Electrical Engineering ⇒ Topic : Short Circuit Test (S.C. Test)
In this test, one winding, usually the low voltage winding is short-circuited as shown in Figure (a). A small voltage is applied to the primary and is increased carefully till the current /1 in the primary winding reaches the rated full-load value. Under these conditions, the copper loss in the windings is the same as that on full-load. On the other hand, since the applied voltage and therefore the flux are only about 3% of the rated voltage and flux, the iron loss is negligibly small and hence the reading of the wattmeter, W. can be taken as only the copper loss in the windings. Also
FIGURE Short-circuit test on a transformer
where, Ze1, Re1 and Xe1 are the equivalent impedance, resistance and leakage reactance of the transformer referred to the primary side.
Short Circuit Test (S.C. Test)
In this test, the low voltage side is generally short circuited by a thick conductor. It is preferred to make it short circuit by an ammeter that may serve the additional purpose of indicating rated load current. In the high voltage side, the voltmeter, wattmeter, and an ammeter are connected. The circuit diagram is shown in Figure (a). The low voltage side is short circuited due to the following reasons:
The applied voltage is usually 5% to 10% of the normal applied voltage. So, there will be greater accuracy in the reading of the voltmeter in the H.V. side.
The rated current in high voltage side is lower than that of L.V. side. So this current can be safely measured with the ammeters available in the laboratory
Figure (a) Short circuit test of a transformer
In this test, the applied voltage is a small percentage of the normal voltage. So, the mutual flux (Φ) produced is also a small percentage of normal value. Hence, core losses can be neglected compared to that of full load copper loss. So, wattmeter reading will indicate the copper loss only.Let W be the reading of the wattmeter, I be the reading of the ammeter, and V be the reading of the voltmeter.
The high voltage winding is supplied at load voltage from a variable voltage supply. The supply voltage is gradually increased until the full-load primary current flows.
As we know,
!! OOPS Login [Click here] is required for more results / answer