Electrical Machines - Basic Vocational Knowledge (IBE - Deutschland; 144 pages) Introduction 1. General information about electrical machines 2. Basic principles 3. Execution of rotating electrical machines 3.1. Size 3.2. Designs 3.3. Degree of protection 3.4. Cooling 3.5. Mode of operation 3.5.1. Definition 3.5.2. Operational mode designation 3.5.3. Frequent nominal cycle ratings 3.6. Heat resistance categories 3.7. Connection designations of electrical machines 3.8. Rotating electrical machines in rotational sense 3.9. Rating plate 4. Synchronous machines 5. Asynchronous motors 6. Direct current machines 7. Single-phase alternating current motors 8. Transformer

#### 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.