Abstract: Abstract:When the current generator compound voltage overcurrent protection is used for generators in expanded unit connection, it does not possess desired selectivity for failed generator. Based on the principle of asynchronous method selective generator compound voltage overcurrent protection, if the fault is judged as fault inside the generator region, then the compound voltage overcurrent protection will trip at setting delay; and if the fault is judged as fault outside the generator region, then the compound voltage overcurrent protection will trip at setting delay plus a short delay. Thus the selectivity problem of the generator compound voltage overcurrent protection used in expanded unit connection was solved effectively. The availability of the scheme was verified by the result of dynamic simulation experiment.

Key words: Key words:expanded unit connection, compound voltage overcurrent protection, asynchronous method current transformer saturation criteria, selectivity