Multifunction dynamoelectric protection system

Abstract

A protection system for a dynamoelectric machine providing a plurality of protective functions comprises a module having as a first function over temperature protection including thermal sensors adapted to be placed in heat transfer relation with the windings of the machine. The sensors which may be connected in series or in parallel are connected to a sensing circuit provided with shorted sensor protection. When connected in parallel a channel is provided for each sensor and is isolated from one another. Other functions include a minimum off delay timer which prevents rapid cycling of the machine. An oil pressure timer particularly useful with a compressor motor to sense oil pressure between the output of the oil pump and the crankcase in order to deenergize the motor should there be inadequate oil pressure for a selected period of time, a low voltage cut out network in the event of the occurrence of low voltage conditions, and a circuit to facilitate use of controls in the output side of the system if desired while permitting operation of the system only on the condition of output current flow. The minimum off delay timer can be modified to provide a manual reset circuit which will lock out or prevent energization of the machine each time the protection circuit is tripped. Reset can be accomplished only by removing power to the module and reapplying said power.