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Stress, Distortions and Harmonics? Acme’s DIT’s Are Designed to Handle It All.


ByJulia Jaskie

You use motor drives because they’re easy to control and they save energy. But did you know that the rectifiers in motor drives can cause damage to transformers and any electrical equipment connected to the circuit?

Basic motor drives use rectifiers, which are made of diode bridges or silicone-controlled rectifiers (SCRs) to convert AC to DC. In three-phase circuits, there is a brief moment when more than one SCR is on at the same time causing a momentary short. That momentary short puts stress on the upstream transformer and can cause a distorted voltage waveform, causing damaging effects on the transformer and any electrical equipment connected to the circuit.

The Acme Drive Isolation Transformer (DIT) was designed to address this issue.

The DIT can handle the mechanical stresses, voltage distortions and harmonics associated with AC and DC variable speed drives. It will maximize the power quality benefits gained from standard isolation transformers by:

  • Preventing overheating due to harmonics
  • Limiting harmonic peaks
  • Increasing the ground fault tolerance of connected variable frequency drives
  • Minimizing the transfer of inverter switching noise

Why Should You Use Acme Drive Isolation Transformers?

  • Wound Cores and Strip Winding mean lower losses. All Acme DITs above 7.5 kVA are wound with strip windings to ensure the lowest possible eddy current losses and DITs 440 kVA and larger use stacked core. In combination, these features significantly reduce losses and operating costs compared to other types of constructions.
  • Copper terminations provide trouble-free operation. All Acme DITs up to and including 220 kVA have copper terminations. The transition from aluminum strip coil conductors to copper terminations is accomplished by a bonding process known as “Koldwelding™” and has been used by Acme for over 25 years to provide a trouble-free, permanent bonding of the two metals.
  • Stress relief. Acme uses strip conductors (above 7.5 kVA) instead of wire for a DIT series that easily accommodates the severe electrical and mechanical stresses found in AC & DC motor drives. The line isolation of these transformers is further enhanced with the extra protection of Acme’s Electrostatic Shield.
  • Lower losses. The harmonic currents generated by AC & DC drives increase eddy current losses (heat) in transformer windings. The thicker the winding conductor, the greater the losses. Acme uses one turn per layer of thin strip conductor which provides lower eddy current losses than comparable wire wound units. Lower losses = cooler operation and longer transformer life.
  • Reduced short circuit forces. Strip windings minimize axial short circuit forces that can cause mechanical displacement of the windings under fault conditions. For extra protection all designs 7.5 kVA and above use primary and secondary coils of equal axial length. This feature tends to negate axial short circuit forces, further improving transformer life expectancy.

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