Okay, this is a fun challenge! You're right, finding a small 240 Delta to 380Y/220 3-phase transformer is a pain and often overpriced. Let's brainstorm some creative (and potentially slightly unorthodox) solutions

Before we dive in, a few crucial safety warnings:
Safety First

Dealing with 3-phase power is dangerous. If you're not a qualified electrician, do not attempt any of these solutions yourself. This is for informational purposes only.

Code Compliance

Any solution needs to adhere to local electrical codes. What's acceptable DIY in one area might be a violation (and a fire hazard) in another.

Grounding is Critical

Ensure proper grounding of the transformer, motor, and enclosure for safety.

Overcurrent Protection

Properly sized fuses or circuit breakers are essential to protect the transformer and motor.

Voltage Tolerance

Motors typically have some voltage tolerance (usually +/- 10%), but consistently running outside that range can reduce lifespan or cause damage.Now, let's explore some ideas:

1. Delta-Wye Bank from Single-Phase Transformers (Your Idea, Refined)



The Core Idea

You're on the right track. Using three single-phase transformers connected in a Delta-Wye configuration is a viable (though sometimes less efficient) way to achieve 3-phase voltage transformation.

The Problem: Finding the Right Transformers

You're struggling to find 240V primary to 220V secondary single-phase transformers. Let's re-think the ratios:

The Correct Ratio is Key

You need a voltage ratio of 240V (primary) to 220V (secondary line-to-neutral). That's a ratio of 1.09:1 (240/220). The secondary line-to-line voltage would be 380 ( 220 SQRT(3))

More Common Ratio

The voltage ratio of 1.1:1 (240/220) is very close to that. You can find a transformer rated at 220VA

Sizing

You'll need to size the single-phase transformers appropriately. Your motor is 0.75 kW, which is roughly 0.75 kVA (assuming a power factor of close to 1). Since you're splitting the load across three transformers, each transformer needs to handle approximately 0.25 kVA or 250VA. However, it's good practice to oversize them a bit (1.25 - 1.5x) to account for inrush current and any potential imbalance. So, look for transformers in the 300-500VA range per transformer.

Connection Diagram

The key is getting the Delta-Wye wiring correct. There are plenty of examples online of delta/wye 3 phase transformer winding diagrams. You will wire 3 single phase transformers to accomplish this.

Important Note

Transformer VA ratings are usually given in the standard kVA rating.

Common Voltages, Close Ratios

Consider control transformers. For example, 240V to 120V (or even 480V to 240V) control transformers are much more common. You could use two stages of transformers to get your voltage. 240V to 120v x 2 parallel would make 240 to 240V . If wired into a Wye secondary 240/SQRT(3) = 138V. This would still not work.

2. Consider a Variable Frequency Drive (VFD)



The Idea

A VFD can take your 240V single-phase power (or potentially 240V 3-phase) and generate the appropriate 380V 3-phase power for your motor.

Pros

Potentially cheaper than a transformer (especially for smaller motors). Provides speed control for your motor, which can be a huge benefit. Can improve motor efficiency.

Cons

Requires programming and understanding of VFD parameters. May introduce harmonic distortion into your power system (though modern VFDs often have mitigation features). Motor needs to be VFD-compatible (most modern motors are).

Important

Check VFD input voltage requirements. Some need 3-phase input.

3. Motor Voltage Change (If Possible)



The Idea

Can you re-wire the motor itself to run on a different voltage? Some motors have dual voltage ratings (e.g., 220-240V / 380-415V). If your motor can be wired for 240V Delta, you could potentially run it directly from your 240V 3-phase supply.

Pros

Simplest and cheapest solution (if possible). No transformer needed.

Cons

Requires motor to be dual-voltage and compatible with your supply voltage. May require changing the wiring inside the motor's junction box.

Caution

Carefully check the motor's nameplate for voltage ratings and wiring diagrams.

4. Search For Obscure Transformers



eBay/Surplus

Scour eBay, surplus equipment dealers, and industrial auctions. You might get lucky and find a used transformer that meets your needs at a fraction of the cost.

Custom Build (Last Resort)

Contact a transformer manufacturer and get a quote for a custom-built transformer. This will likely be the most expensive option, but it guarantees you get exactly what you need.

5. Rent a Transformer



The Idea

Since you said it won't be used much, renting a suitable transformer might be the most cost-effective solution.

Pros

Avoids the capital expenditure of buying a transformer. You only pay for the time you use it.

Cons

Not suitable for continuous use.* Rental costs can add up over time if used frequently.

Recommendation:

I'd start by thoroughly investigating the motor's nameplate and seeing if it can be re-wired for 240V Delta. That's the simplest and cheapest (if possible) solution. If not, I'd seriously consider the VFD option, especially if you want speed control. The Delta-Wye bank using single-phase transformers is viable, but more complex to wire and requires careful sizing of the transformers. The price of the transformers, along with the price of an enclosure, and safety precautions, can easily add up to the price of a new 3 kVA transformer. Flag for review