Guide for Grounding of Instrument Transformer Secondary Circuits and Cases
|Publication Date:||10 December 2014|
This guide contains general and specific recommendations for grounding current and voltage transformer secondary circuits and cases of connected equipment. The practices recommended apply to all transformers of this type, including capacitive voltage transformers and linear couplers, irrespective of primary voltage or whether the primary windings are connected to, or are in, power circuits or are connected in the secondary circuits of other transformers as auxiliary current transformers or voltage transformers. Although most diagrams included in this guide show relaying applications, the recommended practices apply equally to metering and other areas where instrument transformers are used.
Exceptions to grounding are permissible or sometimes required where advantages obtained by not grounding, in certain instances or in certain types of installations, are considered to outweigh the advantages obtained by grounding.
The scope of the guide includes grounding practices presently used and practices that were not previously reported. Specifically, a review of other than North American grounding practices is included.
This guide provides information on the grounding of the following:
- Secondary circuits of electromagnetic CT and VT circuits
- Cases of relays, CTs, and VTs
- Secondary circuits of optoelectronic CTs and VTs
The primary emphases of this guide are personnel safety and proper performance of relays at electric power frequencies.