
Harmonic Filters for VFDs

Industry standard three‐phase variable speed drives draw harmonic currents from three phase voltage sources. If harmonic distortion is left unaddressed, it can further distort the utility grid or cause damage to nearby equipment. The IEEE-519 standard sets a current and voltage distortion limit of 5% for electrical systems. To mitigate the amount of harmonic distortion produced by Variable Speed Drives (VFDs), active and passive filters are used.
Active harmonic filters are effective at reducing the harmonic currents in power systems to safe levels while allowing the VFD to draw the harmonic currents it needs to operate. The active filters rely on active power conditioning electronic devices to compensate for harmonic currents. They are used for more critical and complicated systems because they have a better capability to act in response to drastic disturbances. However, they are more expensive to install than passive filters.
Passive harmonic filters are commonly used on the input side of motor drive systems. They are made up of reactive components like inductors, capacitors and resistors. They are tuned to provide a low impedance path for specific currents with undesirable harmonic frequencies.
Products
Electrical load is an electrical component or portion of a circuit that consumes electrical power. For example, a power source such as a battery or generator will have a load which consumes that power, such as a light bulb, motor or television.
There are three types of electrical loads: capacitive loads, resistive loads and inductive loads. Capacitive loads are similar to inductive loads in that the current and voltage are out of phase with one another, however, capacitive loads see the current reach its maximum before the voltage, while inductive loads see the voltage reach its maximum before the current. Resistive loads typically consist of things like heating elements.
Inductive loads use a coil to produce a magnetic field. The most common types of inductive loads are motors, fans, blenders and pumps. Inductive loads resist change in current, which lags behind the voltage. There are two different types of power with inductive loads. There is real power, which is based off of the work that is actually being done by the motor and there is reactive power, which is the power that is drawn from the power source to produce the magnetic field. The total power of an inductive load combines both the real power and reactive power.