A question about transformers

[herich]

There are primary and secondary coils in a transformers. So, what hat are the difference between when the secondary coil is in 1)open circuit, 2)closed circuit with a load, and 3) shorted circuit?

When can the ideal transformer equation be used? It seems that not only is it related to whether the transformer is ideal or not, but also related to which case (1, 2, or 3 above) the secondary coil is in.

I'm much confused. Please help clarify my concept! Thanks.

 

[cabraham]

1) open circuit - primary current is the magnetizing current plus the hysteresis and eddy current components. The total is called "exciting current". Vp/Np = Vs/Ns, as the P & S voltages are directly proportional to the turns ratio. Open secondary should only be used with voltage transformers, never with current transformers.

2) loaded - secondary current established with load and Ohm's law. If primary is constant voltage driven, then secondary displays constant voltage behavior. Vp/Np = Vs/Ns, and NpIp = NsIs.

3) short circuit - must never be used with voltage transformers, but is ok with current transformers. NpIp = NsIs. This is used when measuring current across an isolation boundary. The secondary is isolated and allows connecting an ammeter so that large currents can be safely measured. If the turns ratio is 50 to 1, then 50 amp line currents can be measured with a 1.0 amp meter.

Does this help?

 

[baba89]

Hello,

Thank you for your question about transformers. The primary and secondary coils in a transformer are essential components that allow for the transformation of electrical energy from one circuit to another. The primary coil is connected to the input voltage source, while the secondary coil is connected to the output load.

The main difference between the secondary coil in an open circuit, closed circuit with a load, and shorted circuit is the presence or absence of a load. In an open circuit, there is no load connected to the secondary coil, meaning that there is no current flowing through it. In a closed circuit with a load, the secondary coil is connected to a load, and current can flow through it. In a shorted circuit, the secondary coil is connected directly to the primary coil, causing a high current to flow through the transformer.

The ideal transformer equation can be used in all three cases, but it is most accurate in an open circuit or closed circuit with a load. In these cases, the transformer is considered ideal because there is no energy loss due to resistance. In a shorted circuit, there is energy loss due to the high current flowing through the transformer, so the ideal transformer equation may not be as accurate.

I hope this clarifies your concept and helps you better understand the role of the secondary coil in different circuit configurations. If you have any further questions, please feel free to ask. Thank you.