Nov. 04, 2024
We know that air compressor is a machine, the life of the machine and the software and hardware have a certain relationship, but playing a decisive role is the structure of the machine and the overall optimization.We can say that the frequency converter has the function of reducing electric shock and rotating speed, etc. Permanent magnet frequency converter also has these advantages.But the main machine is the energy saving "core", the main machine line, design structure, surface finish and other mechanical properties, is the air compressor energy saving main components, relying on electrical parts is not able to significantly reduce the cost.However, a permanent magnet machine has an integrated permanent magnet frequency conversion. Because there is no bearing, it saves the two pairs of friction mechanical pairs of the motor, which seems to be helpful to save energy, but in fact, it also has great disadvantages, which we will describe today.
Can permanent magnet inverter all-in-one machine really "save energy"?This question is a little difficult to answer, because the integrated permanent magnet frequency converter does save mechanical friction, the principle is right.But this is only one aspect of the problem, because the integration means that the temperature of the motor is the same as that of the host machine, but this is also the weakness of the permanent magnet machine. If the temperature is too high, it will not only affect the permanent magnet, but also affect the energy saving, which is unknown to the user and also the reason why the manufacturer will not tell you.Let's talk about the advantages and disadvantages of the permanent magnet all-in-one machine.
As shown in the figure, the structure principle of the screw air compressor and the motor is to extend the shaft of the positive rotor of the screw head out of the head to form a coaxial connection with the rotor of the motor.Then the stator and housing of the motor are fixed on the shell of the screw head, forming the integration of the motor and the head.The stator is cooled through the motor windings and the ventilating slots of the housing through the built-in wind blades on the rotor.This structure is an innovation and development trend in many mechanical and electrical equipment occasions, such as air conditioning compressor, elevator tractor, electric hoist, etc., so it is well received and favored by many users.Air compressor screw all - in - one machine because of small size, simple structure, high system efficiency, low price advantages in the market began to prevail.However, from the point of view of electrical engineering, this design has many disadvantages and potential risks.The main problems are as follows:
Motor temperature is too high: since the operating temperature of the oil-cooled head is between 65 and 80 degrees, the temperature between the motor and the head shaft is transferred to the permanent magnet rotor of the motor, and the body temperature is transferred to the motor housing, so that the actual working environment temperature of the motor reaches about 65 degrees.In general, the maximum temperature rise of a reasonable motor design is 80k, so the maximum temperature of the motor winding may be 145 degrees. According to the magnetic steel demagnetization (development reversible demagnetization) experiment of 38uh, the demagnetization rate at 80 degrees is 2%.100 degrees of 5%;120 degrees is 7%;150 degrees is 12%.It shows that the higher the temperature is, the lower the flux is, and the magnetic flux of magnetic steel is related to the efficiency of the motor, that is, the higher the temperature of the motor is, the lower the reverse electromotive force is, and the lower the given voltage of the frequency converter is.The larger the motor current, the higher the temperature rise of the windings, the greater the resistance, and the greater the stator copper loss.The efficiency drops again, so the actual efficiency of the all-in-one machine can not reach the design value at full pressure and large flow.1. Suppose the working environment temperature of the all-in-one machine is 70 degrees, and the motor environment temperature of the split machine is 30 degrees, and suppose the actual temperature rise of the motor in both cases is 50 degrees. The motor has the same electromagnetic design scheme, and the load of the motor is the same.The working temperature of the all-in-one machine is 120 degrees, and the split machine is 80 degrees.The resistance of the former is about 12.7% higher than that of the latter, and the copper loss is also about 12.7% higher.2. The working temperature of the splitter is the control mode assuming that the current of the motor is zero in the direct axis;The demagnetization rates of magnetic steel at 120 and 80 degrees are 7% and 2% respectively.For this reason, the stator current of the former will be about 5.38% higher than that of the latter when the motor drags the same load, and the copper loss of the motor will be 11.0% higher.3, the total copper loss of the all-in-one machine will be about 25.1% higher than the split machine.Based on the copper loss accounting for one third of the permanent magnet synchronous motor, the design efficiency of the general all-in-one machine is about 94%. When working at 120 degrees, the efficiency decreases to about 93.5%. (tyb series is about 97%), so the relative efficiency difference is 3.5%.In addition, the permanent magnet motor is most afraid of demagnetization, and demagnetization is determined by magnetic steel, which is most afraid of high temperature. The greater the risk of refractory demagnetization (irreversible) under long time high temperature, the higher the demagnetization rate of conventional design value in 15 years is not more than 3%.Due to the development of ndfeb technology in China in recent years, there is no way to verify the service life under long-term high temperature. There are many cases of demagnetization and failure of magnetic steel in the motor industry, such as oil fields, spinning machines and so on.
Protection grade ip23: due to the temperature relationship, it can only be designed as an open motor, air compressor is poor in many applications, and its service life is low due to corrosive gases such as dust, moisture and salt spray.
High failure rate: because the all-in-one machine rotor is directly installed on the screw rotor, the bearing on the rotor side of the screw motor should bear more than 2 times the original load, so the bearing and oil seal on the motor side are more than 2 times less than the original life.
Trouble of maintenance: since the rotor of permanent magnet motor is a permanent magnet, the head must be removed before the motor can be removed during the maintenance of the head, and the permanent magnet rotor has a strong attraction, special tools are needed to take it out, and the personnel need to be professional, otherwise it is easy to cause accidents.
Bound manufacturer's choice: because of the screw head than power quality, the size of the choice of the nose is quite different, so the nose is the core of the air compressor, choose the high quality of the nose and efficient motor to achieve excellent than power and reliability, so any brand air compressor manufacturers to select high quality components to build their own products, this will reflect the quality level of manufacturers, improve product reliability, makes the enterprise brand.
The above five disadvantages make the screw all-in-one machine has a great potential risk, need to be improved.Therefore, the most reliable scheme is the direct connection between the traditional head and the single motor, but a reliable permanent magnet motor is needed.To sum up, the permanent magnet inverter screw air compressor still needs to be optimized in the practical application. From the current point of view, it still needs some way to go before the permanent magnet compressor replaces the power frequency compressor. If it needs to be further improved, the permanent magnet compressor will have a way out!
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Would you like to shave 30% off your compressed air energy bills? If your compressed air demand fluctuates, a variable speed drive (VSD) air compressor could reduce energy consumption for compressed air production by 30% or more&#;in some cases, up to 70%. How do you know if a VSD compressor is right for you? Learn the benefits of VSD, when to use a VSD vs. a fixed-speed compressor, and why you may want to consider using both.
Intec Group, LLC saved $18K on their annual energy bill by upgrading to a VSD compressor. Contact us to calculate your potential savings!
A variable speed drive (VSD) controls the frequency supplied to the drive motor on the air compressor in response to real-time demand on the system. When demand is low, the motor will run at a reduced speed, requiring less energy to operate. When demand for compressed air is higher, the VSD will automatically increase the frequency of the air compressor motor to meet CFM demands.
A fixed-speed rotary screw air compressor, on the other hand, operates at the same RPM at all times. Instead of adjusting the motor speed, the fixed-speed air compressor adjusts the air inlet valve to let more or less air out depending on CFM requirements. Even when compressed air needs are low, the motor is always operating at the same speed, so it is always ready to meet the highest CFM it is rated for.
For example, if you have a 100 HP fixed-speed compressor with no load from the plant, it may still be consuming 30 to 70 percent of its full load energy. A VSD compressor, on the other hand, will be at nearly zero input energy! A 100 HP VSD compressor motor can ramp down to the equivalent of 20-35 HP (depending on the manufacturer) when demand is low. As demand increases, it can operate anywhere between its minimum and its maximum 100 HP. When operating at lower speeds (and when properly sized), a VSD compressor is much more efficient and uses less energy.
So, why choose or upgrade to a variable-speed drive air compressor? A VSD air compressor is able to adjust the amount of power used in response to CFM demand in real-time. This provides significant advantages, especially for companies whose compressed air needs vary over the course of a shift, day or season.
The biggest advantage of a VSD air compressor is energy savings. A fixed-speed compressor always draws the amount of power needed to meet the maximum compressed air demand. VSD will ramp down RPM, and therefore power consumption, when demand for compressed air is lower. Depending on the total volume of compressed air used in your facility and the amount of variability in your processes, this can add up to hundreds, thousands or even tens of thousands of dollars in energy savings each year. Energy savings are maximized for facilities with the greatest amount of variability in their processes. In some cases, operators can slash energy costs for compressed air systems by up to 70%!
Motors controlled by VSD have lower starting currents, eliminating the large spikes in demand seen when a fixed-speed motor turns on. When a fixed-speed motor first energizes, the inrush current can be as high as 600% of the operating current. The VSD converter uses a &#;soft&#; start/stop during operation, automatically controlling acceleration and deceleration levels to reduce amperage peaks. This, in turn, reduces stress on your internal power distribution. Power companies sometimes impose penalties for large amperage spikes, which VSD can avoid.
A VSD motor optimizes motor speeds and compressor performance. This reduces stress on mechanical and electrical components, prolonging the life of your system and minimizing downtime.
VSD air compressors provide more consistent pressure for plant operations. A fixed-speed compressor operates within fairly wide pressure bands due to the way airflow is controlled using the inlet valves. These bands may be as much as +/- 10-30 PSIG, meaning PSI for the system may vary by this much during the course of operation. A VSD compressor uses electronic controls and operates with much tighter tolerances, typically operating within a +/- 1.5 PSIG pressure band. This means much more consistent discharge pressure for all of the applications using compressed air in the facility. Tighter tolerances also mean that the compressor can operate at lower delivery pressures while still maintaining the required minimum working pressure for the system.
Typical Pressure Bands (Variation from Set Operating Pressure) Fixed-Speed Compressor Variable-Speed Compressor +/- 10-30 PSIG +/- 1.5 PSIGMany power companies provide incentives for manufacturers to upgrade to energy-saving systems such as a VSD air compressor. Power companies incentivize these purchases because VSD reduces the overall load on the power grid and minimizes sudden spikes in demand that can overload the grid and cause an outage. These incentives can significantly offset the costs of upgrading to a new VSD air compressor.
Check your power company for incentives:
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Variable-speed drive air compressors have many advantages, but that doesn&#;t mean they are the right choice for every facility. The way you use compressed air, the amount of variability in your processes, and the characteristics of your facility will all impact the choice between a fixed speed and variable speed drive rotary screw air compressor.
Choose a Variable Speed Drive Compressor If&#; Choose a Fixed-Speed Compressor If&#; You experience fluctuating compressed air demands across shifts, weeks or seasons You have little variability in demand and are always operating near the maximum CFM rating for your compressor Your applications require tight pressure band tolerances Pressure tolerances are not a big concern The compressor will have consistent power and operate in reasonably clean, dry conditions You have an inconsistent power supply or the compressor will operate in dirty, dusty or wet conditions You have adequate capital, OR you qualify for energy incentives through your power company You have limited working capital You want to save energy and money for compressed air production You do not anticipate significant energy and cost savings from switching to VSDRemember: The more variability you have in compressed air demand, the greater your potential savings from switching to VSD.
The majority of compressed air users could benefit from upgrading to VSD. VSD air compressors provide the biggest energy savings for facilities with high degrees of variation in their CFM requirements. For example:
VSD is also a good fit for applications that must operate within very tight operating pressure tolerances.
Fixed-speed compressors have lower initial costs, so they can be a good choice for companies with limited access to capital funds. Parts and maintenance are also generally less expensive for a fixed-speed compressor. However, it is important to remember that energy savings for a VSD, combined with incentives from your power company, may largely erase the cost difference between a fixed-speed and variable-speed drive air compressor over time.
A fixed-speed compressor may also be more efficient in scenarios where variations in CFM are minimal, and the system will always be operating near its maximum CFM rating. Fixed-speed air compressors are best for:
In many cases, the best option is to use both a fixed speed and a VSD compressor in tandem. Using multiple smaller air compressors instead of a single large compressor means that you can keep at least part of your facility up and running while one compressor is down for maintenance or repairs; the second compressor can typically meet about 50% of your maximum compressed air needs. Combining both types of compressors allows you to take advantage of the energy savings of VSD while saving some initial capital expenses with the fixed-speed compressor. See how it worked for SCM Group: A Three-Compressor System Maximizes Efficiency.
When operating both types of compressors in tandem, the VSD air compressor should have a larger capacity than the fixed speed. Here&#;s how it works:
For example, instead of installing one 100 HP variable speed drive that has a CFM range of 150 &#; 470 CFM, you could install one 60 HP VSD that has a range of 75 &#; 280 CFM combined with a fixed speed 40 HP compressor that has a CFM capacity of 190. This scenario gives you the same max CFM with the same HP but has a greater overall CFM range, delivering greater efficiency to the system. The system can safely operate at CFM as low as 75 using the smaller VSD compressor alone, while both compressors can work together to meet CFM requirements between 280 and 470 CFM.
This expanded range is beneficial, especially when you have large swings in compressed air demand. With a single 100 HP VSD, you&#;re fine when operating at the higher end of its range, but if demand drops below the 150 CFM minimum rating, the compressor will begin to cycle on and off. This puts more stress on system components and reduces the longevity of your compressor. The 60 HP compressor will also be much more energy efficient at lower CFM ranges, reducing overall energy costs.
If you&#;re not sure whether you should choose a fixed-speed or variable-speed drive air compressor &#; or a combination of both &#; an experienced compressed air system engineer can help you decide. Our system designers can complete a professional air demand assessment
to analyze your compressed air consumption patterns and system requirements and determine which option will be most cost-effective for your needs.
Need help choosing between fixed speed and VSD? We can help. Contact us for an analysis.
The choice between fixed-speed and variable-speed air compressors depends on your specific application and air demand patterns. Fixed-speed compressors are ideal for applications with a consistent demand for compressed air, as they run at a constant speed and are typically more cost-effective upfront. However, they may lead to higher energy costs if the demand fluctuates. Variable speed compressors, on the other hand, adjust their speed based on demand, making them more energy-efficient in situations where air needs vary throughout the day. Over time, the energy savings from a VSD compressor can offset the higher initial investment.
A VFD (Variable Frequency Drive) compressor (also known as a variable-speed drive or VSD compressor) offers several key benefits, particularly in terms of energy efficiency and operational flexibility. By adjusting the compressor's motor speed to match real-time air demand, a VFD compressor can significantly reduce energy consumption, especially in systems with varying loads. This leads to lower utility bills and reduced environmental impact. Additionally, VFD compressors experience less wear and tear compared to fixed-speed models, which can extend the equipment's lifespan and decrease maintenance costs. Overall, VFD compressors provide a more adaptable and cost-effective solution for managing compressed air needs.
Variable speed drives (VSDs) provide enhanced control over compressor operation by allowing the motor to adjust its speed according to the demand for compressed air. This results in several advantages, including substantial energy savings, as the compressor only uses the power necessary to meet current demand. VSDs also contribute to more consistent air pressure, reducing the risk of system downtime or inefficiencies caused by pressure fluctuations. Moreover, the smoother operation of VSD compressors leads to less mechanical stress on components, which can lower maintenance needs and extend the equipment's operational life.
Whether you need a variable-speed drive compressor depends on the nature of your air demand. If your application involves fluctuating air requirements throughout the day, a variable-speed compressor can be highly beneficial. It will adjust its output to match demand, optimizing energy use and reducing operational costs. This is particularly advantageous in environments where energy efficiency is a priority or where air demand is unpredictable. However, if your air demand is steady and predictable, a fixed-speed compressor might suffice, offering reliable performance with a simpler and potentially less expensive setup.
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