A current transformer (or CT) is constructed in a specific way so as to step down the current in a high power circuit for measuring or protective relaying purposes. Typically, it will have a toroidal-shaped iron core with the secondary windings wrapped around it. the primary "winding" is usually the conductor of the main power system passing directly through the hole in the center of the CT. As a result of this construction, if the secondary windings are left open, a very large flux can develop, resulting in damage to the CT and possibly even the other equipment it is attached to. As such, if the CT is not going to be used, its secondary windings need to be shorted.
why does have to short-circuit secondary wire of current transformer ?
Short circuit voltage is the voltage that has to be applied to the primaries of a transformer, so that the nominal current flows through the secondaries, when they are shorted. This value is important, if transformer secondaries shall be used in parallel. Ideally all transformers with parallel secondaries should have the same short circuit voltage. When their short circuit voltages are different, the transformer with the lower short circuit voltage will be loaded more than their relationship of power ratings would predict. The short circuit voltage is also important in the design of a transformer, because it predicts, how much the secondary voltage will drop at nominal output current. This knowledge helps the designer to find out, how many further windings the secondary needs for a certain voltage in relation to an ideal transformer. Short circuit voltage is also known as impedance voltage.
Open Circuit test is done to find out core losses of the transformers.which include Eddy Current Losses and Hysteresis Losses only, if during open circuit test secondary will have some load then I2R losses due to load current in secondary as well primary will be included in test results which is not desired while performing Open circuit test.
transformer is busted; if input voltage is normal you have short circuit or open circuit somewhere
Magnetizing inrush current has bigger 2nd harmonics compare to short circuit current. the second harmonics content is about >60% of fundamental harmonic. magnetizing inrush current happened when we energised the transformer, and short circuit current happened if there is a short circuit between different alive phase.
why does have to short-circuit secondary wire of current transformer ?
A short-circuit test is done to determine the power lost in the resistance of the primary and secondary windings of the transformer. It is done at full load current but with only enough voltage to give the required current with the secondary short circuited. An open-circuit test is done at full load voltage but no current is taken from the secondary, and this enables the power lost in the magnetic core of the transformer to be measured. As well a power, the tests also allow the inductances to be measured as well as the resistances, in order ot characterise the transformer fully.
Short circuit current will increase a lot.
A voltage transformer takes a primary voltage and steps it down to a smaller secondary voltage. This type of transformer will attempt to keep the secondary voltage at a specific ratio of the primary voltage. If you short it, massive current flow in the secondary is required to do this. For a similar reason a CT should never be open circuited - because it attempts to push a specific ratio of primary current through the secondary. If you open circuit the secondary, it takes a massive voltage on the secondary to accomplish this.
Short circuit voltage is the voltage that has to be applied to the primaries of a transformer, so that the nominal current flows through the secondaries, when they are shorted. This value is important, if transformer secondaries shall be used in parallel. Ideally all transformers with parallel secondaries should have the same short circuit voltage. When their short circuit voltages are different, the transformer with the lower short circuit voltage will be loaded more than their relationship of power ratings would predict. The short circuit voltage is also important in the design of a transformer, because it predicts, how much the secondary voltage will drop at nominal output current. This knowledge helps the designer to find out, how many further windings the secondary needs for a certain voltage in relation to an ideal transformer. Short circuit voltage is also known as impedance voltage.
The short-circuit test runs the rated current through the windings of the transformer to measure the copper-loss, or power lost in the winding resistances. Because the transformer is run at low voltage for this test, there is very little additional power loss in the iron core of the transformer.
If you take a power source like a dc battery or AC transformer secondary winding and connect an ammeter directly across these power sources you can read the short circuit current available from that source. This gives a measure of internal resistance of the battery or the available wattage of the transformer.
Winding copper losses of a transformer can be measured in a short circuit test of a transformer. Impedance voltage is given to the primary and the secondary is often shortcircuited. (some times the reverse is done of this). Full load currents are made to flow in both primary and secondary circuits. This current flow heats up the 2 windings of the transformer. Power consumed at this time gives the transformer copper losses.
Open Circuit test is done to find out core losses of the transformers.which include Eddy Current Losses and Hysteresis Losses only, if during open circuit test secondary will have some load then I2R losses due to load current in secondary as well primary will be included in test results which is not desired while performing Open circuit test.
transformer is busted; if input voltage is normal you have short circuit or open circuit somewhere
The basic principle of current transformer is same as that of the power transformer. Like the power transformer current transformer also contains a primary and a secondary winding. Whenever an alternating current flows through the primary winding alternating magnetic flux is produced, which then induces alternating current in the secondary winding. In case of current transformers the load impedance or "burden" is very small. Therefore the current transformer operates under short circuit conditions. Also the current in the secondary winding does not depend load impedance but depends on the current flowing in the primary winding.
The resistance of the winding in the primary of a transformer constitutes a load. As long as there is resistance then there is no short circuit. A short circuit is considered no resistance which develops an instantaneous high current. That is why fuses and breakers are inserted into the circuit to open the high current flow under a short circuit condition.