Understanding Power Factor

Introduction

• Presenter: Paul from TheEngineeringMindset.com
• Topic: Power factor in electrical engineering.
• Structure: Basic concepts, analogies, advanced terms, work examples.

What is Power Factor?

• Definition: A unitless number used in AC circuits.
• Representation: Ratio between true power (KW) and apparent power (kVa).
• Formula: PF = KW / kVa.

Beer Analogy

• Glass of Beer: Represents power consumed.
  • Beer: True power (kW), does useful work.
  • Foam: Reactive power (kVar), less useful but necessary.
• Total Content: Apparent power (kVa), sum of true power and reactive power.

Electrical Engineering Perspective

• Power Triangle: Visual representation.
  • True Power (beer) = Adjacent line.
  • Reactive Power (foam) = Opposite line.
  • Apparent Power: Hypotenuse.
  • Theta (θ): Angle of apparent power from true power.
• Power Factor Calculation: Using trigonometry.

Residential vs. Commercial Use

• Residential Bills: Usually just kWh due to low power factor and consumption.
• Commercial Bills: Itemized including kWh, kVA, kVAr.

Why Electricity Providers Charge for Poor Power Factor

• Implications: Increases current flow, causes voltage drops, reduces distribution capacity.
• Cable Overload Risk: Higher current reduces capacity for new customers.
• Reactive Power Charges: Applied when power factor drops below supplier-defined level (~0.95).

Power Factor Grades in Buildings

• Good: 1 to 0.95.
• Poor: 0.95 to 0.85.
• Bad: Below 0.85.
• Commercial Office: Typically 0.98 to 0.92.
• Industrial: As low as 0.7.

Example: Induction Motors

• Motor Comparison (Both 10 kW)
  • Motor 1: PF = 0.87, draws 11.5 kVA (5.7 kVAr).
  • Motor 2: PF = 0.92, draws 10.9 kVA (4.3 kVAr).
• Calculations:
  • kVA = KW / PF
  • kVAr = sqrt(kVA^2 - KW^2).

Causes of Poor Power Factor

• Main Cause: Inductive loads.
• Resistive Load (Heater): Voltage and current in sync, PF = 1.
• Inductive Load (Motor): Voltage and current out of sync, lagging PF.
• Capacitive Load: Voltage held back, leading PF.

Correcting Poor Power Factor

• Adding Capacitors/Inductors:
  • Lagging PF (Inductive): Add capacitors.
  • Leading PF (Capacitive): Add inductors.

Impacts of Poor Power Factor

• Higher Current Draw: Required to do the same work.
• Larger Cables Needed: Increases installation cost.
• Penalty Fees: From electricity suppliers.
• Equipment Losses: Transformers, heat, reduced life expectancy.

Example: Capacitor Calculation for Correction

• Scenario: 3-phase supply, 50 kW load, PF from 0.78 to 0.96.
• Steps:
  • Current Apparent Power: 50 kW / 0.78 = 64.1 kVA.
  • Current Reactive Power: sqrt(64.1^2 - 50^2) = 40.1 kVAr.
  • Desired Apparent Power: 50 kW / 0.96 = 52.1 kVA.
  • Desired Reactive Power: sqrt(52.1^2 - 50^2) = 14.6 kVAr.
  • Capacitor Size Needed: 40.1 - 14.6 = 25.5 kVAr.

Closing

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