Are you currently using a variable frequency drive (VFD) with your motor system? If so, then you might not be aware of the damages VFD drives and other types of motor control devices have on your running motor. These include electrical currents and harmonics. So, what is the solution? An inexpensive, compact component called a line reactor.
Line reactors are electromagnetic devices used as inductors to protect variable frequency drives (VFDs) and other devices from electrical disturbances such as voltage spikes, surges, and transients. Line reactors can limit your current flow and harmful harmonics from the drive.
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Harmonics are current distortions that occur as a result of running non-linear loads, such as VFDs, along with your machine. Non-linear loads are applied to machine motors in order to reduce energy costs and improve power supply. However, these loads create harmonic distortions as they produce non-sinusoidal currents when operating. If you are experiencing voltage spikes, equipment overheating, or frequent machine failure then you are most likely encountering harmonic distortion. Line reactors reduce current peaks and harmonics by rounding wavelengths.
Most machine motor failures are due to electrical disturbances that occur over time, and although VFD drives increase machine efficiency they are highly sensitive to voltage peaks and transients.
Reactor Functions: Line vs Load
Now that you understand how line reactors function you have two options when choosing a reactor for your system. Reactors can be installed in two different locations within your system and can perform as either line or load reactor. A line reactor, also called input reactor, is installed between the VFD and power source to protect the drive. A load reactor, also referred to as output reactor, is installed between the VFD and motor to protect the machine motor.
Line Reactors
Line reactors are placed in the power distribution side of the drive’s supply line. Line reactors help stabilize electrical currents when VFDs and other devices are in use. In addition, line reactors help reduce transients and harmonics which are harmful to the drive’s life over time. These reactors work as an impedance between the power source and VFD and as a result slow down harmonics and disturbances such as voltage spikes and surges. They can protect your VFD and extend its life in the process.
Line disturbances and harmonics are common in many heavy-duty types of machinery and in machines where power is being switched on and off constantly. Take for example when a toilet Is flushed while the shower is running at the same time. Constant heavy loads like these with rapid changes can cause circuit breaks. With a line reactor installed this can eliminate these power surges and reduce circuits from tripping.
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Line reactors should be used when:
- Line side is prone to surges, transients and harmonics
- If VFD devices are being used in the circuit
- Total Harmonic Current distortion (THID) drive exceeds 5%
- Turning on heavy-duty equipment or machines going through heavy loads
Load Reactors
Load reactors are used in the motor side of the drive’s load. They protect the motor by acting as a buffer when there is a long distance between the motor and VFD. As the drive generates high-frequency noises when it is initially turned “on”, it causes voltage spikes to occur. Load reactors can filter out noise caused by the motor and mitigate noise amplified through long cable lengths. Load reactors are recommended to be used only if motor wiring is more than 100 ft apart.
For extreme distances, DV/DT filters should be used. DV/DT filters also help protect your motor by reducing voltage peaks from VFD devices. Their difference from load reactors lies in their ability to have a longer range of protection. They are commonly applied in systems such as conveyor belts, production lines, and many other machines/equipment with long lead lengths. Please consult your specialized technician as other electronics within your system should be taken into consideration when choosing reactors or filters for your circuit.
Load reactors should be used when:
- Motor wiring is more than 100 ft apart
- Machine experiences voltage spikes that occur as a result of being constantly turning “on” and “off”
- Motor side of the drive needs protection when using a VFD device
Reactor Impedances: 3% or 5%
So how do you choose a reactor to meet your VFD and motor’s need? Line reactors are denoted by impedance (% impedance of load Z or the percent effective resistance of an electric circuit), voltage, and current. A line reactor impedance is determined by the current drawn by the VFD. Percent impedance of the line reactor is the same percentage of the drive impedance given at full load. This is important to note since line reactors are applied in percentages to the current load of the running device. The current rating is presented as the current required by the load measured in amps.
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Line reactors are commonly used at 3% or 5% impedance, meaning a line reactor percent impedance will be applied at the rated current of the device. For example, the greater the current flows through the reactor the great the percentage of impedance is applied. The same is stated when the current flow reduces, so does the percent impedance.
Three percent impedances are the most widely used since they improve true input power factor and reduce harmonics and other disturbances between drives. They are used to reduce transients and prevent circuit tripping. Five percent offer the same benefits of 3% reactors but are used with extreme cases of harmonics.
Using 10% impedance can offer better motor protection when the motor is away from the VFD. Higher impedances should be used in compliance with IEEE 519 standards in order to reduce motor operating noise and temperature. It is important to keep in mind impedances as to not oversize the line reactor for the load of the application.
Additional notes: IEEE 519 restricts total harmonic distortion (THD) higher than 5%. Percentage impedance such as 3% and 5% are both equally used to minimize power line transients.
Why are Line Reactors Important?
Line reactors come highly recommended by many engineers, and when compared to the price of your motor they are inexpensive and easy to install. Line reactors not only protect your VFD but also protect your motor from disturbances such as transient, voltage spikes and surges. Line reactors also aid in lowering harmonics which ruin your motor and VFD over time. Line reactors can be installed in a single installation for multiple devices.
Why you should use a line reactor:
- Reduces harmonics and keeps your local harmonic and emission levels to standards
- Reduces drive tripping during capacitor switching
- Reduces depth of voltage notches found in SCR
- Protects DC-Bus capacitors and front-end diodes
- Line reactors are encouraged when a VFD device is in use
Given the costly amount of purchasing new VFDs and motors, line reactors provide an inexpensive solution in keeping your system safe and running in the long run of your business. Line reactors/load reactors are a small investment that can be extremely effective against the harmonics and harmful disturbances that electronic devices produce. Trimantec offers a range of line reactors with 3%, 5%, and 10% impedances that can match your device’s requirements. If you are unsure about which is right for your application, please contact one of our sales representatives so that we can guide you through the process.
Source: https://t-tees.com
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