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Motor Protection - RWT

 
 

Cutler-Hammer's Reflected Wave Trap (RWT) is installed at the motor terminals to eliminate system over-voltage transients. Resulting from a major research and development initiative by Cutler-Hammer, the patented RWT is ideal for drive-motor systems operating at carrier frequencies ranging from 2 kHz to 12 kHz on 208 to 480 volt systems.

Variable Frequency Drives improve efficiency and operational control. However, many operators, engineers and system integrators report an increasing number of motor control failures due to insulation failure caused by reflective wave transients. Also known as dV/dT, this phenomenon occurs with long cable lengths between the IGBT (and BJT) drives and motors. With today's high speed drives, power cable and AC motor impedances are not matched. This causes significantly higher voltage spikes at the motor terminals. It is common to have reflective wave spikes over 1400 volts (greater than 2 p.u.) causing premature motor failure and costly production downtime.

Application Description
Per NEMA MG1 Part 30 and VDE 530, motors rated for 600V or less are designed to withstand a peak voltage of only 1000V. Existing solutions are not adequate for today's drive systems because they:

  • Have high energy losses
  • Operate at very high temperatures (over 160°C)
  • Are limited to 6 kHz or lower operating speeds
  • Do not protect motors with leads over 600 feet

Features, Functions and Benefits

  • Performance: eliminates reflected wave transients that reduce motor failures and costly downtime
  • Faster: operates up to 12 kHz (compared to 2 to 6 kHz for other designs)
  • Simplicity: universal solution meets all of your needs (sizing to motor horsepower is not required).
  • Flexibility of operation: longer lead lengths between VFD and motor offers great flexibility
  • Safety: maximum surface temperature of 80°C eliminates the possibility of serious burns
  • Easy to install: integral connection cable allows for easy installation and can be installed up to 20 feet (6m) away from the motor terminals without sacrificing performance
  • Matching of motor cable impedance is not required
  • No voltage drops that result in reducing motor torque
  • No maintenance
  • Meets NEMA 4X Class 1, Division II design requirements


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Bomara Associates Phone: 800.5BOMARA (800.526.6272) Phone: 978.452.2299 Fax: 978.452.1169 3 Courthouse Lane, Chelmsford, MA 01824 USA
Phone: 800.5BOMARA (800.526.6272)

Phone: 978.452.2299

 

Fax: 978.452.1169

Email: bobr@bomara.com

  Web: www.bomara.com

3 Courthouse Lane, Chelmsford, MA 01824 USA
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