What is AC generator ? all about it

What is AC generator ? all about it
AC generator

What is electrical generator?

It is that type of machine which converts mechanical energy to AC or DC electrical energy is called a generator. The AC generator works on Faraday’s Law of Electromagnetic Induction principles. Which states that if a conductor is exposed to the changing magnetic fields. It will induce a current.

The generator works on the same principle. There are two different types of generators. The classification is based on the output they produce. One is AC Generator and the other is a DC generator. We will discuss AC Generator in this article.


What is AC Generator?

AC Generator is the type of generator that converts mechanical energy into electrical AC energy. The output electrical energy is in the form of alternating current (AC current). Therefore, AC generators are sometimes referred to as Alternators.

The mechanical energy to the generators is provided in the form of combustion engines, steam, or gas turbines.

Working Principle of AC Generator

We discussed above that generators work on the principle of Faraday’s Law of Electromagnetic Induction. The law states that when a current-carrying conductor is placed in a uniform magnetic field, An EMF is induced.

We can achieve this process by two different methods. Either to place a stationary conductor in a rotating magnetic field or to rotate a current-carrying conductor in a static magnetic field. But the most preferred method is to keep the coil stationary.

AC generator follows the same process. The induced EMF depends upon the number of turns in the armature coil, Speed of the rotating field, and magnetic field strength.

Different Parts of AC Generator

AC generator consists of different parts such as armature, field, slip rings, stator, and rotor. The detailed description of each part is below.

  • Field

The field includes copper conductor coils that receive a voltage from an external source for producing magnetic flux. The magnetic flux cuts the armature flux in the field to produce voltage. Which the output of a generator.

  • Armature

The armature is the part of the Ac generator in which voltage is produced. It consists of an armature coil. The length of the coil wire is enough large to carry a full load current.

  • Prime Mover

It is the mechanical part of the generator used for driving the generator. The prime mover could be a steam turbine, diesel engine or either wind energy.

  • Stator

The static part in the generator is called a stator. It consists of a field or an armature. If we provides excitation to the stator  and will act as a field. If voltage out is generated her the stator will act as an armature.

  • Rotor

The rotating part of the Ac generator is called a rotor. The prime mover is used for driving the rotor. Depending upon the type of generator if we provide excitation here it will act as a field. and if the voltage is generated here the rotor will act as a field.

  • Slip Rings

The electrical connections are used for power transfer from the rotor of an AC generator. The basic function of slip rings is to conduct the flow of current from a stationary part to a rotating part using carbon brushes.

Brush-less AC synchronous generator

As disused above, the current is transferred to the rotor using slip rings and carbon brushes. The brush system needs periodic maintenance and replacement. To overcome this issue brush- less excitation system is used instead.

In very simple form this brush-less excitation is a small generator consists of two parts, One is fixed and called the exciter which is energized from the residual magnetism of the synchronous generator. The second part rotates with the rotor, fixed on rotor shaft and feds the rotor with DC current to produce its field.

What is residual magnetism?

If current pass through a conductor it produces magnetic field around it, When current stops there is magnetic field remains in the coil. This is called residual magnetism.

Control of AC generator

Generators, like all electrical equipment need a control and sensing system. Speed, voltage, current, frequency, oil pressure, cooling water temperature and level, all these quantities need to be measured and analyzed to protect and control the output and performance of the generator. Based on the generator output power the sensing and protection system gets more complicated.

Generator common faults

Generators are machines, and even the largest power plant with the most advanced control and protection system it may has faults as any other small portable generators. The main  difference is the chance of the fault is greater in small generators. On the other hand one major fault in large generator costs a lot.

hereunder some faults which are common

  • Batteries: battery failure is one of the most common failures of generators, Always make sure that battery charger, all cables and connectors in good conditions. Make periodic inspection for batteries.
  • Internal winding short circuit: due to insulation failure. This failure may happen due to humidity.
  • Loss of excitation: Excitation is necessary for power production, excitation loss will cause output power loss.
  • Coolant water level loss: Water is used for cooling cycle and should be in a certain level to work properly.
  • Oil pressure loss: this may lead to shutting down the engine as oil loss is destructive.
  • Running out of fuel: Sometimes fuel indicators gives false level and then the fuel run out.
  • High Fuel Level: This alarm is designed to prevent any overfill of the fuel tank.
  • Circuit breaker trip: due to a reason in the load side like short circuit or overload the CB trips to protect the generator.
  • Frozen fuel:  in very cold areas if no special fuel is used then it may get frozen and stop the engine, specialized fuel is in cold areas.
  • Dirty Air Filters: like your car generators need air filter and these filters should be kept clean for longer life time and effectively.

AC generator protection

Protecting generators should be against inside and outside faults. As we know that a generators are connected to power system (OHTL and transformers) or to a direct load. Any fault in the power system or load side should be cleared fast otherwise it may case the generator damage.

  • Protection against internal short circuit due to insulation failure. Protecting generator using differential rely can help in case of insulation failure or internal short circuit.
  • Stator overheat protection: Many causes can lead stator to overheat, Such as insulation failure, overloading and cooling failure. To detect the excessive temperature rise temperature sensors are used in different point of the stator winding.
  • Cooling water level protection: Loss of cooling liquid may should be detected to prevent any temperature rise.
  • Oil pressure protection: Oil is used as a lubrication liquid, so its pressure is detected and checked for any loss or leakage.
  • Over current protection to protect against load increasing.
  • Over speed protection to keep frequency steady.
  • Fuel level protection.
  • protection against vibration.

Generator main data (name plate important data)

Like any electrical equipment generators have nameplate, on this nameplate the main electrical data like :

  1. generator power.
  2. Output voltage.
  3. Rated current.
  4. frequency.
  5. rotation speed.
  6. number of poles of winding.
  7. manufacturing date.
  8. excitation data, current and voltage.

In fact the larger the generator the larger the nameplate and its data. this name plate is important and should be on the generator body all the time.

Keeping safe with AC generators

Electricity kills! No matter your expertise is, You always should be careful when dealing with generators. Unfortunately generators not only has electricity danger but also has mechanical danger as well.

As an electrical engineer I will focused on electrical hazard and how to keep it away.

  • Only authorized persons to get near the generator.
  • Make sure to read all manufacturer instructions before operating the generator.
  • Don’t expose to life parts of the generator.
  • Periodic electrical inspection for the generator parts and cables.
  • All current carrying parts, cables and connections should be isolated.
  • Electrical connections should tight and properly connected.
  • A good preventive maintenance program will keep the generator safe.
  • Don’t overload the generator as this may overheat the generator and may cause damage and fire.
  • Large generators are loud. This loud may case serious damage or rupture eardrums. Make sure to use earmuffs when working near the generator.
  • Always use proper caution signs in the AC generator location.