IEC TR 61912-2:2009

Low-voltage switchgear and controlgear - Over-current protective devices - Part 2: Selectivity under over-current conditions

IEC 61912-2:2009(E), which serves as an application guide for the determination of selectivity between over-current protective devices of low-voltage switchgear and controlgear, summarises the definitions of the terminology and provides examples of application.

General Information

• Status: Published
• Publication Date: 12-May-2009
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 29.130.20 - Low voltage switchgear and controlgear
• Technical Committee: SC 121A - Low-voltage switchgear and controlgear
• Drafting Committee: MT 9 - TC 121/SC 121A/MT 9
• Current Stage: PPUB - Publication issued
• Start Date: 31-Jul-2009
• Completion Date: 13-May-2009

Standards Content (Sample)

IEC/TR 61912-2 ®
Edition 1.0 2009-05
TECHNICAL
REPORT
Low-voltage switchgear and controlgear – Over-current protective devices –
Part 2: Selectivity under over-current conditions

IEC/TR 61912-2:2009(E)
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IEC/TR 61912-2 ®
Edition 1.0 2009-05
TECHNICAL
REPORT
Low-voltage switchgear and controlgear – Over-current protective devices –
Part 2: Selectivity under over-current conditions

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
V
ICS 29.130 ISBN 978-2-88910-585-4
– 2 – TR 61912-2 © IEC:2009(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 Terms, definitions and abbreviated terms .8
3.1 Alphabetical index of terms .8
3.2 Terms and definitions .9
3.3 Abbreviated terms .10
4 Scope of selectivity requirements .11
4.1 General .11
4.2 Motor protection circuit-breaker / Manual motor starter.12
5 Selectivity determination .12
5.1 Circuit-breaker as UD.12
5.1.1 Selectivity between circuit-breakers.12
5.1.2 Selectivity between a circuit-breaker (UD) and a fuse to IEC 60269-1
(DD) .15
5.1.3 CB/CPS – Selectivity between a circuit-breaker to IEC 60947-2 (UD)
and a CPS to IEC 60947-6-2 (DD) .16
5.1.4 Circuit-breaker/MOR – Selectivity between a circuit-breaker (UD) and
a motor protection overload relay to IEC 60947-4-1 or IEC 60947-4-2
(DD) .17
5.2 Fuse(s) to IEC 60269-1 as UD.18
5.2.1 Fuse/circuit-breaker – Selectivity between a fuse to IEC 60269-1
(UD) and a circuit-breaker (DD) .18
5.2.2 FU/FU – Selectivity between fuses to IEC 60269-1 (UD and DD) .20
5.2.3 FU/CPS – Selectivity between fuse(s) to IEC 60269-1 (UD) and a
CPS to IEC 60947-6-2 (DD).21
5.2.4 FU/MOR – Selectivity between fuse(s) to IEC 60269-1 (UD) and a
motor overload protection relay to IEC 60947-4-1 or IEC 60947-4-2
(DD) .21
6 Residual current devices (RCDs).21
6.1 General .21
6.2 Selectivity – RCD/RCD.22
6.2.1 Selectivity between RCDs in the case of earth-leakage current.22
6.2.2 Selectivity between RCDs in the case of earth-fault (ground-fault)
current.23
7 Zone Selective Interlocking (ZSI).24
7.1 General .24
7.2 Operating principle .24
7.3 Example .25
8 Over-current protection relay (OCR) – Single input energizing quantity measuring
relays with dependent or independent time.26
Annex A (informative) Examples of selectivity between over-current protection devices
Examples of the grades of selectivity applicable to circuit-breakers .27
Annex B (informative) Standing loads – Effect of standing loads on selectivity in the
overload zone .30
Bibliography.33

TR 61912-2 © IEC:2009(E) – 3 –
Figure 1 – Comparison of the operating characteristics of circuit-breakers in the
overload zone .13
Figure 2 – Example of selectivity in the fault current zone with time-delay short-circuit
release .14
Figure 3 – Selectivity in the overload zone between a circuit-breaker (UD) and a fuse
(DD).16
Figure 4 – Circuit-breaker/MOR – Circuit-breaker selectivity with motor overload relay .17
Figure 5 – ICB/MOR – ICB selectivity with motor overload relay .18
Figure 6 – Fuse/circuit -breaker - Verification of selectivity between fuse and circuit-
breaker for operating time in the overload zone (t ≥ 0,1 s for the fuse).19
Figure 7 – FU/CB – Verification of selectivity between fuse and circuit-breaker for
operating time t < 0,1 s .19
Figure 8 – FU/FU – Verification of selectivity between fuses for operating time t ≥ 0,1 s .20
Figure 9 – RCD characteristics showing selectivity on earth-leakage – time-delay
Type S versus non-time delay.23
Figure 10 – Schematic diagram of an installation designed for multiple supplies with
zone selective interlocking .25
Figure 11 – Schematic diagram of mains distribution system with OCR protection .26
Figure A.1 – Circuit-breaker coordination example – 50 kA/9 kA fault levels .27
Figure A.2 – Time-current curves (examples 1 and 2) .28
Figure A.3 – Operation in the fault current zone (examples 1 and 2) .28
Figure A.4 – Circuit-breaker coordination example – 50 kA/20 kA fault levels .29
Figure B.1 – Overload and short-circuit zones.30
Figure B.2 – OCPDs in series .31

Table 1 – Type of selectivity and corresponding subclause number .

– 4 – TR 61912-2 © IEC:2009(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LOW-VOLTAGE SWITCHGEAR AND CONTROLGEAR –
OVER-CURRENT PROTECTIVE DEVICES –

Part 2: Selectivity under over-current conditions

FOREWORD
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