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H.H. Roberts Machinery Limited
1324 Matheson Blvd E., Mississauga, Ontario, Canada. L4W-2Z7
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Rex drive isolation transformer
Rex Drive Isolation Transformers
  

HH Roberts recommends the use of these K-Factor rated transformers to power CNC machines to do two things for the installation:
1) clean up an unbalanced or wild leg power supply to give balanced voltage on all three legs ( measured leg to ground, not leg to leg )
2) avoid feedback of harmonics to the power in the building that could cause interference on other sensitive equipment.  These harmonics are generated within the variable speed drives used by CNC machines. To be effective these transformers must be connected with the X0 tap grounded.

The following is copied from the Rex web site.

 

Overview of K-Factor Rated Transformers Today's modern electronic, electric components and circuitry such as computers, copiers, printers, fax machines and display terminals utilize switching mode power supplies for their operation. These switching mode power supplies are non-linear in nature and can cause significant power system problems:
  • Circuit breakers and fuses blowing far below current ratings
  • Neutrals in transformers and panel boards are much hotter than their ratings
  • Distributions Transformers are overheating even when operating well within their specified nameplate rating
These problems are the results of Harmonics. Solid state switching elements such as SCR, Transistors and capacitors which are found in computers, fax machines, solid state drives, energy efficient drives, etc. Continuously switching on/off producing non-linear or non-sinusoidal wave shapes in the current supplied from the power source.
A linear load uses current from the power source continuously over the sinusoidal cycle. A non-linear load uses current in large pulses from the power source thereby creating harmonic distortion.
Harmonic components are represented by periodic waves that have a frequency that is a multiple of the fundamental frequency.

Example:
  • Fundamental Frequency= 60 Hz
  • 3rd Harmonic Frequency= 3x 60 Hz = 180 Hz
  • 5th Harmonic Frequency= 5x 60 Hz = 300 Hz
Harmonic Frequencies superimpose themselves upon the fundamental waveform distorting and changing its magnitude.
Effects of Harmonic Components on the Sinusoidal Cycle illustrating harmonics on a power lineEffects on Transformer The major components in the harmonic currents of switching mode power supplies are the 3rd and the 5th Harmonics. Harmonics which are even multiples of 3, such as 3rd, 6th, 9th, etc. are called Triplen Harmonics. When triplen harmonics are present in a 3-Phase system, they add together in the neutral conductor. 3rd Harmonics result in high 180Hz current flowing through the transformer's neutral terminal. The core steel of the transformer has stray losses that will increase dramatically with Harmonic Distortion. These effects cause the transformers to operate at significantly higher temperatures.
K-Factor Ratings
A K-Factor Rating applied to a transformer is an index of the transformers ability to supply harmonic content in its load current while operating within its temperature limits. For Dry Type Transformers a K-Factor calculation is made to determine the amount of the Harmonic Content present in a power system. K-Rated Transformers are sized to handle 100% of the fundamental 60Hz load, plus the non-linear load specified. The neutral of the K-Rated transformer is sized at 200% of the current rating of the phase connections.
K-Factor 1: Motors, Incandescent Lighting, Resistance Heating, Motor Generators (without solid state drives)
K-Factor 4: HID Lighting, Induction Heaters, Welders, UPS with optional input filtering, PLC and solid state controls
K-Factor 13: Multiple receptacle circuits in health care facilities, UPS without optional input filtering, Production or assemble line equipment, Schools and Classroom facilities
K-Factor 20: SCR Variable Speed Drives, Circuits with exclusive data processing equipment, Critical care facilities and Hospital operating rooms
What about other K-Factor Ratings? We can calculate K-Factor Ratings or any magnitude when Harmonic Values are given
Application Our Drive Isolation Transformers (DIT) are specifically designed to meet the requirements of AC or DC Variable Speed Drives or Rectifier outputs and are rated to match standard motor HP voltage ratings.
Features
  • Anticipating that harmonics generated by the rectifiers will be present the steel core is increased to operate the transformer at a lower flux density to prevent saturation.
  • Standard K-Factor 4 Rating (others are available)
  • Extra bracing to withstand the mechanical stresses of the current reversals and short circuits associated with SCR drives
  • Isolates the power source from low frequency noise generated by SCR voltage spikes and transient feedback
  • Lower than normal losses and temperature rise for greater life expectancy and overload capability
  • Thermal protectors (Thermostats) for over temperature tripping are provided
  • Reduces short circuit currents
  • Full current rated neutral
    • Class 220 Insulation
    • 150OC Temperature Rise
    • Primary Taps ?2?% & ?5% (?5% up to 14KVA)
    • CSA certified, File No. LR34493
    • UL Listed, File No. E108255
    • ISO9001 Quality Certification
    • Available in Aluminum (Al) or Copper (Cu) windings
Common Part Numbers & Typical Information
Some enclosure dimensions may have changed. Click here for more info Available Options Include
  • Temperature Rise (115oC, 80oC)
  • Other Primary or Secondary Voltages
  • Different frequency (other than 60Hz)
  • Different Nema Rated Enclosure (2, 3R, 4, 4X, 12, etc)
  • Electrostatic Shield (single, double, triple or multiple/ultra)
  • Custom sizes (specific KVA ratings)
  • Open type (Core & Coils only)
  • Special Paint/Finish
* Information is subject to change without prior notice

Drive Rating Recommended
Transformer Size
(DIT)		 Aluminum
Windings
575
460Y/266		 Aluminum
Windings
460
460Y/266		 Aluminum
Windings
460
230Y/133		 Aluminum
Windings
230
230Y/133		 Indoor
Enclosure
Size		 Typical Weight
5HP 8KVA DA8J1P1 DA8H1P1 DA8H1S1 DA8C1S1 #4 135LBS
8HP 11KVA DA11J1P1 DA11H1P1 DA11H1S1 DA11C1S1 #4 150LBS
10HP 14KVA DA14J1P1 DA14H1P1 DA14H1S1 DA14C1S1 #5 182LBS
15HP 20KVA DA20J1P1 DA20H1P1 DA20H1S1 DA20C1S1 #6 247LBS
20HP 27KVA DA27J1P1 DA27H1P1 DA27H1S1 DA27C1S1 #6 275LBS
25HP 34KVA DA34J1P1 DA34H1P1 DA34H1S1 DA34C1S1 #6 310LBS
30HP 40KVA DA40J1P1 DA40H1P1 DA40H1S1 DA40C1S1 #6

336LBS
40HP 51KVA DA51J1P1 DA51H1P1 DA51H1S1 DA51C1S1 #7 455LBS
50HP 63KVA DA63J1P1 DA63H1P1 DA63H1S1 DA63C1S1 #7 485LBS
60HP 75KVA DA75J1P1 DA75H1P1 DA75H1S1 DA75C1S1 #7 565LBS
75HP 93KVA DA93J1P1 DA93H1P1 DA93H1S1 DA93C1S1 #8 755LBS
100HP 118KVA DA118J1P1 DA118H1P1 DA118H1S1 DA118C1S1 #8 820LBS
125HP 145KVA DA145J1P1 DA145H1P1 DA145H1S1 DA145C1S1 #8 890LBS
150HP 175KVA DA175J1P1 DA175H1P1 DA175H1S1 DA175C1S1 #9 1250LBS
200HP 220KVA DA220J1P1 DA220H1P1 DA220H1S1 DA220C1S1 #9 1470LBS
250HP 275KVA DA275J1P1 DA275H1P1 DA275H1S1 DA275C1S1 #9 1750LBS
300HP 330KVA DA330J1P1 DA330H1P1 DA330H1S1 DA330C1S1 #9 1990LBS
400HP 440KVA DA440J1P1 DA440H1P1 DA440H1S1 DA440C1S1 #10

2700LBS
500HP 550KVA DA550J1P1 DA550H1P1 DA550H1S1 DA550C1S1 #40 3100LBS
For a complete catalogue of Rex dry type transformers in pdf format CLICK HERE
To download a SAMPLE connection diagram for a 10 Hp ( 14KVA ) transformer, CLICK HERE.
Additional information is available on the Rex website

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