3 Phase Autotransformer

1. What is a 3 phase autotransformer

3-phase autotransformer is a kind of autotransformer, which is mainly used in high power transmission and transformation occasions.

A 3-phase autotransformer is a special transformer in which the output and input share a set of coils.

Step-up and step-down are implemented with different taps, and the voltage of the part of the tap less than the common coil is reduced, and the voltage of the part of the tap more than the common coil is increased.

In fact, the principle is the same as that of ordinary transformers, the difference is that the primary coil is the secondary coil. In general transformers, the primary coil on the left generates a voltage through electromagnetic induction, and the autotransformer is its own influence.

A 3-phase autotransformer is a transformer with only one winding. When used as a step-down transformer, a part of the turns is extracted from the winding as a secondary winding; when used as a step-up transformer, the applied voltage is only applied to one part of the winding. on the turns.

2. 3 phase auto transformer working principle

The working principle of the 3-phase autotransformer is Faraday’s law of electromagnetic induction. According to this principle, as long as the magnetic field and the conductor change relatively, an electromotive force will be induced in the conductor. Consider a two-winding transformer as shown below.

When an AC voltage is applied to the primary winding, it induces an electromotive force in the primary winding due to the alternating nature of the magnetic field created by the AC source and the static conductors.

According to Faraday’s law of electromagnetic induction, there must be a relative displacement between the field and the conductor, in which case the field is alternating and the conductor is constant.

Therefore, an electromotive force is induced in the primary winding of the transformer.

Now consider the autotransformer circuit diagram shown in the figure below. Compared to the two-winding transformer shown in Figure 1, an autotransformer has a single winding.

When AC power is supplied to the primary circuit, due to Faraday’s law of electromagnetic induction, an electromotive force is induced in the primary part. Since the magnetic field is alternating in nature and the conductor is stationary.

The induced EMF in the primary produces a magnetic flux, called the primary winding flux. This flux connects the secondary winding and induces an electromotive force on the secondary winding due to mutual inductance.

Therefore, the electromotive force is transmitted in the secondary winding. According to the number of turns on the secondary side, the magnitude of the induced electromotive force is determined.

3. 3 phase auto transformer uses

The 3-phase autotransformer has a wide range of applications. It is mainly used to connect power systems of different voltages or improve the quality of line voltage. It can also be used as AC motor step-down starting equipment and laboratory voltage regulation equipment, etc.

4. 3 phase auto transformer kva calculation

A transformer is used to convert the incoming voltage at the location to the correct voltage for the electrical device (the submersible motor in case of ESP). Transformer selection is based on mainly 4 parameters:

• Power rating in KVA (Kilo Volt Amperes),
• Primary voltage,
• Secondary voltage,
• Tap arrangement.

We’ll detail how to calculate the required KVA for a 3 phase autotransformer. Actually, The calculation of KVA capacity for a Three Phase Transformer is based on Winding Voltage and Amperage information. The simple formula to calculate the rating of three phase Transformers are:

KVA = (√3. V x I) /1000
Where: V is the voltage (volts) and I is the current (amps).

5. 3 phase auto transformer connection

The autotransformer can be connected in parallel with loads when a voltage transformation is required. The load must be balanced and unbalanced. In the case of an unbalanced load, it is necessary to use a neutral grounding transformer. Connecting an autotransformer for parallel operation follows the same procedure as connecting any other alternating current transformer.

To connect an autotransformer for series operation, first determine which phase is connected to ground (zero potential) and which phase has no connection to ground (floating).

This can be accomplished by measuring voltage between each pair of phases using a voltmeter or power analyzer.

If two phases are at zero potential while the third remains floating then all three phases are connected in series across the source voltage terminals A1-A2-B1-B2-C1-C2; if any two phases have equal potentials while one remains at zero potential then all three phases are connected in parallel across the source voltage terminals A1-A2; if two out of three have equal potentials while one remains at zero then all three are connected through each other such that their individual connections form part of another circuit consisting entirely from connections within this group plus additional connections inside this group between each pair used for connecting its members together

6. Advantages of 3 Phase Autotransformers

3-phase autotransformers have many advantages over traditional double-wound transformers.

For the same VA rating, they are generally more efficient, smaller in size, and because they require less copper in the construction, they cost less than double-wound transformers of the same VA rating.

In addition, they have better voltage regulation than equivalent two-winding transformers due to their lower core and copper losses, I2R, due to their lower resistance and leakage reactance.

Other advantages of a 3-phase autotransformer over a two-winding transformer are:

• cheaper
• Higher efficiency because losses remain the same as rating increases compared to conventional transformers
• lower excitation current
• better voltage regulation

7. Disadvantages of 3-Phase Autotransformers

Some of the disadvantages of 3-phase autotransformers are:

• higher short-circuit current
• No isolation between primary and secondary windings
• Only suitable for moderately small voltage changes

8. 3 phase autotransformer price

3-phase autotransformers are available in a wide range of prices. First of all, if you want to buy a 3-phase autotransformer, you must first select the power and input and output voltage of the transformer.

This will allow you to get the correct 3-phase autotransformer quote.

Below I have listed the market prices of some commonly used 3-phase autotransformers. for reference only.

This price does not represent the price of Shuogong transformers. If you have a demand for the price of our transformers, you can contact us to inquire.