IEC TS 60076-23:2018

Power transformers - Part 23: DC magnetic bias suppression devices

IEC TS 60076-23:2018(E) specifies requirements for devices for the suppression of DC magnetic bias of power transformers and convertor transformers. It includes requirements for service conditions, structures, testing, packing, transport and storage.
The devices are connected to neutral points of power transformers and converter transformers to suppress DC bias current in the case an HVDC system is operated in monopole ground return mode or bipolar unbalanced mode. In the case of dedicated metallic return HVDC system, the devices are useful to mitigate DC stray current flowing through power transformers and converter transformers during transient conditions such as DC line fault.
This document applies to DC magnetic bias suppression devices for operation at frequencies of 50 Hz and 60 Hz on power systems having voltages above 110 kV.

General Information

• Status: Published
• Publication Date: 08-Jan-2018
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 14 - Power transformers
• Drafting Committee: WG 33 - TC 14/WG 33
• Current Stage: PPUB - Publication issued
• Start Date: 29-Jan-2018
• Completion Date: 09-Jan-2018

Standards Content (Sample)

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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