Abstract: The higher requirements of relay protection for large generator unit have been put forward along with the increment of unit capacity. In this paper the requirements for 1000MW unit relay protection, especially for the generator stator ground protection, were expounded, the conventional stator ground protection of external source injection mode was introduced, and the deficiencies in its application were analyzed. A complete microcomputer protection scheme of stator ground fault based on the balance principle was proposed as an improvement of above protection mode. In the scheme, the influence to protection of external source fault, PT leader breakdown, system harmonic etc. were considered, so the protection device can distinguish reliably the generator stator ground failure.

Key words: 1000MW unit, stator ground protection, injection source, harmonic