1、 AMERICAN NATIONAL STANDARD ANSI/ISA-61241-18 (12.10.07)-2006 (R2011) Electrical Apparatus for Use in Zone 20, Zone 21 and Zone 22 Hazardous (Classified) Locations Protection by Encapsulation “mD” Approved 29 March 2011 ANSI/ISA-61241-18 (12.10.07)-2006 (R2011), Electrical Apparatus for Use in Zone
2、20, Zone 21 and Zone 22 Hazardous (Classified) Locations - Protection by Encapsulation “mD” ISBN: 978-1-936007-91-2 Copyright 2011 by IEC and ISA. All rights reserved. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted
3、, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), without the prior written permission of the Publisher. ISA 67 Alexander Drive P. O. Box 12277 Research Triangle Park, North Carolina 27709 USA- 3 - ANSI/ISA-61241-18 (12.10.07)-2006 (R2011) Preface This pr
4、eface, as well as all footnotes and annexes, is included for information purposes and is not part of ANSI/ISA-61241-18 (12.10.07)-2006 (R2011). This document has been prepared as part of the service of ISA toward a goal of uniformity in the field of instrumentation. To be of real value, this documen
5、t should not be static but should be subject to periodic review. Toward this end, the Society welcomes all comments and criticisms and asks that they be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (9
6、19) 549-8411; Fax (919) 549-8288; E-mail: standardsisa.org. The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Units (SI) in particular, in the preparation of instrumentation standards. The D
7、epartment is further aware of the benefits to USA users of ISA standards of incorporating suitable references to the SI (and the metric system) in their business and professional dealings with other countries. Toward this end, this Department will endeavor to introduce SI-acceptable metric units in
8、all new and revised standards, recommended practices, and technical reports to the greatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System, published by the American Society for Testing b) any specified abnormal conditionsunder fault conditions
9、as specified in 7.2; c) in defined failure conditions. For level of protection “maD” the working voltage at any point in the encapsulation circuit shall not exceed 1 kV. For level of protection “maD“, components without additional protection shall only be used if they cannot damage the encapsulation
10、compound mechanically or thermally in the case of any fault. Alternatively, where a fault of an internal component may lead to failure of the encapsulation system due to increasing temperature, the requirements of 6.2 shall apply. NOTE Certain components whose application is allowed according to thi
11、s standard for level of protection “mbD” can possibly make the protective measure encapsulation ineffective by mechanical or thermal damage as a consequence of internal reactions. This risk should be excluded for level of protection “maD” apparatus. 4.4 Level of protection “mbD“ Level of protection
12、“mbD” shall not be capable of causing ignition in each of the following circumstances: a) in normal operation and installation conditions; b) in defined failure conditionsunder fault conditions as specified in 7.2. 4.5 Supply specifications The limiting values of the supply (rated voltage and the pr
13、ospective short circuit current) shall be stated to ensure that under the relevant level of protection, “maD” or “mbD”, the limiting temperature (see 6.3) is not exceeded. Any protective device used shall comply with the requirements of 7.7. 5 Requirements for compounds 5.1 General The documentation
14、 in accordance with 23.2 of IECANSI/ISA-61241-0 shall specify the compound(s) used and the processing method(s). As a minimum, those properties of the compound(s) on which the encapsulation “mD“ depends shall be provided. Due consideration shall be taken in the selection of encapsulating materialsco
15、mpounds to allow for the expansion of components during operation and in the event of allowable faults. ANSI/ISA-61241-18 (12.10.07)-2006 (R2011) - 18 - 5.2 Specification The manufacturer shall attest on his own responsibility that the material complies with the compound specification. The material
16、specification shall include: a) the name and address of the manufacturer of the compound; b) the exact and complete reference of the material, and, if relevant, percentage of fillers and any other additives, the mixture ratios and the type designation; c) if applicable, any treatment of the surface
17、of the compound(s), for example, varnishing; d) if applicable, to obtain correct adhesion of the compound to a component, any requirement for pre-treating of the component, for example, cleaning, etching; e) if appropriate, the result of the water absorption test in accordance with 8.1. Where this t
18、est has not been performed, the apparatus shall be marked “X“ in accordance with item l) of 29.2 of IECANSI/ISA-61241-0; f) the dielectric strength in accordance with IEC 60243-1 at the maximum temperature of the apparatus determined according to 8.2.2; g) temperature range of the compound(s) (upper
19、 and lower continuous operating temperature); h) in the case of encapsulation “mD“ apparatus where the compound is part of the outside enclosure, the temperature index TI value as defined in 6.1.4 of IECANSI/ISA-61241-0. As an alternative to the TI, the Relative Thermal Index (RTI-mechanical impact)
20、 may be determined in accordance with ANSI/UL 746B; i) the colour of the compound used for the test samples where the compound specification will be influenced by changing the colour. 6 Temperatures 6.1 General The maximum surface temperature and the maximum value of the continuous operating tempera
21、ture of the compound shall not be exceeded during normal operation. The encapsulation “mD“ apparatus shall be protected in such a way that the encapsulation “mD“ is not adversely affected under specified fault conditions. 6.2 Temperature limitation When a protective device is required to limit tempe
22、ratures for safety reasons, it shall be a non-resetting internal or external, electrical or thermal device. One device is required for level of protection “mbD” and two devices for level of protection “maD”. The thermal coupling of the device to the component being monitored shall be sufficient. For
23、 functional reasons the “mD” apparatus may also contain an additional resettable protective device. If the non-resetting protective device complies with IEC 60127ANSI/UL 248-1 or IEC 60691, only one device is necessary for both levels of protection. Where the apparatus may be subject to fault, see 7
24、.2.1, or where there is the possibility of an increased temperature, for example by an unfavourable input voltage in accordance with 7.2.1 or an unfavourable load, these shall be taken into account in determining the limiting temperature. - 19 - ANSI/ISA-61241-18 (12.10.07)-2006 (R2011) 6.3 Determin
25、ation of the limiting temperature values 6.3.1 Maximum surface temperature The maximum surface temperature shall be determined using the test method given in 8.2.2 in accordance with the supply conditions specified in 4.5. 6.3.2 Temperature of the components in the compound The hottest component(s)
26、shall be determined. The maximum temperature in the compound, adjacent to the hottest component(s), shall be determined using the test method given in 8.2.2 for normal operation. NOTE The determination of the hottest component may be done by calculation or manufacturers specification or by a practic
27、al test prior to encapsulating the components. 7 Constructional requirements 7.1 General Where the encapsulationcompound forms part of the external enclosure it shall comply with the requirements for non-metallic enclosures and parts of non-metallic enclosures of ANSI/ISA-61241-0. If additional prot
28、ective measures are required by the user in order to satisfy the requirements of this standard, for example, additional mechanical protection, to indicate this special condition of use, the apparatus shall be marked “X” in accordance with item l) of 29.2 of IECANSI/ISA-61241-0. Appropriate action sh
29、all be taken to accommodate the expansion of components during normal operation and in the event of faults according to 7.2. In 7.2 to 7.7 the requirements differ according to whether the compound adheres to the enclosure. Where adhesion is specified the aim is to prevent the ingress of combustible
30、dust and moisture at the boundary surfaces (for example, enclosure compound, compound parts that are not completely embedded in the compound, such as printed wiring boards, connections terminals, etc.). If additional treatment for the boundary surfaces is required in order to ensure adhesion, this s
31、hall be included in the manufacturers documentation. Where adhesion is specified, it shall be maintained after completion of all the prescribed tests. NOTE The choice of the compound(s) to be used for a specific application is dependent on the task each compound has to perform. In general, testing a
32、 compound once is not sufficient for universal use for encapsulation “mD”. 7.2 Determination of possible faults 7.2.1 Fault examination The encapsulation protection shall be maintained even in the case of an unfavourable input condition (but between 90 % and 110 % of the rated parameter) and unfavou
33、rable output load and of any internal electrical fault (two faults for level of protection “maD” and one fault for level of protection “mbD”), for example, in the event of a short circuit in any component; the failure of any component; ANSI/ISA-61241-18 (12.10.07)-2006 (R2011) - 20 - a fault in the
34、printed circuitry. Infallible components and infallible separation distances shall not be subject to fault. If a fault leads to one or more subsequent faults, for example, due to the overload of a component, the primary and subsequent fault(s) are considered to be a single fault. 7.2.2 Infallible co
35、mponents The following components shall be considered to be infallible if they are encapsulated according to the requirements of this standard, are suitable for the temperature range at the site of installation and if they are not loaded with more than 2/3 of their rated voltage, rated current and r
36、ated power specified by the manufacturer of the respective component: resistors, if they comply with 8.4 of IECANSI/ISA-60079-11, single-layer, spirally wound coils, plastic foil capacitors, paper capacitors, ceramic capacitors, semiconductors, if they are used in accordance with 8.6 of IECANSI/ISA-
37、60079-11. Where semiconductor devices are used to limit current, a single device is adequate for level of protection “mbD“ but two devices shall be used for level of protection “maD“. NOTE In contrast to the requirements for intrinsically safe apparatus with level of protection “iaD” according to IE
38、CANSI/ISA 61241-11, it is not necessary to prohibit the use of active semiconductor regulating circuits, as the effect of a short term transient disturbance is significantly less for encapsulated apparatus. The following components for the segregation of different circuits shall be considered infall
39、ible. a) Optocouplers and relays, if the rated insulation voltage conforms to (2U + 1 000 V) or 1 500 V a.c. whichever is greater (U is the sum of the rated r.m.s. voltages of both circuits). b) Transformers, complying with IEC 61558-2-6 or IEC 61241-11ANSI/ISA-61241-11. c) Coils, transformers and m
40、otor windings that comply with IECANSI/ISA-60079-7, including those that have wire diameters of less than 0,25 mm when they are also protected against inadmissible internal temperatures, are considered infallible. 7.2.3 Infallible separation distances It is not necessary to consider the possibility
41、of a fault occurring as described in 7.2.1 in respect of voltage breakdown, if the distances between bare current-carrying parts of the same circuit, or of a circuit and earthed metal parts, or of two separate circuits (sum of voltages shall be taken as the voltage for Table 1; where one of the work
42、ing voltages is less than 20 % of the other, it shall be ignored), comply with the requirements of 7.2.3.1 and if applicable 7.2.3.2. - 21 - ANSI/ISA-61241-18 (12.10.07)-2006 (R2011) 7.2.3.1 Distances through the compound Distances through compound shall be considered to be infallible if they comply
43、 with the values in Table 1, provided that they were fixed mechanically before encapsulation. Table 1 Distances through the compound Voltage (see Note) U r.m.s. or d.c., V Minimum distance mm 63 0,5 400 1 500 1,5 630 2 1 000 2,5 1 600 4 3 200 7 6 300 12 10 000 20 NOTE Voltages shown are derived from
44、 IEC 60664-1. For all voltages, the actual voltage may exceed the value given in the table by up to 10 %. This is based on the rationalisation of supply voltages given in Table 3b of IEC 60664-1. 7.2.3.2 Distances through solid insulation Distances through solid insulation shall be considered to be
45、infallible if the minimum thickness of solid insulation is 0,1 mm and meets the dielectric strength test of 8.2.4. 7.2.4 Thickness of the compound If the surface of the compound is totally or partly surrounded by an enclosure and the enclosure is part of the protection, the enclosure or parts of the
46、 enclosure shall comply with the enclosure requirements of IECANSI/ISA-61241-01. The minimum thickness of the compound with or without a surrounding enclosure shall comply with the requirements of 7.2.5 to 7.2.7 as applicable. In all cases the encapsulantcompound is additionally subjected to the die
47、lectric strength test of 8.2.4. 7.2.5 Encapsulation “mD“ apparatus with free surface The thickness of the compound between the free surface of the compound and the components or conductors in the encapsulationcompound, as shown in Figure 1, shall comply with Table 2. ANSI/ISA-61241-18 (12.10.07)-200
48、6 (R2011) - 22 - Table 2 Thickness of compound between the free surface of the compound and components or conductors Level of protection “maD“ Level of protection “mbD“ Free surface 2 cm2b distance according to Table 1, but not less than 3 mm c distance according to Table 1 c distance according to T
49、able 1 d 3 mm d 1 mm where b is the distance between the component and the free surface; c is the distance between the component and non current-carrying parts inside the encapsulationcompound; d is the distance between a non current-carrying part and the free surface. 1 b b b b d c IEC 1061/04 Key 1 Non current-carrying part Figure 1 Distances between free surface of compound and components or conductors 7.2.6 Encapsulation “mD“ apparatus with metal enclosure The thickness of the compound between the wall or the free surface of t
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