Synchronous capacitor is
Right Answer is:
An over-excited synchronous motor without mechanical load
An overexcited synchronous motor acts as a power factor correction device and is also known as a synchronous condenser or synchronous capacitor. The variation of armature current and power factor as a function of field current is plotted to give a better insight. In electrical engineering, a synchronous condenser(sometimes called a synchronous capacitor or synchronous compensator) is an Over-Excited Synchronous Motor, whose shaft is not connected to anything but spins freely.
We can state that an over-excited synchronous motor draws a leading power factor current from the mains. The synchronous motor, therefore, when over-excited, in addition to driving some load, will work as a capacitor or condenser. A capacitor draws a leading power factor current. An over-excited synchronous motor draws the leading power factor current from the mains.
An over-excited synchronous motor is also called a synchronous condenser. Synchronous motors are used as constant-speed drive motors. Over-excited synchronous motors are used to improve the power factor of electrical loads in industries. Generally, the motor is run on load, and by overexcitation, the system power factor is also improved.