DL/T Translated English of Chinese Standard: DL/T (DLT ; DLT ) Translated by:

Transcription

1 Translated English of Chinese Standard: DL/T (DLT ; DLT ) Translated by: Wayne Zheng et al. ICS F 24 File No.: PROFESSIONAL STANDARD OF THE PEOPLE S REPUBLIC OF CHINA DL/T Frequency Response Analysis on Winding Deformation of Power Transformers 电力变压器绕组变形的频率响应分析法 Issued on: December 14, 2004 Implemented on: June 1, 2005 Issued by: National Development and Reform Commission of the People's Republic of China 1

2 Table of Contents FOREWORD SCOPE NORMATIVE REFERENCES TERMS AND DEFINITIONS TESTING THEORY REQUIREMENTS OF TESTING INSTRUMENT TEST METHOD ANALYTICAL JUDGMENT OF WINDING DEFORMATION... 9 ANNEX A (NORMATIVE) AUXILIARY JUDGMENT ON DEFORMATION OF TRANSFORMER WINDING THROUGH THE CORRELATION FACTOR R ANNEX B (INFORMATIVE) TYPICAL AMPLITUDE FREQUENCY RESPONSE CHARACTERISTICS CURVE OF DEFORMATION OF TRANSFORMER WINDING REFERENCES AND ORIGINAL CHINESE DOCUMENTS

3 Foreword In accordance with the requirements of the document - "Notice on confirming the formulation and revision planning of power industry standards in 1999" (Guo Jing Mao Dian Li [1999] No.40) issued by the Former State Economic and Trade Commission, this Standard is formulated, with the objective of regulating and guiding field application of the frequency response analysis on winding deformation of power transformer. Frequency response analysis, used to test the deformation of transformer winding, has advantages in high testing sensitivity and convenient in field service; and does not require transformer hood suspending. It has been widely used in the power industry. Annex A is normative and Annex B is informative in this Standard. This Standard is proposed by the China Electricity Council (CEC). The technical committee for standardization of high voltage test technology in power sector governs this Standard and is in charge of the explanation. Drafting organizations: China Electric Power Research Institute (CEPRI), Guangdong Power Experimental Research Institute, Fujian Power Test & Research Institute, Anhui Electric Power Research Institute, North China Electric Power Research Institute, Wuhan High Voltage Research Institute Chief drafting staffs: Wang Sheng, Gao Keli, Lin Chunyao, Ouyang Xudong, Zhang Konglin, Yu Guogang, He Hongming, Ma Jixian, Mei Gang 2

4 Frequency Response Analysis on Winding Deformation of Power Transformers 1 Scope This Standard specifies the basic requirements in the frequency response analysis on deformation of transformer winding. This Standard is applicable to power transformers of 6kV or higher voltage class, and other transformers for special purpose. 2 Normative References The following standards contain provisions which, through reference in this text, constitute provisions of this Standard. For dated reference, subsequent modifications (excluding corrected contents) or revisions do not apply to this Standard. However, all parties reach to agreement according to this Standard are encouraged to study whether the latest edition of these documents is applicable. For undated references, the latest edition of the normative document referred to applies to this Standard. GB Power transformers - Part 1: General (eqv IEC : 1993) GB Power transformers - Part 5: Ability to withstand short circuit (neq IEC : 1976) DL/T 596 Preventive test code for electric power equipment 3 Terms and definitions For the purpose of this Standard, the following terms and definitions shall apply. 3.1 Winding deformation It is referred to axial or radial dimensional variation of power transformer winding caused 3

5 under mechanical force or electro-dynamical action, and usually appears as partial deformation, hunching or displacement of winding. When a transformer is suffered from the short-circuit current rush or crash in transportation, winding deformation may happen. This will directly affect the safe operation of transformer. 3.2 Dual-port network It is referred to network having a pair of input ports and a pair of output ports. The network - consisted of linear resistance, inductance (including mutual inductance) and capacitive components, and without independent power supply inside - is called as active linear dual-port network. When the frequency is higher, the transformer winding may be regarded as active linear dual-port network. 3.3 Transfer function It is referred to the output-input ratio of passive dual-port network, expressed by Laplace transformation. The pole and zero distribution of the transfer function closely relate to built-in components parameters, connecting mode and port-connecting-impedance of dual-port network. 3.4 Frequency response It is referred to the relation between transfer function H(jω) and angular frequency ω of the network, under the sine stable state. Usually, the relation of H(jω) amplitude value changing with ω is called as amplitude frequency response, and the relation of H(jω) phase changing with ω is called as phase frequency response. 3.5 Sweeping frequency 4

6 6 Test Method 6.1 The testing for deformation of transformer winding shall be conducted before all direct-current test items or after full electric discharge of the winding. The windings of a transformer shall be tested one by one according to the wiring requirement and connection mode, and the amplitude frequency response characteristics curves shall be recorded respectively. 6.2 Wiring requirement Before testing, all leading wires connected with the tip of the transformer bushing shall be dismantled, and KEEP the dismantled leading wires as far as possible from the transformer bushing. If the leading wires connected with the transformer bushing cannot be dismantled, the tap at the end of the bushing may be used as response-port for testing, however this must be noted, and the test result under this condition must be compared with the ones under similar condition The amplitude frequency response characteristics of the transformer winding is related to the position of tap-switch, it should be tested at the highest tap position, or it shall be guaranteed that the tap-switch is at the same position for each testing Because the testing signal is weak, all wirings shall be stable, reliable and of minimized contact resistance The earth wires of the two signal detection ports shall be connected reliably onto the obvious ground port (e.g. iron-core s grounding port) on the transformer case. The earth wire shall be as short as possible and without enwinding. 6.3 Wiring mode Signal excitation (input) port and response (testing) port shall be selected according to the mode indicated in Figure 2, so that conducting the standardized management on the testing results in future. 8

7 variation (change) of winding inductance will result in the obvious-shift of the wave crest or wave trough position at low frequency stage in its frequency response characteristic curve. For most of transformers, the response characteristic curve of three-phase windings at low-frequency band shall be highly similar. The root cause must be found out if there is any difference The obvious variation in wave crest or wave trough positions at medium-frequency band (100kHz ~600kHz ) in amplitude frequency response characteristics curve usually indicates the local deformation of the winding like twisting and hunching. There are many wave crests and wave troughs in the amplitude frequency response characteristics curve within this frequency range. They can sensitively reflect the change of distributed inductance and capacitance of the winding The obvious variation of wave crest or wave trough positions at high-frequency band (>600kHz ) in amplitude frequency response characteristics curve usually indicates the change of capacitance-to-ground of the winding, which may be caused by whole coil displacement or leading wire displacement. At higher frequency, the winding has larger inductance and smaller capacitance. Because the inter-pie capacitance is much larger than the capacitance-to-ground, the distribution position of wave crests and wave troughs mainly depends on capacitance-to-ground. 13

8 A.5 JUDGE the deformation degree of transformer winding according to Table A.1 Table A.1 Relation of Correlation factor and deformation degree of transformer winding (for reference) 15

9 References and Original Chinese Documents [1] DL/T Frequency response analysis on winding deformation of power transformers