IEC TS 60076-23:2018

IEC TS 60076-23 ®
Edition 1.0 2018-01
TECHNICAL
SPECIFICATION
colour
inside
Power transformers –
Part 23: DC magnetic bias suppression devices
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IEC TS 60076-23 ®
Edition 1.0 2018-01
TECHNICAL
SPECIFICATION
colour
inside
Power transformers –
Part 23: DC magnetic bias suppression devices

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-5228-4

– 2 – IEC TS 60076-23:2018 © IEC 2018
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Service conditions . 9
4.1 General . 9
4.2 Seismic conditions . 10
4.3 Unusual conditions. 10
5 Selection principle . 10
5.1 Classification and features of the devices . 10
5.2 Selection principle for DC current-limiting devices . 10
5.3 Selection principle for the DC current- blocking device . 11
5.4 Calculation and verification . 11
6 DC current-limiting device. 11
6.1 Functional requirements . 11
6.1.1 General . 11
6.1.2 Resistance . 11
6.1.3 Overvoltage protection . 12
6.1.4 Structure . 12
6.2 Ability to withstand effects of short-circuit current . 12
6.2.1 Ability to withstand thermal effects of short-circuit current . 12
6.2.2 Ability to withstand dynamic effects of short-circuit current . 12
6.3 Temperature rise . 13
6.3.1 Metal chip resistors . 13
6.3.2 Dry-type non-inductive epoxy-resin insulated resistors . 13
6.3.3 Other types of resistors . 13
6.4 Insulation level . 13
7 DC current-blocking device . 13
7.1 Functional requirements . 13
7.1.1 General . 13
7.1.2 Capacitance . 13
7.1.3 Bypass switches . 14
7.1.4 Function of device . 14
7.1.5 Structure . 14
7.2 Ability to withstand effects of short-circuit current . 15
7.2.1 Ability to withstand thermal effects of short-circuit current . 15
7.2.2 Ability to withstand dynamic effects of short-circuit current . 15
7.3 Temperature rise . 15
7.4 Insulation level . 15
8 Tests . 15
8.1 Test classification . 15
8.2 Routine tests. 16
8.2.1 General . 16
8.2.2 Visual inspection . 16
8.2.3 DC resistance measurement . 16

8.2.4 Capacitance measurement . 16
8.2.5 Insulation resistance measurement . 16
8.2.6 Withstand voltage test . 16
8.2.7 Gap discharge test . 17
8.2.8 Function check of DC current- blocking devices . 17
8.3 Type tests . 17
8.3.1 General . 17
8.3.2 Temperature rise test of DC current-limiting device . 17
8.3.3 Thermal stability test . 18
8.3.4 Dynamic stability test . 18
8.3.5 Lightning impulse test . 18
8.3.6 Ingress protection test . 18
9 Packing, transportation and storage requirements . 18
10 Nameplate specification . 18
11 Technical documentation requirements . 19
Annex A (informative) Generation mechanism of DC bias current of power
transformers caused by HVDC system . 20
Annex B (informative) Examples of harmful effects of DC bias current . 21
Annex C (informative) DC current-limiting device . 24
Annex D (informative) DC current-blocking device . 25
Annex E (informative) Information needed to calculate the DC bias current of
transformers . 26
E.1 General . 26
E.2 Information of grounding electrode of HVDC system . 26
E.3 Parameters of equipment in substations and converter stations . 26
E.4 Parameters of power transmission lines . 26
Annex F (informative) Methods of calculation of DC bias current . 27
F.1 Method based on modelling of underground electric field . 27
F.2 Method based on calculation model of resistor network with equivalent
voltage sources. 28
Annex G (informative) Application examples . 30

Figure A.1 – Schematic diagram of DC flowing path in the monopole ground return
mode . 20
Figure A.2 – Resistance network and ground electric field distribution . 20
Figure B.1 –Mechanism of DC bias . 21
Figure B.2 – Damage to transformer . 23
Figure C.1 – Electrical schematic diagram of DC current-limiting device . 24
Figure D.1 – Electrical schematic diagram of DC current-blocking device . 25
Figure F.1 – Schematic diagram of modelling for DC bias current calculation . 28
Figure F.2 – Ground potential around the grounding electrode of HVDC system . 28
Figure F.3 – Schematic diagram for calculation of DC bias current based on the
equivalent voltage source . 29

Table 1 – Test items . 15
Table 2 – Rated insulation level (kV) . 16
Table B.1 – Test results of DC bias influence on DC system . 22

– 4 – IEC TS 60076-23:2018 © IEC 2018
Table B.2 – Vibration data of transformer (mm/s) . 23
Table F.1 – The resistivity and thickness of layered soil . 27
Table G.1 – Test data of DC current, noise and vibration . 30
Table G.2 – Test data . 31

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