Can step down transformer be used as a step up transformer?

Answer 1

If the transformer has two separate windings, then, YES a step-down can be used as a step-up, and vice-versa.

It is more correct to say you are reversing the high and low sides.

By definition Primary is the "IN" side and Secondary is the "OUT" side.

The Primary could be the high voltage side if it is a step-down,
or it could be the low voltage side, if it is a step-up.

Design Considerations

Care must be taken when reversing the operation of a step-down transformer to insure that it does not exceed the ratings of the transformer. For example, let's say we have a 12 VA step-down transformer that takes 120Vac in and is rated to provide 12V at 1 amp at the secondary. If we were to reverse it and apply 12Vac to the new primary (the old secondary), we would have 120Vac at the new secondary, but to keep within the original ratings it could only be loaded to 0.1A @ 120Vac.

As long as you treat the output rating of the step-down transformer as the input rating as a step-up transformer, and don't try to draw current beyond what would normally have been applied to the high voltage primary, you should be fine. Potentially one could push up the voltage on such a transformer beyond what its stated application specified, while making sure not to exceed the power rating of the transformer and not exceeding the breakdown voltage of the transformer's insulation, for example driving the above transformer at 24V to get 0.05A @ 240Vac. It is important to realize though that the rated input voltage for a step-down transformer will likely not be a safe input voltage if you use it as a step-up transformer - for example, applying 120V to the above transformer with the windings reversed would generate 1.2KV!

One important point to remember when reversing a three-phase transformer to a step-up is what kind of windings it has. Most three-phase Transformers use a "delta" configuration on the primary side. This means that there are three "hot wires" and a ground, but not a neutral. (The white wire in a circuit). On the secondary side, transformers are usually wired up in a "Wye" (sometimes called a "star" configuration. Doing this allows the transformer to create a Neutral connection. If a step-down transformer is reversed to make it a step-up, the high (output) side will not have a Neutral connection. If one is not needed, say for a three-phase welding machine, this would not be a probem. However, if a Neutral IS needed ,say for lighting, reversing this transformer would not work. In this case, a listed step-up transformer will be needed. One final thing, if a step-down transformer is used as a step-up, a Neutral wire is not required to be connected to the input side.

Answer 2

Short answer yes they can.

Longer answer. one of the main advantages of AC distribution of power is that you can easily change voltages up or down through the use of transformers. This is true of single phase or 3 phase transformers. for example

Looking at the New Zealand system, power is generated at 11Kv at power stations, this is stepped up through transformers to either 110Kv or 330KV for distribution as it allows the use of cheap aluminum cable in the runs as power loss I2R is reduced by the high voltage, low current distribution. Then it is reduced to 33KV and 11KV for local feeds arround town. finally local street transformers reduced the voltage to 400volt 3 phase and 230 volt single phase feeds for local supplies.

Transformers that raise the voltage are called step up ransformers e.g. if I was to travel overseas, i would take a 100V- 230 step up transformer to allow me to use NZ devices overseas (so long as frequency is not a concern) and to use USA appiances in NZ is use a 230/110 volt step down transformer to reduce the voltage.

Answer 3

Transformers rated 3 KVA and larger three phase and 1 KVA and larger single phase can be reverse connected without any troubling effects or loss in KVA capacity. The reason there is this limitation in KVA size is because the turns ratio is the same as the voltage ratio. On transformers rated below 1 KVA single phase, there is a turns ratio compensation on the low voltage winding. This means the low voltage winding has a greater voltage than the nameplate voltage indicates at no load.

One crucial point that MUST be remembered when using a three-phase step-down transformer as a step-up transformer is the winding configuration. Basically there are two ways a transformer winding can be made, "WYE' (Sometimes called "Star", or "Delta". The exact meaning of this is not important to the discussion, but what IS important is how WYE and Delta windings behave. Usually on a step-up transformer, the "Primary" windings, (the High-voltage side), is a "Delta" configuration. This means there is no "Neutral" wire on the primary side. The low-voltage "Secondary" side is usually a WYE type, and it DOES have a Neutral lug in the transformer. When a transformer is reversed, the new secondary side will usually NOT have a Neutral. If one in needed, a designated step-up transformer will have to be purchased.

Answer 4

reverse the number of coils. A transformer uses the electromagnetic field from one set of wire coils to create a sympathetic field in a neighboring set of coils. The same amount of energy flows between the two sets, so in order to change high voltage into high current, increase the ratio of coils in favor of the high-current side.

Answer 5

It is ok to use a step down transformer to step up a voltage as long as you don't over rate it.

It the step down you're using is rated for 10 amps out put, make sure it will only draw 10 amps (preferably less) when used for step up.

Answer 6

Transformers do not work in DC circuits. They only work in AC circuits.

Answer 7

Yep. Transformers don't really care which direction power is being passed through them (whether it is from higher voltage to lower or from lower to higher).

Answer 8

Yes, but you might detect a slight difference in the voltage ratio.

Answer 9

if reversed so the secondary is primary and the primary is secondary it becomes a step-up transformer.

Answer 10

A transformer converts between two given voltages, and it does not matter which one is is the primary, connected to the supply, and the secondary, connected to the load.