Admin Table of Contents
- 1 How does a separately excited generator work?
- 2 What is the separately excited DC generator?
- 3 Where are separately excited generators used?
- 4 What is the difference between self excited and separately excited generators?
- 5 What is the efficiency of DC generator?
- 6 What are the types of self excited DC machine?
- 7 How is the open circuit of a separately excited DC generator obtained?
- 8 What is the external characteristic of a DC generator?
How does a separately excited generator work?
Modern DC generators with field coils are self-excited generators which get started with the initial current in the field coils. When generator is switched off, a small magnetism is developed in rotor iron which induced electromotive force in the armature due to which current is produced in the field windings.
What is the separately excited DC generator?
A separately excited DC generator is the one whose field winding is supplied by an independent external DC source (like a battery). The magnitude of generated voltage depends upon the speed of rotation of armature and the field current, i.e., greater the speed and the field current, higher is the generated voltage.
What is the purpose of separately excited DC generator?
…the generator is classed as separately excited. Alternatively, it may be noted that the output of the DC generator is unidirectional and therefore may be used as a source to supply its own field current, as shown in Figure 7B. In this case, the generator is referred to as shunt-excited.…
In what respect the separately excited DC generator is superior to self excited DC generator?
Separately excited DC generators have many advantages over self-excited DC generators. It can operate in stable condition with any field excitation and gives wide range of output voltage. The main disadvantage of these kinds of generators is that it is very expensive of providing a separate excitation source.
Where are separately excited generators used?
Applications of Separately Excited DC Generators Because of their ability of giving wide range of voltage output, they are generally used for testing purpose in the laboratories. Separately excited generators operate in a stable condition with any variation in field excitation.
What is the difference between self excited and separately excited generators?
Based on the method of excitation dc generators can be divided into two groups. In a separately excited (S.E.) machine, the field winding is connected to a separate voltage source while, in a self excited generator field winding is connected across the armature terminals (provides its exciting current) .
What is the principle of DC generator?
A DC generator operates on the principle of Faraday’s laws of electromagnetic induction. According to Faraday’s law, whenever a conductor is placed in a fluctuating magnetic field (or when a conductor is moved in a magnetic field) an EMF is induced in the conductor.
What are the three main characteristics of a DC generator?
Generally, following three characteristics of DC generators are taken into considerations: (i) Open Circuit Characteristic (O.C.C.), (ii) Internal or Total Characteristic and (iii) External Characteristic.
What is the efficiency of DC generator?
DC generators are very reliable with efficiency ratings of 85-95%. They are compact and light in weight. They provide consistent and constant output. They can be used to provide variable output power.
What are the types of self excited DC machine?
Self-excited DC generators can further be classified depending on the position of their field coils. The three types of self-excited DC generators are: Series Wound Generators….Self Excited DC Generators
- Series Wound Generators.
- Shunt Wound Generators.
- Compound Wound Generators.
Where is DC generator used?
They are used as portable generators where low power supply is required. They are used in motorcycles as dynamos, in toys such as remote control cars and in appliances such as electric shavers. These generators find uses in arc welding in which huge drop in voltage and constant current are required.
Is generator DC or AC?
Difference between AC and DC generator
| Parameters | AC Generator |
|---|---|
| Output Power | It generates AC electric power |
| Rings | They have slip-rings. |
| Current induction | Its output current can be induced either in the rotor or in the stator |
| Direction of Current | Electrical current reverses direction periodically. |
How is the open circuit of a separately excited DC generator obtained?
For separately excited DC generator, the open circuit characteristics is obtained by conducting an experiment under no-load conditions. An ammeter is connected to the field winding and a voltmeter is connected to the generator to measure the induced voltage. The circuit is connected as shown in the above diagram.
What is the external characteristic of a DC generator?
External or load characteristics give the relation between the terminal voltage and load current at a constant speed. In a separately excited DC Generator, a separate source of DC power is connected to the field winding.
When does a separately excited DC generator have an EMF?
When the field current is zero, for the effect residual magnetism in the poles, there will be a small initial emf (OA) as show in figure. Let us consider a separately excited DC generator giving its no load voltage E 0 for a constant field current.
How is the field current of a DC generator measured?
The field current is varied by connecting an additional resistance (Rheostat) and is measured by an ammeter. At a constant speed, when the field current is increased from zero, the flux and hence the induced emf increases. The values of induced emf corresponding to the field current is measured and tabulated.