Transient state

A system is said to be transient or in a transient state when a process variable or variables have been changed and the system has not yet reached a steady state.The time taken for the circuit to change from one steady state to another steady state is called the transient time.
Examples.
Chemical Engineering.
When a chemical reactor is being brought into operation, the concentrations, temperatures, species compositions, and reaction rates are changing with time until operation reaches its nominal process variables.
Electrical engineering.
When a switch is flipped in an appropriate electrical circuit containing a capacitor or inductor, the component draws out the resulting change in voltage or current (respectively), causing the system to take a substantial amount of time to reach a new steady state.
We can define a transient by saying that when a quantity is at rest or in uniform motion and a change in time takes place , changing the existing state , a transient has taken place.
When a SCR (four-layer PNPN Device) is switched on we have the problem of transients occurring as a result of high values of current and voltage oscillating around the point before normal levels are obtained again. Filtering can prevent damage to SCR by means of LC filters, zener diodes, trans-zorps, and varistors.