Contents
Trigonometric identites Frequently used in complex power calculations
Signal 
Instantaneous Power








Average , Maximum and Minimum power in terms of power factor (PF) 

Complex Power 

1. Apparent Power is the magnitude of the complex power.
2. Average/Real Power and Reactive Power is the real part and imaginary part of the complex power respectively.
3. Unit of reactive power is VARS 
Reactive Power (VARS) 


Average Power/Real Power



Complex Power 

1. Apparent Power =
2. The unit of apparent power is VA
3. Apparent power is the magnitude of the complex power. 
1. Complex Power 2. Real Power 3. Reactive Power 4. Apparent Power 


(Lagging power factor) (Leading power factor)
is the impedance angle, or power factor angle







Average value of 

Average value of 


Inductance of a coil with N turns, cross section area A, length L and core permeability 


Voltage induced across an inductor 


Voltage induced across a coil (w.r.t flux linkage ) 


Flux linkage and current relation 


Energy stored in an inductor 


Magnetic equivalent of electric current 
Source of EMF is battery 
Source of MMF is current coil 




A current entering the dotted terminal of one coil produces voltage with a positive voltage reference at the dotted terminal of the second coil. 



A current entering the dotted terminal of one coil produces voltage with a positive voltage reference at the dotted terminal of the second coil. 

Voltages and currents in terms of phasors 



Coefficient of mutual coupling 






Dot convention and current / voltage polarity reference 

Reflection of secondary into primary

Reflection of primary into secondary


Current and flux direction using right hand rule 

LENZ’S LAW
The direction of the induced voltage( in other words the current direction)will be such that it will oppose the change in the flux 

General Transformer Equation 

primary or secondary RMS Voltage Frequency of RMS Voltage turns of primary or secondary Peak value of flux 

Impedance Matching 
If the transformer is acting as an impedance matching device than


Bridge circuit can be used to determine the value of an unknown resistance.

The bridge is balanced if or.
When the bridge is balanced then




