7.3. Measurement Circuits in Three-phase Installations

Voltage measurement

2 voltage transformers in V-connection

Current measurement

Current measurement

Power measurement

Single wattmeter method

use:

equal phase loading, accessible PEN-conductor

result:

total power = 3 × measuring result

Power measurement

Two-wattmeter method

use:

unequal phase loading, non-accessible PEN-conductor;
measuring instruments of the same type have to be used

result:

total power = P₁ + P₂,
when P₁ > P₂, the total power = P₁ - P₂

Power measurement

Two-wattmeter method
2 movements combined into one instrument

Power measurement

Three-wattmeter method

use: unequal phase loading, accessible PEN-conductor
result: total power = P₁ + P₂ + P₃

Power measurement

Three - wattmeter method
3 movements combined into one instrument

Meter circuit (three-wire meter)

Meter circuit (four-wire meter)

Measurement of the power factor (cos j)

Measurement of the frequency (single frequency meter)

Measurement of the frequency (double frequency meter)

Measurements in a High-voltage Power Plant