1、BRITISH STANDARD BS 4996:1973 Specification for Line traps for power line carrier systems UDC 621.315.052.63:621.316.9:621.372.54BS4996:1973 This British Standard havingbeenapproved by the Electrical Industry Standards Committee, was published underthe authorityof the Executive Boardon 31October1973
2、 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference ELE/89 Draft for comment69/13047 ISBN 0 580 07698 9 Co-operating organizations The Electrical Industry Standards Committee under whose supervision this British Standard was prepared, consists of repres
3、entatives from the following Government departments and scientific and industrial organizations: Associated Offices Technical Committee Association of Consulting Engineers* Association of Manufacturers of Domestic Electrical Appliances Association of Mining Electrical and Mechanical Engineers Associ
4、ation of Supervisory and Executive Engineers British Electrical and Allied Manufacturers Association British Electrotechnical Approvals Board for Household Equipment British Radio Equipment Manufacturers Association British Railways Board British Steel Corporation Crown Agents for Oversea Government
5、s and Administrations Department of Employment (HM Factory Inspectorate) Department of the Environment Department of Trade and Industry Electric Cable Makers Confederation Electric Contractors Association Electrical Contractors Association of Scotland Electrical Research Association Electricity Coun
6、cil, the Central Electricity Generating Board and the Area Boards in England and Wales* Electronic Engineering Association Engineering Equipment Users Association Institution of Electrical Engineers Institution of Electrical and Electronics Technician Engineers Lighting Industry Federation Limited M
7、inistry of Defence National Inspection Council for Electrical Installation Contracting National Physical Laboratory (Department of Trade and Industry) Oil Companies Materials Association Post Office South of Scotland Electricity Board The organizations marked with an asterisk in the above list, toge
8、ther with the following, were directly represented on the committee entrusted with the preparation of this British Standard: BEAMA Transmission and Distribution Association North of Scotland Hydro-Electric Board Amendments issued since publication Amd. No. Date of issue CommentsBS4996:1973 BSI 12-19
9、99 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 General 1 1.1 Scope 1 1.2 Service conditions 1 1.3 Carrier frequency 1 2 Definitions 1 3 Requirements 2 3.1 General requirements 2 3.2 Blocking requirements 2 3.3 Continuous service requirements 3 3.4 Ability to withstand
10、 short-circuit 3 3.5 Inductance of the main coil 3 3.6 Insulation level 3 3.7 Tensile strength of the suspension system 4 4 Rating plates 4 5 Tests 4 5.1 General conditions for tests 4 5.2 Type tests 4 5.3 Routine tests 5 Appendix A Recommended values of rated quantities 6 Figure 1 Example of a circ
11、uit diagram of a line trap tuned for a carrier-frequency band 7 Figure 2 Definition of the bandwidth of line traps 8 Figure 3 Measuring circuit for the impulse voltage test 9 Figure 4 Measuring circuit for the determination of the blocking impedance 9 Figure 5 Measuring circuit for the blocking impe
12、dance at the tuning frequency in the case of line traps utilizing simple resonance 10 Figure 6 Measuring circuit for the determination of the insertion loss 10 Table 1 Limits of temperature rise 3 Table 2 Co-ordination of currents 6 Publications referred to Inside back coverBS4996:1973 ii BSI 12-199
13、9 Foreword This British Standard is technically identical with Publication353 of the International Electrotechnical Commission. 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. Complia
14、nce 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, pagesi andii, pages1 to10, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had
15、 amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS4996:1973 BSI 12-1999 1 1 General 1.1 Scope This British Standard gives definitions, requirements, methods of test and recommended values of rated quantities for line traps intended to be inserted int
16、o high-voltage transmission lines to prevent undue loss of superimposed carrier signal. It does not apply to inductors which may be connected to high-voltage transmission systems for other purposes, such as series reactors. NOTEThe titles of the British Standards referred to in this standard are lis
17、ted on the inside back cover. 1.2 Service conditions Unless otherwise agreed between the manufacturer and the purchaser, the line trap shall be suitable for operation in the service conditions given below, to which the requirements of this British Standard are related: 1) Exposure. Outdoor service,
18、exposed to sunshine, rain, fog, hail, frost, snow and ice. NOTESevere atmospheric conditions such as salt-spray, industrial pollution, etc.,should be covered by special agreement between the manufacturer and the purchaser. 2) Altitude. A height above sea level not exceeding1000m. NOTEProvision is ma
19、de in3.3 and3.6 for tests on line traps designed for operation at greater altitudes. 3) Temperature of cooling medium. An air temperature between25 C and+40 C inclusive, with average temperatures not exceeding the following: +30 C for the daily average, +20 C for the annual average. NOTEProvision is
20、 made in3.3 for tests on line traps designed for higher cooling medium temperatures. 4) Wave-shape. Power-frequency current and voltage of approximately sinusoidal wave-shape. 5) Power frequency. A power system rated frequency between zero (d.c.)and60Hz inclusive. 1.3 Carrier frequency The limits of
21、 carrier frequency shall be the subject of agreement between the manufacturer and the purchaser. 2 Definitions For the purposes of this British Standard the following definitions apply. For other definitions, reference should be made toBS4727. 2.1 General definitions 2.1.1 line trap a piece of elect
22、rical apparatus intended for series insertion into a high-voltage line. Its impedance is negligible at the power frequency, so as not to disturb the power transmission, but relatively high over any frequency band appropriate to carrier transmission a line trap consists of a main coil with a protecti
23、ve device and, usually, a tuning device NOTEFigure 1 shows an example of a line trap circuit. 2.1.2 main coil the inductor which carries the power-frequency current its rated inductance L Nis that value which corresponds to the specified characteristics of the line trap at power frequency 2.1.3 tuni
24、ng device a device which serves the purpose of obtaining a relatively high line trap impedance for one or more frequencies or frequency bands. It consists of capacitors with, possibly, inductors and resistors, and is shunt-connected to the main coil 2.1.4 protective device a device which protects th
25、e line trap against transient overvoltages which may otherwise occur across it. It is shunt-connected to the tuning device and the main coil NOTEAdditional protective devices may be associated with tuning devices to protect individual components. 2.2 Blocking terms NOTEVarious power system elements
26、such as transformers, busbars, lines, etc.,represent an impedance connected beyond the line trap between line and earth. This impedance in series with the impedance of a line trap constitutes a shunt across the carrier-frequency signal path. The loss in signal power resulting from this shunt depends
27、 upon the vectorial sum of the two constituent impedances. In the most unfavourable case, the reactive components of the two impedances may neutralize each other and thus reduce the total shunt impedance to an unacceptably low value. In order to eliminate this possibility, and the further possibilit
28、y of varying shunting effects arising out of system switching, the tuning devices of line traps may include a resistive element, and line trap performance can be assessed in terms of its effective resistance only.BS4996:1973 2 BSI 12-1999 2.2.1 blocking impedance Z b the complex impedance of the com
29、plete line trap within a specified carrier-frequency range The minimum value of the resistive component of the blocking impedance is termed: rated blocking impedance,Z bN 2.2.2 insertion loss A t a measure of the loss of power sustained by a carrier-frequency signal due to the finite blocking abilit
30、y of the line trap. It is defined in terms of the ratio of the signal voltages across an impedance equal to the characteristic impedance of the line with and without shunt connection of the line trap. It is expressed in decibels (dB) but may also be expressed in nepers (Np) the value of the insertio
31、n loss as determined by shunt connection of the resistive component only of the line trap impedance is termed: rated insertion lossA tN NOTE 1The term “tapping loss” is used instead of “insertion loss” in IEC Publication353. In the present context the two terms have the same meaning. NOTE 2The block
32、ing attenuation and the insertion loss are interdependent and therefore cannot be separately specified. 2.2.3 bandwidth %f according to the blocking criterion adopted, either the frequency range %f 1within which the blocking impedance does not fall short of a specified value or the frequency range %
33、f 2within which the insertion loss does not exceed a specified value.(SeeFigure 2) bandwidth expressed in terms of rated blocking impedance or rated insertion loss is termed: rated bandwidth %f 1Nor %f 2N 2.2.4 centre frequency, f c the geometric mean of the bandwidth limit frequencies the mean freq
34、uency derived from the rated bandwidth is termed: rated centre frequency f cN 2.3 Currents 2.3.1 rated continuous current, I N the maximum r.m.s.value of the current flowing continuously at the specified rated power frequency, f pN , through the main coil, without causing the limits of temperature r
35、ise to be exceeded 2.3.2 rated short-time current, I sN the r.m.s.value of the steady-state component of the short-circuit current flowing for a specified time through the main coil without damage, either thermal or mechanical, being caused. The asymmetrical peak value I smof the first half-wave of
36、the rated short-time current is assumed to be2.55times the r.m.s.value 3 Requirements 3.1 General requirements 3.1.1 Main coil. The main coil shall be a single-phase air-cored inductor of dry type, withnatural air cooling. 3.1.2 Tuning device. The tuning device shall be arranged to permit interchang
37、e without removing the line trap. It shall be so designed and arranged that neither significant alteration in the line trap blocking characteristic not physical damage shall result either from temperature rise or from the magnetic field of the main coil at rated continuous current or rated short-tim
38、e current. 3.1.3 Protective device. The protective device shall be a non-linear-resistor type surge diverter complying with the requirements ofBS2914. NOTEIt is recommended that the same rated diverter current be chosen as that of the station diverters installed behind the line trap. In no case shou
39、ld the rated diverter current be less than5kA. The protective device shall be so designed and arranged that neither significant alteration in itsprotective function nor physical damage shall result either from temperature rise or from the magnetic field of the main coil at continuous ratedcurrent or
40、 rated short-time current. It shallneither enter into operation not remain inoperation following transient actuation, at thepower-frequency voltagedeveloped across theline trap by the ratedshort-time current. 3.2 Blocking requirements The blocking requirements shall be the subject of agreement betwe
41、en the manufacturer and the purchaser. However, it is recommended that for the purpose of stating bandwidth a maximum value of2.6dB(0.3Np) be adopted for both insertion loss and rated insertion loss. NOTEThis loss corresponds to a line trap impedance of1.41times the characteristic impedance of a lin
42、e. A typicalcaseis that of a line trap of5707 impedance in a lineof4007 characteristic impedance (the phase-earth impedance of a single-conductor line). The permissible variation of the blocking performance within the bandwidth is also for agreement between the manufacturer and the purchaser.BS4996:
43、1973 BSI 12-1999 3 3.3 Continuous service requirements When tested within the limits of altitude and air temperature given in1.2, the temperature rise of any part of the line trap under rated continuous current conditions shall not exceed the limits specified inTable 1. If the line trap is intended
44、for service where the temperature of the air exceeds one of the maximum values shown in1.2 by not more than10 C, the allowable temperature rise shall be reduced by: 5 C if the excess temperature is less than or equal to5 C, 10 C if the excess temperature is greater than5 C but not greater than10 C.
45、The test requirements for line traps intended for service where the temperature of the air exceeds the values given in1.2 by more than10 C are left for agreement between the manufacturer and the purchaser. For line traps intended for operation at an altitude greater than1000m, but tested at a lower
46、altitude, the limits of temperature rise given inTable 1 shall be reduced by2.5% for each500m above1000m. NOTECertain parts of the line trap may require, or be capable of having, individual temperature specification, depending upon their position relative to the main coil. For bare metallic parts or
47、 windings, the temperature rise should not exceed the limits given for adjacent insulating materials. For terminals, reference should be made toBS3078, noting that in general, the terminals of line traps operate at a higher temperature than do those of isolators, because of the heat generated in the
48、 main coil. Table 1 Limits of temperature rise 3.4 Ability to withstand short-circuit The line trap shall be designed and constructed towithstand, without damage under service conditions, the effects of external short-circuits. Itshall be capable of withstanding the electro-magnetic forces and therm
49、al effects of the rated short-time current for a duration of at least1s after previous operation at rated continuous current at the specified maximum air temperature. NOTEFor the permissible final temperatures reference should be made toBS171. 3.5 Inductance of the main coil The inductance of the main coil shall be determinedat power frequency or any frequency notgreater than1000Hz. The apparent inductance at carrier frequency shall be determinedfrom this measurement and measurement of the self-resonant frequency ofthemain coil. 3.6 Insulation l
