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CLOSE THIS BOOKElectrical Machines - Basic vocational knowledge (Institut fr Berufliche Entwicklung, 144 p.)
3. Execution of rotating electrical machines
3.2. Designs
VIEW THE DOCUMENT3.2.1. Definition
VIEW THE DOCUMENT3.2.2. Designation
3.3. Degree of protection
VIEW THE DOCUMENT3.3.1. Definition
VIEW THE DOCUMENT3.3.2. Designation
3.4. Cooling
VIEW THE DOCUMENT3.4.1. Cooling category
VIEW THE DOCUMENT3.4.2. Cooling category designation
3.5. Mode of operation
VIEW THE DOCUMENT3.5.1. Definition
VIEW THE DOCUMENT3.5.2. Operational mode designation
VIEW THE DOCUMENT3.5.3. Frequent nominal cycle ratings
VIEW THE DOCUMENT3.6. Heat resistance categories
3.7. Connection designations of electrical machines
VIEW THE DOCUMENT3.7.1. Transformers
VIEW THE DOCUMENT3.7.2. Rotating electrical machines
3.8. Rotating electrical machines in rotational sense
VIEW THE DOCUMENT3.8.1. Clockwise rotation stipulation
VIEW THE DOCUMENT3.8.2. Direct current machines
VIEW THE DOCUMENT3.8.3. Alternating current and three-phase machines
VIEW THE DOCUMENT3.9. Rating plate

Electrical Machines - Basic vocational knowledge (Institut fr Berufliche Entwicklung, 144 p.)

3. Execution of rotating electrical machines

3.1. Size

Figure 24 shows the standard dimensions of rotating electrical machines.

Figure 24 - Normed dimensions of rotating electrical machines

1 Shaft and length (drive shaft), 2 Distance between shaft and clearance hole, 3 Distance of clearance holes (longitudinal), 4 Distance of clearance holes (end shield), 5 Distance of clearance holes (transverse), 6 Diameter (clearance holes), 7 Height to shaft centre, 8 Total height

In order to guarantee interchangeability of various machines the “International Electrotechnic Commission” (EEC) has established a uniform norm for sizes which are designated by figures ranging from 56 to 400. The cited numerals simultaneously indicate the axle height of the respective machines,

Survey 6 - Dimensions




















3.2. Designs

3.2.1. Definition

It must be possible to set up the machine as a unit resp. prime mover. This presupposes differing external constructions in order, thereby, to facilitate a coupling between electrical machine, work units or prime mover.

Figure 25 - Designs

(1) Foot machine with end shield
(2) Machine without feet with end shield flange

We comprehend design as the arrangement of machine elements in regard of holding elements, the position of bearings and shaft ends.

3.2.2. Designation

Designs are given code letters “IM” in the same manner as degrees of protection and coolants. The letters also indicate the design group, assembly variety and shaft end execution.


Survey 7 - Design category explanations (first figure)

1 Foot machine with end shields
2 Foot machines with end shields and end shield flange
3 Machines without feet with end shields and flange on one shield
4 Machines without feet with end shields, with casing flange
5 Machines without bearings
6 Machines with end shields and pillow blocks
7 Machines with pillow blocks (without and shields)
8 Vertical machines which are not covered by the categories IM 1 to IM 4
9 Specially constructed machines according to assembly type

Survey 8 - Shaft end type of rotating electrical machines (fourth figure)

0 Without shaft end
1 With a cylindrical shaft end
2 With two cylindrical shaft ends
3 With a conical shaft end
4 With two conical shaft ends
5 With a flange shaft end
6 With two flange shaft ends
7 With flange shaft end on the D-side and cylindrical shaft end on the N-side
8 All other types with shaft ends.

The most common design groups are IM 1001 and IM 3001. The assembly variety is indicated through two numbers. Assembly variety relates to the erection site of the machine regarding the shaft axle and holding elements.

Survey 9 - Frequent design categories

3.3. Degree of protection

3.3.1. Definition

A machine must be protected from penetration of foreign bodies and water. Indeed, this is essential for ensuring disturbance-free operation. Contact protection provisions are also necessary in the interests of labour safety.

Degree of protection denotes a designation indicating how a rotating machine is protected from penetration of water and foreign bodies and how human beings are prevented from coming into contact with electrical conductors and rotating parts.

3.3.2. Designation

An abbreviation has been adopted for designating the degree of protection.

The abbreviation features:


The arrangement of the numerals for contact and foreign body protection along with the numerals pertaining to water protection have been set out in Survey 10.

Survey 10 - Protection grade characteristics

1. Figure (shock and foreign matter protection)

2. Figure (water protection)

0 unprotected

0 unprotected

1 protection from foreign matter greater than 50 mm

1 drip-proof

2 greater than 12 mm

2 inclined up to 15 degrees

3 greater than 2,5 mm

3 rain protection

4 greater than 1.0 mm

4 splash-proof

5 dust protection

5 hose-proof

6 splash-proof

7 pressurized-water-proof

8 permanent pressurized-water-proof

Survey 11 features the degree of protection.

Survey 11 - Degree of protection of rotating electrical machines

First figure (shock and foreign matter protection)

Second figure (water protection)









IP 00

IP 01







IP 10

IP 11

IP 12

IP 13





IP 20

IP 21

IP 22

IP 23














IP 43

IP 44







IP 54

IP 55

IP 56








3.4. Cooling

3.4.1. Cooling category

Undesired heat development results from the joule heat in the windings. The winding insulation can be damaged and the machine destroyed if the permissible conductor temperature is exceeded. Consequently, adequate heat dissipation facilities must be provided.

Cooling category signifies the manner in which heat is dissipated.

We differentiate between the following cooling categories:


The machine is cooled through air motion and radiation without resorting to a ventilator.

natural cooling:

The cooling air for the machine stems from a ventilator attached to the rotor.

separate cooling:

The machine is either cooled through a ventilator which is not driven by the machine shaft or, alternatively, by means of another separately moved coolant instead of air.

3.4.2. Cooling category designation

The coolant category designation indicates:

Type of coolant
Nature of the cooling cycle
Method of the coolant circulation


1. Code letters of the cooling IC

2. Type of coolant








carbon dioxide







(Where air only is used for cooling the letter “A” can be dropped.)

3. Cooling cycle arrangement (1st index)

4. Method of coolant circulation (2nd index)

Coolant designation pattern:



IC 01

air-cooled machine, free cycle, self-cycle cooling


air-cooled machine, two cooling cycles, primary coolant dissipates its heat from the casing surface (4); the primary coolant is in self-cycle (1) whilst the coolant circulates freely (0) coupled with self circulating coolant effects (1)


Primary coolant is hydrogen; the heat is led off from the casing surface, the hydrogen features a self-cycle; air is used as secondary coolant; the air circulates freely during self-cooling.

The openings through which the air enters must remain uncovered. Improper machine erection resp. any obstruction of cooling air passage paves the way for both heat damage and possible emission through soilage. Consequently, all machine cooling devices must be regularly serviced.

3.5. Mode of operation

3.5.1. Definition

Operating an electric motor always gives rise to undesirable energy conversion. This in turn leads to heating up which, above all, strains the winding insulations. The service life of a machine is decisively influenced by its inside temperature. Thermal overloading can engender operational disturbances. Estimates indicate that a temperature increase of 8K reduces machine life by 50 per cent. Heating up results first and foremost through energy passage in the windings. The designation W = I2 · R · t shows that the conversion into heat and the related temperature rise are determined by the current flow and its duration. Temporary overloading is permissible as, due to thermal inertia, the temperature increase remains insignificant.

A torque increase for the work unit, respectively a mass inertia when starting or braking give rise to greater losses in the motor through the flow of higher starting or braking currents. Load starting and braking thus exert an influence on the degree of heating up. Consequently, for reasons related to thermal load, electric motors must be aligned to the load rhythm of the work unit.

Mode of operation relates to the nature and sequence pattern, equally the duration of standstill and idling times, also to the nominal load of electrical machines.

3.5.2. Operational mode designation

Following abbreviations have been stipulated:


permanent operation


short-term operation


intermittent operation with starting or braking influences


intermittent operation with starting influence on temperature


intermittent operation with starting and electric braking influence on the temperature


continuous operation with intermittent loading


uninterrupted operation with starting and electric braking


uninterrupted operation at differing speeds

3.5.3. Frequent nominal cycle ratings

Operational mode S1

Nominal load machine running continues (tB) until machine heating up has attained its final temperature which does not increase further.

Figure 26 - Rated operating type S1

Legend as for Figure 28

The final temperature shall not exceed the limit temperature heat resistance category of the machine.

Operational mode S2

Nominal load machine running continues until the limit temperature of the machine has been attained. Then there is a break which lasts until the machine temperature has attained room temperature. The desired values of 10, 30, 60 and 90 minutes apply for the duration of short-time operation.

Figure 27 - Rated operating type S2

Legend as for Figure 28

Operational mode S3

The machine runs in periodical operation in a permanent sequence of like cycles (tSP). Each cycle includes nominal load or operation and a break (tP) with standstill time whereby the starting current exerts no perceptible influence on heating up.

Figure 28 - Rated operating type S3

1 Power
2 Power loss
3 Operating time (tB)
4 Down time (tP)
5 Cycle play time (TSP)

The machine temperature does not return to room temperature during the standstill period. Intermittent operation is characterised through the relative cycle duration factor tr and the cycle of ten minutes. The cycle duration indicates the various, repeatedly occurring operating conditions. The relative cycle duration factor (t)r is indicated thus:

By way of preference 15, 25, 40 and 60% should apply in respect of the relative cycle duration factor.

3.6. Heat resistance categories

The functional life of machine windings depends to a great extent on the thermal strain of insulations. Constant temperature must, moreover, be so limited as to prevent heating up over a longer period leading to an impairment of electrical and mechanical properties.

Survey 12 - Insulation classes

IC Highest permissible permanent temperature (celsius)

Short characterization of the main categories of insulating materials



non-impregnated insulation materials of cellulose fibres or silks; forming materials on the basis of urea formaldehyde resin



impregnated as insulation or in liquid insulating materials such as oil - trenched insulation materials of cellulose fibres or silks; forming materials on the basis of melamine formaldehyde resin



cellulose fibres or silks with synthetic lacquers as coating means; laminated plastics on phenolic resin basis; forming materials on the basis of phenol, aminotriazine and polyester resins



insulating materials on the basis of mica, asbestos, glass silk or terephthalic acid polyester with organic binding and trenching agents



insulating materials on the basis of mica, asbestos or glass silk with synthetic binding or trenching agents


insulating materials on the basis of silicone elastomers and on the basis of mica, asbestos or glass silk with silicium-organic binding or trenching agents


over 180

mica, glass, quartz or ceramic insulating materials with or without inorganic binding agents

Exceeding the highest permissible constant temperature in line with heat resistance categories significantly decreases the service life of the machine. For example, a motor can only withstand 50 per cent overloading for about two minutes.

A heat resistance category denotes a category to which an insulating material has been allocated in regard to its highest tolerable constant temperature.

3.7. Connection designations of electrical machines

3.7.1. Transformers

Survey 13 - Transformer connection designations

Upper voltage winding

Under voltage winding

Single-phase transformer


u v

Three-phase transformer


u v w

3.7.2. Rotating electrical machines

Survey 14 - Connection designation of rotating electrical machines

Machine type

Winding part

Connection designation

Previous connection designation

Three-phase machine

three-phase winding stator

U1, V1, W1

U, V, W

U2, V2, W2

X, Y, Z

three-phase winding rotor

K, L, M

u, u, w

field winding, field spider

F1, F2

I, K

Direct-current machine

shunt winding

E1, E2

C, D

series winding

D1, D2

E, F

interpole winding

B1, B2

G, H

compensation winding

C1, C2

G, H

interpole and compensation winding

C1, C2

- -

separately excited winding

F1, F2

I, K

armature winding rotor

A1, A2

A, B


work winding,

U1, U2

U, V

asynchronous motor

auxiliary winding stator

Z1, Z2

W, Z

Universal motor

field winding stator

2D1, 2D2


1D1, 1D2


armature winding

A1, A2

A, B

3.8. Rotating electrical machines in rotational sense

3.8.1. Clockwise rotation stipulation

The rotational sense of an electrical machine signifies the rotational direction of the rotor. The rotational sense is always determined with an eye on the shaft end.

Clockwise rotation prevails where the shaft rotates in clockwise direction. Anti-clockwise running is termed left operation.

3.8.2. Direct current machines

The operation of a direct current machine as motor running clockwise means that the current runs through the windings from beginning (1) to end (2).

In order to ensure compliance also with direct current generators, they must run anti-clockwise along with unaltered designation.

3.8.3. Alternating current and three-phase machines

Alternating and three-phase machines must always be switched so that the alphabetical series of connection designations (U, V, W) conforms to the temporal sequence of the external conductors (L1, L2, L3).

3.9. Rating plate

Rating plates of rotating electrical machines must provide information with regard to the keynote date of the machine in point. Such details are, moreover, necessary for assessing the suitability of the machine for linkage to adjacent technical facilities, mains, work units and prime movers. Consequently, rating plates feature a wealth of details concerning technical-physical dimensions and particular design characteristics. Moreover, additional data is similarly required for possible further fixtures. Such on-going data pertains, inter alia, to rated operating type. Machines in the power range of 0.001 kW to 1.1 kW must feature:

- country of origin
- manufacturer or his trademark
- index or type
- nominal voltage and current type
- nominal torque and, if required, additional nominal frequency
- capacity and rated voltage of the capacitor
- machine number, year of manufacture or month resp. week and year of manufacture.

Designation pattern range of machines in the power range over 1.1 kW:

Figure 29 - Rating tag of an electrical machine (sample)

1. manufacturer

2. machine designation - type

3. machine number, year of manufacture; or month and year of manufacturer; resp. week and year of manufacture

4. current type

5. mode of operation (mot; gen; power gen; U; B1 M)

6. winding circuitry

7. rated voltage

8. rated current

9. rated power of supplied rating in W, kW, MW; in VA, kVA and MVA for alternating current synchronous generators and reactive power machines

10. rated frequency

11. capacity, rated voltage of the capacitor (for single-phase motors with starting or working capacitors)

12. rated power factor

(Power factor l = displacement factor cos j applies where current and voltage change sine-shaped.

l = cos j can be used for practical sine-shaped values)

13. torque (all rated speeds; in torque adjustable machines the highest and lowest nominal drive torque of the speed range; in machines over 1.1 kW in series operation and machines with a greater operational torque as compared to rated torque, torque speed and the highest permissible speed shall be given)

14. rotational direction (only if required)

15. rated operational mode (apart from S1)

16. insulation class

17. Rated exciting current; rated exciting voltage (exc....A; esc....V)

18. nominal stillstand voltage between the slip-rings given rated operation (Lf...V)

19. mass

20. number of standard

21. quality sign

22. design

23. degree of protection

Questions for repetition and control

1. What characterises the design of a motor?
2. Which degree of protection must be selected for a motor positioned in moist surroundings?
3. What does operational mode S1 denote?
4. How is clockwise running stipulated for electric motors?