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1、BRITISH STANDARD BS 4999-111: 1987 General requirements for rotating electrical machines Part 111: Specification for built-in thermal protection for electric motors rated at 660 volts a.c. and below UDC 621.313-13:536.587:621.316.825 Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 01:49:54 GM
2、T+00:00 2006, Uncontrolled Copy, (c) BSI BS 4999-111:1987 This British Standard, having been prepared under the direction of the Power Electrical Engineering Standards Committee, was published under the authority of the Board of BSI and comes into effect on 27 February 1987 BSI 02-1999 First publish
3、ed as BS 4999-72 February 1972 First revision as BS 4999-111 February 1987 The following BSI references relate to the work on this standard: Committee reference PEL/1 Revision announced in BSI News October 1986 ISBN 0 580 15780 6 Committees responsible for this British Standard The preparation of th
4、is British Standard was entrusted by the Power Electrical Engineering Standards Committee (PEL/-) to Technical Committee PEL/1, upon which the following bodies were represented: Association of Consulting Engineers Association of Electrical Machinery Trades Association of Manufacturers Allied to the
5、Electrical and Electronic Industry (BEAMA Ltd.) Association of Supervisory and Executive Engineers British Coal Bureau of Engineer Surveyors ERA Technology Ltd. Electricity Supply Industry in England and Wales Engineer Surveyors Section of the ASTMS Engineering Equipment and Materials Users Associat
6、ion Health and Safety Executive Ministry of Defence Power Generation Association (BEAMA Ltd.) Rotating Electrical Machines Association (BEAMA Ltd.) South of Scotland Electricity Board Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Fri De
7、c 01 01:49:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4999-111:1987 BSI 02-1999i Contents Page Committees responsibleInside front cover Forewordii Introduction1 1 General 1.1Scope1 1.2Definitions2 2 Requirements for devices fitted into motor windings 2.1General2 2.2Classification2 2.3Motors fi
8、tted with thermistors3 2.4Motors fitted with thermostats3 3 Temperature sensitive resistors (thermistors) 3.1General4 3.2Characteristics4 3.3Ability to withstand motor manufacturing processes5 3.4Dimensions5 3.5Leads5 3.6Marking5 3.7Type tests5 3.8Routine tests5 4 Thermistor control unit 4.1Terminal
9、s5 4.2Standard operating conditions5 4.3Drop-off (trip) and pick-up (re-set) resistance5 4.4Thermistor applied voltage6 4.5Abnormal conditions6 4.6Minimum voltage hold-in6 4.7Switching rating6 4.8Type tests6 4.9Routine tests7 5 Thermostats 5.1General7 5.2Characteristics7 5.3Ability to withstand moto
10、r manufacturing processes7 5.4Leads7 5.5Marking7 5.6Switching rating7 5.7Overload switching performance7 5.8Type tests on thermostats8 Appendix A Typical characteristic of PTC type thermistor10 Table 1 Winding temperature2 Table 2 Recommended reference temperatures for thermistors2 Publications refe
11、rred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 01:49:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4999-111:1987 ii BSI 02-1999 Foreword This Part of BS 4999 has been prepared under the direction of the Power Electrical Engineering Standards Committee and supersed
12、es BS 4999-72:1972, which is withdrawn. This Part has been issued to implement the decision to renumber all the Parts of BS 4999 to bring the Part numbers more into line with those of IEC Publication 34. In addition to the renumbering of the Part, the inclusion of the Part number in the point number
13、ing system, adopted in Part 72, has been abandoned. No technical changes have been made to the text of BS 4999-72:1972. Whilst this standard sets out the requirements to be met by motors employing built-in thermal protective devices, such protection will not usually be a normal feature of a standard
14、 machine and it will therefore be necessary for it to be specially ordered when required. 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 o
15、f itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 10, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This wil
16、l be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 01:49:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4999-111:1987 BSI 02-19991 Introduction to Part 111 The requirements of the specification are based on the need to provide a
17、simple yet effective means of protecting the motor against damage by overheating but at the same time permitting maximum utilization of the motors capabilities. With current operated protective schemes the level of protection can be related to the rated load of the motor and generally can be adjuste
18、d, but with the thermal protection scheme covered by this standard the degree of protection is governed by the thermal endurance of the winding insulation and the level is not adjustable. The requirements of this standard are intended as far as possible to protect the motor from damage due to the ex
19、cessive overheating (short term) resulting from stalling and single phasing as well as the overheating (long term) caused by persistent overloading, impaired ventilation, etc. This involves a compromise, since the level of protection must not be set so low as to cause nuisance tripping, for instance
20、 when there is a temporary reduction in the supply voltage and the rated motor current is exceeded. The requirements in themselves are not intended to guarantee “normal” motor life but rather to avoid premature thermal ageing. Normal motor life can only be assured by correct selection, application a
21、nd maintenance of the motor in conjunction with the proper application of thermal protection. It should not be assumed that the thermal protection specified is effective for all motors against all faults or abnormal conditions, as the degree of protection depends on a number of factors including the
22、 rate of rise of temperature of the motor windings. The greatest rate of rise of temperature will usually occur under stalled conditions and it may not be possible to protect all machines against these, particularly when the machine is initially cold, while retaining a proper level of protection aga
23、inst other conditions. It is for this reason that the concepts of Class I and Class II have been introduced in 2.2. In addition to the rate of rise of temperature of the motor windings, there are other factors which affect the performance of thermal protection and these are as follows. The temperatu
24、re characteristic and thermal time constant of the device. The location of and the method of installation of the device within the motor and the number of devices used. The tolerances on the temperatures at which the operating conditions are attained. The tolerances on the control system to which th
25、e devices are connected. With thermal protection the margin between the protection level and the rated load conditions depends on the difference between the actual and permitted temperature rise of the protected winding and the difference between the actual and specified cooling air temperature. As
26、the temperature settings of these built-in thermal devices are not adjustable, the level has to be chosen to accommodate the highest cooling air temperature condition and the maximum permissible temperature rise. It is thus possible that motors with this form of protection will operate for long peri
27、ods at elevated temperatures close to the protection level if the driven equipment is able to demand substantial overloads for long periods. While such conditions, within reason, should not give rise to any undue concern for the motor, there are two points which should be appreciated. 1) The effecti
28、ve life of the winding insulation is approximately halved for every 8 C to 10 C increase in continuous operating temperature. 2) If the motor is working in a low ambient temperature the possible overload on the motor is such that special attention may be required in ensuring that the driven apparatu
29、s and or the supply and control gear are capable of handling the overload. In general any overloading should be monitored by the line current of the motors but this may be done automatically by built-in thermal devices and control units designed to give a warning signal when a temperature below the
30、tripping level is reached. If in the latter case the warning device is used to monitor the condition of the load, and if frequent operation of the warning system is anticipated, this fact should be drawn to the attention of the supplier of the control unit, since special arrangements may be required
31、. 1 General 1.1 Scope This Part of this British Standard specifies requirements appertaining to a system of thermal protection applied to the stator windings of cage type induction motors (other than small electric motors complying with BS 5000-11) having a rated voltage not exceeding 660 V. License
32、d Copy: sheffieldun sheffieldun, na, Fri Dec 01 01:49:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4999-111:1987 2 BSI 02-1999 The requirements to be met when the temperature sensitive device is fitted into the motor windings are specified in clause 2. Clause 3 specifies the requirements for tem
33、perature sensitive resistors (thermistors) as components, and clause 4 specifies the requirements for thermistor control units as components. The requirements applicable to thermostats as components are specified in clause 5. Devices which are designed to carry the motor current are excluded. NOTETh
34、e titles of the British Standards referred to in this standard are listed on the inside back cover. 1.2 Definitions The terms used in this specification have the general meaning ascribed to them in BS 4727. In addition, for the purposes of this Part of this British Standard, the following definition
35、s apply. 1) thermistor a thermally sensitive semi-conductor resistor whose primary function is to exhibit an important change in electrical resistance with a change in body temperature 2) reference temperature (Tr) the nominal temperature of the thermally sensitive device at which it is required to
36、cause the protection system to operate 3) thermostat a thermally sensitive mechanical switching device 4) Control unit a device which responds to the resistance change in the thermistor circuit to open or close the switching device controlling the motor or to close an alarm circuit 2 Requirements fo
37、r devices fitted into motor windings 2.1 General Suitably selected thermally sensitive devices having characteristics in accordance with the requirements of 3.2 or 5.2 shall be positioned in the motor windings so that the device shall change its state to cause the supply to the motor to be disconnec
38、ted before the temperature of the winding exceeds the appropriate value specified in Table 1, or to cause the operation of an alarm. The circuit shall be arranged as far as practicable to fail to safety. 2.2 Classification If the motor is protected against overheating both when running on load and w
39、hen stalled, the protection shall be known as Class I. If the motor is protected against overheating only when running on load then the protection shall be known as Class II. NOTEWith certain types of motors, Class I protection may not always be possible. The class of protection together with the nu
40、mber of this specification shall be indicated on the motor rating plate. Table 1 Winding temperature When thermal protective devices are provided to initiate a warning signal on steady overload conditions their reference temperature shall be at least 20 C lower than the reference temperature of the
41、devices providing the drop-off (tripping) function, and the devices for both functions shall be in the same or equivalent position in the windings. The device shall be placed in intimate contact with the end winding and in a position where the temperature will be as close as possible to the average
42、temperature of the winding, i.e. as measured by the resistance method. Owing to differences in arrangements and construction of windings and methods of cooling it is not practicable to specify reference temperatures for the devices and these shall be the subject of agreement between the motor manufa
43、cturer and the device manufacturer. For thermistors recommended values are given in Table 2, but in the case of thermostats, variations such as differences in the size and types available for this application render recommendations of little practical value. Table 2 Recommended reference temperature
44、s for thermistors Condition Temperature Class EaClass BaClass Fa CCC Steady overload Stalled 155 215 165 225 190 250 a Insulation classification in accordance with BS 2757. Function Temperature Class EaClass BaClass Fa CCC Drop-off (tripping) Warning 130 110 140 120 160 140 a Insulation classificati
45、on in accordance with BS 2757. Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 01:49:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4999-111:1987 BSI 02-19993 2.3 Motors fitted with thermistors 2.3.1 General. The thermistors shall be connected to a control unit which, when an operating resi
46、stance change takes place, shall open or close an auxiliary circuit to trip the supply or initiate an alarm (warning). In each thermistor circuit there shall be three thermistors in close thermal contact with the stator winding, at least one thermistor being in each phase of the winding. All the the
47、rmistors in a circuit shall be connected in series. Only the end connections of the thermistor series circuit need to be brought out to a terminal box, and the individual thermistor connections need not be normally accessible. 2.3.2 Terminals and connecting leads. The connecting leads from the therm
48、istor circuit(s) referred to in 2.3.1 shall be brought out for connection to the thermistor control unit. The terminals or connecting leads provided for external wiring shall be marked “T1” and “T2” for single circuits, and where additional circuits are provided the subscript numbering shall follow
49、the same increasing order as the reference temperatures of the respective circuits. Terminals shall be capable of accepting cables up to 7/0.85 mm size (see 4.1). 2.3.3 Type tests on motors fitted with thermistors 2.3.3.1 Overheating tests. Overheating tests shall be carried out to prove compliance with the requirements of 2.1. The running tests (2.3.3.2) shall be carried out on motors having Class I or Class II protection, while the locked rotor test (2.3.3.3) shall only be carried out on motors having Class I protection. 2.3.3.2 Running test. With the motor r