A reactor, also known as a tertiary winding, is a key component found in certain types of transformers. Its primary function is to stabilize the transformer’s performance by compensating for the effects of leakage flux and regulating the voltage under varying load conditions.
The reactor’s design and characteristics are carefully engineered to optimize the transformer’s efficiency and ensure reliable operation across a wide range of operating scenarios.
What Is a Reactor
A reactor is an electrical device designed to introduce reactance into an electrical circuit. In the context of transformers, reactors are used to limit current, stabilize voltage, filter harmonics, and improve power factor.
At its core, a reactor consists of a coil of wire wound around a magnetic core material, such as iron or ferrite. This construction allows the reactor to store energy in a magnetic field when an alternating current (AC) flows through the coil. The interaction between the coil and the core creates an inductance that opposes changes in the current flowing through the reactor.
Working Principle of Reactors in Transformers
Reactors operate on the principle of electromagnetic induction to control the flow of current in electrical power systems. They consist of a coil of wire wound around a magnetic core material such as iron or steel. When an alternating current (AC) voltage is applied to the reactor coil, it generates a magnetic flux that opposes changes in the current flowing through it. This property is known as inductance.
The induced magnetic flux in the reactor core creates an electromotive force (EMF) that counters the applied voltage, limiting the rate of change of current. The higher the inductance of the reactor, the greater its ability to restrict sudden changes in current flow.
In transformers, reactors are connected in series or parallel (shunt) with the primary or secondary windings to achieve specific objectives. Series reactors, placed in line with the transformer windings, add impedance to the circuit, helping to limit fault currents and improve voltage regulation. Shunt reactors, connected in parallel across the transformer terminals, provide a path for absorbing reactive power and stabilizing the voltage level.
Types of Reactors
There are two main types of reactors used in transformers and electrical power systems: series reactors and shunt reactors.
Series Reactors
Series reactors are connected in series with the load or the transformer’s primary winding. They are commonly used for current limitation, short-circuit protection, and harmonic filtering. When a fault occurs, the series reactor limits the fault current, reducing stress on the electrical system components and preventing damage.
Series reactors can also act as a low-pass filter, attenuating high-frequency harmonic currents generated by non-linear loads such as variable frequency drives, rectifiers, and electronic devices. By reducing the harmonic content in the system, series reactors improve power quality and minimize losses in transformers and other equipment.
Shunt Reactors
Shunt reactors are connected in parallel with the load or the transformer’s secondary windings. They are used for voltage stabilization, power factor improvement, and reducing the effects of line capacitance in long transmission lines.
In lightly loaded or no-load conditions, the capacitance of long transmission lines can cause voltage levels to rise above acceptable limits. Shunt reactors absorb the excess reactive power, maintaining the voltage within the desired range.
Shunt reactors also improve the power factor by compensating for the reactive power generated by capacitive loads. By reducing the reactive power demand, shunt reactors minimize energy losses and improve the efficiency of the electrical system.
Functions of Reactors in Transformers
Current Limitation
One primary function of reactors is to limit the magnitude of electrical currents flowing through transformer windings. When a transformer experiences inrush currents during startup or short-circuit currents during faults, reactors act as a current-limiting device. The reactive impedance of the reactor coil opposes sudden changes in current, effectively reducing the peak current levels. This protection helps prevent damage to the transformer’s windings and other connected electrical devices.
Voltage Stabilization
Reactors contribute to voltage stabilization in transformer circuits. By compensating for voltage fluctuations caused by load variations or system disturbances, reactors help maintain a stable voltage level. Series reactors, connected in series with the transformer windings, provide a voltage drop proportional to the current flow. This voltage drop counteracts sudden voltage spikes or dips, resulting in a more stable output voltage. Shunt reactors, connected in parallel, absorb reactive power and help regulate the voltage in long transmission lines or lightly loaded transformers.
Harmonic Filtering
Transformers can be exposed to harmonic currents generated by non-linear loads, such as power electronic devices. These harmonic currents cause additional losses, overheating, and reduced transformer efficiency. Reactors, specifically designed as harmonic filters, mitigate the impact of harmonic currents. By presenting a high impedance to harmonic frequencies, reactors block or attenuate the flow of harmonic currents through the transformer windings. This filtering action helps maintain a clean and undistorted power supply, improving the overall power quality.
Short-Circuit Current Limitation
In the event of a short circuit on the load side of a transformer, reactors can limit the fault current. The impedance of the reactor coil acts as a current-limiting element, reducing the magnitude of the short-circuit current. This current limitation protects the transformer and other connected equipment from potential damage caused by excessive fault currents. By limiting the peak short-circuit current, reactors help ensure the safe operation of the transformer and improve the overall reliability of the power system.
Power Factor Improvement
Reactors can be used to improve the power factor in transformer circuits. Inductive loads, such as motors or transformers themselves, consume reactive power and lower the power factor. By installing shunt reactors in parallel with the transformer, the reactive power drawn by the inductive loads can be compensated. The reactor absorbs the excess reactive power, thereby improving the power factor. A higher power factor reduces the amount of current required to deliver the same amount of active power, leading to improved system efficiency and reduced losses.
System Stability
Reactors contribute to the overall stability of power systems that include transformers. In long transmission lines or weak power grids, reactors help maintain system stability by controlling voltage fluctuations and limiting the impact of transient events. Shunt reactors, in particular, provide reactive power compensation and help stabilize the voltage profile along the transmission line.
FAQs
Do reactors lower voltage?
No, reactors do not lower voltage. Reactors are electrical components that store energy in a magnetic field when current flows through them. They are used to limit current, filter out AC ripple, or tune circuits to specific frequencies. While reactors can affect current flow, they do not directly change the voltage level in a circuit.
