Power Factor disadvantage, cause and correction

This is a first article for this blog. In any electrical power system, there is different types of loads (inductive or resistive or both) which will differ the power factor of the system. Here we will discuss about Power Factor || Disadvantage, cause || power factor correction. The inductive (reactive) load is the primary cause of voltage profile degradation in any power system. Because of the inductive (reactive) load, reactive power enters the equation, and voltage stability is compromised. With the growth of companies and a growing population, there is a greater demand for electrical power. For a power system to be considered dependable, it must be resistant to momentary overloads, maintain a steady voltage, and have minimal transmission and distribution losses.

Power Factor Introduction

Power factor (PF) is the ratio of working(real) power to apparent power i.e Kw/KVA. Apparent power is the measure of the amount of power used to run machinery and equipment during a certain period. Also it is the ‘cosine’ of the phase angle of current and voltage .most of the industrial load are inductive which cause the power factor lagging and lower the power factor. Load will draw more current for lower power factor ,which increase the losses ,voltage drop, reduce system efficiency and more demand charge. So it is necessary to improve the power factor of the system for better voltage regulation, reduce the system losses, increase the load carrying capacity of system.

Power factor correction

Overload circumstances should be adjusted employing facts devices while appropriate compensators. Shunt and series compensation are the two most common kinds of compensation. By connecting a capacitor in series with the transmission line, the total reactance is lowered, and therefore the voltage drop is minimized. Shunt compensation involves injecting reactive power into the line to lower the quantity of reactive power provided by the source. Shunt compensation is a direct acting approach that rapidly alters the voltages at the receiving end. It also boosts the power factor.

Present Scenario

The present power factor correction has a number of disadvantages, including switching operation and system sensing stability. This suggested system will be used to address the problem. The power factor is defined as the cosine of the angle formed by voltage and current. This current and voltage are detected by instrument transformers such as current and potential transformers. or a reactor, and in the following quarter of the cycle, it is transferred back to the power source. As a result, the reactive power oscillates at a frequency equal to two times the rated value between the ac source and the capacitor or reactor (50 or 60Hz). As a result, compensation is required to prevent circulation between the load and the source. We must also adjust for reactive power in order to manage the system's power factor and ensure voltage stability.

Problems in Power factor compensation in industry

Due to a lack of effective approaches that could be used to improve the power factor, numerous sectors ran into or faced various economic and capital problems in the previous decade. These businesses used inductive motors, inductive generators, high-intensity discharge lamps, electric furnaces, and other devices that increased the system's KVAR or consumed reactive power since the current waveform lagged behind the voltage/low power factor operation. Due to the low power factor, there were issues with low efficiency, higher copper loss, higher heat dissipation, high voltage regulation, bigger conductor sizes were required, and the system's handling capacity was lowered.

 DISADVANTAGES OF LOW POWER FACTOR 

1.  The rating of alternator, transformer and switchgear increased (KVA). 
2.  The size of the conductor increases.
3.  Power loss in the system increases.
4.  Poor voltage regulation. 
5.  System efficiency decreases.
6.  Penalty if power factor tariff.
7.  Overall cost increases.

Roles of power factor

• As we know that for lower the power factor, load current will be higher and vice-versa.
• In lower power factor, the transmission lines  should be of greater conductor size
• At low power factor, the conductor carries a large amount of current so the large copper losses occurs
•  Causes more IR² losses. This results in poor efficiency.

Causes of low power factor

• The main cause of low PF is inductive Load (Usually, Induction motor works at poor power factor).
• Varying Load in Power System
• Electrical discharge lamps
• Industrial heating furnaces
• Harmonic Currents etc.

From above information, we can conclude that power factor is much more important in our electrical power system in case of tariff cost, losses, conductor size and so on. So it need to be improved for better operation of the system.

Some methods for power factor correction in power system:- 

• Capacitor banks

Power factor improvement is done by using capacitors is achieved by using static capacitors. The current drawn by the induction motors or electrical equipment working at lagging power factor can be drawn in phasor. The capacitor will draw a leading current by connecting a capacitor across the load, and will help to neutralize the reactive or wattless component of the current drawn by the equipment so that the power factor is improved.

For 3 phase system the capacitors can be connected in star or delta.

i. Star for commercial and industrial loads.

ii. Delta for distribution system.

Advantages:

1.Small losses and higher efficiency.

2.low initial cost.

3.little maintenance owing to absence of rotating parts

4.Easy installation being lighter in weight.

Disadvantages:

1.Short service life (8-10) years.

2.Sensitive to overvoltage.

3.Repair is expensive.

• Synchronous condenser

• An over-excited synchronous motor running on no load is called the synchronous condenser. It behaves like a capacitor.
• Power factor can be improved by using synchronous condenser like shunt capacitors connected across the supply.
•  Synchronous condensers are built in large units and are employed where a large quantity of corrective KVAR (>5,000 KVAR) is required.

Advantages:

i. By varying the field excitation of synchronous machine, the power factor can be improved to a finer value.
ii. Possibility of overloading a synchronous condenser for short periods.

Disadvantages:

i. Comparatively higher maintenance and operating costs.
ii. Lower efficiency due to losses in rotating parts and heat losses.
iii. An auxiliary equipment is required for starting synchronous condensers.

• Static var compensation (SVC)

• SVC stands for static var compensation.
• SVC model is automatic and fast react model for var compensation which is designed to bring power factor near to unity.
• SVC model components:-
• Thyristor controlled reactor (TCR),
• Thyristor switched capacitor (TSC)
• Harmonic filter(s)
• Mechanically switched capacitors or reactors
• It is used in power system (transmission voltage) and large industrial load (improve power factor) due to its fast action.

Advantages:

1. Higher capacity
2. Faster
3. More reliable than dynamic compensation schemes

Disadvantage:

1. More expensive than mechanically switched capacitors

• Phase advancer

1. The phase advancer is a simple AC exciter
2. It can be mounted on the same shaft of the main motor
3. It supplies exciting ampere turns to the rotor circuit at slip frequency.
4. It provides flux which results improve the power factor.
5. If further increase the excitation the power factor goes to lead like over excited synchronous motor.

Hence, it should be maintain always for a power system

Advantages:

1. The lagging power factor KVAR drawn by the induction motor can be considerably reduced by supplying leading ampere-turns at slip frequency.
2.The phase advancer is conveniently employed where the use of synchronous condenser is not suitable.

Disadvantage:

1. They are not economical for motors below 150 KW.