An example of measured values is given in the following table. This measurement was made for a primary coil with turns and a primary voltage of 6 V. If we plot the measured values, we can see that induces secondary voltage is directly proportional to the number of turns on the secondary winding:.
Since voltage in the graph is shown in millivolts, the shown slope of the line and hence the voltage per turn is Note: The power supply used, when set to 6 V, gives the voltage of 6.
Then the ratio of primary voltage and number of turns is 0. Another unconventional view of the transformation ratio is offered in the task Transformer and the experiment Winding of a Coil. Induced Voltage Experiment number : Experiment filter active? Choose required ranks and required tasks.
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Necessary tools Easily obtained tools and equipment Tools and equipment usually found at schools Specific tools and equipment required. Preparation time Under 3 minutes 3—10 minutes Longer than 10 minutes. Duration of experiment Under 3 minutes 3—10 minutes Longer than 10 minutes. This winding is called the secondary winding. The amount of voltage induced in each turn of the secondary winding will be the same as the voltage across each turn of the primary winding; this is referred to as the transformer turns ratio.
If the secondary winding has fewer turns than the primary, a lower voltage will be induced in the secondary. This type of transformer is called a step-down transformer. A secondary coil with twice as many turns as the primary will be cut twice as many times by the magnetic flux , and twice the applied primary voltage will be induced in the secondary. This transformer is known as a step-up transformer.
Note: The primary is always connected to the source of power , and the secondary is always connected to the load. Either the high- or low-voltage winding can be the primary or the secondary. The total induced voltage in each winding is proportional to the number of turns in that winding and the current is inversely proportional to both voltage and number of turns.
E1 is the primary voltage and I1 the primary current, E2 the secondary voltage and I2 the secondary current, N1 the primary turns and N2 the secondary turns. If voltage is stepped up, the current must be stepped down and vice versa. The number of turns remains constant unless there is a tap changer. If the primary voltage of a transformer is volts V , the primary winding has turns, and the secondary winding has turns, what will the secondary voltage be? Since there is a ratio of 1 to 4 between the turns in the primary and secondary circuits, there must be a ratio of 1 to 4 between the primary and secondary voltage and a ratio of 4 to 1 between the primary and secondary current.
As voltage is stepped up, the current is stepped down, keeping volts multiplied by amps constant. This is referred to as " volt amps. Calculate the ratio of each three-phase winding based on the line to neutral voltage of the wye winding. Divide the line-to-line winding voltage by 1.
Check the tap changer position to make sure it is set where the nameplate voltage is based. Otherwise, the turns ratio test information cannot be compared with the nameplate. The turns ratio test is capable of detecting shorted turns in the winding , which indicate insulation failure by determining if the correct turns ratio exists.
Shorted turns may result from short circuits or dielectric failures. Measurements are taken by applying a known low voltage across one winding and measuring the induced-voltage on the corresponding winding. The low voltage is normally applied across a high-voltage winding so that the induced-voltage is lower, reducing hazards while performing the test.
Look at the nameplate phasor diagram to find out what winding on the primary corresponds to a winding on the secondary. The voltage ratio obtained by the test is compared to the nameplate voltage ratio.
The ratio obtained from the field test should fall within 0. New transformers of good quality normally compare to the nameplate within 0. The test is performed and calculated across corresponding single windings. How hard is it to get new test equipment at your company?
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