Design of Machines:
Design may be defined as a creative physical realization of theoretical concepts.
Basic Structure
The machine consists of the following parts:
Magnetic Circuit:
It provides the path for the magnetic flux and consists of air gap, stator and rotor teeth, and stator and rotor cores (yokes).
Thermal Circuit:
The thermal circuit is concerned with mode and media for dissipation of heat produced inside the machine on account of losses.
Mechanical parts:
The important mechanical parts of a machine are its frame, bearings and shaft.
- Good Design
- The major considerations to evolve a good design are:
- Cost
- Durability
- Compliance with performance criteria as laid down in specifications
Limitations in design
Saturation:
Electromagnetic machines use ferro-magnetic materials.
The maximum allowable flux density to be used is determined by the saturation level of the ferromagnetic material used.
A high value of flux density results in increased excitation resulting in higher cost for the field system .
Insulation
The insulating materials used in a machine should be able to withstand the electrical, mechanical and thermal stresses which are produced in the machine.
The type of insulation is decided by the maximum operating temperature of the machine parts where it is put.
The size of insulation is not only decided by the maximum voltage stress but also by the mechanical stresses produced.
For example, for the same operating voltage, thicker
insulation has to be used for large sized conductors than for smaller sized ones.
Power factor
Poor power factor results in large values of current for the same power and, therefore, larger conductor sizes have to be used.
In fact, the length of air gap to be provided in an induction motor IS primarily determined by power factor considerations.
Size of Machines
Small size machines - Up to 7500W
Medium size machines - Up to 250KW
Large size machines - Above 250KW
to 5000KW
Design of Machines:
Basic Structure
The machine consists of the following parts:
Magnetic Circuit:
It provides the path for the magnetic flux and consists of air gap, stator and rotor teeth, and stator and rotor cores (yokes).
Thermal Circuit:
The thermal circuit is concerned with mode and media for dissipation of heat produced inside the machine on account of losses.
Mechanical parts:
The important mechanical parts of a machine are its frame, bearings and shaft.
- Good Design
- The major considerations to evolve a good design are:
- Cost
- Durability
- Compliance with performance criteria as laid down in specifications
Limitations in design
Saturation:
Electromagnetic machines use ferro-magnetic materials.The maximum allowable flux density to be used is determined by the saturation level of the ferromagnetic material used.
A high value of flux density results in increased excitation resulting in higher cost for the field system .
Insulation
The insulating materials used in a machine should be able to withstand the electrical, mechanical and thermal stresses which are produced in the machine.
The type of insulation is decided by the maximum operating temperature of the machine parts where it is put.
The size of insulation is not only decided by the maximum voltage stress but also by the mechanical stresses produced.
For example, for the same operating voltage, thicker
insulation has to be used for large sized conductors than for smaller sized ones.
Power factor
Poor power factor results in large values of current for the same power and, therefore, larger conductor sizes have to be used.In fact, the length of air gap to be provided in an induction motor IS primarily determined by power factor considerations.
Size of Machines
Small size machines - Up to 7500W
Medium size machines - Up to 250KW
Large size machines - Above 250KW
to 5000KW
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