Generation of High Alternating Voltage
- Cascaded transformer method
- Cascaded transformer unit with isolating Transformer
- resonant transformer
Cascaded transformer method
Two or more electrical transformers connected in series to generate high voltage alternating current. high voltage transformers are normally used in high voltage laboratory for testing purpose.
The principle of cascade excitation of transformers, particularly those connected in a circuit in which each transformer in turn is excited from a part of the step-up winding of the preceding transformer, is usually used.
For voltages higher than 400 KV, it is desired to cascade two or more transformers depending upon the voltage requirements. Actually for getting such high voltage, a single transformer has to be very huge in size which is not at all economical. The transformers are usually identical, but transformers of different designs can also be used. With this, the weight of the whole unit is subdivided into single units and, therefore, transport and erection becomes easier.
The primary of the stage-I transformer is connected to a low voltage supply. A voltage is available across the secondary of this transformer. The excitation winding (tertiary winding) of first stage has the same number of turns as the primary winding, and feeds the primary of the second stage transformer. The potential of the excitation is fixed to the potential of the secondary winding.
The secondary winding of the second stage transformer is connected in series with the secondary winding of the first stage transformer, so that a voltage of 2V(Double) is available between the ground and the terminal of secondary of the second stage transformer. Similarly, the stage-III transformer is connected in series with the second stage transformer. With this the output voltage between ground and the third stage transformer, secondary is 3V.
It is to be noted that the individual stages except the upper, must have three winding transformers. The upper most, however, will be a two winding transformer.
The tank of stage-I transformer is earthed. The tanks of stage-II and stage-III transformers have potentials of V and 2V, respectively above earth. therefore, these must be insulated from the earth with suitable solid insulation Through high voltage bushings. the leads from the excitation winding and the high voltage winding are brought out to be connected to the next stage transformer.
- the impedance of transformer is should be less than 5%.
- transformer must be capable for giving a short circuit current for at least more than one minute. and it is depending on design.
- cascade connection of transformer very high voltage is possible to generate at lowest cost.
- size is compact .
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