Internal losses that reduce efficiency of a DC generator
- Copper Losses. Copper loss is the power lost as heat in the windings; it is caused by the flow of current through the coils of the DC armature or DC ...
- Eddy-Current Losses. As the armature rotates within the field, it cuts the lines of flux at the same time that the copper coils of wire that are wound on the ...
- Hysteresis Losses. ...
- Mechanical Losses. ...
What are the different types of losses in a DC generator?
The above tree categorizes various types of losses that occur in a dc generator or a dc motor. Each of these is explained in details below. These losses occur in armature and field copper windings. Copper losses consist of Armature copper loss, Field copper loss and loss due to brush contact resistance.
What is the field copper loss of DCDC generator?
DC generator is not exceptional in this case. Armature copper loss is given by Ia2 Ra, where Ia is the armature current and Ra is the resistance of the armature. For shunt-wound generators the field copper loss is equal to Ish2 Rsh which is practically constant.
What are the losses in a DC power plant?
Also, the losses reduces the efficiency of the machine. The iron losses occur in the armature core of the DC machine since the armature core is subjected to the magnetic field reversal i.e. changing magnetic field. The core losses are of two types viz.
What is the core loss of a generator?
Core losses are constant for shunt and compound generators, as their field currents are approximately constant. Core loss is about 20 % to 30 % of full-load losses. Windage loss or Air friction loss of ratating armature is called as Mechanical loss.
What are the losses present in DC motor?
These include the friction in the motor bearings, friction between the brushes and the commutator, and drag on the rotor caused by turbulence of the air around it (sometimes referred to as windage loss). Mechanical losses increase with motor speed, but if speed is constant, these losses can be assumed to be constant.
What are the losses involved in an electrical generator?
We know generator is a rotating machine it consist of friction loss at bearings and commutator and air-friction or windage loss of rotating armature. We can't neglect this losses because they always present , These are about 10 to 20% of F.L. Losses.
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 losses in AC machine?
Losses in AC machines can be grouped as: Resistive losses (I2R) in the stator circuit. Resistive losses (I2R) in the rotor circuit. Iron losses due to fundamental frequency ac flux in the core.
What are the losses involved in a DC generator how these losses can be minimized?
These losses occur in armature and field copper windings. Copper losses consist of Armature copper loss, Field copper loss and loss due to brush contact resistance. This loss contributes about 30 to 40% to full load losses. The armature copper loss is variable and depends upon the amount of loading of the machine.
What is eddy current loss in generator?
Eddy current losses are the result of Farady's law, which states that, “Any change in the environment of a coil of wire will cause a voltage to be induced in the coil, regardless of how the magnetic change is produced.” Thus, when a motor core is rotated in a magnetic field, a voltage, or EMF, is induced in the coils.
How to understand DC loss?
The most convenient method to understand these losses in a dc generator or a dc motor is using the power flow diagram. The diagram visualizes the amount of power that has been lost in various types of losses and the amount of power which has been actually converted into the output. Following are the typical power flow diagrams for a dc generator and a dc motor.
How does a DC generator work?
A dc generator converts mechanical power into electrical power and a dc motor converts electrical power into mechanical power. Thus, for a dc generator, input power is in the form of mechanical and the output power is in the form of electrical. On the other hand, for a dc motor, input power is in the form of electrical and output power is in the form of mechanical. In a practical machine, whole of the input power cannot be converted into output power as some power is lost in the conversion process. This causes the efficiency of the machine to be reduced. Efficiency is the ratio of output power to the input power. Thus, in order to design rotating dc machines (or any electrical machine) with higher efficiency, it is important to study the losses occurring in them. Various losses in a rotating DC machine (DC generator or DC motor) can be characterized as follows:
What is the Steinmetz formula for hysteresis loss?
Hysteresis loss is given by, Steinmetz formula: Eddy current loss: When the armature core rotates in the magnetic field, an emf is also induced in the core (just like it induces in armature conductors), according to the Faraday's law of electromagnetic induction.
What is iron loss?
Iron losses are also called as Core losses or magnetic losses. Hysteresis loss is due to the reversal of magnetization of the armature core. When the core passes under one pair of poles, it undergoes one complete cycle of magnetic reversal.
What contributes to copper loss?
Brush contact resistance also contributes to the copper losses. Generally, this loss is included into armature copper loss.
What are mechanical losses?
Mechanical losses consist of the losses due to friction in bearings and commutator. Air friction loss of rotating armature also contributes to these. These losses are about 10 to 20% of full load losses.
What is the name of the current that causes a large current to flow in the body due to the low resistance of?
Though this induced emf is small, it causes a large current to flow in the body due to the low resistance of the core. This current is known as eddy current . The power loss due to this current is known as eddy current loss.
Copper Loss
Armature copper loss is given by Ia2 Ra, where Ia is the armature current and Ra is the resistance of the armature. For shunt-wound generators the field copper loss is equal to Ish2 Rsh which is practically constant. For series-wound generators the field copper loss is equal to Ise2 Rse which is also practically constant.
Mechanical Loss
Windage loss or Air friction loss of ratating armature is called as Mechanical loss.
Stray Loss
Stray losses is nothing more than the combination of Core losses and Mechanical losses.
What are the losses in a DC generator?
Losses in DC Machine ( DC Generator and Motor ) 1 Copper losses 2 Iron or core losses and 3 Mechanical losses.
What is eddy current loss?
The eddy current loss appears as heat which raises the temperature of the machine and lowers its efficiency. Eddy current loss.
What are core losses?
Iron or Core losses. These losses occur in the armature of a d.c. machine and are due to the rotation of armature in the magnetic field of the poles. They are of two types viz.,
What is brush contact loss?
There is also brush contact loss due to brush contact resistance (i.e., the resistance between the surface of brush and surface of commutator). This loss is generally included in armature copper loss.
Where does hysteresis loss occur?
Hysteresis loss occurs in the armature of the d.c. machine since any given part of the armature is subjected to magnetic field reversals as it passes under successive poles.
How can eddy current be reduced?
The magnitude of eddy current can be reduced by making core resistance as high as practical. The core resistance can be greatly increased by constructing the core of thin, round iron sheets called laminations. The laminations are insulated from each other with a coating of varnish.
Why is the resistance to eddy current small?
If a continuous solid iron core is used, the resistance to eddy current path will be small due to large cross-sectional area of the core. Consequently, the magnitude of eddy current and hence eddy current loss will be large. The magnitude of eddy current can be reduced by making core resistance as high as practical.
What is the energy loss of a DC machine?
An energy loss takes place due to molecular friction in the material of the armature core i.e. the domains of the core material resist being turned first in one direction and then in the other. Thus, some energy is expanded in the material of the armature core in overcoming this opposition and appears in the form of heat. This loss is known as hysteresis loss. The empirical formula of hysteresis loss is,
What are mechanical losses in DC?
Mechanical losses occur in the moving parts of the DC machine due to friction and windage. These losses are also called rotational losses. The mechanical losses depend upon the speed of the machine. In a DC machine, two types mechanical losses occur, which are as follows
What is the term for mechanical and iron losses?
Important – The iron losses and mechanical losses together are known as stray losses, i.e.,
Where do iron losses occur?
The iron losses occur in the armature core of the DC machine since the armature core is subjected to the magnetic field reversal i.e. changing magnetic field. The core losses are of two types viz.
What causes mechanical losses?
Mechanical Losses. Rotational or mechanical losses can be caused by bearing friction, brush friction on the commutator, or air friction ( called windage), which is caused by the air turbulence due to armature rotation. Careful maintenance can be instrumental in keeping bearing friction to a minimum. Clean bearings and proper lubrication are ...
What causes Eddy current loss?
As the armature rotates within the field, it cuts the lines of flux at the same time that the copper coils of wire that are wound on the armature cut the lines of flux. Since the armature is made of iron, an EMF is induced in the iron, which causes a current to flow.
What is copper loss?
Copper loss is the power lost as heat in the windings; it is caused by the flow of current through the coils of the DC armature or DC field. This loss varies directly with the square of the current in the armature or field and the resistance of the armature or field coils. Armature:
What are internal losses?
Internal losses that reduce efficiency of a DC generator. There are four internal losses that contribute to lower efficiency of a DC generator.
How to reduce the loss lost in a DC machine?
To reduce magnetic and hysteresis damage, cover the magnetic core to prevent eddy currents.
What causes DC machine damage?
There are different types of DC machine damage that are caused by different types. But this loss is caused by heat and its effects. The temperature inside the machine can be increased. So that the life and performance of the machine especially the insulation can be reduced. Therefore, the rating of a DC machine can be directly affected by different losses.
What type of loss occurs in stator windings and armature windings in DC machines?
Electrical or copper losses occur in stator windings and armature windings in DC machines. This type of loss includes different types of loss. Such as copper loss armature damage caused by contact with a copper brush.
Why is the armature core losing its armature?
This loss in the armature core is due to reverse magnetism.
What is mechanical damage?
Mechanical damage can occur due to the impact of machines. This loss can be divided into two main parts, one bearing friction and the other windage. This damage can occur to moving parts inside a DC machine. The air in a DC machine is also known as windage loss.
What is the loss of power due to current flow called?
And the loss of power due to current flow is called heel current loss. This can be achieved as a loss The heel is given by the current loss
How to determine the efficiency of a DC machine?
The efficiency of the machine can be obtained from the ratio of output power to input power. That is why it is important to know the damage that can be done to a DC machine when designing a rotary machine with high efficiency. In this article, we will look at the various losses that can occur in a DC machine.
1. Copper Loss in DC Machine winding
The copper loss is caused by the ohmic resistance offered by the winding of the DC machine. When the current flows through the winding the heat loss takes place in the winding. The heat loss is proportional to the square of the current and the resistance of the winding. The copper loss in the winding is I2R.
2.Brush Contact Resistance Loss
The armature is a rotating part of the DC machine, and brushes are used to provide DC supply to the rotating part of the DC machine.Ideally, the contact resistance between the brush contacting area with commutator surface must be zero.However, in reality it is impossible to have zero contact resistance. The voltage drop takes place across the carbon brushes.
3. Core Losses or Iron Losses in DC Machine
The armature winding of the DC machine is wound around the magnetic core. The flux generated by the field coil gets linked to the armature conductors through magnetic core. Two types of losses namely hysteresis and eddy current loss occur in the magnetic core.
4. Mechanical Loss in DC Machine
In DC machine, the field is a stationary part and the armature is a rotating part. The armature rotates on the bearings. The energy loss in the form of heat occurs due to friction between the inner cage and outer cage of the bearing.
5. Stray Losses in DC Machine
Stray losses are miscellaneous losses which are difficult to determine. The various reasons of the stray losses in DC machine are short circuit current undergoing commutation,distortion of flux etc. The stray losses in DC machine are about 1 % of the total losses.
