Industrial control transformers are designed for industrial applications that require relays, solenoids, and other electromagnetic devices. They contain capacitors or other filtering devices to minimize variations in output, and are well-suited for applications that require constant current or constant voltage with a low volt-amp or low power rating.
Industrial control transformers are insulated and vacuum impregnated, often with a polyester resin. Oven-curing is used to seal the transformer surface and eliminate moisture. Waterproof, environmentally-resistant, and other specialized products are available.
Performance specifications for industrial control transformers include:
- Operating temperature
- Power rating
- Operating frequency range
- Maximum primary voltage rating
- Maximum secondary voltage rating
- Minimum voltage required
Additional performance specifications for industrial control transformers include:
- Total steady-state VA
- Volt-amperes (VA) that the device must deliver to the load circuit
- Total inrush VA, the volt-amperes that the transformer must deliver when the control circuit is first energized
Inrush power factor, which is typically a 40%
Phase, Output Voltage, and Winding Turns
Industrial control transformers differ in terms of phase, output voltage, and winding turns.
There are two choices for phase: single phase and three phase (polyphase).
There are two choices for output voltage: alternating current (AC) and direct current (DC).
Four choices for winding turns are available:
- One-to-one industrial control transformers have a turn ratio of 1:1, or near 1:1.
- Variable transformers feature a setting for changing the turn ratio as needed.
- With step-up transformers, the secondary voltage is larger than the primary voltage.
With step-down transformers, the secondary voltage is smaller than the primary voltage.
Mounting style or form factor is an important parameter to consider when specifying industrial control transformers.
Chassis mounted devices have tabs while dish or disk mounted products attach with a metal disk, rubber washer, and screw.
Printed circuit board (PCB) mounted devices use either surface mount technology (SMT) or through hole technology (THT).
Larger industrial control transformers may mount on poles, concrete pads, or H-frames.
Tiny chip transformers with a form factor of an integrated circuit (IC) chip are also available.
Modular jacks are used with the RJ-45 form factor.
In addition to applications and approvals, industrial control transformers differ in terms of available features.
Some devices contain fuses to limit that amount of current. Others are equipped with enclosures that meet safety, environmental, or other standards from the National Electrical Manufacturers Association (NEMA).
For example, industrial control transformers may be designed to comply with NEMA ST-20 sound levels. Products that have been seismically tested and qualified may meet the requirements of the Uniform Building Code (UBC).
CSA E61558-2-2 - Safety of power transformers, power supply units and similar.