Are You Correctly Applying Line & Load Reactors on VFDs?

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Are You Correctly Applying Line & Load Reactors on VFDs?

Today’s electronic equipment requires clean, consistent power for optimal performance.  The presence of power distortions between VFDs and motors can damage equipment, jeopardize productivity, and decrease profitability.

We see line and load reactors are often applied on AC variable frequency drives (VFD) without a solid understanding of when and why they should be used. VFDs solve a host of industrial motor control issues, but can introduce power quality problems to the electric grid and/or the VFD-controlled motor.

Eliminate the worry and headaches caused by poor power quality from VFDs by using solutions from MTE. Their products are designed to absorb everyday power line disturbances that can damage or shut down VFDs and other sensitive equipment.

What is a Reactor?

Essentially a reactor is an inductor. Physically, it is simply a coil of wire that allows a magnetic field to form around the coil when electrical current flows through it. More loops give a higher inductance rating. Typically, a ferrous material such as iron is added as a core to the winding. This concentrates the lines of magnetic flux making a more effective inductor. Reactors can be applied to both a VFD’s input and output, but the reasons for application differs.

Harmonic Distortion

VFDs create waveforms that contain harmonic distortion. Harmonics can cause many problems such as: increasing the utility current required to power the system resulting in the need for larger wires, transformers and circuit breakers; increases the motor’s operation costs; causes the overheating of components; inaccurate power measurements; nuisance trips; and telecommunication interference.

Adding an input line reactor helps reduce the creation of harmonics by smoothing out the input waveform. Another reason to add an input line reactor is to help protect the input semi-conductors from transient voltage spikes. This is very important on drive systems that do not utilize an isolation transformer. Compared to the overall cost of a VFD installation, an input line reactor is a small investment to help protect a VFD and provide a reduction in total harmonic distortion.

Peak Voltages & Rise Time

On the output side of a VFD, reactors are used for very different reasons. VFDs vary the speed of a motor by simulating a sinusoidal waveform with pulse width modulation (PWM). The PWM waveform is essentially a square wave created by fast switching on/off of the output semi-conductors (IGBTs). With every on/off transition there is a momentary voltage spike of up to 1400 volts. These spikes can create issues such as reflected wave, corona, and capacitive coupling. Applying an output reactor helps to smooth out the PWM waveform, reduce the voltage spikes and reduce common mode voltage. A reduction in voltage spikes and common mode voltage can help to reduce motor insulating heating and the creation of bearing currents.

Common Mode

Another issue that VFDs can create is common mode voltage which can cause a motor to break down over time. Common mode is created due to an imbalance of voltage in the three-phase output with respect to ground. This voltage seeks a path back to ground or the source it was created (in the case of a VFD, the DC bus). Many times this path to ground is through the motor bearings which can cause arcing and pitting in the bearing raceways and ultimately bearing failure. Applying an output reactor, or dV/dT filter, helps to balance the three-phase output thus reducing the common mode voltage.

The dV Sentry™ Filter from MTE is a revolutionary solution for motor protection. With its unique all-in-one design, the dV Sentry provides common mode reduction, peak voltage protection and rise time reduction. Its small footprint and easy terminations make installation faster and easier. It runs quietly and radiates less heat than previous filters.

French Gerleman stocks MTE line and load reactors. If you have further VFD related questions, please contact your French Gerleman Account Manager.

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LUTZE DRIVEFLEX® Cable for VFD and Motor Applications

Variable frequency drive (VFD) cables have distinct advantages over traditional cables when used in drive and motor applications. When installed properly, VFD cables reduce cross coupling between drives and the shield contains and drains the electrical noise created by the drive. Their noise mitigation helps with the proper function of adjacent control systems and they help to reduce motor shaft voltage and bearing currents.

LUTZE DRIVEFLEX® cables are designed to cope with the power distortions in VFD applications. They offer superior electrical values for VFD or servo applications and are UL listed type “Flexible VFD Servo Cable, Flexible Motor Supply Cable” to comply with codes and standards regarding electrical wiring of VFDs. DRIVEFLEX® XLPE insulation has very low capacitance, high impedance and high voltage breakthrough resistance.  DRIVEFLEX® cables are safer and more efficient compared with traditional PVC/Nylon power tray cables or THHN wires in conduit.

LUTZE has recently expanded their DRIVEFLEX® line to include series A106 and A107, which are smaller diameter, general purpose series drive cables. Which type you use will depend on your specific project and requirements.

  • A106 series is great for most VFD applications and motors up to 40 HP and features a small outer diameter (OD) for easy routing and use in conduit.
  • A107 series cable is similar to the A106, but includes one shielded pair for brake or control signals.

Don’t trust your VFD and motor operations to tray cable or THHN.  Interested in learning more about DRIVEFLEX® or ordering it for your next project? Give your French Gerleman Account Manager a call today!