Sir my question is how integral component eliminates the steady state error and physical significance of integral and derivative component in a PID controller.
An integrator has infinite gain for steady signal therefore any sudden error (due to a step change in demand for instance) will progressively become amplified until the action of feedback minimizes that error to zero.
Why not just have proportional gain at infinity? This would likely cause severe instability problems - a control system would hunt about the set point in many, many situations. Integration provides a "calmer" and more gradual way of dispensing infinite gain.
Derivative is a means of slowing down the action of a control system when faced with a step change in demand - this naturally means that mechanical overshoots are not as great and therefore some systems can "come into lock" quicker.