Electrical Reactor: What are They? (Line Reactors)

What is a Line Reactor?

A line reactor (also referred to as an electrical reactor or a choke) is a variable frequency drive (VFD) accessory that consists of a coil of wire that forms a magnetic field as current flows through it. This magnetic field limits the rate of rising of the current, thus reducing harmonics and protecting the drive from power system surges and transients.

Types of Electrical or Line Reactors

A reactor has many roles to play in an electrical power system. The reactors are normally classified according to their modes of application. Such as:

1. Shunt Reactor

2. Current Limiting and Neutral Earthing Reactor

3. Damping Reactor

4. Tuning Reactor

5. Earthing Transformer

6. Arc Suppression Reactor

7. Smoothing Reactor etc.

From a constructional point of view, the reactors are classified as:

1. Air Core Reactor

2. Gapped Iron Core Reactor

From an operational point of view, the reactors are classified as:

1. Variable Reactor

2. Fixed Reactor.

In addition to this, the reactor can also be classified as:

1. Indoor Type or

2. Outdoor Type Reactor.

Shunt Reactor

This reactor normally connected in parallel in the system. The normal purpose of a shunt reactor is to compensate for the capacitive component of current in the system. That means this reactor is mainly used for absorbing VAR (Reactive Power) generated due to the capacitive effect of the system.

In a substation, shunt reactors are connected normally between line and ground. The VAR absorbed by the reactor can be fixed or variable depending on the system requirement. The variation of VAR in the reactor can be achieved by using phase control thyristors or by DC magnetizing of the iron core. This variation can also be achieved by offline or online tap changer associated with the reactor.

A shunt reactor can be either single-phase or three-phase depending upon the configuration of the power system. A shunt reactor can be either air-cored or gapped iron cored depending upon its designing feature. This can also magnetically shield or without a magnetic shield. The shunt reactors can also be designed with additional loading winding for supplying auxiliary power to the system.

Series Reactor

Current Limiting Reactor is a kind of Series Reactor. Series Reactors are connected to the system in series. They are normally used to limit the fault current in the system or to facilitate proper load sharing in a parallel power network. When a series reactor is connected with alternator, we refer it to is Generator Line Reactor. This is to minimize the stresses during three-phase short circuit fault.

The series reactor may also be connected in series in the feeder or electrical bus to minimize the effect of short circuit fault at other parts of the system. As an effect of short circuit current in that portion of the system becomes limited, the short circuit current withstand rating of the equipment and conductors of that portion of the system can be smaller. This makes the system cost-effective.

When a reactor of suitable rating is connected between neutral and earth connection of a system, to limit the line to earth current during earth fault in the system, it is called Neutral Earthing Reactor.

When a capacitor bank is a switch on in uncharged condition there may be a high inrush current flowing through it. To limit this inrush current reactor is connected in series with each phase of the capacitor bank. The reactor used for this purpose is known as damping reactor. This damps the transient condition of the capacitor. It also helps to suppress the harmonics present in the system. These reactors are typically rated with their highest inrush current in addition to its continuous current carrying capacity.

The wave trap connected in series with the feeder line is a kind of reactor. This reactor along with the Coupling Capacitor of the line creates a filter circuit to block the frequencies other than power frequency. This type of reactor is mainly used to facilitate Power Line Carrier Communication. This is called Tuning Reactor. As it is used to create a filter circuit, it is also called a filter reactor. Commonly and popularly it is known as Wave Trap.

In a delta connected power system, a star point or neutral point is created by using zigzag star connected 3 phase reactor, called an earthing transformer. This reactor may have secondary winding to obtain power for auxiliary supply to the substation. That is why this reactor is also referred to as an earthing transformer.

The reactor connected between neutral and earth to limit single phase to earth fault current is called Arc Suppression Reactor.

A reactor is also used to filter out harmonics present in DC power. A reactor used in DC power network for this purpose is called smoothing reactor.

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