Circuits, Formulas and Tables Electrical Engineering  Basic vocational knowledge (Institut für Berufliche Entwicklung, 201 p.) 
7. Measurement Circuits 

Voltage measurement
2 voltage transformers in
Vconnection
Current measurement
Current measurement
Power measurement
Single wattmeter method
use:
equal phase loading, accessible PENconductor
result:
total power = 3 × measuring result
Power measurement
Twowattmeter method
use:
unequal phase loading, nonaccessible PENconductor;
measuring instruments of the same type have to be used
result:
total power = P_{1} + P_{2},
when P_{1} > P_{2}, the total power = P_{1}  P_{2}
Power measurement
Twowattmeter method
2 movements combined into one instrument
Power measurement
Threewattmeter method
use: unequal phase loading, accessible PENconductor
result: total power = P_{1} + P_{2} + P_{3}
Power measurement
Three  wattmeter method
3 movements combined into one instrument
Meter circuit (threewire meter)
Meter circuit (fourwire 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 Highvoltage Power
Plant