Generator stator protection

When considering protection for the generator stator, the engineer must balance the expense of applying a particular relay or relay system against the consequences of losing a generator. The total loss of a generator may not be catastrophic if it represents a small percentage of the investment in an installation. However, the impact on service reliability and the upset to loads supplied also must be considered. Damage to and loss of production in continuous processes can represent the dominating concern rather than the generator unit. Accordingly, there is no standard solution based on the MW rating. However, it is expected that a 500 kW, 480 V standby reciprocating engine will have less protection than a 400 MW base load steam turbine unit. One possible common dividing point is that the extra CTs needed for current differential protection are less commonly seen on generators less than 2 MVA, less than 600 V or those never paralleled to other generation sources.