1、STD.AECflA PREN 2853-ENGL 1998 lnl1231l 00111308 2b Edition approved for publication AECMA STANDARD NORME AECMA AECMA NORM C2 Chairman Comments should be sent within six months after the date of publication to prEN 2853 EdWnPl Janury lSS8 PUBLISHED BY THE EUROPEAN ASSOCIATION OF AEROSPACE INDUSTRIES
2、 (AECMA) Gulledelle 94 - B-1200 BRUXELLES - Tel. (+32) 2 775 81 10 - Fax. (+32) 2 775 81 11 ICs: 49.060 Descriptors: Aerospace industry, aircraft equipment, electric cables, current ratings, conductors ENGLISH VERSION Aerospace series Current ratings for electrical cables with conductor EN 2083 Srie
3、 arospatiale Intensits admissibles dans les cbles lectriques conducteur EN 2083 Luft- und Raumfahrt Strombelastbarkeit von elektrischen Leitungen mit Leiter nach EN 2083 This “Aerospace Series“ Prestandard has been drawn up under the responsibility of AECMA (The European Association of Aerospace Ind
4、ustries). It is published on green paper for the needs of AECMA-Members. It has been technically approved by the experts of the concerned Technical Committee following comment by the Member countries. Subsequent to the publication of this Prestandard, the technical content shall not be changed to an
5、 extent that interchangeability is affected, physically or functionally, without re-identification of the standard. After examination and signature of the AECMA Standard Checking Centre (NPSI and formal agreement of the Official Services of the Member countries it will be submitted as a draft Europe
6、an Standard to CEN (European Committee for Standardization) for formal vote. 1998-01-30 AECMA Gulledelle 94 E1 200 BRUXELLES Mr Peuetta aecma 1998 STDmAECHA PREN 2053-ENGL 1998 1012311 00143I17 7b2 M Page 2 prEN 2853: 1998 Contents list 1 Scope 2 Normative references 3 Definitions 4 Rationale 5 Tabu
7、lated data Annex A (informative): Supplementary notes Annex B (normative): Current rating tests STD-AECMA PREN 2853-ENGL 1998 LO1231l 0014310 484 Page 3 prEN 2853: 1998 1 Scope 1.1 EN 2083. This standard specifies current rating data for cables produced with conductors as defined in 1.2 requirements
8、 of EN 3197, 5.4 and 6.1, are satisfied. Electrical ratings for continuous and short term conditions are tabulated such that the 1.3 A procedure for establishing cable current ratings is given in annex B of this specification. 1.4 The basis for determining current of cables has been to employ a 40 O
9、C rise as the electrical contribution to operating temperature. Note is made in this standard that, in practice, the voltage drop requirements of EN 2282 will often dictate lower current densities. Additionally, reference to appropriate aerospace series standards for cable terminations and connector
10、s will show constraints which may dictate cable size. 1.5 It is stressed that the current ratings given in this document relate solely to copper and copper alloy conductors as defined in EN 2083. The values are based upon historical evidence and are subject to the caveat given in 4.1. Accordingly th
11、e acceptance of data without verification in any particular case is a matter of discretion by both the aircraft design and certification authorities. 2 Normative references This European Standard incorporates by dated or undated reference provisions from other publications. These normative reference
12、s are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the late
13、st edition of the publication referred to applies. EN 2083 Copper and copper alloy conductors for electrical cables - Aerospace series 1) EN 2282 Aerospace Series - Characteristics of aircraft electrical supplies EN 3197 Aerospace Series - Installation of aircraft electrical and optical interconnect
14、ion systems 2) EN 3475-1 O0 Aerospace series - Cables, electrical, aircraft use - Test methods - Part 100: General 2) 3 Definitions For the purpose of this standard the definitions for electrical cables are to be found in EN 3475 and EN 31 97, with the following additions: 3.1 Tu: lhe unpowered cond
15、uctor temperature of a cable when in an operating environment. 3.2 any combination of electrical heating and ambient condition shall not be prejudicial to design life. Tr: The maximum rated temperature of a cable. Operation at or below this temperature by 3.3 stated without causing the specified val
16、ue of Tr to be exceeded. Duty cycle rating: The load current which may be passed through a cable for the duration 1 ) Published as AECMA Standard at the date of publication of this standard 2) Published as AECMA Prestandard at the date of publication of this standard 4 Rationale 2s 4.1 It is recogni
17、zed that the determination of precise current ratings for every cable construction and size can be shown to be a complex matter. Factors such as the thermal conductivity and thickness of insulation, test methods and the criteria employed will all have some effect. The intent of this standard is that
18、 the data presented should be sufficiently accurate to permit good engineering judgement to be exercised in the context of EN 3197. However, to enable verification of precise cable rating as noted in clause 1, a preferred method of measurement is given in annex B of this standard. 10 s I I min 4.2 C
19、able current ratings are provided primarily, to facilitate selection of the appropriate size to carry a given load. These ratings are also employed to assist, but not solely to determine, the setting of electrical protection levels. Historically some agencies have specified ?short term current ratin
20、gs? in cable specifications and such data represented current values and durations which were deemed to be just below the overload damage point. Implicitly these were fault conditions and were to be experienced on only rare occasions. In this standard this approach has been changed and the short ter
21、m ratings given herein are those which may be employed within a duty cycle, without prejudice to installed life. As noted in clause 1, cable rating has been determined as that current which will cause conductor temperature to rise by 40 OC and therefore this same value has been employed for short te
22、rm ratings. 4.3 Annex A of this specification provides supplementary notes to the foregoing clauses. 5 Tabulated data 5.1 Current ratings Table 1 : Current ratings for aircraft cable with copper conductors Copper alloy conductors * Take care of compatibility between load current of cables and that e
23、mployed for terminations and circuit breakers. NOTE 1: The Duty cycle ratings and the continuous ratings are current values which may be employed without detriment to normal life. They have been determined from cables rates at a Tr of 135 OC which have been heated by electrical loading from a Tu of
24、95 OC. These 40 OC temperature rise data are for single cables in free air but are generally applicable as noted in 1 and 4 and annex A of this specification. NOTE 2: Approximate current ratings which correspond to a conductor temperature rise of dT of other than 40 OC may be calculated by applying
25、the following formula: Tr - Tu ?2 = II j; Where 11 is the rated current to give 40 OC rise, see table 1 12 is the new rating Tr is the rated temperature Tu is the unpowered conductor temperature (local ambient) NOTE 3: Annex B of this specification describes a test method for determining current rat
26、ing of cables and formula for the interpretation of results. STD.AECMA PREN 2853-ENGL 1798 L0123LL 0034332 257 6 Page 5 prEN 2853: 1998 5.2 Table 2 lists the voltage drop obtained for a range of cable sizes when operated singly in free air such that a temperature rise of 40 OC is obtained from an un
27、powered temperature Tu of 95 OC (as in table 1). The voltage drop figures are for a 1 O rn length. Voltage drop at rated current Table 2: Voltage drop at rated current STD*AECMA PREN 2853-ENGL 3998 LO32311 0034333 393 D Page 6 prEN 2853: 1998 Annex A (informative) Supplementary notes A.l This standa
28、rd gives ratings for single cables in free air, which has been taken as the design case for electrical heating. Experimental and practical experience has shown that cables within a bundle benefit from proximity with cables which are lightly loaded intermittently. A.2 No account has been taken in thi
29、s standard or in EN 3197 of the effect of altitude on heat dissipation. The view has been taken that cables which are likely to be electrically loaded to a level approaching their rated temperature would be in the pressurized zones of an aircraft, which does not create any significant altitude de-ra
30、ting. Cables in unpressurized areas generally experience very low temperatures when at altitude which more than offset any altitude de-rating. A.3 It is accepted that the adoption of a 40 OC rise by electrical heating may appear to be slightly cautious. The establishment of this datum recognizes the
31、 disadvantage of having “hot cables“ in aircraft in respect of the effect upon the installation, risks to servicing personnel, the reduction of “resistance to failure“ and the adverse effect upon installed life. The limiting effect of voltage drop and the design limitation of associated wiring acces
32、sories has been recognized in this standard. A.4 The significance of the rating of cables to the setting of electrical protection levels has been noted. It is, however, now widely appreciated that such protection only has relevance to faults which represent a classic overload. Electrical faults taki
33、ng the form of high resistance joints or intermittent splashing and arcing between cables or to ground (earth) usually are not identifiable as overloads until the fault is considerably developed. Clearly the adoption of the lowest rating of protection trip level, short of unreliability, is desirable
34、. STD.AECMA PREN 2853-ENGL 1798 LO123LL OOL4311i 02T = Page 7 prEN 2853: 1998 Annex B (normative) Current rating tests B.l General As noted in this standard, it may be necessary to establish current rating figures for a cable construction or cable application which differs form the established norms
35、 or for certification purposes. This annex gives a method for establishing the continuous rating of cable and also short duration “duty cycle“ ratings. The shortest duration has been set at 2 s because, in practice, current ratings at shorter periods would be difficult to achieve due to factors such
36、 as cable voltage drop and power supply regulation. However, the test method may be employed for duration of less than 2 s if this is required for purposes such as protection co-ordination. B.2 Test Rationale B.2.1 The basic test method requires that a single cable be raised in temperature from a va
37、lue Tu by a set increment, typically 40 OC as in this specification, to a value Tr, the rated temperature of the cable. The current values given in table 1 herein were established for a cable with a Tr of 135 OC. Therefore Tu in this case is (Tr - 401 OC = 95 OC B.2.2 Determination of cable temperat
38、ure rise is achieved by monitoring the change in resistance of the test specimen, this being calculated from voltage and current measurements. For larger sizes of cable it may be practical to measure conductor temperature with a thermocouple, placed under the cable insulation tightly against the con
39、ductor. It shall not form a heat sink. B.3 Test equipment B.3.1 An enclosure should be constructed which provides a draught free environment in which test specimens may be mounted horizontally with appropriate instrumentation and electrical power connections. This enclosure should be mounted in an a
40、ir circulation oven of sufficient volume and thermal capacity to heat the air within the enclosure to desired test temperature Tu. It should be noted that the specimens produce heat when tested and ovens should be appropriately instrumented and controlled to maintain a stable Tu within the test encl
41、osure. B.3.2 value of current for the time periods specified. The power supply may be a.c. or d.c. and shall capable of supplying a controllable constant B.3.3 k 10 ms and voltage and current to f 1 %. Measuring and recording equipment shall be such that time is measurable to an accuracy of STD-AECM
42、A PREN 2853-ENGL 1798 = 1012311 0014315 Tbb Page 8 prEN 2853: 1998 B.4 Test procedure B.4.1 Apply the required value of test current Irn and monitor the voltage drop Vrn across the specimen whilst ensuring that the air within the test enclosure remains at temperature Tu. From the values of Vrn calcu
43、late the conductor temperature using the formula and where rn denotes test run number. TU - T2O RU - R2O NOTE: New test samples should be employed if cable samples are heated significantly beyond Tr. The determination of cable ratings requires that the results be presented as a series of curves, plo
44、tted on a log scale of temperature Trn against time for a series of test currents Irn. B. 5 Presentation of results B.5.1 The plots produced in 4.1 represent temperature rise against current for the test specimens and shall be corrected for the worst case of cables having a conductor resistance of R
45、 max., where R max. (at 20 OC) is specified in the applicable product standard. The true rated currents are the test R20 currents adjusted by application of the multiplying factor B.5.2 Using the plots of temperature against time, with numerical current values adjusted as above, draw a line parallel
46、 to the x-axis at the temperature Trn (e.g. Tu + 40 OC). Use the values of time where this line crosses the individual current plots to construct a further log/log curve giving the desired relationship between current (y-axis) and time (x-axis). Such data may be presented in tabular form for the specified times as in table 1 of this standard.
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