IEEE C62.92.2-1989 pdf free.IEEE Guide for the Application of Neutral Grounding in Electrical Utility Systems, Part II – Grounding of Synchronous Generator Systems.
1.1 Scope. This section summarizes the general considerations in grounding synchronous genera tor systems and discusses the factors to be consid ered in the selection of a grounding class and the application of grounding methods. The guidelines apply to both the large and small generators found in electric utility systems.
It should be borne in mind by the user that this report is intended solely as a guide. Statements are necessarily of a general nature and, therefore do not take into account the requirements of special situations that can differ considerably from those discussed.
2. Objectives of Generator Grounding
The principle objective of grounding a synchronous generator system is the protection of the generator and associated equipment against dam age caused by abnormal electrical conditions. The specific objectives in the protection of the generator are as follows:
(1) Minimizing damage for internal ground faults.
(2) Limiting mechanical stress in the generator for external ground faults.
(3) Limiting TOVs (temporary overvoltages) and transient overvoltages on the generator insulation.
(4) Providing a means of generator system ground fault detection.
(5) Coordinating the protection of the generator with the requirements of other equlp ment connected at generator voltage level.
The choice of grounding class is largely determined by the relative importance to the user of each of the above objectives. The degree to which each of the possible grounding methods accomplishes the desired objectives is discussed in the following paragraphs.
2.4 Providing a Means of Generator System Ground-Fault Protection. The grounding class chosen for a generator has a significant impact on the sensitivity and speed of ground-fault relaying for the generator and other apparatus connected to the generator voltage system. In general. ungrounded, high-resistance, and resonant grounded systems allow for the most sensitive ground-fault detection, In systems where genera tors are bussed together at generator voltage or where feeders are taken out at the generator volt age, relaying requirements may dictate a ground ing class other than one which would provide maximum sensitivity for generator stator ground faults.
The effects which the choice of grounding class may have on ground relaying are discussed in a general way in Section 3. A complete discussion of generator ground-fault protection, including specific relaying systems, can be found inANSI/ IEEE C37.101-1985.IEEE C62.92.2-1989 pdf free download.