Rex  Line reactors,  Load reactors & dvdt filter reactors for variable frequency drive (VFD) applications.

Stocked in Western Canada and Eastern Canada. 

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Rex Manufacturing Line and Load Reactors are Today's Solution to SCR Drive - Inverter Application Problems

Inductors placed at the input and output of electrical equipment, can provide protection and improve performance. Line Reactors absorb many power line disturbances which could damage or shut down your inverters, variable frequency drive (speed controllers) or other voltage sensitive equipment

  • Rex Line Reactor designs conform to UL, CSA, and IEC international standards.
  • Three phase AC line reactors when used as input or output filters on inverter electronic speed drive applications provide several significant benefits.
  • When applied as Line reactors placed ahead of an AC inverter drive, the reactor absorbs many power line disturbances which could damage or shut down the inverter. Additionally, the Line reactor protects sensitive surrounding equipment from transients associated with quick switching of IGBT devices in the drive.
  • When applied as Load reactors placed on the output of the AC inverter drive, the reactor provides two principal benefits. The load reactor will slope the edges of PWM waveforms applied to long cables and conductors, thereby reducing the dv/dt and stress due to uneven voltage distribution. However, load reactors used alone are only partially effective in reducing the peak voltage appearing at the end of long lines. For conductor lengths (between the drive and motor) in excess of 50 feet, the Rex Motor Guarding Transient Filter is recommended.
  • Long lines, particularly long cables, have capacitive effects producing charging currents in the order of 10 to 20 amperes which can cause spurious protective trips in small or low power drives. Reactors reduce cable charging current, producing higher reliability of operation and freedom from nuisance tripping.
  • Rex Motor Guarding Transient Filters, incorporate reactors, resistors, and capacitors. When these devices are placed on the output of adjustable frequency drives they protect the motor windings from the damaging voltage spikes associated with the fast switching effects of IGBT's and long lines and cables.

     
    Features Benefits
    • Easy to install
    • Smaller and less expensive than isolation transformers
    • Reduce harmful surge currents
    • Available in open or NEMA 1 enclosed construction
    • Conforms to CSA, UL and IEC standards
    • Built to ISO9001 quality levels
    • Available in a wide range of standard ratings
    • Reduce electrical line noise
    • Extend the life and protect SCR's and transistors
    • Filter power line disturbances
    • Limit short circuit currents
    • Important in achieving compliance to IEEE 519
    • Reduce harmonic distortion
    • Reduce nuisance tripping
    • Reduce telephone influence factor (TIF)

The Problem

The steep voltage wave fronts of the Pulse Width Modulated (PWM) output of the Adjustable Frequency Drives (AFD) produce high frequency effects which may damage the insulation of motors operated by the equipment. The problems result from two distinct effects.

  • High DV/DT Effects
    The rapid rate of voltage rise (dv/dt) at the leading edges of each output pulse of the PWM inverter, produces an uneven distribution of voltage within the motor windings. The result is a concentration of the voltage at the particular points of the winding causing abnormal stress leading to breakdown of the insulation. This phenomena has been described as "first coil breakdown" and is well documented.
  • Reflections in Long Lines & Cables
    A long cable, in addition to resistance, has distributed inductance and capacitance, producing effects similar to a transmission line as shown below.

The high frequencies present in the output of PWM wave forms cause reflections in long conductors connecting the motors to the drives (see image below). Harmful effects with conductors as short as 10 meters have been observed. However, the effects are most severe with cables of lengths greater than 50 meters leading to the doubling of the applied voltage. This translates to voltage peaks approaching 1600 volts in 575 volt systems.

On the output of PWM inverters the voltage peak due to reflections in long cable lines can be 200% (as shown in the image above).

The combination of these two effects stresses the winding insulation considerably beyond design limits and has been known to shorten the insulation life and in some instances leads to early catastrophic failure of motors.

The Solution

It has been demonstrated that these transient effects can be reduced by using filters placed at the AFD's thereby allowing safe operation of the motors and an expectation of full insulation life (see figure below). After years of experience and research, Rex Manufacturing has developed a comprehensive line of state of the art output filters suitable for a wide range of prospective applications. The filters are constructed using optimized combinations of inductors, capacitors and resistors.

                                          Cable Input & Output Voltage - Using Rex Filter

By adding a Rex motor guarding filter to the output of PWM inverters the voltage peak is reduced to less than 125% appearing at the motor as shown above.

Features of Rex AFD Output Filters

  1. The dv/dt is reduced to less than 200 volts per micro second thereby insuring uniform voltage distribution along the motor winding.
  2. The prospective spike of 200% of applied voltage due to reflections in long cables is reduced to less than 125% as shown above. This and the combination of low dv/dt translates to safe operation even at 575 volts input.
  3. Filter designs are suitable for a wide range of applications including drive frequencies of 5 kilohertz and lines up to 200 meters in length.
  4. Filter designs are capable of suppressing reflection transients even in the most severe cases involving cables with grounding metal casings.
  5. The losses introduced in the use of these filters are small and approach the losses experienced in using cables without filters. The use of Rex Output Filters generally introduce no additional losses but merely transfer losses associated with charging and discharging the line capacitance, from the cable to the filter. Thus the use of Rex filters practically has no effect on the efficiency of the system.
  6. Components used in the filters are specified for specialized qualities and are operated at a fraction of their design limitations to reduce stress and provide reliability. These steps insure that the filters will operate without overheating while exhibiting full performance even at the limits of their specifications at the extremes of the longest metal sheathed cables.


Provided by; Electram Rotary Equipment Ltd..
Edmonton Alberta Canada

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