What is a Synchronous Condenser?
A synchronous condenser is a synchronous motor running at no load and in over-excited mode. A synchronous motor in over-excited mode behaves as a capacitor which is indicated by a leading current or supply of VARs in the circuit by a synchronous motor.
Working Principle of a Synchronous Condenser:
As synchronous condenser is a synchronous motor so its principle of working will be as same as principles of synchronous motor. A synchronous motor works on the principle of motional EMF that is, a conductor tends to rotate due to the effect of the magnetic field. To provide a magnetic field, two ways are used that is a three-phase AC supply and a constant DC power supply to the stator.
The purpose of providing two ways of excitation is that it can rotate at synchronous speed as the synchronous motor works on the interlocking of the magnetic field produced due to the stator and dc field winding.
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Changing the DC field excitation which may result in three possible outcomes, which are given as follows:
- On increasing dc supply initially, the armature current decreases which show that the stator is using less current for producing flux. It also shows that the motor is drawing less reactive (lagging) current. This is called under-excited mode.
- On further increase in dc field excitation, a point comes where the armature current is the least and the motor is said to be working at unity power factor. All the field excitation requirements are met through dc source (no field from stator ends required). This mode is called the normal-excited mode of synchronous motor.
- On the further increase of the field current through dc supply, the flux overly increases, and to counterbalance it, the stator starts supplying reactive power instead of absorbing it. As a result, the motor will draw a leading current.
The above-mentioned third outcome of the Synchronous Motor forms the working principle of a Synchronous Condenser.
Applications of Synchronous Condenser in power systems:
Due to the advantage of adjusting the VARS (reactive power) of a synchronous motor by changing the field excitation, the synchronous motor can be used for many applications (Power factor correction, VAR compensator, Inertia) that are discussed HERE.
Limitations of a Synchronous Condenser:
- Not economical for less than 500KVAR compensation
- Noise and transient production
- Separate excitation required, increasing cost
- High maintenance cost
- There are significant losses in motors
- Cost of protective devices increases due to high Short Circuit Rating
Substitutes of Synchronous Condensers:
- Static VAR compensator (SVC)
- Static synchronous compensator (STATCOM)
- Series capacitor and reactors
- Shunt capacitors
- Transformer tapping
- FACT (Flexible AC Transmission) device
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