Standard No.:	GB/T 1094.3-2017
English Name:	Power transformers—Part 3:Insulation levels,dielectric tests and external clearances in air
Chinese Name:	电力变压器 第3部分：绝缘水平、绝缘试验和外绝缘空气间隙
Chinese Classification:	K41    Transformer
Professional Classification:	GB    National Standard
Issued by:	AQSIQ; SAC
Issued on:	2017-12-29
Implemented on:	2018-7-1
Status:	valid
Superseding:	GB/T 1094.3-2003 GB 1094.3-2003 Power transformers？Part 3:Insulation levels,dielectric tests and external clearances in air
Language:	English
File Format:	PDF
Word Count:	23000 words
Price(USD):	570.0
Delivery:	via email in 1 business day

GB/T 1094 consists of the following parts under the general title of Power Transformers: —Part 1: General; —Part 2: Temperature Rise for Liquid-immersed Transformers; —Part 3: Insulation Levels, Dielectric Tests and External Clearances in Air; —Part 4: Guide to the Lightning Impulse and Switching Impulse Testing—Power Transformers and Reactors; —Part 5: Ability to Withstand Short Circuit; —Part 6: Reactors; —Part 7: Loading Guide for Oil-immersed Power Transformers; —Part 10: Determination of Sound Levels; —Part 10.1: Determination of Sound Levels—Application Guide; —Part 11: Dry-type Transformers; —Part 12: Loading Guide for Dry-type Power Transformers; —Part 14: Design and Application of Liquid-immersed Transformers Using High-temperature Insulation Material; —Part 16: Transformers for Wind Turbine Applications; —Part 18: Measurement of Frequency Response. This part is Part 3 of GB/T 1094. This part is developed in accordance with the rules given in GB/T 1.1-2009. This part replaces Power Transformers—Part 3: Insulation Levels, Dielectric Tests and External Clearances in Air (GB/T 1094.3-2003). The main technical changes from GB/T 1094.3-2003 are as follows: —The normative references are modified (see Clause 2; Clause 2 of edition 2003); —The rated voltage of winding is defined (see Clause 3; Clause 3 of edition 2003); —The marking of insulation level is modified (see Clause 5; Clause 5 of edition 2003); —The sequence and contents of insulation tests are modified (see Clause 7; Clause 7 of edition 2003); —Switching impulse test is required for Um=126 kV transformers (see Clause 7; Clause 7 of edition 2003); —Induced voltage (withstand) tests are now based on Ur, and the pre-applied voltage, test voltage and test duration, and limits for measurement of partial discharge have been modified (see Clause 11; Clause 12 of edition 2003); —The insulation levels of winding and neutral point, and external clearances in air for transformers with the nominal value of 750 kV and1000 kV, and related test requirements are added (see Clause 7 and Clause 16; Clause 7 and Clause 16 of edition 2003); —The line terminal AC withstand test (LTAC) of winding is regarded as a separate test subject (see Clause 7 and Clause 12; Clause 7 of edition 2003); —The requirements for lightning impulse tests and switching impulse tests are modified (see Clause 13 and Clause 14; Clause 13, Clause 14 and Clause 15 of edition 2003); —The external clearances in air are modified (see Clause 16; Clause 16 of edition 2003); —The annexes have been modified as follows: Appendix “ACSD Test Voltage” has been removed; Appendixes “Information on Transformer Insulation and Dielectric Tests to be Supplied with an Enquiry and with an Order” and “Basis for Dielectric Tests, Insulation Levels and Clearances” have been introduced (see Appendix B and Appendix D; Appendix D of edition 2003). This part is prepared by redrafting with modification made with respect to IEC 60076-3:2013 Power transformers—Part 3: Insulation levels, dielectric tests and external clearances in air. This part includes technical changes with respect to IEC 60076-3:2013. The Clause and subclause concerned are identified by a vertical single line (|) located in the blank on its external margin of the page. These technical changes and reasons are listed in Appendix A. The following editorial changes are made in this part: —The voltages exampled in this part have been adjusted according to the actual conditions in China; —The “Note” in 3.6 of IEC 60076-3:2013 has been removed; —The “Note” under “Chopped wave lightning impulse test for the line terminals (LIC)” in 7.1 of IEC 60076-3:2013 has been removed; —It is indicated that the phase-to-phase induced voltage during the test may exceed the specified insulation level in 7.3.2.1; —“Chopped wave lightning impulse test (LIC)” and “Lightning impulse test on the neutral terminal (LIN)” in 7.3.2.2 of IEC 60076-3:2013 have been adjusted to type tests and are incorporated into 7.3.2.2 of this part, and the other three tests in 7.3.2.2 of IEC 60076-3:2013 are kept as special tests and incorporated into 7.3.2.3 of this part; —“Chopped wave lightning impulse test (LIC)” in 7.3.3.1 of IEC 60076-3:2013 and “Lightning impulse test on the neutral terminal (LIN)” in 7.3.3.2 of IEC 60076-3:2013 have been adjusted to type tests and are incorporated into 7.3.3.2 of this part; the other three tests in 7.3.3.1 of IEC 60076-3:2013 are kept as routine tests and incorporated into 7.3.3.1 of this part; the other two tests in 7.3.3.2 of IEC 60076-3:2013 are kept as special tests and incorporated into 7.3.3.3 of this part; —Table 1 of IEC 60076-3:2013 has been adjusted to E.1 of this part; —Table 2 and Table 3 of IEC 60076-3:2013 have been adjusted to E.2 of this part; —7.4 of IEC 60076-3:2013 have been adjusted to E.3 of this part; —A note about the full-wave lightning impulse test voltage with a neutral connection not brought out and its application way for three-phase transformers with uniform insulation is added to 13.4.1; —The note in Clause 9 and Note 2 in 16.1 of IEC 60076-3:2013 have been removed; —The contents on the determination principle and value for minimum external clearances in air given in Clause 16 of IEC 60076-3:201 haven been adjusted to E.4 of this part; —The sequence of appendixes has been modified as follows: Appendix A is added to this part, and Annex A of IEC 60076-3:2013 has been changed to Appendix F of this part, Annex B of IEC 60076-3:2013 to Appendix C of this part, Annex C of IEC 60076-3:2013 to Appendix D of this part, Annex D of IEC 60076-3:2013 to E.5 of this part, Annex E of IEC 60076-3:2013 to Appendix B of this part. This part was proposed by the China Electrical Equipment Industrial Association. This part is under the jurisdiction of the National Technical Committee on Transformers of Standardization Administration of China (SAC/TC 44). Drafting organizations of this part: Shenyang Transformer Institute Co., Ltd., Baoding Tianwei Baobian Electric Co., Ltd., China Electric Power Research Institute, China National Transformer Quality Supervision Testing Center (CTQC), TBEA Shenyang Transformer Co., Ltd., Xi'an XD Transformer Co., Ltd., Chint Electric Inc., TBEA Hengyang Transformer Co., Ltd., Changzhou XD Transformer Co., Ltd., State Grid Jilinsheng Electric Power Supply Company/Electric Power Research Institute, Sunten Electric Equipment Co., Ltd., Pearl Electric Co., Ltd., Newonder Special Electric Co., Ltd., Guangdong Power Grid Corporation/Electric Power Research Institute, State Grid Shaanxi Electric Power Company/Electric Power Research Institute, Guangdong Orion Transformers & Electrics Co., Ltd., Guangdong Champon Electrics Co., Ltd., Guangzhou Zhongche Junfa Electrics Co., Ltd., Baoding Baoling Transformers Co., Ltd., Baoding Tianwei Group Tebian Electric Co., Ltd., China Nuclear Power Engineering Co., Ltd. Chief drafters of this part: Zhang Zhongguo, Zhang Xile, Zhang Xianzhong, Li Hongxiu, Li Shicheng, Ren Xiaohong, Li Yunlong, Wang Jian, Shuai Yuanming, Li Jinbiao, Sun Shubo, Nie Sanyuan, Guo Mansheng, Ao Ming, Liu Yan, Cai Dingguo, Zong Baofeng, Lin Chunyao Liu Xiaowei, Wang Wenguang, Zhou Yuemei, Fan Jianping, Wang Weizheng, Zhao Feng, Zeng Lingjun. The previous editions replaced by this part are as follows: —GB 1094.3-1971, GB 1094.3-1979, GB 1094.3-1985 and GB/T 1094.3-2003. Introduction This part specifies the insulation requirements and the corresponding insulation tests with reference to specific windings and their terminals. It also recommends external clearances in air for power transformers (Clause 16). The insulation levels and dielectric tests which are specified in this part apply to the internal insulation only. Whilst it is reasonable that the rated withstand voltage values which are specified for the internal insulation of the transformer should also be taken as a reference for its external insulation, this may not be true in all cases. A failure of the non-self-restoring internal insulation is catastrophic and normally leads to the transformer being out of service for a long period, while an external flashover may involve only a short interruption of service without causing lasting damage. Therefore, it may be that, for increased safety, higher test voltages are specified by the purchaser for the internal insulation of the transformer than for the external insulation of other components in the system. When such a distinction is made, the external clearances should be adjusted to fully cover the internal insulation test requirements. Appendix B sets out some of the principles used in assigning the dielectric tests, test levels and external clearances in air to the transformer according to the highest voltage for equipment Um. Power Transformers—Part 3: Insulation Levels, Dielectric Tests and External Clearances in Air 电力变压器 第3部分：绝缘水平、绝缘试验和外绝缘空气间隙 1 Scope This part of GB/T 1094 specifies the applicable dielectric tests and minimum dielectric test levels for power transformers. Recommended minimum external clearances in air between live parts and between live parts and earth are given for use when these clearances are not specified by the purchaser. This part applies to power transformers as defined by and in the scope of GB/T 1094.1. For categories of power transformers and reactors which have their own standards, this part is applicable only to the extent in which it is specifically called up by cross reference in the other standards. 2 Normative References The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. GB/T 311.1 Insulation Coordination—Part 1: Definitions, Principles and Rules (GB/T 311.1-2012, IEC 60071-1:2006, MOD) GB/T 1094.1 Power Transformers—Part 1: General (GB/T 1094.1-2013, IEC 60076-1:2011, MOD) GB/T 2900.95 Electrotechnical Terminology—Transformers, Voltage Regulators and Reactors (GB/T 2900.95-2015, IEC 60050-421:1990, NEQ) GB/T 4109 Insulated Bushings for Alternating Voltages above 1 000V (GB/T 4109—2008, IEC 60137 Ed.6.0, MOD) GB/T 7354 Partial Discharge Measurements(GB/T 7354—2003, IEC 60270:2000, IDT) GB/T 16927.1-2011 High-voltage Test Techniques—Part 1: General Definitions and Test Requirements (IEC 60060-1:2010, MOD) GB/T 16927.2 High-voltage Test Techniques—Part 2: Measuring Systems (GB/T 16927.2-2013, IEC 60060-2:2010, MOD) 3 Terms and Definitions For the purposes of this document, the terms and definitions given in GB/T 1094.1, GB/T 2900.95 and the following apply. 3.1 highest voltage for equipment applicable to a transformer winding Um highest r.m.s. phase-to-phase voltage in a three-phase system for which a transformer winding is designed in respect of its insulation 3.2 rated voltage of a winding Ur voltage assigned to be applied, or developed at no-load, between the terminals of an untapped winding, or a tapped winding connected on the principal tapping, for a three-phase winding it is the voltage between line terminals Note 1: The rated voltages of all windings appear simultaneously at no-load when the voltage applied to one of them has its rated value. Note 2: For single-phase transformers intended to be connected in star to form a three-phase bank or to be connected between the line and the neutral of a three phase system, the rated voltage is indicated as the phase-to-phase voltage, divided by , for example 500/ kV. Note 3: For single phase transformers intended to be connected between phases of a network, the rated voltage is indicated as the phase-to-phase voltage. Note 4: For the series winding of a three-phase series transformer, which is designed as an open winding, the rated voltage is indicated as if the windings were connected in star. 3.3 rated insulation level set of rated withstand voltages which characterise the dielectric strength of the insulation 3.4 rated withstand voltage value of the assigned test voltage applied in one of the standard dielectric tests that proves that the insulation complies with the assigned test voltage 3.5 uniform insulation of a transformer winding insulation of a transformer winding that has all its ends connected to terminals with the same rated insulation level 3.6 non-uniform insulation of a transformer winding insulation of a transformer winding when it has a neutral terminal end for direct or indirect connection to earth, and is designed with a lower insulation level than that assigned to the line terminal 4 General The insulation requirements for power transformers and the corresponding insulation tests are given with reference to specific windings and their terminals. For liquid-immersed or gas-filled transformers, the requirements apply to the internal insulation only. Any additional requirements or tests regarding external insulation which are deemed necessary shall be subject to agreement between manufacturer and purchaser. If the purchaser does not specify any particular requirements for external clearances in air of transformer then the provisions of Clause 16 shall apply. If the purchaser intends to make the connections to the transformer in a way which may reduce the clearances provided by the transformer alone, this shall be indicated in the enquiry. Bushings shall be subject to separate type and routine tests according to GB/T 4109 (including appropriate bushing test levels for the particular transformer test level), which verify their phase-to-earth insulation, external as well as internal. When a transformer is specified for operation at an altitude higher than 1000 m, clearances shall be designed accordingly. It may then be necessary to select bushings designed for higher insulation levels than otherwise required for operation at lower altitudes, see Clause 16 of this part and GB/T 4109. The manufacturer may shield the bushing terminals if necessary during the dielectric tests but any shielding of the earthed parts closest to the terminals shall form part of the transformer structure in-service except for shielding required only during partial discharge measurement. Bushings and tap-changers are specified, designed and tested in accordance with the relevant standards. The dielectric tests on the complete transformer constitute a check on the correct application and installation of these components. In the case of tap-changers which according to GB/T 10230.1 are not subjected to dielectric routine tests at the tap-changer manufacturer’s works then the tests performed according to this part also serve as the only dielectric tests routinely performed on this component. The temperature of the insulation system shall not be less than 5 °C during the tests, but temperatures higher than those given in GB/T 1094.1 may be used. The transformer shall be completely assembled as in service in respect of all elements that might influence the dielectric strength of the transformer. It is normally assumed that the insulating liquid or gas is not circulated during the tests and coolers do not need to be assembled. Any equipment designed to collect or detect free gas produced by faults in the insulation shall be installed and monitored during the tests. If free gas is detected during any test, the nature and cause of the gas shall be investigated and any further actions shall be agreed between purchaser and manufacturer. Note 1: External overvoltage protection devices such as surge arresters do not need to be assembled and bushing spark gaps can be removed or their spacing increased to avoid operation during the tests. Note 2: It is common practice for larger transformers for oil samples to be taken for dissolved gas analysis before and after dielectric tests. Liquid immersed transformers shall be tested with the same type (mineral, ester, silicone, etc.) and specification (with respect to the properties that might affect the test performance) of liquid that it will contain in service. Note 3: Some purchasers can require that the insulating liquid be circulated on OD cooled transformers during an IVPD test to detect the possibility of static electrification, but this is a very specific requirement and is not covered by this part. Transformers for cable box connection or direct connection to metal-enclosed SF6 installations may be designed so that temporary connections can be made for dielectric tests, using temporary bushings, if necessary. By agreement between manufacturer and purchaser, the service liquid to SF6 bushings may be replaced by appropriate liquid to air bushings for test. In this case the design of the end of the bushing inside the transformer including the positions of the live parts and the clearances of the substitute bushings inside the transformer shall be the same (within the normal variation of dimensions of the bushing associated with manufacturing tolerances) as those of the in-service bushings. When the manufacturer intends to use non-linear elements (for example surge arresters or spark gaps), built into the transformer or tap-changer or externally fitted, for the limitation of overvoltage transients, this shall be brought to the purchaser's attention by the manufacturer at the tender and order stage and shall be indicated on the transformer rating plate circuit diagram. If any terminals of the transformer are to be left open when the transformer is energised in service then consideration needs to be given to the possibility of a transferred voltage occurring on the open terminals, see Appendix C. During the lightning impulse tests all non-tested line and neutral terminals are normally connected to earth, see Clause 13. 5 Highest Voltage for Equipment and Rated Insulation Level A value of highest voltage for equipment Um is assigned to both the line and neutral end of each winding, see GB/T 1094.1. The rules for dielectric testing depend on the value of Um. When rules about tests for different windings in a transformer are in conflict, the rule for the winding with the highest Um value shall apply for the whole transformer. See Table 1 for the test requirements for different Um of windings. Series windings (for example found in autotransformers and phase shifting transformers) where the rated voltage of the winding is less than the rated voltage of the system, shall be assigned a value of Um corresponding to the rated voltage of the highest voltage system to which the winding is connected. Standardized values of Um are listed in Table 2. Unless otherwise specified, the value to be used for a transformer winding is the one equal to, or nearest above, the value of the rated voltage of the winding. Note 1: Single-phase transformers intended for connection in star to form a three-phase bank are designated by phase-to-phase rated voltage divided by , for example 500/ kV. The phase-to-phase value determines the choice of Um in this case, consequently, Um = 550 kV (see also GB/T 1094.1). The same principle applies to single-phase transformers intended for use in a single phase system in that the maximum phase to earth voltage is multiplied by to obtain the equivalent Um in order to define the test voltages. Note 2: For transformer windings intended to be used for example in railway supply applications where two opposite phase to earth voltages are supplied, Um relates to the phase to phase voltage unless otherwise specified. Note 3: It might happen that certain tapping voltages are chosen slightly higher than a standardized value of Um, but the system to which the winding will be connected has a system highest voltage which stays within the standard value. The insulation requirements are to be coordinated with actual conditions, and therefore this standard value should be accepted as Um for the transformer, and not the nearest higher value. Note 4: In certain applications with very special conditions the specification of other combinations of withstand voltages may be justified. In such cases, general guidance should be obtained from GB/T 311.1. Note 5: In certain applications, delta-connected windings are earthed through one of the external terminals. In those applications, a higher withstand voltage with respect to the highest voltage for equipment Um may be required for this winding and should need to be agreed between manufacturer and purchaser. The highest voltage for equipment Um and the rated insulation level (the set of assigned rated withstand voltages) determine the dielectric characteristics of a transformer. These characteristics are verified by a set of dielectric tests, see Clause 7. The value of highest voltage for equipment and the rated insulation level which are assigned to each winding of a transformer are part of the information to be supplied with an enquiry and with an order. If there is a winding with non-uniform insulation, the assigned highest voltage for equipment and the rated insulation level of the neutral terminal shall be as specified in Table 3. The rated insulation level of winding shall be characterised as follows: Um / SI / LI / LIC / AC with the associated values (see examples below) for the line terminals of each winding. If the winding does not have an assigned SI or LIC withstand level then the abbreviation is omitted from the rating so for terminals without an assigned switching impulse withstand level or chopped wave lightning impulse withstand level and for neutral terminals the abbreviation would be: Um / LI / AC together with the associated values of the winding terminal If the neutral terminal of a winding has the same rated insulation level as the line terminal then the rated insulation level of the neutral does not need to be shown separately. The abbreviations here and in the examples below have the following meaning: SI—the rated switching impulse withstand voltage level for the line terminals of the winding with the highest Um; LI—the rated lightning impulse withstand voltage level for the terminal of each individual winding; LIC—the rated lightning impulse withstand voltage level for the line terminals of each individual winding if a chopped wave lightning impulse test was performed; AC—the highest rated AC withstand voltage level to earth designed for the terminals of each winding.

Foreword i Introduction iv 1 Scope 2 Normative References 3 Terms and Definitions 4 General 5 Highest Voltage for Equipment and Rated Insulation Level 6 Transformers with Re-connectable Windings 7 Dielectric Tests 8 Dielectric Tests on Transformers that have been in Service 9 Insulation of Auxiliary Wiring (AuxW) 10 Applied Voltage Test (AV) 11 Induced Voltage Tests (IVW and IVPD) 12 Line Terminal AC Withstand Test (LTAC) 13 Lightning Impulse Tests (LI, LIC, LIN, LIMT) 14 Switching Impulse Test (SI) 15 Action Following Test Failure 16 External Clearances in Air Appendix A (Informative) Technical Changes between This Part and IEC 60076-3:2013 and Their Reasons Appendix B (Informative) Basis for Dielectric Tests, Insulation Levels and Clearances Appendix C (Informative) Overvoltage Transferred from the High-voltage Winding to a Low-voltage Winding Appendix D (Informative) Information on Transformer Insulation and Dielectric Tests to be Supplied with an Enquiry and with an Order Appendix E (Informative) Requirements and Tests for Different Categories of Windings, Test Voltage Levels, Assigning Um and Test Voltages to the Neutral Terminal of a Winding, Minimum Clearances in Air, and Neutral Insulation Voltage Level Calculation in IEC 60076-3: Appendix F (Informative) Application Guide for Partial Discharge Measurements on Transformers Bibliography