Okay, let's break down your power situation and the transformer options for your ABB robot. You're right to be cautious about fluctuations and ensuring you have the correct equipment. Using a transformer "backwards" (stepping up voltage) can work, but it's essential to choose the right type and understand the potential limitations.

Understanding Your Needs



Robot Requirements



Voltage

475V 3-phase

Power

7.2 kVA (Kilovolt-Amperes) - This is the apparent power your robot needs. It accounts for both real power (watts) and reactive power (VARs).

Shop Supply

208V 3-phase

Why Your Concerns Are Valid


Voltage Fluctuations

Your electricians are likely suggesting using a common step-down transformer "backwards" to step up the voltage. While this often works, standard step-down transformers aren't designed to tightly regulate output voltage when used in reverse. If your 208V supply fluctuates (which it will, even slightly), the 475V output will fluctuate proportionally. Robots, especially the sensitive electronics and drives, are often intolerant of significant voltage variations. A fluctuation of even 5% could cause issues and potentially damage components over time.2.

Transformer KVA Rating

Undersizing a transformer is a recipe for overheating, failure, and voltage drop. Oversizing is generally better (within reason) than undersizing.

Addressing the KVA Rating



Minimum KVA

You need a transformer rated at least at the robot's 7.2 kVA requirement.

Oversizing

It's good practice to add a safety margin of 20-25% to the transformer's kVA rating to account for:

Future Load Growth

If you plan to add other equipment to the same circuit later.

Inrush Current

Motors and some electronic components can draw a much higher current when they first start up. This is called inrush current. A larger transformer can handle this better.

Voltage Regulation

A slightly larger transformer will generally maintain a more stable output voltage under load.

Calculation

7.2 kVA 1.25 (25% safety factor) = 9 kVA. So, ideally, you should look for a transformer rated 9 kVA or higher. A 10 kVA transformer would be a common and good choice.

Transformer Options and Considerations


Standard Step-Up Transformer

This is the best solution, if available. These are specifically designed for stepping up voltage and typically offer better voltage regulation than running a step-down transformer in reverse. Look for a transformer that is designed to output 480v, since you are likely to see voltage drop in your wires.2.

Step-Down Transformer (Used Backwards)

If this is the route you must take, it's crucial to select the correct transformer and be aware of the limitations.

Voltage Taps

Look for a transformer with multiple voltage taps on the secondary (the 480V side when used normally) or even on the primary (the 208V side when used normally). These taps allow you to fine-tune the output voltage to get as close to 475V as possible. Without taps, you're stuck with whatever the transformer's inherent ratio provides.

Regulation

Ask the transformer supplier about the transformer's voltage regulation specification. This tells you how much the output voltage will change as the load (your robot) varies. Ideally, you want a transformer with good (low) voltage regulation.

Insulation

Make sure the transformer insulation rating is adequate for the voltage levels involved (especially the 475V side).3.

Buck-Boost Transformer

These are specifically designed for making small voltage adjustments (either up or down). They are not suitable for large voltage changes like 208V to 475V. Buck-boost transformers typically correct voltage by a relatively small percentage.4.

Autotransformer

An autotransformer could be an option, but they don't provide electrical isolation between the input and output. This can be a safety concern in some applications, especially if there are grounding issues. Autotransformers are often used for voltage adjustments but are not as common as isolation transformers for large step-up ratios.5.

Solid State Power Conditioner/Voltage Regulator

These are the most sophisticated (and expensive) option. They actively regulate the output voltage to maintain a constant level, even with fluctuating input voltage and load changes. They offer the best protection for sensitive equipment. These usually cost quite a bit more than traditional transformers.

Crucial Steps to Take


Consult with an Experienced Industrial Electrician

This is non-negotiable. They need to thoroughly evaluate your shop's electrical system, the specific transformer options available, and the robot's requirements. They can also advise on proper wiring, grounding, and safety measures. Make sure you're working with someone who understands 3-phase power and industrial equipment.2.

Get Specifications from the Transformer Supplier

Don't just rely on general advice. Get the exact specifications (voltage taps, regulation, insulation, etc.) for any transformer being considered.3.

Consider the Long-Term Cost

While a cheaper transformer might seem appealing initially, the potential cost of damaging the robot due to voltage fluctuations far outweighs the savings.4.

Check Local Electrical Codes

Ensure that any transformer installation complies with all applicable local electrical codes and regulations.

Key Questions to Ask Your Electrician (or a Transformer Supplier)

"What is the voltage regulation of this transformer?" "Does this transformer have voltage taps to allow fine-tuning of the output voltage?" "Is this transformer suitable for continuous operation at the robot's rated load?" "What is the inrush current rating of this transformer?"* "Will this transformer provide adequate isolation between the input and output?" (If considering an autotransformer, this is particularly important).

In summary: While running a step-down transformer backwards can work, it's not ideal for a sensitive piece of equipment like an industrial robot. Prioritize a proper step-up transformer or, at the very least, a step-down transformer with voltage taps and a sufficient kVA rating. Consult with a qualified electrician and get detailed specifications before making any decisions. It's better to spend a little more upfront to ensure the robot operates reliably and is protected from damage. Good luck! Flag for review