Power frequency lock
One of the main features of synchronous motor is the close correlation with the power frequency that helps it to keep a constant velocityjust so. In most nations, the power supply frequency is the number of current cycle changes per second in a power system, given in Hertz (Hz), which is around 50Hz or 60Hz. A synchronous motor’s speed is linked to the poles of the motor and is proportional to the power supply frequency. In view of this, since the stability of the motor is directly dependent the stability of the power supply frequency, a change in frequency of the power supply has a significant effect on the speed of the motor.
Motor performance in industrial settings depends much on frequency stability. Power System Automation’s 2022 journal publication states that if the power frequency variation exceeds ±1Hz, industrial equipment failure rate rises by 20 percent and production efficiency drops by 15%. Particularly in equipment needing great precision, including robot arms, precision machining machines, etc. , power frequency variations will directly impact the accuracy of the performance and might even cause equipment damage or misoperation.
In 2021, a top supplier of automation equipment discovered that under high frequency fluctuations, the synchronous motors used in its product line usually suffered from overload issues that impaired the equipment’s dependability. By including a high-precision frequency compensation unit, the company increased the equipment failure rate by 17% and fine-tuned the power frequency control system after research. The company has lowered annual maintenance expenditures by 12% and seen notable return on investment increases from this technology.
Technically, the formula for determining the speed of the synchronous motor is: 700 rpm.
ns=120×fPn_s = \frac{120 \times f}{P}ns=P120×f
NSN_SNS is the synchronous speed, fff is the power supply frequency, and PPP is the motor poles number. This formula says the speed of the synchronous motor is directly influenced by the f change. By means of the best control of power frequency, the motor can be guaranteed to remain stable throughout the delivery process, hence increasing productivity and lowering breakdowns.
Among the factors causing fluctuations in the frequency of the power supply are variations in the power load, in the system’s power gaps, and so on. To solve this problem, modern power systems frequently use Phase-Locked Loop (PLL) technology to continuously track the power frequency and make fast corrections to maintain the engine running smoothly.
In practical use, the integration of PLC (programmable logic controller) system and inverter might also quickly respond and vary the motor’s operating parameters when the power frequency changes to prevent overload-induced harm. After a manufacturing behemoth introduced a frequency converter, for instance, the motor failure rate dropped 30 percent, while the production efficiency rose 18%.
The number of poles determines the speed
Another important feature of synchronous motors is that the number of poles plays a major role in their performance. The number of poles of a synchronous motor directly defines the speed at which the motor will run. In simple terms, the more the number of poles, the lesser is the synchronous speed of the motor. The number of poles and the frequency of the power supply affects the operation characteristics of the motor under study. One additional pair of poles decreases the speed of the motor by a certain percentage. The understanding of this principle is of prime importance for the design and optimization of industrial equipment.
While designing a motor, an engineer generally needs to measure the proper number of poles for a specific application in which it is to be worked out to carry a certain load. For high-speed applications, such as high-speed railway traction motors and wind turbines, low pole motors are preferred. Under the Motor Design Manual (Revised 2021 edition), the same motor at the same power elevated speed up to 3600rpm but not special for high-pole motors that usually do not exceed 1800rpm.
This was proven in a developing electric vehicle manufacturer in the year 2019. The new model in motor design by the company has so modified the number of poles that the speed of the motor improved from 2200rpm to 2500rpm, not only improving the acceleration performance of the vehicle but also having an 12% improvement in energy efficiency ratio. This design optimization leads to almost an 8% reduction in the energy consumed and increases the lifespan of the motor by reducing high-frequency vibrations at the same time.
It is on the basis of this that for different categories of industrial machines, the selection of the poles would directly impact production efficiency. In 2019, while optimizing production line motors, an aerospace parts manufacturer realized that reducing poles improved motor efficiency by 5% and hence increased production line output by 10% overall. The annual energy saving cost for the enterprise through this strategy is as high as 150,000 yuan.
High-speed motors usually have fewer poles, as these are designed principally to improve both efficiency and response time. More commonly, heavy industrial machines incur torque for operation, for which large number of poles is better suitable in motor selection. For example, a standard 3000rpm motor generally uses a 2-pole motor, while a 1500rpm motor might feature a 4-pole motor. Thus, the choice becomes essential for load capacity optimization and operating stability of motor under different working conditions.
Rotor synchronization mechanism
This is the main reason why synchronous motors have stable running characteristics, that is, they can run at constant speed as a consequence of synchronization between rotor and stator magnetic field. More clearly, the rotor of the motor is pulled by the rotating magnetic field of the stator so as to be formed in a “follow” position to achieve constant speed. Behind it is the magnetic field coupling between rotor and stator. The particular movement of the rotor is in sync with the stator’s magnetic field frequency, which is known as synchronous speed. The running speed of a rotor in this type of electric machine will have a very close relation to the frequency of the power supply and the number of poles of the motor.
According to quantitative details under “Motor System Optimization” (IEEE Journal 2021), when synchronizing the motor speed for optimization, the rotor material and structural design can achieve control on the speed fluctuations of the motor at ±1%, which is down by 66% from that of traditional design error of about ±3%. The benefits cover not only reliability improvement of equipment but also fewer times for maintenance and lower failure rates. In contrast, enterprise equipment failure rates oftentimes exceed 5% for enterprises with traditional motor design, and this figure dropped to approximately 1.5% for enterprises’ cases post optimization of synchronization mechanism.
Such as optimization in production lines of synchronous motors for well-known world home appliance brands in 2022; this made the products have longer service life and more stability. Using the efficient synchronous rotor structure, the failure rate of the motor became significantly low, while its stable operating hours increased from the original 5,500 hours to 8,000 hours, thus producing a gain of about 15% of ROI. Also, the average energy efficiency of appliances using the motor increased by 12%. All these optimizations have gone ahead and consolidated the market position of the company in an extremely competitive market.
A synchronous motor gets to rotate at synchronous speed because the rotor creates a magnetic field like that of the stator, owing to the interaction of a conductive material like copper or aluminum with an external current. External magnetic fields then act on the rotor to keep it in a synchronous rotating position. The design of the motor has to ensure that appropriate magnetic fields are accurately regulated to synchronize the rotor and the stator, especially when site load conditions make it very high, and also to sustain constant speed.
In addition, modern synchronous motors also apply permanent magnet synchronous technology, i.e., using permanent magnets to improve the stability of the magnetic field further and enhance the speed accuracy. A famous electric vehicle manufacturer applied this technology into its high-performing motor in 2023, successfully keeping the speed variation within 0.5% and still being able to run stably even at high loads, thus showing the advantage that synchronization can have.
Excitation current regulation
The use of field current regulation technology, which enables synchronous motors to sustain a constant speed, has been essential. The strength of the rotor magnetic field is directly proportional to the excitation current, which also determines the speed and load-bearing ability of the motor. Generally, at the beginning of the operation of the machine, the excitation current is very low. However, as operation continues, the excitation current should be modulated accordingly due to the changing load and thus maintain stable speed of the machine. The control system of the motor thus monitors load in almost real time and adjusts excitation current according to feedback to maintain speed that is always synchronized to that of power frequency.
According to the report of the 2022 Journal, Electrical and Electrical Engineering, synchronous motors equipped with advanced excitation regulation technology can improve power factors by above 20% hence recording a net overall improvement in energy efficiency by 8%. The application can not only enhance output power of the motor but also save wasteful reactive power. An intelligent excitation current regulation system enables energy savings by 10% on power costs for such a large manufacturing industry. Such an intelligent system at an enterprise enhances production line stability and accuracy. Overall, the annual report of the company showed that the overall ROI of the device improved by 25 following the adoption of this technology.
In fact, the regulation of the excitation current has an application of a closed-loop control technology that is usually given to practical motors. This system dynamically varies the excitation current by correlating real-time measurements of the relative stator and rotor magnetic field strengths. When the load is low, the system decreases the excitation current and therefore conserves energy. At high loads, on the other hand, the excitation current is automatically increased to stabilize the speed of the motor. A heavy machinery building company has recently applied this dynamic regulation to its synchronous machine, which entails high current shocks during start-up, thereby reducing overall energy consumption by approximately 8% during operations.
In regulating the modern synchronous motors, a digital control system is employed to put electromagnetic field measurement into full operation. It is through high-precision sensors that the working status of the motor can be automatically controlled via these methods of excitation regulation: constant power, constant current, and load feedback based. By virtue of load feedback, it is basically the most efficient technology: making the current dynamically adjust according to actual load gives the best working state.
The new electric vehicle produced by one of the world’s leading electric motor manufacturers in 2021 comes with this technology which integrates highly efficient and quicker response characteristics of the motor, thus achieving a vehicle range increase of 12%. The battery charging efficiency of this vehicle is improved, thus reducing energy consumption and operating costs.
Load sudden response
Sudden change of load is also a general phenomenon in the running of synchronous motor. The speed of the motor will show instantaneous deviation through the sudden change of load, which can cause the equipment to malfunction or even fail in serious situations. Therefore, how to deal with the sudden load effectively has become the key point to realize the continuous and stable running of the motor.
According to a journal paper of Motor Control Technology in 2023, a smart load feedback control system is adopted to control the sudden change of the load. The graphs show that such a control system is able to keep the variation of the speed of the motor at ±2% when changing the load, but the variation of the original speed is generally larger than ±5%. In the production of a manufacturing firm, the intelligent control system helped it lower the rate of equipment failure resulting from load fluctuations, the rate of failure was reduced by 35%, and the maintenance cost annually was saved by about 12%.
In some applications, based on real-time monitoring of the motor load changes, this intelligent control system, by adjusting the excitation current control and adjusting the rotor speed, the motor speed can be quickly restored to a stable state from the load changes. In this process, the system will compare the preset value to load and the real-time load, and make an accurate adjustment plan so as not to make the motor unstable with too many changes of the load.
In 2021, a steel company applied this load regulation technology to the motor system of its high-load smelting furnace and saw equipment downtime due to load fluctuation during smelting decrease by 40%. This optimization also significantly improved production capacity and production line efficiency, increased ROI by 18%, and saved more than 3 million yuan in maintenance and downtime.
The most critical technology of intelligent control system is load prediction algorithm, which is built upon real-time load data and the law of load change in the past to simulate, so that accurate prediction can be achieved. This allows the control system to react before the possible load mutations, thus achieving stable motor running. In this process, sensors of high speeds are most often utilized to monitor real-time variation of speed and current for the purpose of adjusting the system output in due time.
Other than that, newer synchronous motors can also improve response speed via frequency converter and load adaptation algorithm integration to reduce the impact of rapid change in load on motor performance. In 2022, a global power equipment maker reduced the response time of the motors to sudden loads by up to 30% using such approaches, significantly improving the working efficiency and reliability of its equipment.
Damping windings prevent out of step
Synchronous motor also used damping winding, another important technology. An effective method to stop out-of-step, the damping winding is usually mounted in the engine’s rotor. When the motor load is too great or the power frequency changes significantly, the rotor and stator magnetic fields no longer track together, causing uncontrolled speed. By supplying the necessary damping force to the rotor, the damping winding prevents out-of-step phenomenon and guarantees stable motor operation.
Synchronous motors fitted with damping windings, according to a study in the journal Motor Design and Optimization (2022), have a more powerful anti-out-of-step capacity than unused motors. When the load changes, the data reveal that using damping winding causes the motor to lose step rate reduced by over 80%. Furthermore, under certain high loading circumstances, the damping winding might limit the phase difference between the rotor and the stator to within 1. 5°; the motor minus damping winding usually attains 4°, therefore the damping winding offers much benefit in preventing out-of-step phenomenon.
One of the world’s top mining companies, for instance, installed damping windings in the motors of their mine transport system in 2020. This technology allows them to lower the motor’s out-of-step frequency from the original twice a month to once a year, hence notably enhancing the dependability and stability of the equipment, decreasing maintenance expenses by 25%, and simultanuously significantly improving the operation efficiency of the mine production line.
Connected to the rest of the rotor, damping windings generally include unique conductors (like copper or aluminum strips) set in the iron core of the rotor. The rotating magnetic field produced by the stator will affect the rotor while the engine runs, and the throttle winding can counteract the out-of-step phenomenon by producing the opposing magnetic field. Usually, the design of damping winding calls for strong heat resistance and high electrical conductivity to guarantee they can under high load and high-temperature conditions keep decent working level.
Adding a better damping winding improved the rotor design of a fan synchronous engine of a wind energy firm in 2021. Years of testing revealed that the design not only effectively stops the out-of-step phenomenon but also boosts the power generation efficiency of the fan by 8%. By helping the fan to keep consistent power output even at lower wind speeds, this enhancement further increases the financial and environmental benefits of wind energy generation.
