114 1-800-447-2371 www.lutze.com LUTZE Technical Overview LUTZE DRIVEFLEX® VFD and Servo Motor Cables A Variable Frequency Drive (VFD) is a device designed for alteration of a motor’s rotational speed by changing the frequency and the voltage of the electrical power supplied to it. In this manner, the rotational speed can be adjusted within a wide range from standstill to above the nominal rotation speed at 60 hertz. The second main feature of a VFD is that it offers motor torque control. To avoid overload of the motor, the torque has to decrease when running the motor at higher speeds and vice versa. In VFD applications the constant frequency of 60 hertz in a sinusoidal waveform is altered into a variable frequency as shown in the illustration. The use of VFD technology poses high demands on the cable connecting the motor to the drive. Standard 600V control cable does not meet the requirements of VFD applications, thus causing operating malfunctions and may result in premature cable failure. High switching frequencies and harmonic waves cause high capacitive charging current and overvoltage spikes well beyond the 600V rating of standard control cables. These problems put tremendous stress on cables and the stress increases even further the longer the distance between drive and motor. Another stress factor is called “corona discharge effect”. Insulated conductors have very small gaps between the copper strands and the insulation material caused by the irregular surface of stranded conductors. This can lead to an uncontrolled corona discharge across these gaps and break down the insulation over time. This problem is well known in medium voltage applications. Therefore, thermoset XLPE insulation is frequently used in medium voltage applications due to its inherent resistance to corona discharge. Our internal and external tests have proven that PVC/Nylon insulation commonly used in power tray cables is prone to failure due to corona discharge in 480V VFD applications. With each corona discharge (or partial discharge) the thermoplastic PVC/Nylon insulation is stressed, and pitting occurs. Once the pitting has reached a certain threshold, the microarc will develop into a full short circuit and the cable will be destroyed. This process will occur quicker if the cable lead length from drive to motor is long and moisture is present. Cable failure due to corona discharge is very dangerous, as the operator will typically receive no warning other than nuisance trips, if any at all, before a catastrophic cable failure occurs. LUTZE offers a premium solution to address the different requirements for VFD and motor cable: LUTZE DRIVEFLEX® VFD and Servo Cable A premium solution with thermoset XLPE insulation XLPE is an insulation material with very low capacitance offering superior electrical characteristics for use as a VFD cable, especially in long cable runs. The XLPE insulation is a thermoset material with a very high voltage breakdown level, thus inherently addressing the corona discharge effect and making it the premium insulation for any type of drive application. XLPE insulation is recommended by most drive manufacturers, and LUTZE DRIVEFLEX® exceeds the VFD cable requirements by Rockwell* as stated in the “Wiring and Grounding Guidelines for Pulse Width Modulated (PWM) AC Drives” document. The extra thick insulation offers a nominal voltage rating of 1000V 90°C per UL Flexible VFD & Servo cable specifications. The insulation is designed to withstand even higher voltage spikes and power distortions that can commonly occur in VFD applications. A foil and braid shield combination with drain wire ensures compliance with EMC requirements. LUTZE DRIVEFLEX® XLPE is the most flexible XLPE cable in its class - offering easy stripping & installation, thus saving time and money. DRIVEFLEX® has also been evaluated as flexible VFD and Servo cable and is UL listed for use on drives and servos, as well as tray cable exposed run (TC-ER). The DRIVEFLEX® cable family includes many different configurations compatible with many standard drive and servo systems. For more information, please visit www.driveflex.com. LUTZE Technical Overview LUTZE DRIVEFLEX® VFD and Servo Motor Cables A Variable Frequency Drive (VFD) is a device designed for alteration of a motor’s rotational speed by changing the frequency and the voltage of the electrical power supplied to it. In this manner, the rotational speed can be adjusted within a wide range from standstill to above the nominal rotation speed at 60 hertz. The second main feature of a VFD is that it offers motor torque control. To avoid overload of the motor, the torque has to decrease when running the motor at higher speeds and vice versa. In VFD applications the constant frequency of 60 hertz in a sinusoidal waveform is altered into a variable frequency as shown in the illustration. The use of VFD technology poses high demands on the cable connecting the motor to the drive. Standard 600V control cable does not meet the requirements of VFD applications, thus causing operating malfunctions and may result in premature cable failure. High switching frequencies and harmonic waves cause high capacitive charging current and overvoltage spikes well beyond the 600V rating of standard control cables. These problems put tremendous stress on cables and the stress increases even further the longer the distance between drive and motor. Another stress factor is called “corona discharge effect”. Insulated conductors have very small gaps between the copper strands and the insulation material caused by the irregular surface of stranded conductors. This can lead to an uncontrolled corona discharge across these gaps and break down the insulation over time. This problem is well known in medium voltage applications. Therefore, thermoset XLPE insulation is frequently used in medium voltage applications due to its inherent resistance to corona discharge. Our internal and external tests have proven that PVC/Nylon insulation commonly used in power tray cables is prone to failure due to corona discharge in 480V VFD applications. With each corona discharge (or partial discharge) the thermoplastic PVC/Nylon insulation is stressed, and pitting occurs. Once the pitting has reached a certain threshold, the microarc will develop into a full short circuit and the cable will be destroyed. This process will occur quicker if the cable lead length from drive to motor is long and moisture is present. Cable failure due to corona discharge is very dangerous, as the operator will typically receive no warning other than nuisance trips, if any at all, before a catastrophic cable failure occurs. LUTZE offers a premium solution to address the different requirements for VFD and motor cable: LUTZE DRIVEFLEX® VFD and Servo Cable A premium solution with thermoset XLPE insulation XLPE is an insulation material with very low capacitance offering superior electrical characteristics for use as a VFD cable, especially in long cable runs. The XLPE insulation is a thermoset material with a very high voltage breakdown level, thus inherently addressing the corona discharge effect and making it the premium insulation for any type of drive application. XLPE insulation is recommended by most drive manufacturers, and LUTZE DRIVEFLEX® exceeds the VFD cable requirements by Rockwell* as stated in the “Wiring and Grounding Guidelines for Pulse Width Modulated (PWM) AC Drives” document. The extra thick insulation offers a nominal voltage rating of 1000V 90°C per UL Flexible VFD & Servo cable specifications. The insulation is designed to withstand even higher voltage spikes and power distortions that can commonly occur in VFD applications. A foil and braid shield combination with drain wire ensures compliance with EMC requirements. LUTZE DRIVEFLEX® XLPE is the most flexible XLPE cable in its class - offering easy stripping & installation, thus saving time and money. DRIVEFLEX® has also been evaluated as flexible VFD and Servo cable and is UL listed for use on drives and servos, as well as tray cable exposed run (TC-ER). The DRIVEFLEX® cable family includes many different configurations compatible with many standard drive and servo systems. For more information, please visit www.driveflex.com.
