Power factor plays a crucial role in efficient power usage and reducing energy losses in electrical systems. In industries and commercial installations, a low power factor leads to higher electricity bills and penalties. This article covers why power factor improvement is important, the methods used, and how to calculate the required capacitance for correction using capacitor banks.
🔍 What is Power Factor?
Power factor (PF) is the ratio of real power (kW) to apparent power (kVA). It indicates how effectively electrical power is being converted into useful work output.
Formula:
Power Factor (PF) = Real Power (kW) / Apparent Power (kVA)
It is also equal to the cosine of the angle between voltage and current:
PF = cos(θ)
⚠️ Importance of Power Factor
- High PF reduces power losses in cables and transformers.
- Increases the efficiency of the power system.
- Reduces electricity bills and avoids penalties.
- Enables better voltage regulation and system capacity utilization.
💸 Penalties for Low Power Factor
In India and many other countries, utility companies impose penalties if the power factor drops below a specified value (usually 0.9 or 0.95). The consumer may be charged extra if:
- Lagging PF causes increased demand (kVA).
- It increases the burden on the supply system.
For example, if an industry has a monthly PF of 0.75 instead of the desired 0.95, it may pay up to 20–30% extra in demand charges.
⚙️ Methods for Power Factor Improvement
The following methods are commonly used to improve power factor in industries:
1. Capacitor Banks
Capacitor banks are the most widely used method for power factor correction. They supply leading reactive power (kVAR) to neutralize the lagging reactive power drawn by inductive loads like motors and transformers.
Types of Capacitor Banks:
- Fixed Capacitor Bank
- Automatic Power Factor Correction (APFC) Panel
- Detuned Filter Capacitor Bank (for harmonic environments)
🔢 Formula to Calculate Required Capacitance:
To improve power factor from initial value (cos φ1) to desired value (cos φ2):
Qc = P × (tan φ1 - tan φ2)
Where:
- Qc = Reactive power (kVAR) to be supplied by capacitor
- P = Active power in kW
- φ1 = cos-1(initial PF)
- φ2 = cos-1(desired PF)
📌 Example:
Suppose a factory has a 100 kW load with an initial power factor of 0.75 lagging and wants to improve it to 0.95.
- Find φ1 = cos-1(0.75) = 41.41°
- Find φ2 = cos-1(0.95) = 18.19°
- Qc = 100 × (tan 41.41° - tan 18.19°) = 100 × (0.88 - 0.33) = 55 kVAR
So, a 55 kVAR capacitor bank is required for correction.
2. Synchronous Condensers
A synchronous condenser is an over-excited synchronous motor that runs without a mechanical load. It generates leading reactive power and improves the system’s power factor.
Advantages:
- Can adjust reactive power output dynamically.
- Provides short-circuit support.
- More suitable for large-scale and dynamic load conditions.
Disadvantages:
- High initial cost and maintenance.
- Needs excitation and protection systems.
3. Phase Advancers
These are special devices used to improve PF in large induction motors. They are installed on the rotor side and reduce the lagging component of current drawn by the stator.
📈 Benefits of Power Factor Correction
- Reduces electricity bill by lowering demand charges.
- Increases load carrying capacity of the system.
- Reduces transformer and generator losses.
- Improves voltage level at load terminals.
- Reduces CO₂ emissions due to improved energy efficiency.
🧮 Capacitance Calculation from Reactive Power
After calculating the required kVAR (Qc), you can determine the capacitance (C) needed:
Formula:
C = Q / (2 × π × f × V²)
Where:
- C = Capacitance in Farads
- Q = Reactive power in VAR
- f = Frequency (usually 50 Hz)
- V = Line voltage in Volts
Ensure to convert kVAR to VAR and use RMS phase voltage or line voltage accordingly (based on connection: star or delta).
🛠️ Practical Tip:
Industries often use Automatic Power Factor Controllers (APFC) which monitor the PF in real time and switch capacitor steps as needed. This maintains the PF close to 1.00 without manual intervention.
📚 Conclusion
Maintaining a high power factor is essential for reducing losses, avoiding penalties, and improving the overall performance of electrical systems. Capacitor banks are the most popular and cost-effective solution, while synchronous condensers are suitable for large and dynamic systems. Accurate calculation and timely correction can result in substantial savings for industries.
❓FAQs on Power Factor Improvement
Q1. What is a good power factor?
- A good power factor is typically above 0.95. Most utilities recommend PF > 0.95 lagging.
Q2. What are the penalties for low PF?
- Industries may face higher kVA demand charges or penalties ranging from 15% to 30% on their electricity bills.
Q3. Which device is used for power factor correction?
- Capacitor banks, synchronous condensers, and phase advancers are used to correct power factor.
Q4. Can PF be greater than 1?
- No, power factor cannot exceed 1. Leading power factor near 1 is possible using capacitors.
Q5. What is kVAR?
- kVAR is the unit of reactive power. It measures the power stored and released by inductive and capacitive elements.