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

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.

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.

Cable Input & Output Voltage

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: