SOUTH AFRICAN NATIONAL STANDARD

Transcription

1 ISBN IEC :2013 SOUTH AFRICAN NATIONAL STANDARD Power transformers Part 3: Insulation levels, dielectric tests and external clearances in air This national standard is the identical implementation of IEC :2013, and is adopted with the permission of the International Electrotechnical Commission. WARNING This standard references other documents normatively. Published by SABS Standards Division 1 Dr Lategan Road Groenkloof Private Bag X191 Pretoria 0001 Tel: Fax: SABS

2 IEC :2013 Table of changes Change No. Date Scope National foreword This South African standard was approved by National Committee SABS/TC 067/SC 05, Electricity distribution systems and components Electricity distribution, in accordance with procedures of the SABS Standards Division, in compliance with annex 3 of the WTO/TBT agreement. In the case of distribution transformers, national deviations from this SANS document (if required) will be given in SANS 780. This SANS document was published in February This SANS document supersedes SANS :2000 (edition 2 (incorporating IEC corr.) as modified by nat. amdt 1:2007). SABS

3 INTERNATIONAL STANDARD NORME INTERNATIONALE IEC Power transformers Part 3: Insulation levels, dielectric tests and external clearances in air Transformateurs de puissance Partie 3: Niveaux d'isolement, essais diélectriques et distances d'isolement dans l'air INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE PRICE CODE CODE PRIX XA ICS ISBN Warning! Make sure that you obtained this publication from an authorized distributor. Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé. Registered trademark of the International Electrotechnical Commission Marque déposée de la Commission Electrotechnique Internationale

4 IEC:2013 CONTENTS FOREWORD... 4 INTRODUCTION Scope Normative references Terms and definitions General Highest voltage for equipment and rated insulation level Transformers with re-connectable windings Dielectric tests Overview Test requirements General Test voltage levels Test sequence Test requirements for specific transformers Tests for transformers with U m 72,5 kv Tests on transformers with 72,5 kv < U m 170 kv Tests on Transformers with U m > 170 kv Assigning U m and test voltages to the neutral terminal of a winding Transformers with U m 72,5 kv Transformers with U m > 72,5 kv Dielectric tests on transformers that have been in service Insulation of auxiliary wiring (AuxW) Applied voltage test (AV) Induced voltage tests (IVW and IVPD) General Induced voltage withstand test (IVW) Induced voltage test with partial discharge measurement (IVPD) General Test duration and frequency Test sequence Partial discharge (PD) measurement Test acceptance criteria Line terminal AC withstand test (LTAC) Lightning impulse tests (LI, LIC, LIN, LIMT) Requirements for all lightning impulse tests General Tap positions Records of tests Test connections Full wave lightning impulse test (LI) Wave shape, determination of test voltage value and tolerances Tests on transformers without non-linear elements Tests on transformers with non-linear elements Chopped wave lightning impulse test (LIC)... 31

5 IEC: Wave shape Tests on transformers without non-linear elements Tests on transformers with non-linear elements Lightning impulse test on a neutral terminal (LIN) General Waveshape Test sequence Test criteria Switching impulse test (SI) General Test connections Waveshape Test sequence Test criteria Action following test failure External clearances in air General Clearance requirements Annex A (informative) Application guide for partial discharge measurements on transformers Annex B (informative) Overvoltage transferred from the high-voltage winding to a lowvoltage winding Annex C (informative) Information on transformer insulation and dielectric tests to be supplied with an enquiry and with an order Annex D (informative) Neutral insulation voltage level calculation Annex E (informative) Basis for dielectric tests, insulation levels and clearances Bibliography Figure 1 Time sequence for the application of test voltage for induced voltage test with partial discharge measurement (IVPD) Figure A.1 Calibration circuit for partial discharge measurement using the test tap of condenser type bushing Figure A.2 Circuit for partial discharge measurement using a high-voltage coupling capacitor Figure B.1 Equivalent circuit for capacitive transfer of overvoltage Table 1 Requirements and tests for different categories of windings Table 2 Test voltage levels (1 of 2) Table 3 Test voltage levels used in special cases Table 4 Minimum clearances in air (1 of 2)... 38