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close this bookElectrical Machines - Basic vocational knowledge (Institut für Berufliche Entwicklung, 144 p.)
close this folder1. General information about electrical machines
View the document1.1. Definition of terms
View the document1.2. Types of electrical machines
View the document1.3. Operations of electrical machines
View the document1.4. System of rotating electrical machines (generators, motors, converters)
View the document1.5. System of stationary electrical machines (transformers)

1.1. Definition of terms

An electrical machine converts energy from one category into another. Thereby at least one energy category features as electric power.

Survey 1 - Energy transformation of electrical machines

Mechanical system (prime mover)




Electrical system (mains)

Mechanical system




Electrical system (mains)

Electrical system (mains)


Rotating converter and transformer


Electrical system (mains)

Irrespective of manifold features, for instance the external shapes of the electrical machines, they all comprise two electric circuits which have been coupled through a magnetic circuit.

An electrical machine is an energy converter in which two electric circuits have been coupled by means of a magnetic circuit.

1.2. Types of electrical machines

The components, namely the bearers of both electric circuits are rigid to one another in stationary electrical machines. Conversely, the bearers of the electric circuits are mobile to one another in rotating electrical machines. This explains the system of electrical machines.

Survey 2 - System of electrical machines

1.3. Operations of electrical machines

The operation of electrical machines results from their incorporation into the process of energy conversion in the generation, transmission and consumption of electric power.

Thus, for example, in a power station the combustion heat of coal, natural gas, etc. is employed in boilers for steam generation. The energy flow of the steam drives the turbine which is coupled to a turbine generator that converts the flow energy into electric energy. The efficient transmission and distribution of electric energy is ensured through the high voltages generated by the transformers. Thereby, the high voltages are switched to consumer voltage and directed to a motor whose mechanical energy drives machines in industry, the home and traffic.

Survey 3 - Tasks of electrical machines in power flow

1.4. System of rotating electrical machines (generators, motors, converters)

Since the energy direction of an electrical machine is reversible, the rotating electrical machine can operate, without constructional changes, as a motor or generator and transform the stationary electrical machine upwards or downwards. For this reason rotating electrical machines are generally systematized in accordance with their operating principles.

Survey 4 - System of rotating electrical machines

1.5. System of stationary electrical machines (transformers)

Stationary electrical machines (transformers) can be differentiated through manifold features, for example according to design, coolant, mode of operation, special purpose, etc. Survey 5 features by way of example the system of small transformers.

Survey 5 - System of small transformers

Differentiated according to


Protective function

Protective transformers; Isolating transformer

bell transformer

toy transformer

thawing transformer

hand lamp transformer

Special purposes

mains contact transformer

control transformer

ignition transformer

leak transformer

generator protective transformer