Not familiar with that term/meter in synchronizing application. A null meter that is used for resistance testing has no direct use there. Describe the null meter your know about.
Perhaps something related to voltage matching of generator voltage and line voltage, but I've never come across this terminology in a synchronizing system.
My understanding of a null meter is that it is used to indicate the balance between an AVR auto and field current channel, not directly related to synchronizing
I agree with GTstartup, it is a term sometimes seen when multiple controllers are tracking each other in an AVR, typically the main and standby auto systems and the manual controller. It's purpose is to aid a bumpless transfer between sources, i.e. if the null meter isn't zero there will be a definite 'bump'.
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