Current-compounded self excitation of synchronous motors

When the load on a synchronous motor is liable to substantial variation, there is much to commend the use of some form of excitation control to provide either constant power factor or constant reactive power for all normal motor loading. The basic principles of control by static current-compounded self excitation are discussed in the paper, and ways in which the controlled quantity may be adjusted by voltage, current, or control-impedance shift are explained. An alternative method of adjustment over a given range simply by means of a variable resistor is also outlined. The use of a capacitor and nonlinear control reactor to compensate for errors due to changes in supply voltage or motor temperature is explained. Experimental results are given showing a motor power factor very accurately controlled over a wide range of loading and operating conditions, together with a pullout torque much greater than is obtained with reasonable values of constant excitation.