Drive Isolation Transformers
Transformers built for rectifier and drive loads, with the shielding, thermal margin and voltage matching a general-purpose unit does not give.
Built for Rectifier Load, Not Just Rated for kVA
A drive isolation transformer feeds a VFD or DC drive. It is designed for the harmonic heating and short pulses of current that a rectifier front end draws, and it usually has an electrostatic shield between primary and secondary to reduce common-mode noise coupling into the plant.
You typically need one to derive a new grounded neutral, to isolate a drive from an ungrounded or corner-grounded delta supply, to match a voltage the drive cannot take directly, or to add impedance ahead of the drive. Our article Drive isolation transformers: when you actually need one goes through each case. For harmonic cancellation, see 18-pulse and 24-pulse phase-shifting designs.
Where Drive Isolation Transformers Fit
- ■ AC VFDs: Pumps, fans, compressors and conveyors on large drives.
- ■ DC drives: SCR DC drives on mills, extruders and winders.
- ■ Elevators: Elevator drive supplies and modernizations.
- ■ Ungrounded or corner-grounded supplies: Deriving a grounded wye for the drive.
- ■ Voltage matching: Feeding 480 V drives from 600 V or other supplies.
Drive Isolation Transformer Specification Guide
| Parameter | Typical options | Notes |
|---|---|---|
| kVA | Sized to drive input kVA, not just motor horsepower | Rectifier current adds heating |
| Primary / secondary voltage | e.g. 480 to 480Y/277, 600 to 480Y/277, 480 delta to 460 V | Confirm drive input range |
| Electrostatic shield | Single shield between windings is common | Reduces common-mode noise coupling |
| Impedance | Often around 5 to 6 percent | Limits fault current and helps with line notching |
| Insulation and rise | 220 C insulation, 80/115/150 C rise | Lower rise means more thermal margin |
| Enclosure | NEMA 1, 3R, 12 | Sealed enclosures change the thermal design |
What to send for a fast, accurate quote
- Drive make, model, horsepower and input current
- Supply voltage and grounding (wye, delta, corner-grounded)
- Required secondary voltage and neutral
- Whether a shield or specific impedance is required
- Enclosure, ambient and altitude
- Quantity and project schedule
Specifying a Drive Isolation Transformer?
Send the drive data and the supply details. We match it to a manufacturer and return a quotation with ratings and delivery confirmed by the factory.
Open the transformer spec sheet Contact usDrive isolation transformers: common questions
How do I size a drive isolation transformer?
Size it from the drive's input kVA, not only the motor horsepower. Drive manufacturers publish a recommended transformer kVA for each drive rating; the rectifier's harmonic current means a general-purpose transformer of the same kVA can run hot.
Do I need a drive isolation transformer or a line reactor?
A line reactor adds impedance and reduces harmonics and transients, but it does not isolate, change voltage, or derive a neutral. If you need isolation, a new grounded neutral, or a different voltage, you need a transformer. If you only need impedance, a reactor is smaller and cheaper.
What does the electrostatic shield do?
It is a grounded conductive layer between primary and secondary windings that diverts capacitively coupled noise to ground, reducing common-mode noise passed between the supply and the drive.
Is a K-factor transformer the same as a drive isolation transformer?
Not exactly. Both handle harmonic heating, but K-factor units are rated for a general harmonic spectrum on mixed loads, while drive isolation transformers are designed around a specific drive rectifier load and usually include a shield.
Does AMP Magnetics stock drive isolation transformers?
No. AMP Magnetics is an independent manufacturer's representative. We match your requirement to a manufacturer and coordinate the quotation; ratings and delivery are confirmed by the manufacturer.