April 23, 2021

1.Power factor

1.Power factor Definition

power factor is “cosine angle between voltage and current is told of power factor”. Power factor is a simple, unit-less ratio of real power to apparent power. Real power is the power used at the load measured in kilowatts (kW). Apparent power is a measurement of power in volt-amps (VA)

Power factor is an expression of energy efficiency. It is usually expressed as percentage and the lower the percentage.

Power factor is the ratio of working power, measured in kilowatts, to apparent power, measured in kilovolt amperes (kVA) apparent power. It is found by multiplying (kVA=V*A). The result is expressed as kVA units.

Power factor expresses the ratio of true power used in a circuit to the apparent power delivered to the circuit. A 96% power factor demonstrates more efficiency than a 75% power factor. PF below 95% is considered inefficient in many regions.

If a circuit were 100% efficient, demand would be equal to the power available. When demand is greater than the power available a strain is placed on the utility system. Many utility add a demand charge to the bill of large customers to offset differences between supply and demand.

For most utilities, demand is circulated based on the average load placed within 15 to 30 minutes. If demand requirement are irregular, the utility must have more reserve capacity available than if load requirements remain constant.

Peak demand is when demand is at its highest. The challenge for utilities is delivering power to handle every customer peak. Using power at the very moment it is in highest demand can disrupt overall supply unless there are enough reserves. Therefore, utilities bill for peak demand. For some larger customer, utilities might even take the larger peak and apply it across the full billing period.

Utilities apply surcharge to companies with a lower power factor. The coast of lower efficiency can be steep akin to driving a gas guzzling car.  The lower the power factor, the less efficient the circuit and the higher the overall operating coast.

The higher the operating coast, the higher the likelihood that utilities will penalization a customer for over utilization. In most ac circuits there is never power factor equal to one because there is always some impedance on the power lines.

2.How to calculate power factor

Power analyser that measures both working power (KW) and apparent power (KVA), and to calculate the ratio of KW/KVA.

The power factor formula can expressed

PF= (true power) / (apparent power) 

Cosø=KW/KVA=power factor

As this diagram demonstrates, power factor compares the real power being consumed to the apparent power, or demand of the load. The power available to perform work is called real power.

Power triangle figure:

electrical knowledge bank( power factor triangle)

COSØ= P/ VI

COSØ= KW/KVA

COSØ= true power/ apparent power

COSØ= R/Z

COSØ= KW/KVA =POWER FACTOR

  • apparent power in AC circuit has two components, active OR working power and reactive power
  • from trigonometric relation

                cosø =  working power / apparent power = KW/KVA

  • Thus the power factor of circuit may also be defined as the ratio of active power to the apparent power.
  •  For leading current, the power triangle becomes reversed.

3.Method of power factor improvement

there are three type of improve the power factor

*capacitor bank

*phase advancer

*synchronous condenser

3.1 capacitor bank

improve power factor means reducing the phase difference between voltage and current. since the majority of loads are inductive nature they require some amount of reactive power for them to faction

A capacitor or capacitor bank of installed parallel to the load provided the reactive power.

capacitor bank is reduce phase difference between voltage and current.

3.2 phase advancer

phase advancer mainly use to increase ampere turn in motor and operate leading power factor

phase advancer is AC exciter mainly use improve power factor of induction motor. they are mounted in shaft of the motor and connect to rotor circuit of motor.

3.3 synchronous condenser

synchronous condenser is like capacitor. its drawn the lagging current from supply. synchronous condenser are 3 phase synchronous motor with no load attend to its shaft.

synchronous motor operate in lagging, leading and unity depend on excitation.

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