A DC generator operates based on the working principle of Faraday’s laws of electromagnetic induction. According to Faraday’s law, whenever a conductor is located in a dynamic magnetic field, an electromotive force gets induced in the conductor. The induced electromotive force (emf) is measured via the emf equation of the DC generator.
When the conductor is displayed with a closed path, the current will be induced and flows back in the lane. The DC generator field coils will generate the electromagnetic field, and the armature conductors are turned back into the field. Thus, the electromagnetically electromotive force will be produced inside the armature conductors. In comparison, Fleming’s right-hand rule will specify the direction of induced current.
Consider an armature rotating in a clockwise manner and a conductor at the left moving upward. If the armature finishes its half rotation, the direction of the motion of the conductor will get reversed downward. Now the direction of the current will be alternating in every armature. When the connections of the armature conductor are reversed, a current reversal occurs. That’s why we get the unidirectional current at the terminals of a DC generator.
E. M. F Equation Of DC Generator
According to Faraday’s Laws of Electromagnetic Induction, the emf equation of dc generator is Eg= PØZN/60 A
Where,
1. E.g., is the produced e.m.f throughout any parallel path?
2 P is the number of poles present in the generator.
3. Ø is a magnetic pole or flux generated.
4. the tot number of armature conductors in a generator.
5. N shows the rotation speed of armature in rpm.
6. A is the total number of parallel lanes within the armature.
7. N/60 is the total number of turns per second
What Is A DC Generator?
As the name suggests, a DC generator stands for a direct current electric generator. The major function is to convert mechanical energy into electric energy. The energy conversion process uses the induction principle of Faraday’s Laws. Even when the conductor circuit is closed, the electromotive force generated can cause a flow of currents. The electrical energy produced is then transmitted and distributed via a powerline for commercial and domestic use. Typically, these generators are suitable for off-grid applications.
Types Of DC Generator
DC generators are classified into two categories, i.e., separately excited and self-excited. Self-excited is further classified into; series generators, shunt generators and compound generators, respectively.
Separately Excited
In this type of generator, the field coils are energized from an independent DC source.
Self-Excited
In this type, the field coils are energized from the current produced within the generator. The produced emf causes a part of the current to flow in the field coil. As a result, the field flux is reinforced, increasing the emf generation. The self-excited DC subdivision is explained here:
1. Series generators– field winding is with the armature winding.
2. Shunt generators– armature winding in parallel with the field winding
3. Compound generators– it’s the combination of series and shunt winding.
What Are The Differences Between DC Generators And AC Generators?
It doesn’t matter whether the electrical generator is AC or DC since all depend on the principle of magnetic inductions regardless of their sizes. In an AC generator, the armature may be the rotor or stator. While in DC, the armature is always the rotor. But as much as both generators generate current via the same process, they have their differences. The differences are based on its designs, mechanisms, types, output connection and their uses as follows:
Design Differences
Both AC and DC generators generate currents using electromagnetic induction. With AC generators, the magnet is moving while the coil is fixed. The south poles and magnet’s north make the current flow opposite sides, thus generating alternate currents. On the other hand, in the DC generators, the coil rotates in a fixed field. Its two ends connect to a commutator that is different halves of singles rotating the split ring. The split rings are connected via metal brushes to an external circuit. Finally, the commutator balances the current, leaving and returning to the generator, generating a current that doesn’t change direction.
Mechanism
DC and AC generators follow the principle of electromagnetic induction, but the two machines differ when it comes to the way they collect and transfer induced electromotive forces in their external circuit. Since the armature and the external circuit connection varies between the two, it shows the difference in how their electromotive forces are collected before being transferred.
Furthermore, AC generators have two commutators, and DC generators have one only. Also, the split ring for DC’s has two semi-circular metal rings which are insulated from one another. In addition, AC generators produce the alternator voltage while DC types produce a dynamic output voltage.
Uses Of AC And DC Generators
These two generators serve different uses. AC generators are suitable for powering small motors and household electrical appliances such as kitchen appliances like food mixers, juicers, and vacuum cleaners. Electrical fixtures, as well, can be operated perfectly using AC generators. On the other hand, DC generators are functional in supplying power to various electric motors like those needed for subway systems. They deliver a reliable and effective energy supply that can charge banks of batteries used for mobiles or off-grid uses.
Output Connections
Through the alternators used in AC generators, the produced alternate currents are led to the load unchanged with slip rings. As for DC generators, the emf produced in the armature windings is changed from AC to DC via the commutator.
Types
The types of AC generators are the rotating field alternator and rotating armature. The single phase of this generator generates 25 KW. Polyphase produces two or more AC voltages in two, three or six phases.
What Are The Advantages Of DC?
DC generator is needed in various fields for the following reasons;
1. DC generators system is designed to effectively supply the high current at a low voltage for battery charging and operating DC loads.
2. DC generators are very simple and built plainly.
3. Voltage regulations do not affect DC generators.
4. Paralleling and load sharing with other machines through DC generators are easier compares to AC machines.
5. These generators require lower costs to install and operate.
6. They are suitable for operating large motors and electrical devices that need direct control.
7. DC generators are light and compact as well.
8. Used to produce uneven output power
9. DC generators are very consistent with 85-95% of efficiency ratings.
What Are The Disadvantages Of A DC Generator?
DC generators have their limitations which include;
1. Should not be used with transformers
2. Have low efficiency due to many losses from copper, mechanical, eddy current, hysteresis etc.
3. A voltage drop over a long distance can occur.
4. DC generators use a split ring commutator, which complicates the machine design.
5. High maintenance is needed.
6. Spark risk as energy is generated
7. More energy is lost during transmission.
Is DC Power Cheaper Than AC?
There has been endless debate regarding the cheapest between AC and DC. But analysis shows that the DC power system is at least 20% cheaper than the AC ones. Even so, the biggest cost savings lies still in the potential to shorten the architecture and get the same or higher savings with less equipment.
Why Is DC Not Used In Homes?
DC is not generally used in our home because they are very difficult and expensive to change from one voltage to another. On the other hand, AC is commonly used as it is easier and cheaper to change one voltage to another. Besides, the DC is not good for home due to the following:
1. Compared to AC, DC is more lethal for the same voltage since it’s simply harder to let go when touched because the voltage doesn’t go through zero.
2. DC is more problematic when it comes to electrolytic corrosion.
3. Its arc doesn’t quench easily since the voltage doesn’t go through zero.
4. DC motors need brushes and commutators or complicated electronic switching. In contrast, AC inductions are simple to maintain and make.
How Is The Voltage On A DC Generator Controlled?
You can control the voltage of a payment- magnet generator via its speed which needs to be controlled. The voltage is transferred first to a converter or voltage regulator. So, the voltage of a separately excited DC generator is controlled by regulating the generator speed through a variable field supply or using both combinations. A self-excited DC generator is controlled using generator speed or via rheostat or electronic circuit, which reduces the field current.
How Is A Generator Different From A Motor?
An electric generator machine is used to convert mechanical energy to electricity, whereas an electrical motor machine converts electrical energy to mechanical energy. Apart from its definition, the two differ in the rule applied, principle, current usage and driving force for shaft etc., as follows;
| Differentiating Factor | Motor | Generator |
| Rule | It follows Flemings left-hand rule | It follows Fleming’s right-hand rule |
| principle | The working principle for the electric motor is based on the current-carrying conductor that experiences a force if it is kept in a magnetic area. | As for generators, the working principle is based on electromagnetic induction. |
| Current Usage | Current is delivered to the armature winding. | Currents are generated in the armature winding. |
| Driving Force For Shaft | It’s driven by a magnetic force that is developed between the armature and field. | The shaft is connected to the rotor that is driven by mechanical force. |
| Examples | Cars, ceiling fan etc. | In a different power station, generators are used to generate electricity. |
Conclusion
Generators are very important machines that supply backup energy during power outages for home and commercial use. However, generators don’t create electric power but rather convert mechanical or chemical energy into electric energy. Depending on their output, generators are classified into AC or DC generators. They are equally significant in their application, even if each of them has its limitations. Nonetheless, both AC and DC are very dangerous and can kill you if safety precautions are not taken seriously. Please read and understand your manual to know how your DC generator work before using it.
