EducationWhat is synchronous condenser - Advantages and disadvantages, Modes, Power Factor

What is synchronous condenser – Advantages and disadvantages, Modes, Power Factor

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Synchronous condenser is an synchronous motor synchronous generator that is operating with no any load (at idle) Its purpose is to offset reactive power generated by the system of power. The adjustment of the power factor is achieved by changing the current of excitation:

  • In the under-excitation state the compensator has the appearance as an inductive load
  • In the condition that there is overexcitation, it has the appearance of an capacitive receiver
  • At the point of intermediate excitation, the nature of an RF receiver that is resistive

The capability to alter the characteristics of the current generated from the synchronous motor is employed to boost the power factor of the network.

A synchronous condenser is an actual synchronous motor that is running at on idle and properly exuberant. It draws its power from the grid and uses only a small quantity of power to compensate any possible losses to the machine as well as its capacitive power that is inherent to its operation. When it draws capacitor reactive energy, the machine uses active power.

synchronous condenser
Fig. 1 Equivalent diagram and vector diagram of the synchronous condenser

The capacitor is inductive and has reactive power, thereby improving the power balance of reactive power in a system with numerous inductive loads. The power efficiency of the network is increased. To allow the synchronous compensator to generate the capacitive reactive power, it has to be exaggerated. The primary feature that defines the synchronous compensator is the relation

with U = const, I = const

that is a particular instance of the V-curve family. This feature demonstrates how the excitation current needs to be adjusted to obtain the desired increase in load current.

If the synchronous machine is only used to compensate for power that is reactive and is not designed to be used for generator or motor operation, its shaft has minimally small amounts of force when compared to generators or motors with similar dimensions. Because of this, it is evident that the shaft used for compensation is quite small, and the shaft’s ends being unable to extend beyond the housing.

Synchronous condenser mode

The synchronous condenser is an synchronous machine that runs in motor mode but not loading the shaft by alternating fields of current.

Synchronous condenser
Fig. 2 Synchronous condenser

In the over-excited state, the current is ahead of the line voltage, which is capacitive regard to the voltage, and in the mode of under-excitation, it is delayed, or inductive. In this case it’s the synchronous machine is transformed into a compensator which is an active current generator.

The over-excited function that is present in the synchronous condenser is normal when it delivers an electrical power source to the grid.

Therefore, dilators like those that are used to serve the same function capacitor banks found in consumer substations can be known as Generators of reactive power. However, in periods that consumers are under less load (for instance, during the night) in most cases, it is required for synchronous condensers also to function under energy mode, which is when they draw inductive current as well as reactive energy from the grid because in these instances, the voltage of the grid tends to increase, and in order to keep the level at a normal level, it is required to overload the grid with currents that result in voltage drops within the grid.

In order to achieve this, each synchronous condenser has an automated voltage or excitation regulator which regulates the strength of its excitation current to ensure it is that the current at both junctions of the condenser stays constant.

The greatest values of power and current in the under-excitation mode can be achieved during passive operation.

In most instances under-excitation requires lower power than an overexcitation mode but there are instances when it is necessary to use more power. This can be accomplished with increasing the spacing however, this can lead to an improvement in price of the device this is why the need for an excitation current module that is negative is being pushed up recently. Because that the power active synchronous capacitor is only loaded with losses, as per the researcher, it is also able to be stable even with a tiny negative excitation.

In certain instances in dry times the hydroelectric generators may be utilized to work as compensation units.

For a grid-connected generator to go in synchronous condenser-mode, you only need to block the steam (or water) access to the turbine. When this is the case, an hyperexcited turbogenerator starts drawing only a tiny amount of active energy from the grid to compensate for the loss of rotation (mechanical as well as electrical) and then transmits the reactive energy back to grid.

When operating in synchronous condenser, the turbine is able to run for a prolonged period of duration, and it is dependent only on the operational circumstances for the engine.

If needed the turbogenerator could be utilized as an synchronous condenser, both with its turbine running (together together with the engine) and also with the coupling removed, i.e. disassembled.

The steam turbine being rotated on the other side of the generator, that has entered drive mode, may cause the tail end of the generator to become overheated.

Synchronous condenser advantages and disadvantages


The benefit of the advantages of a synchronous capacitor lies in the fact that it can regulate the power factor of the system without having to adjust to the demand. If you have a capacitor bank that is static this exact management of power factors isn’t possible. Instead the capacitor bank boosts the power factor over time.

MVARs derived from synchronous devices are extremely dynamic as they’re controlled by an automatic voltage regulator (AVR) within the system of excitation in a non-step method, which means there is no transient switching is required to generate or absorb MVARs. This means that the synchronous machine offers more reliable the grid’s voltage.

Furthermore, heavy-rotating synchronous machines keep kinetic energy stored in the shaft’s rotation to ensure critical inertia when there are grid disturbances. They also enhance the amount of short-circuits near the point where they connect to grid, allowing for the greater use into renewable sources of energy.

Installed as a stand-alone unit in the transmission grid The synchronous capacitor supplies the power needed to operate and also voltage support.

Alternately, power plants that have been shut down are retrofitted, and their synchronous generators are able to operate in the form of synchronous capacitors.

Converting synchronous generators to synchronous motors optimizes the use of the existing infrastructure, protects the inertia of generators, and also provides the ability to generate a continuous source of power that can be used to improve the security and reliability for the system of power as well as ensure the highest use of renewable energy sources.

The most important benefits can be summarized in the following manner:

  • Synchronous capacitors offer dynamic MVARs that improve stability of voltage.
  • Synchronous capacitors boost short-circuit voltages at the point where grid connections are made.
  • GT-based synchronous capacitors are able to provide support for MW (generation mode) support to complement renewable energy generation.
  • Synchronous capacitors don’t require modifications to the GT generator or power system core, and take advantage of the proven designs that are used in the Genset fleet.
  • LSPT along with GG are built on low-friction rollers and ball bearings that reduce the parasitic load of auxiliary loads.
  • When the capacitor is in synchronous capacitor mode there is no fuel used up because that power source to the capacitor has been shut off.
  • The switch between the power generator and synchronous capacitor modes doesn’t necessitate resynchronizing the generator to the grid.


While it is a good idea, the synchronous condenser has its drawbacks. It isn’t quiet due to the fact that the synchronous motor is required to spin constantly.

The most significant disadvantages of synchronous condensers are:

  • The upfront capital cost,
  • Long lead-time
  • Incomplete redundancy (i.e. in the event of failure),
  • High operating costs (electricity to stimulate) in addition to the fact it’s an undiscovered technology for many renewable energy developers and operators.

When the workload on the synchronous motor increases, the current of the stator Ia will increase regardless of the excitation. In the case of over and under-excited motors the energy ratio (p.f.) tends to reach 1 with increasing load. The increase the power factor can be more than that of the Ia change due to the increase in load. The strength of the armature current is dependent on the intensity of excitation. The current is large at both low and high levels of excitation. In between, it is a minimal value which corresponds to specific excitation. The various variations of

I with excitation are referred to as V curves due to their form. With the same output load the armature current is varied over a wide spectrum and will cause the power factor to change in line with. If the motor is over-excited, it is running with the highest power factor, and with a lower power factor when under-excited. Between them the power factor and equal. The armature current at the minimum is equal to the power factor of unity.

Synchronous condenser power factor
Fig. 3 Synchronous condenser power factor

An Series SC, which is a light or not loaded synchronous machine that can deliver the necessary reactive power dynamically. It is SC can be connected with the power supply, and is deliberately operated in an overexcited state. The intensity of the excitation is determined by the power factor correction that is desired and the power factor that is detected by the condenser control. The condenser can adjust the level of excitation to ensure that the power factor remains at the right level. After it is installed, the SC series SC installs, it constantly checks the power factor and generates the proper amount of VAR required to rectify any power factor that is not switching transients. It is also not disturbed by harmonic currents created from solid state motor drives.

The Series SC can also improve the overall quality of power by decreasing the frequency of voltage transients as well as reducing issues caused by harmonic distortion that is common in manufacturing processes. The Series SC is available in 100 kVAR through 10 000 kVAR units, with 480 volts the 15-kV range. The use of the use of a synchronous condenser to power factor correction offers numerous benefits with no risk. The process of correcting power factor by using condensers is smoother and won’t adversely impact systems that are filled by current harmonics. Condensers are an impedance source with low impedance and is inductive to the loads. Additionally, this Series SC is easy to maintain (a simple annual maintenance routine) and easily adapts to the changing demands of a plant. (Dynamic Correction).

The SC comes with a variety of user-friendly features like the automatic restart following the power is cut off. The SC is also equipped with a state of the art touchscreen display that is integrated into the control interface. Controls are made to be user-friendly and easy to comprehend so that users can manage the SC through the panel. The touchscreen displays the current, voltage power factor, voltage, and power information to an absolute minimum.


Michal Pukala
Electronics and Telecommunications engineer with Electro-energetics Master degree graduation. Lightning designer experienced engineer. Currently working in IT industry.