Question

An autotransformer is used to connect a 10.4 kv distribution line to a 11.9 kv distribution line. it must be capable of handling 1.5 mva. there are three phases, connected y-y with their neutrals solidly grounded. round your answers to only two digits to the right of the decimal point.

(a) what must the turns ratio be to accomplish this connection?
(b) how much apparent power must the windings of each autotransformer handle?
(c) if one of the autotransformers were reconnected as an ordinary transformer, what would its ratings be? autotransformer connecting two three phase power systems.

Answer 1

For an autotransformer connecting a 10.4 kV line to an 11.9 kV distribution line, the turns ratio would be 11.9 kV / 10.4 kV. Each phase would need to handle 1.5 MVA / 3 of power. If reconfigured as an ordinary transformer, the ratings may differ and would need to be determined based on standardized transformer ratings.

Step-by-step explanation:

An autotransformer can connect different voltage levels within a power distribution network. In the given scenario, a 10.4 kV line must be connected to an 11.9 kV line, and the autotransformer must handle 1.5 MVA of power. Since the transformer is connected in a Y-Y configuration with solidly grounded neutrals, we can calculate the necessary parameters.

Autotransformer Turns Ratio

The turn ratio of an autotransformer is determined by the ratio of the voltages it connects. Here the ratio would be 11.9 kV / 10.4 kV.

Apparent Power Per Phase

For a three-phase system, the total MVA rating is shared among the three phases, which means that each winding must handle a third of the total power. This comes down to 1.5 MVA / 3.

Reconfigured as an Ordinary Transformer

If the autotransformer were to be reconfigured as a conventional transformer, the voltage and power ratings could differ depending on the configuration. Typically, you would need to refer to standardized ratings to determine the potential capacity when used as an ordinary transformer.