When selecting a motor, pay special attention to the motor load characteristics to ensure that the motor can meet the application requirements. The International Electrotechnical Commission IEC 60064-1 (rotating electrical machines) defines ten load characteristics, grouped as continuous, short-term or periodic, denoted as S1 to S10. Load characteristics include the frequency and duration of typical operations, including starting, no-load or full-load operation, electric braking, and rest. S1 Continuous Duty motor operates at a constant load for a sufficient time to achieve temperature equilibrium.
Abbreviation S1 Short-time duty motor is operated at a constant load, but not for a period long enough to reach temperature equilibrium. The rest period is long enough for the motor to reach ambient temperature.
Abbreviation S2 is followed by an indication of the duty duration. For example S2 60 minutes S3 Intermittent Periodic Duty Continuous, identical cycles of operation and rest with constant load. Temperature equilibrium is never reached. The starting current has little effect on the temperature rise.
The abbreviation S3 is followed by a cycle duration factor. For example S3 25%S4 Intermittent cyclic operation with starting Continuous, identical cycles of starting, running and resting with constant load. Temperature equilibrium is not reached, but the starting current affects the temperature rise.
The abbreviation S4 is followed by a cycle duration factor, the moment of inertia of the motor (Iм) and the moment of inertia of the load (Iɩᴑᴀᴅ) both refer to the motor shaft. For example S4 25% Iм=0.15Kgm² Iɩᴑᴀᴅ=0.7Kgm²S5 Intermittent cyclic duty with electric brake Continuous, identical cycles of starting, constant load operation and no-load operation. No rest periods.
The abbreviation S5 is followed by a cycle duration factor, the moment of inertia of the motor (Iм) and the moment of inertia of the load (Iɩᴑᴀᴅ) referring to the motor shaft. For example S5 30% Iм=0.2Kgm² Iɩᴑᴀᴅ=0.8Kgm²S6 Continuous operation with intermittent load Sequence of constant load operation and no-load operation, identical cycles. No rest periods.
The abbreviation S6 is followed by a cycle duration factor. For example, S6 40%S7 runs continuously through electric braking in the same order of starting, constant load operation and electric braking. There is no rest period.
The abbreviation S7 is followed by the moment of inertia of the motor (Iм) and the moment of inertia of the load (Iɩᴑᴀᴅ), both referring to the motor shaft. For example S7 Iм=0.4Kgm² Iɩᴑᴀᴅ=7.5Kgm²S8 The same duty cycle of a continuous running sequence with periodic changes in load and speed is run at a constant load and a given speed, and then run at other constant load and speed. There is no rest period.
The abbreviation S8 is followed by the moment of inertia of the motor (Iм) and the moment of inertia of the load (Iɩᴑᴀᴅ), both referring to the motor shaft, and the load, speed and cycle duration factors for each speed condition. For example S8 Iм=0.5Kgm² Iɩᴑᴀᴅ=6Kgm²16kW 740r/min 30%40kW 1460r/min 30%25kW 980r/min 40%S9 Loads with non-periodic load and speed changes, load and speed change periodically within the permissible operating range. Overloads may occur frequently.
Abbreviation S9 Loading with discrete constant load and speed A discrete number of load/speed combinations which are maintained long enough to reach thermal equilibrium.
The abbreviation S10 is followed by the quantity p/∆t per unit of the corresponding load and its duration, and the quantity TL per unit of the relative expected thermal life of the insulation system. The reference values for the expected thermal life are the expected thermal life under continuous operating load and the permissible temperature rise limit based on load type S1. During de-energized and stationary times, the load shall be indicated by the letter r. The value of TL shall be rounded to the nearest multiple of 0.05.
For example S10 p/∆t = 1.1/0.4;1/0.3;0.9/0.2;r/0.1TL = 0.6 For this duty cycle type, a properly selected constant load based on duty cycle type S1 shall be used as the reference value “Pref” for the discrete load. The load characteristics are the various duty cycles of the motor at specific time intervals and constant load, which differ in terms of start and stop times and the application of the braking system. The continuous duty cycle is well suited for machines that need to perform load-driving operations for a long time, while other types of duty cycles have their own unique waveforms and cycle duration factors. Therefore, the load characteristics are an important parameter that must be considered when selecting a motor.
