OPERATION OF 3 PHASE INDUCTION-MOTORS CONNECTED TO ONE PHASE SUPPLY

An interesting mode of unbalanced operation of three-phase induction motors is that resulting from a one-phase network supply. It is not a common operating condition but it may happen, for instance, in an emergency, when loss of one or two phases occurs or even when the machine is intentionally connected to a one—phase network. The present paper analyzes the behavior of a three-phase induction motor operating according to the Steinmetz connection, conceived to allow operation of small rating motors connected to a one—phase supply and with a small degree of voltage unbalance. The conditions for cancelling negative sequence component of stator winding terminal voltages and currents are also established.?Results presented by considering a capacitor in parallel to one of those phases connected to the motor terminal switched off from the three-phase supply allow us to define the requirements for correct capacitor selection and switching off in order to obtain a proper motor behavior in the whole slip range from starting to the final operating point. © 1990 IEEE