Transformer Tests

 We will continue our study on transformers, but today we will talk about the transformer in the event that there is no load on the secondary winding (At No Load) and in the event of a load (On Load):

In the case of no load (At No Load):

 That is, if the transformer is not loaded with loads and as we know that they are on the secondary coils, that is, in the secondary part it is considered an open circuit

 (Open Circuit), the aim of which is to determine the ratio of the voltage of the two windings and the power loss in the no-load state where one of the coils is connected

 Transformer coils with an electrical source of voltage and frequency equal to the rated voltage and frequency of the transformer, leaving the other coil open. and is connected

Voltmeter, ammeter, wattmeter in the circuit connected to the electrical source as shown

In the following figure as well as a voltmeter in the secondary open circuit. From the readings of the measuring devices, the following can be determined: K = V1 / V2

We find that the transformer in this case has a loss of power even though there is no load. The types of losses are divided into:

•  copper losses: I^2 .R
• Iron Losses (Core Losses): Caused by Eddy Current
• Hysterisis Losses: This type means that in the presence of a voltage source, the iron mold is magnetized until the density of the flux reaches

 (B) to a greater value, i.e. to (B1), and when the current is disconnected, the field strength (H) will not exist and the presence of
The flux density in the iron mold keeps decreasing until it reaches (B2), which is a value less than (B). And when it is turned on again, it returns to (B1), so it does not return to zero.

 In the event of a load on the transformer (At On Load), this test aims to:

• Determination of the equivalent impedance value of the transformer (equivalent resistance and equivalent reactance).
• Determine the value of the loss in copper in the case of total load, thus the efficiency of the transformer can be determined.
• Determining the value of the voltage loss in the transformer and thus determining the percentage change in the voltage regulation.

In this test, both ends of the secondary winding are connected to a thick rod (Short ct.) and a low voltage is applied to the primary winding (about 10%) so that it passes in the circuit approximately the value of the full load current, as shown in the following figure and since the value of the voltage It is low and therefore the flux in the iron core decreases and the loss in iron decreases with it, so it can be considered that the reading of the power device W (wattmeter) expresses the loss in copper.