What Is The Process Inside An Electric Generator?

Electric generators produce electricity by using magnets and movement of wires to induce a current. At a basic level, they operate through electromagnetic induction – when a magnetic field interacts with a conductor like a wire, it causes electrons in the wire to move, generating a current. This happens when either the magnetic field changes near the conductor, or the conductor moves and cuts through magnetic field lines.

Inside a generator, a shaft spins coils of wire within a fixed magnetic field produced by electromagnets. As the coils spin, they continually cut across magnetic field lines, producing an alternating current (AC). Additional systems like rectifiers convert this into direct current (DC) that can be used to power devices. Generators scale up this basic working principle to commercial scales, but rely on the interactions between magnetic fields and conductors to produce electricity.

Table of Contents

Electromagnets

An electromagnet is produced when an electric current passes through a coil of wire wrapped around an iron core. When the current flows through the wire, it creates a magnetic field around the coil. The strength of the magnetic field depends on three factors:

The number of loops of wire in the coil – More loops produces a stronger magnetic field
The material of the core – An iron core will concentrate and amplify the magnetic field
The amount of current flowing through the coils – Higher current creates a stronger magnetic field

In a generator, electromagnets serve two key functions:

They induce a voltage/current in the rotor coils
They provide a magnetic flux path for the rotor coils to cut through

By optimizing the electromagnet design and construction, generators can produce higher voltages and power outputs.

Stator

The stator is the stationary part of the electric generator that contains electromagnets. It generally consists of a set of electromagnets that produce a spinning magnetic field to generate electro-mechanical energy.

The stator contains the electromagnets which are wound wire coils placed around laminated steel. When current runs through these wire coils, it produces a magnetic field, transforming them into electromagnets.

This magnetic field is focused in the air gap where the rotor rotates. The rotating magnetic field induces a voltage or current in the rotor, which then powers the generator.

The windings inside the stator are typically arranged in a defined pattern, such as a 3-phase configuration, which allows the stator to produce a proper rotating magnetic field to turn the rotor electromechanically.

By controlling the electrical signals into the stator windings, the intensity and direction of magnetic field can be precisely regulated to control the power output.

Rotor

The rotor, also known as the armature, is the rotating part of an electric generator. The rotor sits within the surrounding stator and contains magnets or electromagnets that rotate within the generator’s electromagnetic fields. It is the rotation of the rotor within the magnetic field that generates electricity in an electric generator.

The rotor usually contains electromagnets composed of conductive windings of copper or aluminum wire wound around a steel core. As the rotor spins, electric current is induced in its coils from the magnetic field between the rotor and the surrounding stator coils. The moving rotor generates a changing magnetic field around itself which cuts across the windings of the stator, causing a varying current to flow and voltage to be generated which can then be drawn out for use through conductors.

The rotor usually spins at a very high rate of speed, sometimes over 3,600 rotations per minute depending on the specific generator design. This allows it to quickly cut through the magnetic field lines and generate the required induced current. The high speed rotor is a key component enabling efficient power generation in an electric generator.

Induction

Induction is the process by which motion in the rotor generates voltage in the stator windings. As the rotor spins inside the stator, it cuts across the magnetic field lines created by the stator’s electromagnets. This changing magnetic flux induces current to flow in the stator windings. The greater the rotor speed, the more magnetic flux changes occur per second, which induces a higher voltage to be generated in the stator.

The rotating magnetic field created by the rotor interacting with the stator’s stationary magnetic field is key to generating electricity. It allows a changing magnetic field to constantly cut across the stator windings and induce current without relying on physically moving wires or magnets. This induction process is what ultimately transforms the generator’s mechanical energy into electrical energy.

Rectifier

Inside the electric generator, the current generated in the rotor windings is produced as alternating current (AC). However, many electrical devices need a direct current (DC) power supply. Therefore, a rectifier is typically included in an electric generator to convert the AC power output to DC power.

The rectifier is essentially a specialized circuit made of one or more diodes capable of converting AC to DC. The rectifier blocks the negative half of the AC cycle to produce only positive pulses of DC. The diodes only allow current to flow in one direction, resulting in the conversion of AC to DC. The rectified DC current can then be smoothened with capacitors and regulated to the correct voltage for electrical equipment to run.

Voltage Regulation

Voltage regulation controls the generator’s output voltage and ensures the voltage stays within acceptable levels. A few key components and controllers are used to regulate voltage:

The automatic voltage regulator (AVR) constantly monitors and adjusts generator output to maintain steady voltage.

Sensing devices alert the AVR if voltage falls outside the set limits, triggering adjustments.
Exciters receive signals from the AVR to regulate the power going into the rotor, which controls voltage.
Var compensators maintain voltage by managing reactive power flow in transmission lines.

Maintaining proper voltage is critical for delivering consistent and reliable power from the generator to electrical loads. Quality voltage regulation prevents damage to connected equipment and fluctuations in power delivery.

Cooling System

Generators produce high levels of heat from being under a constant electrical load. If not properly cooled, excessive heat can damage major components inside the generator, like the rotor, stator, and exciter.

To prevent overheating, generators are equipped with an internal cooling system. It circulates air, hydrogen gas, or even water to absorb and carry heat away from internal components. Cooling fluid is passed along dedicated cooling channels to dissipate heat to the exterior of the generator housing.

Keeping all generator components within safe operating temperatures ensures they function properly over long periods of running time. Well-designed cooling systems allow generators to provide a reliable supply of power continuously, without risk of failure from overheating.

Exciter

An exciter is a small power generation system within a larger generator. Its purpose is to produce an electric current to flow through the field windings on the rotor. By inducing a current in the rotor, this allows the rotor to become a magnet known as the field poles. These field poles act to cause a rotation of the stator magnetic field so that an alternating current can be induced during generator operation. This device has also been called the field rheostat or alternator.

The exciter itself consists of a rotor assembly and a rotating rectifier assembly. The rotor assembly is typically powered by received shaft power from the prime mover turbine. The rectifier assembly converts the generation system’s electricity from direct current to alternating current, so it is the proper format for the rotor electromagnets. So in summary, the exciter works to power and excite the rotating field electromagnets within the generator which is critical to producing electricity.

Conclusion

Electric generators are vital components that convert mechanical energy into usable electric energy. As discussed, they rely on electromagnets and electromagnetic induction to produce alternating current electricity. The key internal components covered were:

The stator – the stationary set of electromagnets
The rotor – the rotating electromagnet

The exciter – which powers the rotor’s electromagnet
The rectifier – converts AC to DC
The voltage regulator – controls generator output

The cooling system – prevents overheating

Understanding how these components work together to generate electricity is crucial for operating and maintaining generators properly. As one of the fundamental means of producing electricity commercially and privately, generators provide the essential power that runs equipment and electrical devices across many industries and our daily lives.