Basic Electrical Engineering (3110005)

 

1. Static Capacitor (Capacitor Bank)
2. Synchronous Condenser
3. Phase Advancer

 

Method 1: Static Capacitor

• We know that most of the industries and power system loads are inductive that take lagging current which decrease the system power factor.
• For Power factor improvement purpose, Static capacitors are connected in parallel with those devices which work on low power factor.
• These static capacitors provides leading current which neutralize (totally or approximately) the lagging inductive component of load current (i.e. leading component neutralize or eliminate the lagging component of load current). Thus, power factor of the load circuit is improved.
• These capacitors are installed in Vicinity of large inductive load e.g. Induction motors and transformers etc., and improve the load circuit power factor to improve the system or devises efficiency.

 

Advantages

• Capacitor bank offers several advantages over other methods of power factor improvement.
• Losses are low in static capacitors
• There is no moving part, therefore need low maintenance
• It can work in normal conditions (i.e. ordinary atmospheric conditions)
• Do not require a foundation for installation
• They are lightweight so it is can be easy to installed

 

Disadvantages

• The age of static capacitor bank is less (8 – 10 years)
• With changing load, we have to ON or OFF the capacitor bank, which causes switching surges on the system.
• If the rated voltage increases, then it causes damage it.
• Once the capacitors spoiled, then repairing is costly

 

Method 2: Synchronous Condenser

• When a Synchronous motor operates at No-Load and over-exited then it’s called a synchronous Condenser.
• Whenever a Synchronous motor is over-exited then it provides leading current and works like a capacitor.
• When a synchronous condenser is connected across supply voltage (in parallel) then it draws leading current and partially eliminates the re-active component and this way, power factor is improved. Generally, synchronous condenser is used to improve the power factor in large industries.

 

Advantages

• Long life (almost 25 years).
• High Reliability.
• Step-less adjustment of power factor.
• No generation of harmonics of maintenance.
• The faults can be removed easily.
• It’s not affected by harmonics.
• Require Low maintenance (only periodic bearing greasing is necessary).

 

Disadvantages

• It is expensive (maintenance cost is also high) and therefore mostly used by large power users.
• An auxiliary device has to be used for this operation because synchronous motor has no self-starting torque.
• It produces noise.

 

Method 3: Phase Advancer

• Phase advancer is a simple AC exciter which is connected on the main shaft of the motor and operates with the motor’s rotor circuit for power factor improvement.
• Phase advancer is used to improve the power factor of induction motor in industries.
• As the stator windings of induction motor takes lagging current 90° out of phase with Voltage, therefore the power factor of induction motor is low.
• If the exciting ampere-turns are excited by external AC source, then there would be no effect of exciting current on stator windings.
• Therefore, the power factor of induction motor will be improved. This process is done by Phase advancer.

 

Advantages

• Lagging kVAR (Reactive component of Power or reactive power) drawn by the motor is sufficiently reduced because the exciting ampere turns are supplied at slip frequency (fs).
• The phase advancer can be easily used where the use of synchronous motors is Unacceptable.

 

Disadvantage

• Using Phase advancer is not economical for motors below 200 H.P. (about 150kW).