Identical) IEC354:1972 CP1010:1975 Loading guide for oil-immersed transformers (Technically equivalent) Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pag
9、es1 to4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS5611:1978 BSI 12-1999 1 1 Scope This application guide is intended to assist in the
10、selection of suitable on-load tap-changers for use in conjunction with the tapped windings of transformers or reactors which, in the following text, are referred to as transformers. As in the second edition of IEC Publication214, On-load Tap-changersrevision of Publication214(1966), the designation
11、“on-load tap-changer” is shortened to “tap-changer” in the remainder of this guide and all the tap-changers referred to shall be presumed to comply with the requirements specified in IEC Publication214. The recommendations of the application guide are not mandatory and only represent advice to the t
12、ap-changer manufacturer and purchaser. The responsibility for the correct application of the fully assembled tap-changer in connection with the transformer is with the manufacturer of the transformer. 2 Selection of a tap-changer 2.1 General remarks Since the tap-changer represents only a small part
13、 of the total cost of the equipment in which it is used, it should be freely chosen to suit the equipment. However, account should be taken of the available standard types of tap-changers. 2.2 Insulation level The following values occurring on all tapping positions of the transformer should be check
14、ed against the tap-changer manufacturers declared values in accordance with Sub-clause8.6.4 of IECPublication214: 1) Normal power-frequency operating voltages appearing on the tap-changer in service. 2) Power-frequency voltages appearing on the tap-changer during tests on the transformer. 3) Impulse
15、 voltages appearing on the tap-changer during tests on the transformer or in service. NOTEWith some winding arrangements, the voltages appearing on the transformer can be abnormally high, e.g.: neutral point tappings in auto-transformers, line-end tappings, and booster transformer arrangements. Thes
16、e voltages can be affected considerably by the choice of linear, coarse/fine or reversing tapping arrangements. Methods of catering for voltage variation which involve variations in the magnetic flux in the transformer core can also affect the voltages appearing on various parts of the tap-changer (
17、seeIECPublication76, Power Transformers). 2.3 Current The tap-changer should satisfy the following conditions: 2.3.1 Rated through-current The rated through-current of the tap-changer as defined in Sub-clause4.17 of IEC Publication214 should be not less than that resulting from the highest value of
18、tapping current of the tapped winding of the transformer(in accordance with Sub-clause4.2 of IEC Publication76-1, Part1:General). 2.3.2 Overload current When tap-changers are fitted on transformers which are subjected to overload conditions in accordance with IEC Publication354, Loading Guide for Oi
19、l-immersed Transformers, they should generally be restricted to the occasional overload conditions stated in Sub-clause4.2 of IEC Publication76-1, unless specifically ordered for other overload conditions by the transformer manufacturer. The above requirements are met: a) If the maximum rated throug
20、h-current of the tap-changer is at least1.2times the highest tapping current of the transformer, or b) if the tap-changer manufacturer is able to demonstrate that the temperature-rise limits given in Sub-clause8.1 of Publication214 are not exceeded when the contacts carry1.2times the maximum rated t
21、hrough-current. (The values of current to apply for the other tests of Clause8 of Publication214 remain based on the value of the maximum rated through-current.) The number of tap-changes for each occasional overload period should be limited to the number of operations corresponding to one-half of o
22、ne complete operating cycle and the peak temperature rise of the transition resistors should not exceed360 C for air-environment tap-changers or300 C for oil-environment tap-changers. Where tap-changers are subject to overload conditions not in accordance with the limitations stated in IEC Publicati
23、on76-1 with regard to the loading guide for oil-immersed transformers, the tap-changer manufacturer should be consulted and given the current magnitude and duration so that the correct tap-changer can be recommended for the duty required.BS5611:1978 2 BSI 12-1999 2.3.3 Short-circuit current The shor
24、t-circuit current of the tap-changer as given in Sub-clause8.3 of IEC Publication214 should be not less than that resulting from the overcurrent of the associated transformer as given in Sub-clause 1.2 of IEC Publication76-5, Part5:Ability to Withstand Short Circuit. NOTEParticular care should be ta
25、ken to check this current on low-impedance and booster transformers. In some instances, the fault-current value could dictate the choice of tap-changer. 2.4 Breaking capacity The highest tapping current and the voltage per step of the transformer should be within the values of rated through-current
26、and relevant rated step voltage declared by the tap-changer manufacturer for the particular tap-changer. For values outside of those declared, the tap-changer manufacturer should be consulted. For application to transformers with several different currents and step voltages, the transition impedance
27、 should be designed so that the switched current and recovery voltage in the tap-changer do not exceed those covered by the type tests. NOTEIn certain applications, such as furnace transformers, the tap-changer may be called upon, if required, to operate during periods of momentary overloads of two
28、to three times the transformer continuous maximum rating. The diverter switch or selector switch should be chosen so that it is capable of meeting this condition. Where appropriate, consideration should be given to the effect on the step voltage, and in consequence on the breaking capacity, of metho
29、ds of voltage variation giving variations in the magnetic flux in the transformer core. 2.5 Number of tapping positions The number of inherent tapping positions of the tap-changers is generally standardized with various manufacturers equipment. The selection of the number of service tapping position
30、s should preferably be made within that range. As the extent of the tapping range increases, the voltages to be catered for also increase and it is essential that precautions be taken to avoid excessive voltages over the tapping range when operating or testing at minimum winding positions. The effec
31、t can be very marked on furnace and rectifier transformers feeding electrolytic plants where wide tapping ranges are often necessary and the tap-changer is in the constant voltage winding, i.e.wide variations in the magnetic flux in the transformer core occur. 2.6 Discharge problems with change-over
32、 selectors It should be noted that, under certain conditions, tap-changers with change-over selectors can allow momentary disconnection of the tapped winding. In such cases, discharges between the opening and closing contacts can occur during the operation of the change-over selector, and in order t
33、o avoid difficulties with regard to the dielectric stress and the formation of gases which could arise when the tap-changer operates under high voltage to earth, special precautions will be necessary. There are many different methods of overcoming the problem but some examples are the use of two-way
34、 change-over selectors, control resistors, or capacitive control between the main winding and the tapped portion of the winding. 2.7 Mechanical life The mechanical duty may need consideration if the expected number of operations per annum exceeds20000, for example, this can occur on transformers for
35、 use on rolling-mills, electrolytic plants or furnace supplies. 2.8 Motor-drive mechanism If the motor-drive mechanism is purchased from a manufacturer other than the manufacturer of the tap-changer, then it is the purchasers responsibility to ensure that the motor-drive mechanism is suitable for al
36、l its necessary duties. 2.9 Pressure and vacuum tests Where applicable, the tap-changer when fully assembled has to withstand all the pressure and vacuum tests of its associated transformer. In such cases, all the relevant information should be given in the order to the manufacturer of the tap-chang
37、er. 2.10 Low-temperature conditions Should the tap selectors, diverter switches or selector switches be located in separate containers outside the transformer tank, in air, and the ambient temperature can be lower than25 C, it is advisable to specify the quality of the insulating and/or lubricating
38、oils. Should the tap selectors, diverter switches or selector switches be located inside the transformer tank and the oil temperature can be lower than25 C during operation, the tap-changer manufacturer shall be consulted, taking the quality of the transformer oil into consideration.BS5611:1978 BSI
39、12-1999 3 If necessary, automatically controlled heating devices could be provided or, alternatively, means of preventing tap-change operation at abnormally low temperatures may be considered. 2.11 Continuous operation If the tap-changer is required to operate continuously, the temperature condition
40、s may need to be checked and the tap-changer manufacturer should be consulted. 3 Location of oil-immersed tap-changer components 3.1 Tap selectors Unless otherwise agreed between the manufacturer and the purchaser, the tap selectors may be located within the main transformer oil. 3.2 Diverter and se
41、lector switches To prevent contamination of the main transformer oil, oil-immersed diverter or selector switches should be in a separate container which may be located inside or outside the main transformer oil. When located in the main transformer oil, it is not necessary for the container to be ab
42、solutely oil-tight, providing that precautions are taken to avoid any mixture of the switch oil with the transformer oil and that the oil in the container can be changed easily without lowering the oil level in the transformer tank. Where appropriate, arrangements should be made for it to be made cl
43、ear in the transformer maintenance instructions that the main transformer oil should not be drained until all of the oil has been removed from the diverter switch container. If an oil-tight container is required, it should be specified by the purchaser. 3.3 Oil level alarm contacts If oil level alar
44、m contacts are required, they should be specified by the purchaser. 4 Field service 4.1 Safety of operation 1) Such protective devices as may be considered necessary should be connected in accordance with the manufacturers instructions. 2) In order to minimize switching under excessive overload or s
45、hort-circuit conditions, it is recommended that, in the case of motor control, a protective device should be fitted to prevent, or if initiated interrupt, an operation of the motor-drive mechanism when the transformer load exceeds the agreed value. NOTEIn the case of manual control, protective devic
46、es are not considered necessary as it is not normal practice to tap-change manually during periods of overload and the probability of coincidence of a tap-change operation under short-circuit conditions is negligible. 4.2 Parallel operation In the case of parallel operation of transformers with tapp
47、ed windings, care should be taken by the manufacturer and the user of the transformer to ensure that the currents circulating between the transformers are limited to an acceptable value. 4.3 Contact erosion and oil contamination Tap-changers have expendable items in their construction and the manufa
48、cturers figures should be noted for maintenance periods in terms of time and in numbers of operations. Generally, expected contact life for a particular tap-changer is given at maximum rated through-current. If the load current of the transformer is less than this value, contact life is increased. T
49、he number of operations before oil-change is necessary is conditional on the oil being in good condition originally and maintained in a dry state. For good utilization of the tap-changer, it is necessary to follow the maintenance instruction book of the tap-changer manufacturer, which generally gives the above as a function of: 1) rated through-current; 2) the service duty of the transformer. 5 Information required with enquiry or order In order that the correct tap-changer can be specified, the following information should be given by the transformer manufactu
