VSDs & Isolation Transformers – What / When / Why

Why Use an Isolation Transformer with a VSD/VFD?

Variable Speed Drives (VSDs) — also known as Variable Frequency Drives (VFDs) — are a powerful tool for improving efficiency and control in electric motor systems. But while VSDs offer great performance benefits, they can also introduce electrical noise, harmonics, and safety concerns that need to be managed.

At SES Transformers, we often supply 3-phase isolation transformers specifically for VSD applications — and for good reason.

VSD’s entered industry in the 80’s and 90’s, but It has really been in the last 10 years that the use of VSD’s has really gone crazy, becoming a near-standard inclusion in most motor control systems. They are more integrated into building management, automation and industrial applications across the board. And with good reason. They provide great benefits, such as energy saving, extended equipment lifespan, and precise equipment control.

What Is a VSD and Why Does It Matter?

VSDs are electronic devices that control motor speed by varying the supply frequency and voltage. They’re widely used in:

• Industrial automation
• Pumps and fans
• HVAC systems
• Conveyors and processing equipment

However, because VSDs convert AC to DC and back to variable-frequency AC, they can produce:

• Harmonics and electrical noise
• Voltage transients and spikes
• Earth leakage currents

This is where an isolation transformer can play a critical role.

5 Key Reasons to Use an Isolation Transformer with a VSD

✅ 1. Electrical Safety and Galvanic Isolation

Isolation transformers separate the input supply from the output circuit, preventing direct electrical connection. This is especially important:

• When feeding VSDs from an untrusted or noisy supply
• In installations requiring extra fault protection or earthing separation
• To protect personnel and equipment during fault conditions

✅ 2. Harmonic Mitigation and System Protection

VSDs generate harmonics that can impact upstream equipment. A properly designed transformer:

• Reduces harmonic distortion on the supply side
• Helps prevent interference with other systems
• Improves power quality and compliance with standards
• Bonus: Transformers with electrostatic shielding can further reduce high-frequency noise.

✅ 3. Voltage Matching (Step Down or Step Up)

Many VSDs are designed for 400V input, but Australia’s standard 3-phase supply is 415V. An isolation transformer can:

• Match voltage for optimal VSD operation
• Convert from 415V to 380V, 400V, 220V, or other international voltages
• Provide both voltage conversion and isolation in a single unit

✅ 4. Surge and Transient Protection

Isolation transformers provide a buffer between the VSD and the incoming supply, helping to absorb:

• Voltage spikes
• Switching transients
• Electrical disturbances from industrial equipment
• This improves the longevity of both the VSD and the motor.

✅ 5. Better Grounding Strategy

In some systems, especially those with sensitive electronics or long cable runs, isolating the ground reference can:

• Prevent ground loops
• Minimise nuisance tripping
• Improve EMC (Electromagnetic Compatibility)

When Is It Not Required?

In some simpler or lower-risk installations, a VSD may be directly connected to the mains with minimal filtering or protection. In these cases, line reactors or EMI filters might be used instead of a transformer.

But when safety, reliability, or compliance are critical — an isolation transformer is often the smarter choice.

SES Transformer Solutions for VSD Applications

At Southern Electronic Services, we build custom 3-phase isolation transformers specifically tailored to:

• Match VSD input voltage requirements
• Withstand harmonic-rich environments
• Improve safety and electrical performance
• All our transformers are built in Australia to AS/NZS 60076 and AS/NZS 61558 standards, using copper windings and Class H insulation for long-term reliability.

We have supplied isolation transformers for specific VSD applications to companies such as Fuseco, ABB, Microsoft, ARA and many, many others.

Need Help Choosing the Right Transformer?
If you’re installing or upgrading a VSD and want to ensure maximum protection and performance, get in touch with the SES team. We can help you select or design the right transformer for your application.

👉 Contact us today