Power transformers - Part 25: Neutral grounding resistors
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.
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.