British Standard I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
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BRITISH STANDARD
Electrical relays — I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
Part 1: Specification for contact performance of electrical relays
UDC 621.318.5.066.6 621.318.5.066.6
BS 5992-1: 1980 IEC 255-0-20: 1974
BS 5992-1:1980
Cooperating organizations The General Electrotechnical Engineering Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the following: British Approvals Service for Electric Cables Ltd. Associated Offices Technical Committee British Electrical and Allied Manufacturers’ Association (BEAMA) British Radio Equipment Manufacturers’ Association British Steel Corporation I S Department of Energy (Electricity) B ) Electric Cable Makers’ Confederation c ( , Electrical Contractors’ Association y p Electrical Contractors’ Association of Scotland o C Electricity Supply Industry in England and Wales* d e Electronic Components Industry Federation* l l o r Electronic Engineering Association t n Engineering Equipment Users’ Association o c ERA Technology Ltd. n U Health and Safety Executive , 2 0 Home Office 0 2 Institution of Electrical Engineers* r e Ministry of Defence* b National Coal Board m e t Oil Companies’ Materials Association p e Post Office* S 0 2 The organizations marked with an asterisk in the above list, together with the , d following, were directly represented on the Technical Committee entrusted a with the preparation of this British Standard: h r e B Telecommunication Engineering and Manufacturing Association (TEMA) l a The Transmission and Distribution Association (BEAMA) n o i s a N m a i l o r This British Standard, having t e been prepared under the direction P of the General Electrotechnical , Engineering Standards i t Committee, was published a y under the authority of a the Executive Board and h r comes into effect on Amendments issued since publication o 31 October 1980 N . Amd. No. Date of issue Comments s © BSI 07-1999 M n a The following BSI references u relate to the work on this P standard: : y Committee reference GEL/5 p Draft for comment 78/30873 DC o C d e ISBN 0 580 11652 2 s n e c i L
BS 5992-1:1980
Contents
Cooperating organizations National foreword
I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
1 1.1 1.2 2 3 3.1 3.2 3.3 3.4 4 4.1 4.2 4.3 4.4 5 5.1 5.2 6
General Scope Object Definitions Standard rated values Rated voltages Rated currents Frequency of operation Duty factor Test conditions General Test circuit Relay energization Criteria of contact failure Assessment of contact performance General Evaluation Presentation of performance
1 1 1 1 3 3 3 3 3 3 3 4 4 5 5 5 6 7
Appendix A Standard test circuit Appendix B Duty levels for d.c. and a.c. Appendix C Assessment of test results Appendix D A simplified method for assessment of contact ratin gs
8 9 9 15
Figure 1 Figure 2 Figure 4 — Weibull probability chart
1 7 14
Table I — Characteristics of test circuits Table A Table B — Median ranks (m.r.) at the tabulated sample sizes
4 9 13
Publications referred to
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Inside back cover
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National foreword This Part of this British Standard, which has been prepared under the direction of the General Electrotechnical Engineering Standards Committee, is identical with IEC Publication 255-0-20 “Contact performance of electrical relays”, published in 1974 by the International Electrotechnical Commission (IEC).
I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c ii i L
Those Parts of IEC Publication 255 “Electrical relays” which are concerned primarily with protection relays are incorporated where required into BS 142:1980 “Specification for electrical protection relays”. All other Parts of IEC Publication 255 which are implemented as British Standards form, or will form, Parts of this British Standard. In the UK, it has been found necessary to supplement this standard in the case of electrical protection relays. The additional requirements for the contact performance of electrical protection relays are specified in BS 142. Classification of relay standards. Some Parts of IEC Publication 255 are designated first level documents, i.e. they cover the requirements of all relays within the scope of IEC Technical Committee No. 41, Electrical relays. Other Parts of IEC Publication 255 are designated lower level documents, i.e. they are concerned with the requirements of a family of relays (second level) and of smaller and more specialized groups of relays within such a family (third and fourth level). According to this system of classification, this is a first level document. Terminology and conventions. The text of the international standard has been approved as suitable for publication, without deviation, as a British Standard. Some terminology and certain conventions are not identical with those used in British Standards; attention is especially drawn to the following. Wherever the word “recommendation” appears, referring to this standard, it should be read as “British Standard”. Cross-references. Where reference to other Parts of IEC Publication 255 is made, the appropriate Part of this standard or of BS 142:1980 should be consulted, as applicable. Although some Parts of IEC Publication 255 have not been implemented as British Standards, the committee responsible for the preparation of this standard is satisfied that any particular technical requirements which may have been invoked from those Parts of t he international standard are fully acceptable for the purposes of this British Standard. Currently, the other published Parts of BS 5992 are as follows. International standard
Corresponding British Standard
IEC 255-1-00:1975 BS 5992 Electrical relays (second level document) Part 2:1980 Specification for all-or-nothing electrical relays (Identical) IEC 255-5:1977 Part 3:1980 Specification for the insulation testing of (first level document) electrical relays (Identical) For other international standards referred to in the text, the corresponding British Standards are as follows. International standard
Corresponding British Standard
IEC 85:1957
BS 2757:1956 Classification of insulating materials for electrical machinery and apparatus on the basis of thermal stability in service (Technically equivalent)
© BSI 07-1999
BS 5992-1:1980
The technical committee has reviewed the provisions of IEC 410, to which reference is made in 5.2.1, and has decided that they are acceptable for use in conjunction with this standard. The related British Standard is BS 6001 “Sampling procedures and tables for inspection by attributes”. In 3.4 reference is made to the International Electrotechnical Vocabulary (IEC 50). The appropriate definition is as follows: I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
Duty factor in intermittent periodic duty or in continuously running duty with intermittent loading: The ratio of the duration of the period of working under load to the duration of the cycle; it is included between 0 and 1 and can also be expressed as a percentage. The relevant related British Standard for the International Electrotechnical Vocabulary is BS 4727 “Glossary of electrotechnical, power, telecommunication, electronics, lighting and colour terms” Part 1:Group 03 “Relay terminology”. In 4.3.2 a) reference is made to a specific part of IEC 255-3 and IEC 255-4. The appropriate information is given in 14.1.1 of BS 142-2.1:1980. 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 immunity from legal obligations.
Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 16, 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. © BSI 07-1999
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I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c iv i L
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BS 5992-1:1980
1 General 1.1 Scope This recommendation is applicable to contact assemblies of relays within the scope of the IEC. It covers basic considerations which are, in general, common to all types of relays covered by IEC Publication 255, Electrical Relays, but supplementary requirements may be necessitated by specific designs or application. It applies only to relays in a new condition. I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
NOTE This first publication is based on certain types of relays (e.g. general purpose relays) and will be expanded in future editions as more data becomes available.
1.2 Object The object of this recommendation is to state, for relay contact assemblies: — definitions of terms used, — preferred rated values, — preferred test conditions, — basic criteria of contact failure, — assessment of performance data, — presentation of performance data.
2 Definitions For the purpose of this recommendation, the following definitions shall apply: NOTE For definitions of general terms not defined in this recommendation, reference should be made to the other parts of Publication 255 and to the IEC International Electrotechnical Vocabulary.
2.1 contact circuit (see A, Figure 1, page 1) the whole of the electrically conductive parts of a relay which are intended to be connected to a given external circuit which is to be closed or opened by the relay NOTE
A change-over contact involves two contact circuits.
2.2 contact assembly (see B, Figure 1) an assembly of contact members, with their insulation, which close or open their contact circuit by their relative movement 2.3 contact member (see C, Figure 1) a conductive part of a contact assembly which is electrically isolated from other such parts when the contact circuit is open 2.4 contact tip (see D, Figure 1) a conductive part of a contact member designed to co-act with another to close the contact circuit
Figure 1
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2.5 make contact a contact which is open when the relay is in its unenergized condition and which is closed when the relay is in an energized condition 2.6 break contact a contact which is closed when the relay is in its unenergized condition and which is open when the relay is in an energized condition
I S 2.7 B ) contact gap c ( , the gap between the contact tips, under specified conditions, when the contact circuit is open y p 2.8 o Ccontact force d the force which two contact tips exert against each other in the closed position under specified conditions e l l 2.9 o r 1) t n limiting continuous current of a contact circuit o c the highest value of current (r.m.s. if a.c.) which a previously closed contact circuit is capable of carrying n continuously under specified conditions U , 2 2.10 0 limiting short-time current of a contact circuit 1) 0 2 the highest value of current which a previously closed contact circuit is capable of carrying for a specified r e short period under specified conditions b m2.11 e t limiting making capacity1) p e S the highest value of current which a contact assembly is capable of making under specified conditions 0 2.12 2 1) , limiting breaking capacity d a the highest value of current which a contact assembly is capable of breaking under specified conditions h r e 2.13 B limiting cycling capacity1) l a n under consideration o i s 2.14 a Nbounce mcontact tips bounce when, after having touched each other for the first t ime, they separate transiently one a i l or more times before definitively closing t he contact circuit o r NOTE Bounce can also occur during the opening of contacts. This is under consideration. t e P 2.15 , bounce time i t a for a contact which is closing its circuit, the time which elapses between the instan t when the contact circuit y a is first closed and the instant when the circuit is finally closed. It applies at a specified value of the h r energizing quantity and for a specified load on the contacts o NNOTE Bounce can also occur during the opening of contacts. This is under consideration. . s 2.16 M contact follow (contact over-travel) n a under consideration u P : y p o C d 1) The limiting values (see Sub-clauses 2.9, 2.10, 2.11, 2.12 and 2.13) may be greater than the corresponding rated values. e s n e © BSI 07-1999 c 2 i L
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2.17 contact wipe under consideration additional definitions are under consideration
3 Standard rated values Standard rated values for contact circuits given below are selected from other parts of IEC Publication 255. I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
Values indicated as preferred have been chosen so as to minimize test conditions and to provide reference values for comparison of data. 3.1 Rated voltages Preferred values: — d.c.: 12 — a.c.: 12
24 24
48 48
60 110 125 220 V, 110 220 V (r.m.s.).
Other voltages are acceptable, but have not been preferred in this document. 3.2 Rated currents For rated continuous currents, a.c. and d.c.: 1
1.25 1.6
2
2.5 3.15
4
5
6.3
8
or the decimal multiples or submultiples of these figures in amperes. 1, 2 and 5 are preferred values. For rated making, breaking and cycling capacity, no values are listed. 3.3 Frequency of operation Preferred values (cycles per hour): 6
30
120 45 000
600 1 200 1 800 3 600 7 200 72 000 90 000 108 000 180 000
12 000 18 000 36 000 360 000 720 000
3.4 Duty factor (see 10-05-395 of the International Electrotechnical Vocabulary, Chapter 10). Unless otherwise stated by the manufacturer, the duty factor referring to the energizing circuits shall be 50 %.
4 Test conditions 4.1 General a) At the commencement of each test, the relay, including contacts, shall be in an effectively new and clean condition in so far as the given test is concerned, unless otherwise stated by the manufacturer. b) The relay shall be mounted in the manner intended for normal service, in its case and with cover, if any, in position. c) Ambient temperature for make, break and cyclic tests shall be stated by the manufacturer and shall be not less than the reference value. d) Ambient temperature for continuous tests: at the upper limit of the nominal range of temperature. e) Relative humidity: 45 % to 75 %. f) All other influencing quantities and factors shall be at their reference values as given in IEC Publication 255. g) The atmosphere shall be sensibly free from dust and other contaminations. h) When lubricants or other preparations are recommended by the manufacturer, they should be applied before commencing the test. i) During any given sequence of tests, the contacts should be neither cleaned nor touched. j) The rate of testing shall not exceed that stat ed by the manufacturer. It shall be such that there is no harmful cumulative heating of the contacts or harmful cumulative ionization within the relay case. k) When testing on a.c. loads, actuation of the relay shall ensure that mechanical contact operation is random with respect to the point on the wave (voltage for make duty, current for break duty).
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l) All specified protective devices or quenching circuits which are part of the relay design, or stated by the manufacturer as necessary for particular contact ratings, should be in position during tests. m) If the relay has a device or circuit for suppressing radio interference frequencies, t his device shall be included in the contact circuits during contact tests. n) During the life test, the test facilities shall be so arranged as to provide the degree of monitoring and/or control required by the test clauses. o) The length and arrangements of all the test circuit leads can affect the contact performance of the contacts and must be agreed upon between manufacturer and user. Short test leads may be necessary for resistive loads to minimize the effects of stray capacitance. The leads sha ll have such a cross section that no significant heat is conducted from the test cables to the contact or vice versa (see also Appendix A).
I S B ) c ( , 4.2 Test circuit y p The test circuit shall be in accordance with Appendix A unless otherwise agreed. The test conditions, o Cstandard values, etc., shall preferably be selected from those given in Clause 3 and Table I, page 4, but d other values, e.g. lower voltages for duty level categories I and II given in Appendix B, may also be used. e l l The declared value of the current shall be expressed in terms of the steady-state (r.m.s. if a.c.) value of o r current in the contact circuit. t n o 4.3 Relay energization c n The following conditions are applicable unless other values are specified in the appropriate part of U , IEC Publication 255. 2 0 4.3.1 All-or-nothing relays 0 2 a) Energizing quantities r e For making, breaking and cycling capacity tests, the relay shall be energized with the rated values of b m input and auxiliary energizing quantities ( ± 2 %). The value of the energizing quantities for drop-out e t shall be stated by the manufacturer. p e b) Polarities S 0 Where polarities are not marked on the terminals of the input circuit and/or contact circuits, the tests shall 2 be made under the most severe conditions of polarity. , d Table I — Characteristics of test circuits a h r Standard values e Duty levels B Test circuit detail Power source Tolerances Notes l in Appendix B a D.C. A.C. n o i Voltage ± 2% Preferred and other I and II Voltage across the load s a specified values including the closed contact ± 5% III N ± 2% Frequency Standard m a rated i l values o r t L=0 I and IIA e Resistive load L u R × 10 –7 or R is the load resistance in P ohms , at least L u 10 –4 i t L is the load inductance in a –6 IIB and III y L u R × 10 or henrys a h at least L u 10 –4 r o cos Î = 1 + 0 – 0.01 N . I and IIA ± 15% L s Inductive load ---- = 0.005 s R M n IIB and III L a ---- = 0.040 sa u R P : cos Î = 0.4 ± 0.1 y p Capacitive or On request only for special o C non-linear load cases, see also Sub-clause 4.1 d a e Other values than 0.040 s may be acceptable, but must be agreed upon between manufacturer and user. s n e © BSI 07-1999 c 4 i L
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4.3.2 Measuring relays a) Input energizing and characteristic quantities The same as those applicable for mechanical endurance test, in Parts 3 and 4 for measuring relays. b) Auxiliary energizing quantities For making, breaking and cycling capacity tests, the relay shall be energized with the rated values (± 2 %). I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
For continuous duty of a make contact, the relay shall be energized at the upper limit of the operative range (± 2 %). The ambient temperature shall be at the upper limit of the nominal range. c) Polarities Where polarities are not marked on the terminal input circuit and/or contact circuits, the tests shall be made under the most severe conditions of polarity. 4.4 Criteria of contact failure A contact under test shall be deemed to have failed when one or more of the following conditions occur: a) It is no longer capable of performing the duty claimed for it and relevant to the particular tests. b) It fails in any of the modes listed in Sub-clause 4.4.2. c) It causes consequential failure of any other part of the relay. 4.4.1 Types of failure Temporary failure: a failure which is self-correcting. Permanent failure: not self-correcting. 4.4.2 Modes of failure a) All-or-nothing relays: operative range reduced. b) Measuring relays (regarding the characteristic quantity) and specified time relays (regarding the specified time): the error limits exceed twice the class index. c) Operating, resetting, pick-up or drop-out times are outside stated values with tolerances. d) Failure due to open circuits or contact resistance exceeding a prescribed limit. NOTE Standard values of maximum contact resistance are under consideration and in the meanwhile the manufacturer shall state the maximum value of contact resistance used in determining contact failure and the test conditions (e.g. voltage and current).
e) Welding or other forms of adherence. f) Sustained arcing. g) Dielectric failure, if the contact circuit, in the open position, fails to withstand dielectric voltage tests at a level 0.75 times the test voltage specified for a new relay (to earth, to other circuits or between open contacts). h) Insulation resistance failure, when relevant resistance values fall to a value below 0.1 times the value specified for a new relay in relevant parts of IEC Publication 255. i) Overheating, if any associated insulation reaches temperatures higher than the appropriate class (IEC Publication 85, Recommendations for the Classification of Materials for the Insulation of Electrical Machinery and Apparatus in Relation to their Thermal Stability in Service). j) Signs of damage and/or permanent distortion or change in the component parts of the contact circuits (e.g. ligaments) or other parts of the relay caused by the contact tests.
5 Assessment of contact performance 5.1 General The manufacturer shall state the rated performance of the contacts in terms of current, voltage, number of operations, maximum frequency of operations, failure rate, etc., under the declared test conditions. For contacts operating in circuits with level categories I and II in Appendix B, other data can be stated supplementary to the normal data, e.g. lower limits of voltages and currents, number of operations and failure rate at values of voltages and currents as agreed upon between manufacturer and user.
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The requirements for make, break and cyclic duty concern each contact separately, and for continuous duty to not less than 50 % (or the nearest higher value of the number if contacts is not even) of each type of all make contacts (or 50 % of all break contacts if this case is more severe). If derating is necessary when more than one contact is loaded at the same time, and at their rated value, this shall be declared by the manufacturer. NOTE 1 For small relays with many contacts and enclosed by a cover, derating can be applied when necessary, in one or more of the following ways: — as a lower frequency of operation for cyclic duty to avoid cumulative ionisation within the cover, — and/or as a lower continuous current capacity to limit temperature rise, I — and/or as a lower rated voltage to avoid flash-over between contacts in different circuits loaded at the most severe polarity S conditions. B ) NOTE 2 It may be necessary to take account of the physical position of the contact(s) within the relay.
c ( , 5.1.1 Making capacity y p The contact shall make and carry the appropriate current for: o C — 200 ms for level category III, d — 25 ms or a time equal to the duty factor (see Sub-clause 3.4) divided by the frequency of operation, e l l whichever is the lower value for level categories I or II. o r t n The load shall be resistive for both d.c. and a.c. and the current shall not be interrupted by t he contact itself o but by independent means. c n NOTE Other values may be agreed upon between manufacturer and user when using other test circuits than in Appendix A and Uin Table I. In addition to resistive load, inductive d.c. load may be considered when the bounce time is longer than the L/R value. In , 2 that case, the current shall be broken after 5 times the L/R value of the load. 0 0 5.1.2 Breaking capacity 2 r The circuit shall be closed independently and the contacts shall break the appropriate current with an e b inductive load, unless otherwise stated, for both d.c. and a.c. m5.1.3 Cyclic capacity e t p The contacts shall make and break the sam e current, unless otherwise stated, with inductive load for both e S d.c. and a.c. (the conditions will usually be the same as for the determination of breaking capacity). 0 NOTE When agreed upon between manufacturer and user, a higher current for make than for break may be specified. 2 , d 5.1.4 Continuous capacity a The circuit shall be closed and opened by independent means, unless otherwise stated, and the contacts h r e shall carry the appropriate current with a resistive load for both d.c. and a.c. The test shall continue for B sufficient time to ensure the thermal equilibrium of the contacts. l a n 5.1.5 Short time capacity o i s The circuit shall be closed and opened by independent means and the contacts shall carry the appropriate a Ncurrent for 1 s, unless otherwise stated, with a resistive load for both d.c. and a.c.
m5.2 Evaluation a i l The rigorous method of assessing contact performance (see Sub-clause 5.2.1) inevitably involves a o r considerable amount of testing, but can yield data which accurately represent the performance limits of a t e P given contact and the manufacturer shall therefore normally state characteristics according to this method . , i t In some instances, the costs implicit in the rigorous assessment may not be justifiable; but where a circumstances permit, it may be possible to use simpler methods by agreement between manufacturer and y a user. One example of such a simplified method is given in Appendix D. h r o If a simplified method of assessment is used as a basis for performance claims, the manufacturer shall Ndescribe his method. . s 5.2.1 Rigorous method of assessment M n The rigorous method of assessing contact performance refers essentially to th e design evaluation testing of a contact life. Lot-by-lot assessment of contact performance for quality assurance (or conformance tests) is u P under consideration. For the present, this may be covered by agreement between manufacturer and user. : y IEC Publication 410, Sampling Plans and Procedures for Inspection by Attributes, can be used as a basis. p o C d e s n e © BSI 07-1999 c 6 i L
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5.2.1.1 Basic assessment An assessment in this form is required of all proving tests in accordance with Sub-clause 5.2.1. The significance of this assessment is described in Appendix C. a) Unless otherwise declared, 20 contact circuits shall be tested. The claimed number of operations shall be less than the number of operations giving the first failure.
I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
A claim corresponding to the number at first failure (see Sub-clause 4.4) implies a reliability of approximately 89 % (i.e. less than 11 % of similar contact circuits would fail). This claim would have an associated confidence level of 90 % (see table in Appendix C). If only one failure occurs before the claimed number of operations, 20 further contacts may be tested. These contacts shall operate without failure up to at least the claimed number of operations. In this case, for a confidence level of 90 %, the reliability will be approximately 88 %. b) Alternatively, the manufacturer may declare other reliability levels at other confidence levels, but at least 10 contact circuits shall be tested. The relationship between sample size, reliability and confidence levels shall be in accordance with Appendix C. 5.2.1.2 Extended assessment (by graphical methods) Further information can be deduced from these test data (see Appendix C, Clause 3). In order to make statistical inferences possible at a sufficiently high confidence level and to keep costs of testing as low as possible, the tests shall preferably continue until most of the contacts in the samp le have failed or, if no failures occur, up to at least three times the claimed number of operations. 5.2.2 Simplified method of assessment (See example in Appendix D.)
6 Presentation of performance When detailed data concerning contact performance is required, it may be presented as a family of curves preferably using logarithmic scales (see Figure 2) or in suitable tables.
where: U 1, U 2 and U 3 = test voltages (see Clause 3) N = claimed number of contact operations I = contact current
Figure 2 NOTE 1 Care should be taken to ensure that a sufficient number of points are determined when plotting the above curves. NOTE 2 Additional data should be associated with the curves or tables (e.g. a.c. or d.c., resistive or inductive load, frequency of operation, confidence level for a stated reliability).
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Appendix A Standard test circuit
I S B ) c ( , y p o C d e l l o r t n o c n U , 2 For standard values and tolerances for -L --- or cos Î , see Sub-clause 4.2, Table I 0 R 0 2 A.1 Load resistors r e The non-linearity of the resistors due to temperature coefficient and other causes must not exceed 2 %. b A.2 Load inductors m e B t The non-linearity in the magnetizing curve % -------- must not exceed 2 %, including maximum influence from p B e the hysteresis. C-cores with defined minimum air-gap and series resistance can be used to reduce the S non-linearity. 0 2 B , NOTE The non-linearity % -------- has to be determined in the hysteresis loop at the working point B by drawing, a parallel (b) at the d B a distance % B to the ideal line (a) and tangential to the switch-off curve of the inductor. h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N A.3 Test leads and scheme . s If the test source is earthed at one pole, the contact under test shall be connected in the pole which gives M the most severe conditions (the longest arcing time). See also Sub-clauses 4.3.1 b) and 4.3.2 c). n a The length of the test circuit leads can affect the contact performance of the contacts and must be agreed u P upon between manufacturer and user. : y NOTE The influence of the circuit capacitance on the transient phenomena after breaking (with respect to frequency and transient p recovery voltage) is under consideration. o C d e s n e © BSI 07-1999 c 8 i L
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Appendix B Duty levels for d.c. and a.c. Level
I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
Voltage
Current
I
< 0.02 V
II
0.02 to 250 V < 1 A
III
< 0.1 A
0.02 to 600 V < 100 A
Application field or type of relays
Low level See Note 1 Special light duty Internal make and break in electronic equipments A) Telecommunications field Data processing
6 to 60 V; < 0.2 A
B) Measuring relays Domestic equipments Control equipments Signalling systems
24 to 250 V; < 1 A
A) All-or-nothing relays, e.g. general 24 to 600 V; 0.1 to 10 A purpose relays, trip relays B) Industrial Traction Heavy duty
NOTE 1 NOTE 2
Typical voltages and currents
24 to 600 V; 1 to 100 A
The zone below 0.02 V and within 0.1 to 100 A is not covered in the table since application fields have not been defined. A contact may be designed for one or more duty levels or may cover only a part of the range of one duty level.
Appendix C Assessment of test results C.1 Introduction Claims of contact performance are, in general, based on the results of tests of similar contact asssemblies. Such tests are necessarily made of a limited number on contact assemblies, and from the results an inference must be made of the performance of a potentially large number of assemblies (which, since the tests are destructive, cannot be fully proved). The ultimate result of the initial tests will be a declaration of performance in the following general terms: “The stated performance (or better) will be achieved, in x % of all cases; this means a reliability of x per cent. This statement is made with a confidence level of ¾ %”. However, other valuable inferences can often be drawn from the test data. When a manufacturer wishes to make the maximum possible claims of performance, the evidence upon which those claims are to be based will obviously need to be more complete than when a lower claim is made. Sub-clause 5.2.1 therefore envisages two complementary approaches to assessing the performance, referred to below as basic assessment and extended assessment. C.2 Basic assessment The basic assessment adopted in this recommendation is based on the first failure in the test sequence occurring beyond the claimed number of operations and does not assume any particular distribution of failures. In statistical terms, it is a distribution-free method based on the first order statistic. Table A gives the estimated maximum percentages p of the population which would fail under identical circumstances of test and design and at a given confidence level ¾. Table A Sample size
Maximum value of p (in %) for a confidence level ¾ of:
n
50 %
70 %
80 %
90 %
10
6.7
11.3
14.9
20.6
20
3.4
5.8
7.7
10.9
© BSI 07-1999
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BS 5992-1:1980
Example It can be said with a confidence level ¾ of 90 % that the population of which the sample of 20 contacts is representative will contain not more than 10.9 % failures at the number of operations below that at which the failure in the sample occurs. The data in Table A may be extended by the use of the following formula: p - n * = 1 – 1 – -------- 100
I Reference can also be made to standard textbooks, etc. (see Clause C.4). S B C.3 Extended assessment (by graphical methods) ) c Since the pattern of failure distribution may not be known in advance of the tests, a generalized system of ( , y analysis must be used which can take account of different patterns and identify them when possible. p In the preferred approach, the failures are arranged in an ascending order of number of operations at o Cfailure, and from this each can be plotted in terms of its “rank”. It is preferable to plot in terms of the d “median ranks” as shown in Table B, page 13. e l l When these data are plotted on appropriate graph paper, the resultant curve can be used for analytical o r t purposes. One of the most powerful analytical approaches is the use of the Weibull distribution which, by n o correctly choosing the parameters, can match a wide range of possible curves. c n The Weibull distribution is given by: U , 2 0 0 2 r where: e b N = number of operations at contact failure, m e N c = scale parameter: the characteristic number of operations (at 63.2 % failures), t p e S µ = location parameter: the number of operations up to which no failures can occur; generally µ = 0, 0 ¶ = shape parameter: ¶ indicates the slope of the Weibull distribution. 2 , d The corresponding Weibull failure rate function (or hazard function) is given by: a h r e B l a From this, it can be seen that the failure rate decreases when ¶ < 1 (early failures), remains constant n o when ¶ = 1 (random failures) and increases when ¶ > 1 (wear out). So the slope ¶ of the Weibull distribution i s plot enables one to distinguish between: a N — early failures, m — random failures, a i l — wear out failures. o r t e Figure 3, page 38, shows a Weibull probability chart. P , Weibull probability paper is derived from the Weibull distribution function in the following way: i t a y a h r o N . s or M n a u P : y p o C d e s n e © BSI 07-1999 c 10 i L
BS 5992-1:1980
1 So a linear relationship exists between ln ln ----------------------- and ln N . 1 – F ( N ) To obtain a straight line as a Weibull plot, the Weibull distribution paper has a double logarithmic scale on the vertical axis and a single logarithmic scale on the horizontal axis. 1 On the right are the corresponding values of ln ln ----------------------- and on the top the corresponding values of ln 1 – F ( N ) N , on linear scales. If N = N c, it follows that: I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
1 lnln ----------------------- = 0 1 – F ( N ) and the corresponding value of: 1 F ( N ) = 1 – --- = 0.632 e Therefore the zero on the vertical linear scale of ¶ corresponds with 63.2 % failures, as shown by the dotted line. In this way, the characteristic number of operations N c can be estimated. The point (1; 0) on the linear scale: ln N = ln N c = 1 from which it follows that every straight line through (1; 0) intersects the vertical axis (at which l n N = 0) at a distance ¶ from the origin [0.0] (see Figure 4, page 14).
The value of ¶ can be read from the right-hand vertical scale. The mean È and the standard deviation B of the failure distribution can be estimated by using the nomograms shown to the extreme right and above the probability paper. This is possible because --4---- and N c --B ---- are functions of " only. N c
Example In a life test, contacts failed according to the following table (sample size n = 20 contacts). i
N (× 106 operations)
Median rank × 100 %
1
2.7
3.4 %
2
3.4
8.3 %
3
4.4
13.1 %
4
5.2
18.1 %
5
5.3
23.0 %
6
5.6
27.9 %
7
5.7
32.8 %
8
6.5
37.7 %
9
7.5
42.6 %
10
8.7
47.5 %
11
9.7
52.3 %
No failures up to 9.7 × 106 operations 20
© BSI 07-1999
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BS 5992-1:1980
The following procedure is adopted: 1. Find median rank (m.r.) from Table B (page 13) or, if the sample size n is not given there, calculate m.r. from: i – 0.3 m.r. = -----------------n + 0.4 The values for the example are given in the third column of the above table. 2. Plot the median ranks at the corresponding number of operations on the Weibull probability chart (Figure 4).
I S B 3. Fit, when possible, a straight line to the plots. ) NOTE If a single straight line cannot be drawn, it is probable that more than one failure mechanism exists. c ( 4. Estimate the characteristic life (N c) at the intersection of the drawn line with the “63.2 %” line: , y p N c = 9.3 × 106 operations o C 5. Draw a parallel line through (1; 0). The intersection with the zero vertical axis gives: shape d parameter: ¶ = 2.6 e l l o The failure mechanism is wear out, since ¶ > 1. r t n 6. From the nomogram, read: o c È Ö n -------- = 0.89 and -------- = 0.365 U N c N c , 2 0 from which: 0 2 — mean: ( È) = 0.89 × 9.3 × 106 = 8.2 × 106 operations, r e b — standard deviation: ( ) = 0.365 × 9.3 × 106 = 3.2 × 106 operations. Ö m e t p C.4 Bibliography e S For the benefit of those wishing to study the detailed theory of this subject, the following bibliography 0 recommended: 2 , References d a 1) Kao, John H. K. (Ireson), “Reliability Handbook”, New York, McGraw Hill, 1966. h r 2) Johnson, L. G., “The median ranks of sample values in their population with an application to certain e B fatigue studies”, Industrial Mathematics, No. 2, 1951. l a 3) Cramer, H., “Mathematical Methods of Statistics”. n o i 4) Johnson, J. G., “Theory and technique of variation research”, Elsevier Publishing Company, 1964. s a N 5) Goldthwaite, Lynn R., “Failure rate study for the lognormal life time study”, Nat. Symposium reliability by quality control, Philadelphia, 1961. m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e © BSI 07-1999 c 12 i L
BS 5992-1:1980
Table B — Median ranks (m.r.) at the tabulated sample sizes Cumulative number of failures 10
i
I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
Sample size n
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
6.7 16.2 25.9 35.5 45.2 54.8 64.5 74.1 83.8 93.3
15
4.5 10.9 17.4 23.9 30.5 37.0 43.5 50.0 56.5 63.0 69.5 76.1 82.6 89.1 95.5
20
30
40
50
3.4 8.3 13.1 18.1 23.0 27.9 32.8 37.7 42.6 47.5 52.5 57.4 62.3 67.2 72.1 77.0 81.9 86.9 91.7 96.6
2.3 5.5 8.8 12.1 15.4 18.7 22.0 25.3 28.6 31.9 35.2 38.5 41.8 45.1 48.4 51.6 54.9 58.2 61.5 64.8 68.1 71.4 74.7 78.0 81.3 84.6 87.9 91.2 94.5 97.7
1.7 4.2 6.6 9.1 11.6 14.1 16.5 19.0 21.5 24.0 26.4 28.9 31.4 33.9 36.4 38.8 41.3 43.8 46.3 48.8 51.2 53.7 56.2 58.7 61.2 63.6 66.1 68.6 71.1 73.6 76.0 78.5 81.0 83.5 85.9 88.4 90.9 93.4 95.8 98.3
1.4 3.3 5.3 7.3 9.3 11.3 13.3 15.2 17.2 19.2 21.2 23.2 25.2 27.2 29.1 31.1 33.1 35.1 37.1 39.1 41.1 43.0 45.0 47.0 49.0 51.0 53.0 55.0 57.0 58.9 60.9 62.9 64.9 66.9 68.9 71.0 72.0 74.8 76.8 78.8 80.8 82.8 84.8 86.8 88.7 90.7 92.7 94.7 96.7 98.6
The median rank can be approximated by the formula: i – 0.3 m.r. = -----------------n + 0.4
© BSI 07-1999
(i = cumulative number of failures)
13
c ( , y p 1 o 4 C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M © n B a S u I P 0 7 : -1 y 9 p 9 o 9 C d e s n e c i L
B S 5 9 9 2 -1 : 1 9 8 0
Figure 4 — Weibull probability chart
BS 5992-1:1980
Appendix D A simplified method for assessment of contact ratings D.1 General An example of a simplified method of assessment referred to in Sub-clause 5.2.2 is described below. This method is approximately valid for contacts of some general-purpose relays of conventional design, but is not valid for every type of contact. This simplified method gives lower rated values than the rigorous method, but minimizes testing. The formulae are approximately valid up to the given limits of 105 operations. I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b
D.2 Simplified method of assessment D.2.1 The rated limiting making capacity I LM and the rated limiting breaking or cyclic capacity I LB are based on ten operations without failure for each of the contact circuits. D.2.2 The rated contact current for the given making capacity I M related to 104 operations shall be I M = 0.5 I LM and for breaking or cyclic capacity I B related to 104 operations shall be I B = 0.7 I LB. D.2.3 The performance at lower currents and a higher number of operations N than specified in Sub-clause 2.2 may be estimated in accordance with the following formulae: N 1 =
I M 1.5 10 ⋅ ------- I 1 4
1.5 4 I B N 2 = 10 ⋅ ----- I 2
for making capacity in the range 104 to 105 operations
for breaking and cyclic capacity in the range 104 to 105 operations
where: N = number of operations at current I for making capacity
BS 5992-1:1980
Appendix D A simplified method for assessment of contact ratings D.1 General An example of a simplified method of assessment referred to in Sub-clause 5.2.2 is described below. This method is approximately valid for contacts of some general-purpose relays of conventional design, but is not valid for every type of contact. This simplified method gives lower rated values than the rigorous method, but minimizes testing. The formulae are approximately valid up to the given limits of 105 operations. I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
D.2 Simplified method of assessment D.2.1 The rated limiting making capacity I LM and the rated limiting breaking or cyclic capacity I LB are based on ten operations without failure for each of the contact circuits. D.2.2 The rated contact current for the given making capacity I M related to 104 operations shall be I M = 0.5 I LM and for breaking or cyclic capacity I B related to 104 operations shall be I B = 0.7 I LB. D.2.3 The performance at lower currents and a higher number of operations N than specified in Sub-clause 2.2 may be estimated in accordance with the following formulae: 1.5 4 I M N 1 = 10 ⋅ ------ I 1
for making capacity in the range 104 to 105 operations
1.5 4 I B N 2 = 10 ⋅ ----- I 2
for breaking and cyclic capacity in the range 104 to 105 operations
where: N 1 = number of operations at current I 1 for making capacity N 2 = number of operations at current I 2 for making and cyclic capacity (I 1 < I M and I 2 < I B and normally I B < I M) NOTE The above formulae can be used beyond the limit of 105 operations and/or using another exponent in the range 1.5 to 3 as agreed between manufacturer and user.
© BSI 07-1999
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I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c 16 i L
blank
BS 5992-1:1980
Publications referred to See national foreword.
I S B ) c ( , y p o C d e l l o r t n o c n U , 2 0 0 2 r e b m e t p e S 0 2 , d a h r e B l a n o i s a N m a i l o r t e P , i t a y a h r o N . s M n a u P : y p o C d e s n e c i L
© BSI 07-1999
BS 5992-1: 1980 IEC 255-0-20: 1974
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