Generator and Transformers Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. A transformer is a voltage-controlled device.

1. True
2. False

Ans. The correct answer is a. True

Explanation: A transformer is a device that regulates the voltage by either increasing or decreasing it.

Ques. In which of the following transformers is N_p < N_s?

1. Step-down transformer
2. Step-up transformer

Ans. The correct answer is b. Step-up transformer

Explanation: Here N_p stands for the number of turns of winding in the primary coil and N_s stands for the number of turns of winding in the secondary coil. A step-up transformer is a device that transforms a low voltage to a high voltage. The number of turns in the primary coil is smaller than the number of turns in the secondary coil.

Ques. Which type of generator is a Shunt-wound generator?

1. DC generator
2. AC generator

Ans. The correct answer is a. DC generator

Explanation: A DC shunt generator is a type of DC generator in which both windings, such as the armature and field, are connected in parallel.

Ques. Transformer is a/an _____

1. Passive component
2. Active component

Ans. The correct answer is a. Passive component

Explanation: Transformers are passive components that may transmit electrical energy from one electrical circuit to another or multiple circuits.

Ques. The generator converts _____ energy into electrical energy.

1. Thermal
2. Solar
3. Chemical
4. Mechanical

Ans. The correct answer is d. Mechanical

Explanation: An electrical generator is a machine that continually moves several wires through magnetic fields to create a steady electrical current, converting the motion's kinetic energy (a component of mechanical energy) into electrical energy.

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Short Answers Questions [2 Marks Questions]

Ques. Define an electric generator.

Ans. An electric generator is a device that converts mechanical energy into electrical energy by magnetic induction. This is possible because of the revolution of coils in a magnetic field, i.e., an external field generator, as well as the revolution of two electromagnets around a stationary coil, i.e., an interior field generator.

Ques. What is a transformer?

Ans. A transformer is an electrical device used to transfer electrical energy from one alternating-current circuit to another or multiple circuits using electromagnetic induction. To step up or step down voltage, a transformer uses the principle of electromagnetic induction.

Ques. Name the important parts of a transformer.

Ans. A magnetic circuit with a laminated iron core and clamping structures, a primary and secondary winding, an insulating oil tank, a vent pipe, a winding temperature indicator, an oil temperature indicator, and a radiator are all essential parts of a transformer.

Ques. What are the components of an electric generator?

Ans. The frame, engine, alternator, fuel system, voltage regulator, cooling system, lubrication system, exhaust system, charger, and main control system are the components of an electric generator.

Ques. What is the equation to find the EMF of the DC generator?

Ans. The equation of the EMF of the DC generator is given by

E = PΦNZ / 60A

Where

• Z is the total number of armature conductors
• P is the number of field poles
• N is the rotational speed of the armature in RPM
• Φ is the flux produced per pole in Weber
• A is the number of parallel paths in the armature

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Long Answers Questions [3 Marks Questions]

Ques. What are the various types of transformers?

Ans. There are two types of transformers

• Step-up transformers: A step-up transformer's secondary voltage is increased from the low primary voltage. Because the primary winding in this type of transformer has a lesser number of turns than the secondary winding, the primary-to-secondary winding ratio will be larger than one. Step-up transformers are commonly used in electronics stabilizers, inverters, and other devices that convert low voltage to much greater voltage. A step-up transformer is also used in electrical power distribution.
• Step-down transformers: A step-down transformer converts the primary voltage to a lower voltage across the secondary output. The primary side of a step-down transformer has more windings than the secondary side. As a result, the overall secondary-to-primary winding ratio is never greater than one. Step-down transformers are used in electrical systems that transmit power over long distances and operate at extremely high voltages to ensure low loss and cost-effective solutions. A step-down transformer is used to convert high-voltage supply lines to low-voltage supply lines.

Ques. How is the transformer classified based on the design?

Ans. The transformer is categorized according to its design as follows:

• Core-type transformer: Windings in core-type transformers are cylindrical former coiled and installed on the core limbs. The cylindrical coils are made up of multiple layers, each of which is isolated from the others. Insulation materials include paper, fabric, and mica. Because low-voltage windings are easier to insulate, they are positioned closer to the core.
• Shell-type transformer: The coils are wound and mounted in layers with insulation between them. A shell-type transformer may have a simple rectangular design or a distributed form.

Ques. What are the advantages of AC generators?

Ans. The following are the advantages of AC generators

• These generators usually remain maintenance-free since they do not require brushes.
• These generators are smaller in size than DC generators.
• Losses are lower than in DC machines.
• AC generator breakers are much smaller than DC breakers.

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Very Long Answers Questions [5 Marks Questions]

Ques. What are the various types of generators?

Ans. Generators are categorized into two types: AC generators and DC generators

AC Generators: Alternators are another name for AC generators. Its operation is based on the principle of electromagnetic induction. There are two types of AC generators:

• Induction Generators: There is no need for DC excitation, frequency control, or regular control. Induction occurs when inductor coils rotate in a magnetic field, creating a current and a voltage.
• Synchronous Generators: These are large generators that are commonly seen in power facilities. These are the rotating field or armature types. The armature is at the rotor end of a revolving armature, while the field is at the stator end. Brushes and slip rings conduct electricity through the rotor armature. These generators are used in applications that require low power requirements. However, because of its great power-generating capabilities and lack of the need for slip rings and brushes, the rotating field type of alternator is frequently utilized.

DC Generators: The DC generator converts mechanical energy into direct current electricity.

• It is commonly seen in off-grid applications. 
• Without the usage of innovative equipment, these generators provide continuous power supply straight into electric storage units and DC power systems. 
• The functioning concept of the DC generator is likewise based on Faraday's law of electromagnetic induction. 
• An electromagnetic force is produced in the conductor when it is put in a changing field. 
• The magnitude of this induced emf may be calculated using the emf - equation for DC generators. 
• Induced current circulation takes place within its closed path. 
• The direction of the induced current may be calculated using Fleming's right-hand rule.

Ques. What is the working principle of a Generator?

Ans. It is made out of a rectangular coil with copper wires wound over an iron core. The coil is referred to as the armature. It is used to increase magnetic flux. 

• A powerful permanent magnet is used, and the armature is rotated between the magnets so that the magnetic lines are perpendicular to the armature's axis. 
• The armature's arms are connected by two slip rings. 
• They act as moveable contact points. To transfer current from the armature to the slip rings, two metallic brushes are connected to the slip rings. 
• The current flows through a load resistance connected across the slip rings. 
• The position of the armature changes at various time periods. 
• When the magnetic field lines are perpendicular to the coil, the coil rotates in the magnetic field, increasing the induced e.m.f. This occurs at this position due to the largest number of intercepting magnetic field lines.

Ques. What are the applications of various types of DC generators?

Ans. DC Generators are classified into three types:

• Permanent Magnet DC Generator: Permanent magnet-type DC generators do not require external field excitation since the flux is produced by permanent magnets.

Applications: These are useful for low-power applications such as dynamos.

• Separately Excited DC Generator: For the magnetic flux to be produced, this separately excited DC generator requires external field excitation. We may also change the excitation here to achieve varying output power.

Applications: These are used in electroplating and electrorefining processes, among other applications.

• Self-Excited DC Generator: When there is residual magnetism in the stator poles, self-excited DC generators can create their magnetic field. The design is quite simple, and no external circuit is required to change the field excitation. These self-excited DC generators are further divided into three types: shunt, series, and compound.

Applications: These generators are used in applications such as battery charging, welding, and general lighting.

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