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Level of high voltage increased in secondary of CT and no current in PT.
CT secondary will develop a very high voltage when secondary is open circuited
CT primary energised also secondary energised, but open circuited . it will burn
pt open circuit the voltage stable and not shorted because it give small current and need higher secondary resistance
Because high voltage develop in secondary of CT and in PT there is no such current develop
I assume you meant the secondaries and would like to divide the Answer in two portions.First, Why CT secondary is short circuited (if no burden is connected)?The current in the primary of CT is independent of secondary current. The primary is always in series with the load. Hence all load current, let's say Ip, must pass through the primary of CT. When CT is short circuited the current in the secondary (Is) will be in relation with the primary current(Ip). Now assume the secondary being opened, the secondary current will be zero but current in primary is still equal to the load current. Now keeping in mind the equivalent circuit of a transformer all this current will become magnetizing current. This magnetizing current(which in normal case is negligible) will increase the flux and hence there will be a great voltage induced on the secondary which will be in the order of kV. Since the terminals of secondary are very near in CT and are not insulated for that much voltage, a breakdown will occur between the terminals and will destroy CT.Second, Why PT secondary should be kept opened?when the secondaries are opened for a PT a very minor current is present in primary that is only magnetization current(or current due to other losses in reality). No suppose the secondary is short-circuited, the voltage presence on the secondary will make a huge amount of current in the order of kA to pass through the secondary of the PT. This current will damage the windings of the transformers.
