What type of motors are commonly used by utilities for power factor correction?

Synchronous motors are commonly used by utilities for power factor correction because they have the ability to operate at leading, lagging, or unity power factor. This capability allows them to adjust the reactive power in an electrical system, which is essential for improving power factor. When synchronous motors are operated in a leading mode, they supply reactive power to the grid, thus compensating for the lagging power factor typically caused by inductive loads like transformers and induction motors.

Furthermore, the synchronous motor can be designed to be adjustable in terms of its excitation level, enabling precise control over the amount of reactive power supplied or absorbed. This property makes synchronous motors particularly effective for power factor correction across a range of load conditions.

In contrast, while induction motors are widely used in various applications, they inherently operate with a lagging power factor and do not have the capability to correct it. Capacitor motors, a term not commonly used in the same context as synchronous motors, generally refer to motors designed with capacitors to improve starting torque but do not serve the purpose of dynamic power factor correction. Series motors are less relevant in this context as they are typically used for applications requiring high starting torque under load, rather than addressing power factor issues.