If we are visiting a switchyard and there are number of ct’s and cvt’s then how could we differentiate between cvt and ct?

If you mean ct as current transformer and cvt I'm not sure what you mean but if it means the voltage transformer, well visiting a switchyard by closely examining the connections of the bare cables to these devices, you can pin-point which is CT and/or VT. You can observe the ct is situated and connected along only one cable path in one phase while the vt you can see some cables connecting across to the other phases of the device. It just goes that measuring current is only in one phase while measuring voltage shall be taken across two phases.