Specifications

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Precaution while using Insulation tester (megger):
1. Portable testers (meggers) come in 50, 100, 250, 500 or 1000 volts. It is important to
use the right tester for the right system. Low voltage testers are required for low voltage
systems, and high voltage testers for high voltage. Higher voltage is generally used for
commercial systems, motors or transformers. Some digital testers work over a range
of voltage and can be set for higher or lower volts.
2. Before applying the tester, be sure to disconnect the power from the system being
tested.
3. Disconnect all electronics. These can get damaged during the testing process. Double
check to be sure all electronics are disconnected prior to testing. This is a common
and very costly mistake.
7.5 MEASUREMENT OF POWER:
In a DC circuit: The power in DC circuit is given by P = V x I,
Where V = Voltage and I = current. The power can be measured practically with the help of just
voltmeter and Ammeter. The circuit diagram for measuring power in DC circuit is shown in Fig. 7.10.
Fig.7.10 - Voltmeter – Ammeter method
Total power (P) = Voltmeter meter reading x Ammeter reading
In 1-phase AC circuit:
Power in 1-phase AC circuit is given by P = VICosφ,
Where V = Voltage, I = current and , Cosφ = power factor.
Wattmeter Wattmeter is used to measure power in AC circuits. The circuit diagram is
shown in Fig.7.11
Fig.7.11 - Power measurement in 1-phase AC circuit
Total power (P) = Wattmeter reading = VICosφ.
From this power factor can be calculated as follows
Cosφ = P/ VI