Here we will study about the some factor which are used to electrical machine size and rating selection. we have know that how size and rating select of electrical machine.
Electrical machine size and rating selection criteria
Limitation in design
A part from availability of suitable materials, facilities available for manufacture of required machine parts and facilities required machine parts and facilities required for transportation, the following considerations impose limitations on design.
Electromagnetic machines use ferromagnetic materials. The maximum allowable flux density to be used is determined by the saturation level of ferromagnetic material used. A high value of flux density results in increased excitation resulting in higher cost for the field system.
It is also most important factor of electrical machine size and rating selection criteria. It makes selection of size and rating of machine simple. The most sensitive part of a machine its insulation. The operating life of a machine depends upon the type of insulating material used in its construction and the life of the insulating in turn materials depends upon the temperature rise of the machine.
The electrical machine size and rating selection criteria are also depend on insulation property. The insulating material used in a machine should be able to withstand the electrical, mechanical and thermal stresses which are produced in the machine. The mechanical strength of insulation is particularly important in the case of transformers. Large axial and radial forces are produced when the secondary winding of a transformer is short circuited with the primary on. Therefore, while designing insulation for transformer, due consideration must be given to the capability of the insulation to withstand large mechanical stresses that are produced under short circuit condition as apart from electrical and thermal breakdown considerations.
The Efficiency is also an important factor which is use to electrical machine size and rating selection.
The efficiency of a machine should be as high as possible to reduce the operating costs. In order to design a highly efficient machine, the magnetic and electric loading used should be small and this requires the use of large amount of material.
The construction of an electrical machine has to satisfy numerous technological possible and also it is technologically good it is carried cut using simple and economical means with as little labor as possible. But the technological techniques should be consistent with the requirements of performance, reliability and durability.
The design of mechanical parts is particularly important in the case of high speed machine. ‘for example, while designing a turbo-alternator, the rotor slot dimensions are so selected that the mechanical stresses at the bottom of rotor teeth do not exceed the maximum allowable limit.
In large machines, the size of the shaft is decided by considering the critical speed which depends on deflection on the shaft.
The problem of commutation is important in the case of commutator machines as commutation conditions limit the maximum output that can be taken from a machine. For example, at present the maximum power output of a single unit d.c. Machine is approximately 10 MW and this limitation is solely on account of commutation difficulties.
Poor power factor results in large values of current for the same power and, therefore, larger conductor size has to be used.
This problem of power factor is particularly important in the case of induction motors.
It is also most important factor for electrical machine size and rating selection criteria.
The limitations imposed by consumer’s specifications on the design of electric machinery are oblivious. The specifications as laid design evolved should be such that it satisfies all the specifications and also the economic constraints imposed on the manufacturer.
These specifications are the biggest strain o the design because both the manufacturer as well as the consumer cannot get away from them without satisfying them.
Hence these are electrical machine size and rating criteria . which are used to selection of any electrical machine. if you will find any incorrect in above article you must comment below in comment box.