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BS EN IEC 60076-25:2023

BS EN IEC 60076-25:2023

$142.49

Power transformers – Neutral grounding resistors

Published By Publication Date Number of Pages
BSI 2023 30
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IEC 60076-25:2023 applies to dry type natural air-cooled resistors, for neutral grounding of transformers and generators, in order to limit the earth fault current in power systems by means of metallic resistive elements. For the purposes of this document, the resistor can be:

  • used alone or in combination with other electrotechnical products not covered by this document, such as (but not limited to): a step-down single-phase transformer, an open triangle or zig-zag transformer (where the neutral point is not available) and a Petersen coil reactor (in order to increase active power contribution to the fault or reduce time constant for proper protection operation or both);
  • designed, manufactured and verified on a one-off basis or fully standardized and manufactured in quantity.

Both terms “neutral grounding resistor” (NGR) and “neutral earthing resistor” (NER) can be used. However, for the purposes of this document and in order to avoid any confusion with “neutral earthing reactor” (NER), the term “neutral grounding resistor” (NGR) is used. This document specifies:

  • the characteristics of the NGR;
  • the service conditions requirements for NGRs;
  • the tests and test methods for confirming that these conditions have been met;
  • the requirements relating to marking for NGRs.

Annex A provides guidance on how to consider the effect of resistance variation with temperature.

PDF Catalog

PDF Pages PDF Title
2 undefined
5 Annex ZA (normative)Normative references to international publicationswith their corresponding European publications
6 Blank Page
7 English
CONTENTS
9 FOREWORD
11 1 Scope
2 Normative references
12 3 Terms and definitions
14 4 Service conditions
5 Ratings
5.1 Rated ambient temperature
5.2 Rated resistance (R)
5.3 Maximum resistance variation
5.4 Rated time
5.5 Rated voltage (Ur)
15 5.6 Rated insulation level
5.7 Rated short time current
5.8 Rated continuous current
5.9 Rated frequency
Table 1 ā€“ Rated insulation levels
16 6 Rating plates (Nameplates)
6.1 General
6.2 Minimum information to be provided
7 Design and construction
7.1 General
7.2 Resistive elements
17 7.3 Resistive banks
7.4 Electrical connections
7.5 IN and OUT terminals
7.5.1 General
7.5.2 IN terminal
7.5.3 OUT terminal
Table 2 ā€“ Maximum temperature rises above ambient for resistive elements
18 7.6 Insulators
7.6.1 General
7.6.2 Insulators between resistive elements
7.6.3 Insulators between resistor banks and enclosure
7.6.4 Creepage distance
7.7 Enclosure
7.7.1 Protection against contact with live parts, ingress of solid foreign bodies and water
7.7.2 Design
19 7.7.3 Protection against corrosion
8 Tests
8.1 General
8.2 Test classifications
8.2.1 Routine tests
8.2.2 Type tests
Table 3 ā€“ Tests classifications
20 8.2.3 Special tests
8.3 Test documentation
8.4 Routine tests
8.4.1 Visual inspection and dimensional verification
8.4.2 Rated resistance measurement
8.4.3 Power frequency withstand voltage test
21 8.4.4 Insulation resistance
22 8.5 Temperature rise tests
8.5.1 General
8.5.2 Continuous current duty
8.5.3 Rated time duty
23 8.5.4 Tolerances
8.5.5 Acceptance criteria
8.6 Special tests
8.6.1 Inductance measurement
8.6.2 Lightning impulse test
8.6.3 Mechanical design verification
24 8.6.4 Protection degree of enclosure
25 Annex A (informative)Resistance variation
A.1 General
A.2 Material properties
A.3 Effect of NGR resistance variation
26 A.4 Rate of variation
Figure A.1 ā€“ Ground fault protection settings example
Table A.1 ā€“ Resistance and current change with temperature rise
27 A.5 Consecutive faults
A.6 Protection coordination
A.7 System capacitive charging current
A.8 Conclusion
28 Bibliography

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BS EN IEC 60076-25:2023
$142.49