A Reactor is a coil constructed and used predominantly for its inductance or reactance property. For a given current flow, a definite voltage drop exists across the winding. The current flowing through them is all exciting current, so the magnetic circuit is designed to give the required exciting current at the desired voltage drop.
AC Line Reactor
AC line reactors are added to the input of the drive and placed in series with the incoming line. They help mitigate harmonics and because they are between the line and the drive, they are able to act as a buffer for surges and other transients. The intended purpose of a line reactor is not to offer high levels of surge protection and, if greater protection is desired, a dedicated protective device such as a metal oxide varistor (MOV) or a transient voltage surge surpressor (SPD) is a better solution. The disadvantage of an AC line reactor is tht they are normally larger than DC chokes and typically are more expensive.
DC chokes are connected between the diodes and the DC bus and can be slightly less or slightly more effective at removing harmonics than AC line reactors depending on the order of harmonic being observed. DC link chokes are typically smaller than AC chokes and they add the necessary impedance for harmonic reduction without a drop in voltage. While the DC choke does not add any extra buffering from voltage surges seen by the rectifier, it will protect against current surges.
A choke (or line reactor) is a coil of wire around a magnetic core that creates a magnetic field when current flows through it. This magnetic field increases the impedance of the line and reduces the total harmonic content injected from the drive onto the facilitie's electrical system.
The following examples show how Iron Core Reactors are most commonly used:
- “To increase the reactance of one branch of parallel circuits so the load will divide properly among the branches,
- “To limit the current of an circuit (ex. arc furnace transformer),
- "Filter reactors, as a tuned reactor in Harmonic Filter Banks or as a input filter in DC Power Supplies"
“The major effect of adding an iron core to a coil is a great increase in the inductance...” which “often permits the reduction of the coil dimensions, the winding resistance, the reactor weight, or all three.
“The principle application of air-core reactors is for current-limiting reactors, where the short-circuit current of the system may be many times normal current, with values from ten to twenty times the normal current being typical.”
One type of air-core reactor is a current limiting reactor. Air-insulated (air-core) reactors “consist of a cable wound in a helical form…and supported on a concrete structure with columns of insulating material to support the turns at frequent intervals.” Often, air-core reactors are supported above ground using porcelain insulators.
However, another application may be in "shunt reactors operating at nearly constant voltage to compensate for the leading charging current of a long transmission line."
Current Limiting Reactors
Inherent available fault currents often exceed the capacities of protective/control equipment such as circuit breakers. Current limiting reactors limit the fault currents to safe levels within the capacity of such equipment, providing for a very cost-effective solution.
Neutral-grounding Reactors (earthing reactors) are an effective means to increase the ground fault impedance when connected between the neutral of power system and earth. This limits the ground fault current to a safe value within the capacity of the protective system.
Smoothing reactors provide a low impedance path to DC currents, while presenting a high impedance to the higher frequency harmonic currents and ripple in DC systems, thus reducing them.
Hamronic Filter Reactors
Harmonic filter reactors are part of tuning (filter) circuits which include capacitors and resistors. They present low impedance to the harmonic currents desired to be filtered out from the networks, thus reducing harmonic distortion levels. Harmonic currents cause higher network losses, generally interfere with computer and telecommunications equipment and triplen harmonics cause high neutral currents.
A Saturable Reactor has a main AC winding and a DC control winding. The combination provides for a continuous variation of the reactance of the main AC winding by controlling the DC current in the control winding. The DC in the control winding controls the magnetization of the magnetic core, thus controlling the inductance of the AC winding. Variation of impedance occurs by altering the DC current in control winding. Once the DC of the control winding saturates the core, the inductance of the saturable reactor drops dramatically. This allows low level signal in the DC winding to control the flow of high level AC current in the main AC winding.
Dampening reactors limit the inrush and outrush currents of capacitor banks.
Motor Starting Reactors
Motors take considerably high current at start when the rotor is at rest. The current drops to normal as the motor speed picks up. Motor starting reactors are temporarily connected in series with a motor to limit the starting current during the motor starting operation.