Side-by-side comparison
| Parameter | Active | Reactive Load |
|---|---|---|
| Definition | Load that consumes real power (P in watts) and converts it to work or heat | Load that exchanges reactive power (Q in VAR) with the source without net energy consumption |
| Power Factor | Unity (PF = 1.0) for purely resistive load | <1.0; inductive loads: lagging PF; capacitive: leading PF |
| Current Phase Relationship | Current in phase with voltage (φ = 0°) | Current lags (inductive) or leads (capacitive) voltage by φ |
| Energy Billing | Billed in kWh — every watt-second consumed is paid | Not directly billed but penalized via kVA demand charge or PF tariff |
| Effect on Feeder Current | Increases I in proportion to P | Increases apparent current; same cable carries more I for same P delivered |
| Examples | Resistive heater (PF=1), incandescent lamp, DC motor with resistive load | Induction motor (PF=0.8 lagging), transformer at no-load (PF≈0.1), capacitor bank |
| Voltage Sensitivity | Active load current nearly independent of voltage (for resistive types) | Reactive load current highly sensitive to voltage — Q ∝ V² |
| Voltage Stability Impact | Moderate — voltage drop is IR type | Significant — voltage collapse risk if reactive demand exceeds supply capability |
| Correction Method | Not correctable — P consumed is the desired output | Shunt capacitors, SVCs (Static VAR Compensators), STATCOM |
| Feeder Loss Contribution | I²R loss proportional to active current component | Additional I²R loss from reactive current component |
Key differences
An active (resistive) load converts electrical energy directly to another form — a 2 kW resistive heater draws 2000/230 = 8.7 A at unity power factor; all current is in phase with voltage. A reactive load (induction motor, PF=0.85) drawing the same 2 kW draws 2000/(230×0.85) = 10.2 A — 17% more current through the feeder for the same delivered power, increasing I²R losses by (10.2/8.7)² − 1 = 38%. Reactive power varies with V²: if bus voltage drops 10%, reactive demand drops by 19%, which can trigger voltage collapse in a heavily loaded system. SVCs and STATCOM units dynamically compensate reactive load in transmission systems to maintain voltage within ±5% of nominal.
When to use Active
Minimize active load current by selecting high-efficiency equipment (IE3 motors, LED vs fluorescent) and controlling load scheduling — demand-side management reduces peak kW consumption and lowers maximum demand charges in commercial billing.
When to use Reactive Load
Compensate reactive loads using shunt capacitor banks at the load bus (fixed banks for base reactive demand) and SVCs or STATCOM units (for dynamic reactive compensation in grids with variable motor loads and arc furnaces).
Recommendation
Understand that reducing reactive load does not reduce kWh billing — it reduces apparent power (kVA) and feeder losses. Install capacitor banks to bring plant PF above 0.9 and eliminate TNEB PF penalty. Active load reduction (energy efficiency) reduces kWh billed. Both strategies are needed but target different line items on the electricity bill.
Exam tip: Examiners ask you to state why reactive current increases feeder losses even though it does no useful work — write "reactive current flows through feeder resistance, creating I²R losses; these losses are real power, wasted in the distribution system, not in the load."
Interview tip: Interviewers at power utilities (BESCOM, TSSPDCL) ask how voltage stability is related to reactive power — state that Q ∝ V² means voltage collapse risk increases as reactive demand rises, and that STATCOM injects capacitive Q dynamically to prevent this.