Session 10 Basics of Power Power in D

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

Power ü Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. ü Simply the power drawn is denoted by the product of current and voltage i. e. P = V x I watt (DC Power) ü D. C Power - P = V x I watt ü 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

Relation between Apparent, Active and Reactive Power

Definition: 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

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

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

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

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: ü Single phase (1ϕ) induction type meter ü Poly phase energy meter ü Digital Energy meter