If I am using the car in a particular city, what premium rate is applied?

For the purpose of applying premium rate, the place where the vehicle is registered is reckoned (not the place where the vehicle is used). If your vehicle is registered in Chennai, the rate applicable for Zone A is charged. Even when you shift to a different city / town, the same rate will continue to be applied. Similarly if a vehicle is registered in a town, it attracts Zone B premium rate. Subsequently if the owner shifts to a metro, he will continue to be charged the Zone B rate.