The question of asynchronous or synchronous motor arises when designing a new production site, modernizing a workshop, or replacing failed equipment. Both types of machines are widely used at enterprises in Tashkent, but differ in operating principle, efficiency, cost and complexity of maintenance. In this article, we will analyze the key differences and tell you which motor is more advantageous in specific tasks.
Definitions and principle of operation
An asynchronous motor is an alternating current electric machine in which the rotor speed is always less than the speed of the stator magnetic field. The frequency difference is called glide and is typically 2–6%. The rotor can be a squirrel-cage rotor or a phase rotor with slip rings. It is asynchronous machines with a squirrel-cage rotor that make up about 90% of the industrial park.
A synchronous motorrotates strictly synchronously with the frequency of the supply network - without slipping. The rotor contains either an excitation winding powered by direct current through brushes and rings, or permanent magnets (PMSM). Thanks to this, the synchronous motor maintains rotational speed regardless of the load and is capable of operating with adjustable cos φ.
Large comparison table
| Parameter | Asynchronous | Synchronous |
|---|---|---|
| Slip | 2–6% | 0 % |
| Typical efficiency | 85–94% | 92–98% |
| Power factor cos φ | 0.75–0.88, inductive | 0.9–1.0, adjustable |
| Starting current | 5–7 I nom | Requires a starting system |
| Rotor design | Short-circuited or phase | With excitation or with magnets |
| Startup complexity | Direct start, soft starter, inverter | Asynchronous acceleration + synchronization |
| Frequency control | Inverter scalar/vector | Inverter vector, servo |
| Cost itself machines | Basic, affordable | 1.5–3 times higher |
| Installation cost | Low | Higher due to the excitation system |
| Complexity repair | Average | High |
| Dimensions at equal power | More | Less (especially PMSM) |
| Resource with proper operation | 15–25 years | 20–30 years |
Control and regulation
An asynchronous motor is easy to start: it can be connected directly to the network, through a soft starter or through a frequency converter. For most tasks - pumps, fans, conveyors, compressors - this is enough. Speed control via a modern vector frequency converter provides an accuracy of ±0.5% and dynamics close to a servo drive. With direct starting, the starting current reaches 5–7 nominal values, which requires a powerful cable line and automation, but is carried by the machine itself without consequences.
A synchronous machine requires a more complex start-up. In classic machines with an excitation winding, asynchronous acceleration is used to subsynchronous speed, after which direct current is supplied to the rotor. Modern permanent magnet PMSMs work only with a vector frequency converter, but provide record efficiency and precise positioning without sensors. It is important to consider that a synchronous motor in steady state strictly follows the mains frequency - during voltage sags it may fall out of synchronism and require a restart.
Energy efficiency in real operation
For a constant load, a difference of 3–5% in the efficiency of a synchronous motor results in significant savings. For example, when a 500 kW compressor operates for 8,000 hours per year, the savings on electricity alone will be about 100–150 MWh. Additionally, the synchronous motor compensates for reactive power, unloading transformers and cable lines - this reduces losses and extends the service life of cable facilities. Asynchronous motors, on the contrary, consume reactive power, and with large fleets of machines, the enterprise often pays extra for low cos φ or installs capacitor units.
When to choose an asynchronous motor
- Standard drives of pumps, fans, compressors up to 315 kW.
- Conveyor lines, crushers, mills with variable load.
- Crane and lifting and transport equipment - crane asynchronous motor with a wound rotor is often used here.
- Elevator installations of low and medium load capacity.
- The budget is limited, and the requirements for efficiency and cos φ are standard.
- The network is prone to voltage sags: an asynchronous machine tolerates vibrations more easily.
When to choose a synchronous motor
- Powerful drives over 500 kW - compressors, main pipeline pumps, rolling mills.
- Productions where reactive power compensation is required (synchronous works as a cos φ compensator).
- Precision servo drives for CNC machines, robots, packaging equipment (PMSM).
- Tasks with constant speed, regardless of load - textile machines, papermaking.
- Energy-intensive industries, where savings of 3-5% of electricity quickly pay for the difference in price.
Comparison of repair complexity
Repair of an asynchronous motor is well established and is available in almost every specialized workshop. Typical work - rewinding the stator, replacing bearings, turning the shaft, balancing the rotor. Repair time is 3–10 working days. Spare parts (bearings, wire, insulation) are in stock.
Repairing a synchronous motor is more complicated: it requires servicing the slip rings and brush apparatus, checking the excitation system, and diagnosing the thyristor exciter. Rewinding a rotor with an excitation winding takes more time and requires precise adherence to the diagram. In the case of PMSM, careful work with magnetized elements is required - their demagnetization when heated above 120 °C means replacing the rotor. Therefore, it is better to trust the repair of synchronous gears to a workshop with experience - for example, perform rotor rewinding at Elektromotors with a guarantee.
Industries and examples of application in Uzbekistan
Where asynchronous machines operate
In Tashkent, asynchronous motors are the basis of the fleet of most enterprises: textile combines, cement factories, food industry, water utilities, COD, elevator facilities of residential complexes. They are chosen for their reliability, ease of maintenance and availability of spare parts. Service centers carry out repair of asynchronous electric motors on a regular basis - this is the most popular segment. A typical example: a water utility pumping station, where 4–8 machines of the AIR 75–250 kW series operate, and when one of them fails, replacement and parallel repairs are carried out within 24 hours by an on-site team.
Where synchronous machines operate
Synchronous motors are used at large compressor stations in the gas industry of Uzbekistan, in metallurgy (rolling stand drives), in high-power cement mills, and as part of powerful pumping stations for main water supply. PMSMs are found in modern CNC machines at machine-building plants in Tashkent, in robotics and in energy-efficient premium elevators. The fleet of synchronous machines is usually small, but each unit is expensive, so decisions on repair or replacement are made after a comprehensive diagnosis and calculation of the remaining life.
Hybrid scenarios
In modern production, a mixed fleet is often found: the main drives are asynchronous with frequency drives, and the critical powerful units are synchronous. This configuration provides an optimal balance of price, reliability and energy efficiency. When planning a modernization, you should immediately make room for reactive power compensators or powerful synchronous machines - this simplifies the further development of the enterprise.
Checklist for making a decision
- Determine the operating power range and the required rotation speed.
- Assess the mode: continuous, intermittent, cyclic.
- Count the operating hours per year - this is the basis for saving on efficiency.
- Check the quality networks: voltage sags, harmonics, phase imbalances.
- Consider the cost of ownership: machine price + 5 years of electricity + standard repairs.
- Coordinate the choice with the capabilities of the service partner - the availability of spare parts and competencies is critical.
Bottom line: how to make the right choice
If the task is standard and the power is up to 200–300 kW, choose an asynchronous motor. This is a proven, cheap and repairable solution. If the power is high, maximum efficiency, precise speed or reactive power compensation are important - a synchronous motor will pay for the difference in price in 2-4 years of operation. All other things being equal, the asynchronous machine wins in terms of flexibility and availability of service, the synchronous machine wins in terms of efficiency and speed stability.
Do you need help with selection or diagnostics? Contact the engineers of Elektromotors in Tashkent - we will perform diagnostics, calculate the economics of replacement and carry out repair of industrial electric motors of any type. Leave a request - our specialist will call you back within an hour.