Measuring three-phase power – Which instrument(s) are used? Statement: “Power is measured in a three-phase load by using an ammeter.” Choose the correct evaluation.

Introduction / Context:
Accurate measurement of real power in three-phase circuits is critical for energy audits, motor testing, and tariffs. Knowing the correct instruments and methods prevents large errors that would arise from current-only measurements.

Given Data / Assumptions:

• Three-phase, possibly unbalanced load, with sinusoidal voltages.
• Conventional measurement techniques apply (one-, two-, or three-wattmeter method).
• Goal: real power (not just current).

Concept / Approach:

Real power depends on voltage, current, and phase angle: P = √3 * VL * IL * cos(phi) for balanced three-phase systems. An ammeter measures only current magnitude. Real power requires wattmeters that sense both voltage and current with proper phase relation.

Step-by-Step Solution:

Verification / Alternative check:

Compare computed power using only current against true wattmeter readings in a lagging power-factor load; discrepancies prove that current alone is insufficient.

Why Other Options Are Wrong:

Any qualified “True” still fails because even with known voltage, unknown power factor makes ammeter-only insufficient for real power.

Common Pitfalls:

Confusing apparent power (kVA) with real power (kW); overlooking unbalance and harmonic effects requiring appropriate instruments.

Final Answer:

False.