1. Session - 10 Basics of Power Power in D.C and Power in A.C.
Types of instruments (wattmeter) for measurement of power
Working of EDM type wattmeter
Power factor
Measuring Instruments
Energy

2. Power
Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit.
Simply the power drawn is denoted by the product of current and voltage i.e. P = V x I watt (DC Power)
D.C Power - P = V x I watt
A.C Power - P = V x I Cos φ
Unit of power:
watt or W - Active Power or Real Power
or True Power
VA - Apparent Power
VAR - Reactive Power

3. Relation between Apparent, Active and Reactive Power

4. Definition: P = V I Cos φ Active Power:
Capacity of the circuit for performing work in a particular time
Apparent Power:
It is the product of current and voltage
Reactive Power:
It is the resultant power in watts of an AC circuit when the current waveform is out of phase with the waveform of the voltage, usually by 90 degrees if the load is purely reactive, and is the result of either capacitive or inductive loads.
Power Factor:
It is the ratio of the real power flowing to the load to the apparent power in the circuit. It is a dimensionless number.
P = V I Cos φ

5. Instruments for Measuring Power
EDM wattmeter
Ferro dynamic wattmeter
Low power factor wattmeter
Thermocouple wattmeter
Three Phase (3 ϕ) wattmeter

6. EDM wattmeter
Current Coil(CC) – To Sense Current
Voltage Coil or Pressure Coil – To sense voltage

7. Instruments to Measure Power Factor
Single phase (1ϕ) EDM power factor meter
Three Phase (3θ) EDM power factor meter
Moving Iron power factor meter

8. Energy
Definition:
It is the total power delivered or consumed over a time interval
Energy = power x time
Unit of Energy:
joule or watt second (one watt over an interval of one second)
Measuring Instruments:
Single phase (1ϕ) induction type meter
Poly phase energy meter
Digital Energy meter