If a circuit is switched from one condition to another either by a change in the applied voltage or change in a circuit parameter, there exists a transitional period during which the branch currents and voltage drops change from their former values to new ones. After transition period, the circuit becomes steady.
The transient disturbances in the electrical circuits are disturbances caused by sudden switching off and on or short circuit of the circuit and sudden change in the applied voltage. The current developed in the circuit due to this disturbance is called the “transient current”. The “resultant current” in the circuit is the steady state current with a transient current superimposed. The transient currents are found to be associated with the changes in stored energy in capacitors and inductors. Hence in a purely resistive circuit no transient current is developed since there is no stored energy in a resistor.
Single energy and double energy transients :
• Single energy transient is the transient disturbance where only one form of energy, either electromagnetic or electrostatic is involved e.g., transient disturbance in a circuit consisting of resistor and inductor i.e., R-L circuit or a circuit consisting of resistor and capacitor i. e., R-C circuit.
• Double energy transient is the transient disturbance where both electromagnetic and electrostatic energies are involved e.g., transient disturbance in a circuit consisting of resistor, inductor and capacitor i.e., R-L-C circuit.