Rotary frequency converters have long been a standard application for adjusting power systems to achieve more precise frequency control. Now, how exactly do they work, and are these still the converters of choice, given the changing face of technologies? This blog provides a rather in-depth insight into the very essentials of rotary frequency converters, listing their merits and demerits to enable you to weigh options fairly. A must-read for engineers, entrepreneurs, and amateurs alike, it provides equally informative insights into their operation, efficiency, and applicability to a wide array of uses. Follow this article to see what really makes these devices the backbone of power conversion and if they fit into amid-oriented systems, modern-day leading to.
What is a Rotary Frequency Converter?
Basically, a rotary frequency converter constitutes a mechanical device for the conversion of electrical power from one frequency to another. It generally consists of a motor and a generator combined into a single unit; the motor works at the input frequency, while the generator produces power at the desired output frequency. Such converters are often installed in plants where the operation of a piece of equipment designed for a frequency other than the frequency of the power supplied has to be ensured at compatible precision and satisfactorily.
How does a rotary frequency converter work?
To generate with an AGC-01 frequency conversion, the motor and generator were combined into a single unit to convert electrical power from one frequency to another. The motor is connected to the input supply and runs at the input frequency. It uses mechanical energy to turn the generator, which supplies power at the required output frequency. To give a simple example, a frequency converter converts a 60-degree source to 50 degrees for machines and equipment built to the other standard.
The main operating principle depends on the controlled transfer of mechanical energy between the motor and the generator. Modern rotary converters use precision bearings, good cooling systems, and strong control systems for faultless operation with extremely reliable outputs. Some achieve efficiency levels of 90+%, making them perfect for industrial applications in aerospace, manufacturing, and marine.
Other than high load handling, rotary converters can also maintain voltage regulation under fluctuating load conditions. They can work in power ranges from a few kW to hundreds of MW, making them good candidates for various operational conditions. The ruggedness of these machines contributes to their long service life and a minimal maintenance requirement, allowing cost-effective performance in the long run.
What are the components of a rotary frequency converter?
A rotary frequency converter is one that is made of several important components, each essential for its proper functionality and operational efficiency.
- Motor-Generator Set: At the core of the system is a motor-generator set, including a motor that drives the generator. The motor changes electrical energy into mechanical energy, which is utilized by the generator to produce a steady output where the output frequency is different from the input frequency.
- Flywheel: Many rotary frequency converters have a flywheel installed, which helps to stabilize the system, damp fluctuations in speed, and sustain constant rotational speed to achieve greater accuracy of frequency and minimum mechanical stress.
- Control Panel: The control panel is the interface that enables a person to monitor and control the operation of the converter. It incorporates control for voltage adjustment, frequency setting, and safety devices such as overload protection.
- Bearings and Couplings: Great bearings and couplings are needed to reduce friction and mechanical wear. They ensure smooth rotation for long-term operation.
- Cooling System: Rotary frequency converters usually have some cooling method, including a fan or, in some cases, liquid cooling, to dissipate the heat that arises during operation, making the system run within a safe temperature range and efficiency.
- Electrical Connections and Switchgear: Aside from connecting the power, circuit breakers, wiring, and switchgear also provide safety. They protect the converter against electrical faults and allow easy integration into other power networks.
- Enclosure: The enclosure acts as a layer for protecting the internals from contaminations like dust, moisture, or debris, hence contributing to durability and smooth performance.
Likely of more general use, modern rotary frequency converters are designed to work with precise frequencies with good operational strength. The elements thus work together, ensuring high performance and reliability under changing conditions.
How does it compare to a static frequency converter?
While analyzing these converters, one must look through the lenses of application, conversion principle, efficiency, etc. According to Lee, rotary converters have the advantage of being mostly mechanical devices in nature,e with an electric motor and a generator to convert electrical energy from one frequency to another. With this construction, the power converter is well suited to heavy and medium industrial power loads due to its rugged design and ability to provide reliable power when the load varies.
Static frequency converters, in contrast, consist of solid-state electronics such as rectifiers and inverters to accomplish the required frequency conversion. From the point of view of design and engineering, these are principles of construction that define static converters and include the elimination of moving parts designed to create the highest possible degree of energy efficiency. These converters can best serve operations where precision, less maintenance, and small spatial designs dominate- aerospace, telecommunications, or computer systems.
However, static converters may have difficulty with load shifts and demanding operational environments, while a rotary converter can take the abuse and compensate for it. It is essential that the choice depends on the application’s specific constraints, which will weigh heavily on power requirements, load stability, cost considerations, and durability in long-term operation.
What are the Advantages of Using a Rotary Frequency Converter?
- High Reliability: Rotary frequency converters cater to load variations in a huge range, so during adverse conditions, they ensure an undisturbed and steady power supply.
- Durable Performance: It ensures the converter’s ability to go through continuous operational stresses, thereby making them inexhaustible in the realm of heavy or industrial applications.
- Superior Load Handling: These machines can run different power loads, which leads to anti-interruption in their functioning equilibrium.
- Longevity: A Lesser number of electronics components when compared to a static converter; thus, rotary converters have a longer timeline, requiring refit maintenance less frequently.
- Compatibility: Works perfectly fine with sensitive equipment so that the right frequency conversion can be done for its correct performance without harming the equipment.
Why choose a rotary frequency converter for three-phase power?
Among the main reasons to opt for a rotary converter for three-phase power would be its characteristics: reliability, efficiency, and quality of engineering. Its capability to deal with fluctuating power loads, ensuring smooth running during the conversion process, and supplying exact frequency conversion makes it a picture-perfect option for sensitive equipment. From an operational perspective, efficiency refers to its long working life with minor maintenance needs, which ultimately ends up becoming the most cost-effective and reliable means in the long run.
How does it improve voltage and frequency stability?
A rotary frequency converter improves voltage and frequency stability by maintaining a consistent output regardless of fluctuations in the input power. It achieves this through its mechanical inertia, which helps to smooth out variations, and by precisely converting the input frequency and voltage to the required specifications. This ensures the reliable operation of connected equipment and minimizes the risk of power-related disruptions.
What benefits does it offer for variable frequency applications?
- Enhanced Equipment Longevity
The frequency converters maintain a constant frequency and voltage output, protecting the sensitive components from damage by power surges, voltage spikes, or frequency fluctuations, therefore providing enhanced life to the equipment connected.
- Precise Control of Motor Speed
The frequency converters offer fully adjustable choices for motor speed to enhance performance and efficiency in variable frequency applications like conveyors, HVAC systems, and pumps.
- Energy Efficiency Improvements
Since they can optimize speeds according to the demands of the tasks, frequency converters become efficient tools to cut down on useless consumption of energy and hence huge savings from the operating side, and also attain sustainability.
- Reduced Mechanical Stress
During startup, frequency converters gradually ramp up motor speeds, thereby lessening mechanical wear and tear and contributing to fewer requirements for maintenance and downtime.
- Versatility in Global Applications
The frequency converter can adjust equipment designed for one frequency standard (50 Hz) to work smoothly in a region with other frequency standards (60 Hz), adding to their utility in international operations.
- Improved Process Control
Stability and precision in power output must be higher to ensure accurate, reliable operation of production lines and other automated processes, resulting in high-quality products and operational consistency.
- Cost-Effective Power Management
By maintaining consistent levels of performance and optimizing their use, frequency converters lessen operational inefficiencies, thereby bringing down energy costs and total cost of ownership.
- Noise and Vibration Reduction
Since both voltage and frequency are regulated smoothly, noise and vibrations due to motor operation are reduced, making the work environment quieter.
Frequency converters count among the very few tools that address the core concerns in variable frequency applications and, hence, are a must-have for any industry that demands efficiency, reliability, and adaptability in power management.
What are the Disadvantages of a Rotary Frequency Converter?
- Maintenance Requirements
– Being those types of machines with a mechanical moving part, they require periodic maintenance to ensure constant performance and minimize mechanical wear.
- Size and Weight
– Generally, rotary converters are much larger and heavier than static ones, and so they are seldom used if space and weight are important factors.
- Energy Efficiency
– Because of velocity and energy loss due to mechanical rotation, these converters can be less energy efficient, making for a revenue-related conversion in the long term.
- Noise Generation
– The mechanical hardware can make annoying noises, which may be undesirable in an environment where quiet operations are required.
- Initial Cost
– The initial purchase price of the rotary frequency converters may be higher than that of some chromies, depending on the application and specification.
What are the common challenges in using a rotary frequency converter?
- Energy Efficiency
Depending on the load profile, rotary frequency converters can have a lower efficiency value than static converters. This might be a major drawback for industries aiming to reduce their power consumption and operational costs.
- Maintenance Requirements
Because of moving mechanical components in rotary systems, periodic maintenance becomes mandatory for a level of reliability and life expectancy. Bearings, brushes, and other mechanical components wear out with time, making the costs of maintenance skyrocket and sometimes even adding downtime.
- Heat Generation
Heat generation has been an evident characteristic of rotary frequency converters during their normal functioning. By adding an external cooling requirement, the whole system becomes more complex and costly to operate.
- Noise Levels
One demerit of rotary frequency converters is the noise-polluting sound emitted during operation because of their mechanical nature. For any establishment where noise pollution matters, say a hospital or a laboratory, this becomes a huge setback.
- Size and Weight
They are generally bulky and heavy, which renders them mostly inconvenient in installations where space is constrained or portability is a factor.
- Limited Scalability
Large-scale changes accompanied by increased operational requirements may not be so easy to modify in a rotary frequency converter. In the case of business growth or if there is a requirement to design a versatile power system, then this limitation may be a hindrance.
- Environmental Conditions
Rotary frequency converters would be vulnerable if under adverse environmental conditions-extreme climatic conditions. Dust, humidity, or temperature extremes may cause decreased performance of these machines and increased damage risk to themselves, so protective measures must be undertaken.
Armed with such knowledge about the limitations, one might select a conversion system well suited to the operational requirements and conditions. Despite the unique capabilities of rotary frequency converters, their limitations must be examined to ensure their deployment in the right application.
How does it affect energy efficiency?
Rotary frequency converters can exert an influence over energy efficiency in two or more different ways, depending on the type and the balancing applied thereon. These systems typically attain efficiency levels of anywhere in the 85% to 95% range, with the latest advances increasing the upper range. In determining energy efficiency, other factors such as load conditions, maintenance, and the surrounding environment are influential.
The motorized components of rotary converters introduce some mechanical losses from friction and heat dissipation, possibly dragging down efficiency somewhat compared to static converters. But rotary converters work well in high-power applications with low distortion on the electrical side, which is very much suitable for industries. Furthermore, innovations in materials and lubrication systems, along with improved cooling techniques, have enhanced the performance of rotary frequency converters in recent years, thereby reducing energy losses and a greater life expectancy.
Energy losses may also be limited by maintaining the converters within their optimum load range. Overloading and frequent start-stop cycles could possibly cause inefficiencies; hence, an emphasis on system design must contemplate what each individual case actually requires. Neglecting these factors would foster a downfall, but paying full attention will assist rotary frequency converters in good energy control and saving operational expenses.
What are the maintenance requirements and costs involved?
The rotary frequency converters need periodic maintenance to maintain efficiency and prolong their life. These maintenance procedures include inspection of mechanical components, such as bearings and belts, to keep them from wear and tear. Moving parts must be lubricated to reduce friction and prolong the life of the equipment. The electrical connections should be regularly inspected and tightened to prevent potential performance problems.
Maintenance costs depend mostly on the complexity and the size of the converter. Usually, maintenance for regular equipment costs around $500 to $2,000 annually, with growing expenditures for more refined systems. Maintenance contracts for regularly scheduled maintenance tend to be a cheaper way of making sure that service is applied when due and avoiding those unexpected repair days. On the other hand, a neglected maintenance schedule can give way to huge bit-of-wrong-incidents-in-time-costs; therefore, deterrence is recommended over cure. Through this, they cut down on operational interruptions and make sure their rotary frequency converters give out their best for a longer time.
How Does a Rotary Frequency Converter Compare to Other Solutions?
Rotary frequency converters do boast several advantages when compared to other options. They provide the highest reliability and durability, making them suitable for long-term use in arduous applications. Unlike their static counterparts, rotary converters may operate under higher overload capacity for a short period and guarantee the best performance at varying loads. Also, they are very flexible and capable of converting power for almost any type of equipment, irrespective of input or output frequency requirements. They are seemingly more costly initially than some static systems, but rotary frequency converters are a cheaper option to consider over time, considering efficiency, robustness, and flexibility. Rotary frequency converters generally outdo others whenever industries require stable and flexible power conversion.
Rotary vs. Static Frequency Converters: Which is better?
On comparing these two types of frequency converters, we must take into account the very requirements of the application, operational efficiency, durability, and cost implications. Rotary frequency converters are known to give good stability and power quality. Due to their mechanical construction, high surge loads can be absorbed with ease, and the voltage output is smoother, a feature appreciated by more delicate or complex equipment. Rotary frequency converters also have the advantage of longevity, with an average life of about 20 years if well maintained, making them a good investment from an industrial perspective.
Static frequency converters, conversely, use solid-state electronics alone, making them lighter, smaller in size, and generally being able to outprice rotary sets at the beginning. They are best used in any system where space is limited or sound levels have to be kept low because static converters are far quieter in operation. On the downside, they cannot handle heavy load variations as well as rotary converters, and given they run on electronic components, their life is relatively short, somewhere around 10 to 15 years, mostly dependent on how much they’re used and under what temperatures.
As per statistical data, the growing preference for one of these systems can be gauged across industries. For instance, precision machinery industries, such as aerospace or medical device manufacturing, tend to invoke rotary converters for consistent power output and reliability in operation. The data center industry, in view of optimizing space and keeping it functional, most of the time prefers static converters.
Drawing the line between rotary and static frequency converters is more so an issue of comparing initial investment with long-term costs, operational requirements, and performance expectations. Both systems have their strong points, and an educational check on the nuances will set one up to make a suitable decision.
Can a variable frequency drive replace a rotary frequency converter?
Yes, depending on the application, a VFD may be used instead of a rotary frequency converter. VFDs offer excellent motor-speed control and efficiency in systems with variable loads. On the other hand, rotary frequency converters are possibly better for scenarios where high power quality is needed, together with voltage conversion, or for complex loads. Choice depends on the kind of performance and operation conditions the system requires.
What are the industrial applications for each type?
- HVAC Systems
VFDs are used in HVAC systems to control the speeds of fans, pumps, and compressors. This configuration provides energy efficiency by matching motor speed to system requirements and, consequently, reduces operational costs.
- Pumping Systems
Variable speed control in water supply, wastewater treatment, and irrigation systems provides exact flow and pressure control, minimizing energy waste and wear and tear of mechanical parts.
- Material Handling Equipment
VFDs give various manufacturers and logistics the advantages of precision acceleration and deceleration on conveyor belts, cranes, and hoists for increased safety.
- Industrial Automation
Greatly important in industrial automation, VFDs adjust machine speed for performance optimization and change according to load or operational conditions.
- Renewable Energy Systems
In wind and solar energy systems, VFDs are necessary to control generator or motor operation to ensure stable output and grid compatibility.
Industrial Applications of Rotary Frequency Converters
- Aerospace and Defense
Rotary frequency converters are used in testing and operation with high power quality and frequency conversion requirements, like in radar systems or aircraft ground support equipment.
- Marine Applications
They’re employed on ships to convert power frequencies to serve special equipment, irrespective of the ship’s power system.
- Industrial Machinery
These converters are widely used in industries dealing with equipment imported from other countries that are manufactured on different power standards, as they provide reliable voltage and frequency transformation.
- Data Centers
Rotary frequency converters are used in data centers for clean and stable power to critical systems where high-quality electricity is demanded for uninterrupted operation.
- Medical Equipment
Certain high-sensitivity medical equipment, such as MRI machines, relies upon the stability and precision supplied by rotary frequency converters.
Depending on the environment and system requirements, VFD and rotary frequency converters serve a particular industrial need. These unique challenges optimizing operational performance are targeted by the unique industrial need.
When Should You Use a Rotary Frequency Converter?
Rotary frequency converters are suitable for complex machinery when precise and stable frequency conversion is required for sensitive equipment or systems. Since converters fabricate the power with high-grade electricity, they are ideally suited in any situation for industrial machinery operations or for aerospace-type-up tests, and medical devices where exact frequency control is significant. These units are suited best to carry on operations with varying loads or operating environments requiring reliable and durable guarantees.
What are the ideal scenarios for its application?
- Industrial Manufacturing
Frequency converters are key in industrial manufacturing where precision and efficiency play an important role. For example, VFDs ensure optimum motor control and save energy for up to 30% in systems like conveyors, pumps, and assembly lines. This, in the long run, fosters more output and reduces operational costs.
- Aerospace and Defense Testing
The aerospace and defense industries take advantage of frequency converters for use in the most advanced testing equipment. These converters are required since they simulate conditions in which aircraft components, radar systems, or satellite equipment must be tested with exact frequency outputs. Consistent and stable frequencies are ensured so critical test procedures can be carried out to maintain integrity and safety.
- Medical Technology
MRI machines, CT scanners, or ultrasound equipment require free and uninterrupted electrical inputs; however, any distortion can hamper correct diagnosis. Such distortions can be entirely prevented by converters ensuring that these sensitive medical devices always operate at the right frequencies. It is of utmost importance in emergency and intensive care situations.
- Renewable Energy Systems
As renewable energy technologies are growing, frequency converters are being used to balance and integrate variable energy outputs from wind turbines and solar panels into a conventional power grid. Converters regulate and stabilize incoming power so that its frequency matches that of the grid, thereby enabling clean energy to be effectively harnessed while keeping the grid disruption at a minimum.
- Maritime and Shipping Applications
Ships and vessels have loads varying hugely; frequency converters enable smooth operation of variable speed motors and generators. They lend flexibility, and with the aid of these, they can manage gradient propulsion systems, ventilation, and other auxiliary services with great efficiency.
- Data Centers
Data centers must receive a continuous and stable power supply in order to support server functioning. Any power fluctuation is denied by means of frequency converters so that such fluctuations do not have the chance to interfere with any operation. These devices also prevent damage to sensitive IT infrastructure that may arise as a result of inconsistent inputs.
This application of frequency converters also illustrates their great versatility and relevance to so many fields. Technology advancement in recent times has ensured that frequency converters provide better efficiency, energy conservation, and reliability, hence becoming a bottleneck in other fields.
How to Determine the Appropriate Converter for Your Power System?
Selecting the appropriate frequency converter for your power system is determined by several major factors aimed at obtaining optimal performance, energy efficiency, and system life:
- Power Requirements
Determine the power consumption of the system, which is generally expressed in kilowatts (kW) or horsepower (HP). The frequency converter must accommodate the maximum power load plus a safety margin for increased demand or possible power surges.
- Voltage and Frequency Compatibility
Identify the input and output voltage requirements and the input and output frequency. For example, if your system runs on a 50 Hz supply while your equipment needs 60 Hz, you should procure a converter exactly matching the wanted parameters.
- Type of Load
Depending on your system, determine whether the load is constant or varying torque. Heavy machinery, like compressors, needs special kinds of converters with high starting torque, while pumps and fans use variable torque converters.
- Efficiency Ratings and Energy Savings
Modern frequency converters often have energy-efficient designs with efficiency ratings greater than 95%. Going for an efficient device will help cut down tremendously on energy cost and lessen the impact on the environment.
- Control Features and Connectivity
Look for advanced control features such as programmable logic controls (PLCs), remote monitoring abilities, or compatibility with smart systems. This provides greater operational flexibility and confidence when linking to complex industrial networks.
- Environmental Conditions and Durability
Look at the operational environment. For harsh environments, such as extremes in temperature, dust, or humidity, converters with sturdy enclosures rated IP65 or NEMA 4X should be considered.
- Regulatory Compliance and Safety Standards
Ensure that the converter complies with all applicable industrial standards and certifications, such as IEC, UL, or CE marking. This ensures that the unit complies with safety and quality standards.
A commercial decision must be made with complete regard for these factors and studying the technical specifications; this decision, however, shall be tailored to the unique needs of the respective power system. With frequency converters chosen aptly, performance is enhanced while also assuring operational savings in the long term and enhancement in system reliability.
What are the considerations for choosing the right converter motor?
Making this selection, therefore, requires consideration of a few key things in order to ensure maximal performance, reliability, and efficiency:
- Load Requirements
The application should be analyzed for specific requirements of torque, speed, or power. For example, high-torque industrial applications may favor larger and sturdier motors, while precision applications require servo or stepper motors.
- Efficiency Ratings
Select motors that fulfill international efficiency standards (such as IE2, IE3, or IE4). A higher efficiency motor consumes less energy and also has lower operating costs in the long run. It has been revealed by recent studies that IE4 “Super Premium Efficiency” motors can save up to 10% more energy compared to IE3 motors.
- Environmental Conditions
Consider environmental conditions such as temperature, relative humidity, dust ingress, and chemical exposure. Select the motors that have appropriate IP (Ingress Protection) ratings that will withstand such adverse conditions. An IP65-rated motor gives total protection from dust and low-pressure water jets.
- Voltage and Frequency Compatibility
Confirm that the motor is suitable for that particular voltage and frequency offered by the power supply. In places with variable power supplies, frequency converters might come into the picture to ensure that the motors operate without interference.
- Size and Weight Constraints
Applications with spatial limitations would dictate compact or lightweight motors. Newer designs focus on reducing the footprint as much as possible without compromising motor performance for industries such as robotics and automation.
- Maintenance and Operational Costs
Motors intended with self-lubricating bearings and or thermal management systems require less maintenance and hence are more cost-effective over time. Predictive maintenance has become a good practice in modern models to accurately foresee potential failures before they occur.
- Compliance and Certifications
Compliance with standards like IEC or NEMA ensures the equipment’s safe and reliable operation. Similarly, motors bearing UL or CE approval are likewise known to have conformed to stringent safety and performance regulations.
Approaching the above factors systematically will enable various industries to tailor their motor selection to their unique missions and maximize operational efficiency, while ensuring durability. For a thorough consideration, it is crucial to evaluate the application’s requirements based on the manufacturer-provided specifications.
Reference Sources
-
Comparison of solid-state frequency converter and rotary frequency converter in 400Hz power system – IEEE Xplore – A detailed comparison of rotary and solid-state frequency converters, highlighting their characteristics and applications.
-
Modern rotary converters for railway applications – IEEE Xplore – Explores the use of rotary frequency converters in railway systems and their operational benefits.
-
A rotary frequency converter model for electromechanical transient studies of 1623 Hz railway systems – ScienceDirect – Provides insights into the modeling and stability studies of rotary frequency converters in railway applications.
- Top Rotary Frequency Converter Suppliers In China
Frequently Asked Questions (FAQs)
Q: What is a rotary phase converter, and how does it work?
A: A rotary phase converter is a device that converts single-phase power into three-phase power, allowing you to run three-phase machinery on a single-phase power supply. It uses an electric motor (generator) to generate the additional phase needed for three-phase power.
Q: What are the pros and cons of using a rotary phase converter?
A: The pros include its ability to power multiple machines simultaneously and its compatibility with various types of equipment. The cons are that it can be noisy, less efficient than other converters, and may require more maintenance.
Q: How does a rotary phase converter differ from a static phase converter?
A: A rotary phase converter uses a generator to provide continuous three-phase power, whereas a static phase converter uses capacitors to create the third phase only during startup, which may not provide full power for all three-phase applications.
Q: When should I use a frequency inverter instead of a rotary phase converter?
A: A frequency inverter, or variable speed drive, is ideal when you need to change the frequency and voltage to control the speed of an electric motor. It is more suitable for applications requiring variable speed and precise control.
Q: Can a rotary phase converter be used to change the frequency of power?
A: No, a rotary phase converter does not change the frequency of power; it only converts single-phase to three-phase power. For frequency conversion, you would need a solid-state frequency converter or a frequency changer.
Q: What types of machinery benefit most from a rotary phase converter?
A: Machinery that requires three-phase power but is located in areas with only single-phase power availability, such as mills, lathes, and other industrial equipment, benefits most from a rotary phase converter.
Q: How do I determine the size of the rotary phase converter I need?
A: The size of the rotary phase converter needed depends on the total horsepower of the three-phase equipment you intend to run. It is essential to match the converter’s capacity with your equipment’s power requirements.
Q: What is the role of a generator in a rotary phase converter?
A: In a rotary phase converter, the generator (often an electric motor) helps create the third phase by spinning and generating the necessary electrical power to convert single-phase power into three-phase power.
Q: Are there solid-state alternatives to rotary phase converters?
A: Yes, solid-state frequency converters and frequency inverters are alternatives that can provide more efficient, quieter, and maintenance-free solutions for converting single-phase to three-phase power and adjusting frequency for specific applications.
Q: Can I use a rotary phase converter for residential purposes?
A: While technically possible, using a rotary phase converter in residential settings is not common due to noise and space considerations. It is primarily used in industrial and commercial applications where three-phase power is necessary.
