Measurement Circuits

7. Measurement Circuits

7.1. Measurement Circuits in Direct-current Installations

Voltage measurement (A)

Voltage measurement (B)

By connecting in series of a resistor (Rv), an extension of the measuring range of the voltmeter is obtained

Current measurement (A)

Current measurement (B)

By connecting in parallel a shunt resistor (Rp), an extension of the measuring range of the ammeter is obtained.

Voltage and current measurement for the determination of the resistance

The current-exact connection is used when the resistance (Rx) to be determined, is very high.

Current and voltage measurement for the determination of the resistance

The voltage-exact connection is used when the resistance (Rx) to be determined is very small if the resistance Rx is calculated according to the following equation:

7.2. Measurement Circuits in Alternating-current Installations

Voltage measurement (low voltage)

Voltage measurement (high-voltage - voltmeter with voltage transformer)

Current measurement

Current measurement (amperemeter with current transformer)

Power measurement (low voltage)

Power measurement (high voltage)

electric meter connections

electric meter connections

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