What is VFD and its principle, why VFD is used?
WHAT IS A VFD (Variable Frequency Drive)?
- WORKING OF VFDs. A variable frequency drive controls the speed of an AC motor by varying the frequency supplied to the motor.
- VFD BLOCK DIAGRAM
- VFD SPEED CONTROL METHODS. Wondering can a VFD increase motor speed? ...
- ADVANTAGES OF USING VARIABLE FREQUENCY DRIVES. ...
What does VFD actually stand for?
“VFD” stands for many things, but their main name is “Volunteer Fire Department,” indicating that they put out fires — literal and metaphorical — of their own volition. For most of the organization’s existence, the members were required to get a tattoo of an eye on their left ankles.
What are the major components of a VFD or VSD?
Understanding VFD circuit
- The first section of the VFD is called the rectifier section or converter. ...
- The second section of the VFD is called the DC intermediate section & it contains the filter components.
- The third block of the VFD is called the inverter section because this is where the DC voltage is turned back into three-phase AC voltage.
What does VFD really mean?
VFD stands for Variable Frequency Drive. They are used for controlling the speed of an AC motor. They are also used for ramping up a motor for a smooth startup, or to prevent a heavy load from straining the motor on startup. This is accomplished by adjusting the frequency delivered to the motor.
Why use a VFD on a pump?
VFDs were increasingly tapped to help reduce energy consumption in large pump applications and eventually in HVAC fan systems. VFDs are a critical component of motor speed control. They improve efficiency, reduce wear on mechanical components and improve system performance.
What is a VFD in a pump station?
A variable frequency drive (VFD) is simply a power supply to your AC pump motor. To be very specific, it is a variable frequency inverter. Its job is to control the motor input frequency and voltage and, therefore, control your pump.
How does a VFD operate?
Pulse Width Modulated Variable Frequency Drives. When operated from a constant frequency power source (typically 60Hz), AC induction motors are fixed speed devices. A variable frequency drive controls the speed of an AC motor by varying the frequency supplied to the motor.
Can a VFD be used with a centrifugal pump?
It is increasingly common for pumps to be operated by motors that are controlled by variable frequency drives (VFDs). VFDs control motor speed by varying the frequency of the power being sent to the motor.
What is disadvantage of VFD?
DISADVANTAGE OF VFD THAT USES SCRs to convert ac voltage to dc voltage- IT can cause harmonics on the line that causes overheating of transformers and motor and can cause fuses to blow and circuit breakers to trip.
Can you add a VFD to any motor?
While we've solved the single-speed problem of AC induction motors by introducing the variable frequency drive, not all motors are VFD compatible. Some motors are specifically designed to run on VFD power, while others need a few components added to the system to be compatible.
How does a VFD change frequency?
VFDs manipulate the frequency of their output by rectifying an incoming AC current into DC, and then using voltage pulse-width modulation to recreate an AC current and voltage output waveform. However, this frequency conversion process causes 2% to 3% loss as heat in the VFD — caloric energy that must be dissipated.
Is VFD AC or DC?
AC voltageThe premise of a VFD (variable frequency drive) is to normally take in AC voltage, uses BLACK MAGIC to change it to DC voltage and then uses VODOO to send manipulated voltage a to the AC motor.
What is advantage of VFD?
Saves energy and cost: A VFD regulating a pump motor that usually runs less than full speed can cut down energy consumption over a motor running at constant speed for the same period. In addition, it eliminates the need for mechanical drive components, which also helps reduce overall costs.
Can any pump use a VFD?
A. Motors of any base speed can be used with VFDs, so there is no particular advantage of one speed motor over another for VFD operation. You should always select pumps with the most appropriate speed motors for the duty point that they must serve, regardless of whether a VFD is being used or not.
How do you select a VFD for a pump?
Multiply the motor FLA by two and select a VFD rated for twice the motor's FLA. For example, if you have a 10 HP motor with a FLA of 28 amps, you'll need a VFD rated more than 56 amps and around 20 HP. For small shops or home use, keep in mind that VFDs are the number one power polluters on the planet.
How do you control pump flow rate?
Therefore, to control the flow of a centrifugal pump, simply set the output pressure to the point on the P-V diagram that allows the pump to deliver the desired flow rate. The output pressure of the pump is set using a back pressure regulator. Once the pressure is set, the flow rate to the process is established.
Can any pump use a VFD?
A. Motors of any base speed can be used with VFDs, so there is no particular advantage of one speed motor over another for VFD operation. You should always select pumps with the most appropriate speed motors for the duty point that they must serve, regardless of whether a VFD is being used or not.
How do you select a VFD for a pump?
Multiply the motor FLA by two and select a VFD rated for twice the motor's FLA. For example, if you have a 10 HP motor with a FLA of 28 amps, you'll need a VFD rated more than 56 amps and around 20 HP. For small shops or home use, keep in mind that VFDs are the number one power polluters on the planet.
Can we use variable speed drives with the pumps?
Variable frequency drives are also known as adjustable frequency drives (AFD), variable speed drives (VSD), AC drives, or inverter drives. Variable frequency drives are widely used on pumps and machine tool drives, compressors and in ventilations systems for large buildings.
What is electrical VFD?
A variable frequency drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage of its power supply. The VFD also has the capacity to control ramp-up and ramp-down of the motor during start or stop, respectively.
How does a VFD work?
The higher the frequency sup plied to the motor, the faster it will run. Power applied to the motor through the VFD can make the motor working speed lower than the nameplate base speed, or increase the speed to synchronous speed and higher. Motor manufacturers list the maximum speed at which their motors can safely be worked.
What does VFD do to a motor?
Power applied to the motor through the VFD can make the motor working speed lower than the nameplate base speed, or increase the speed to synchronous speed and higher. Motor manufacturers list the maximum speed at which their motors can safely be worked.
What type of motor is used for variable frequency?
Three phase motors are usually preferred, but some types of single phase motors can be used with single phase variable frequency drives. Motors that are designed for fixed-speed main voltage operation are often used, but certain enhancements to the standard motor works offer higher reliability and better performance.
How does an AC induction motor work?
The AC-induction motor can have its speed changed by changing the frequency of the voltage used to power it. This means that if the voltage applied to an AC motor is 50 Hz (used in countries like China), the motor works at its rated speed. If the frequency is increased above 50 Hz, the motor will run faster than its rated speed, ...
What was the purpose of VFDs in the 1960s?
In the 1960s, VFDs had rather small solid-state components that limited the amount of current the VFD could supply to the motor . This usually limited the size of the motor that could be controlled by a frequency and they were not commonly used. When larger transistors became available in the 1980s, VFDs allowed the largest motors to have their speed controlled. The earliest VFDs used linear amplifiers to control all aspects of the VFD. Jumpers and dip switches were used provide ramp-up (acceleration) and ramp-down (deceleration) features by switching larger or smaller resistors into circuits with capacitors to create different slopes.
How does an inverter work?
Inverter - The basic working principle of an inverter is switching the DC on and off so rapidly that the motor receives a pulsating voltage that is similar to AC. The switching rate is controlled to vary the frequency of the simulated AC that is applied to the motor.
What is a VFD?
VFD is shorted for Variable Frequency Drive (also known as AC Drives and Inverters) -- that's used to make an AC motor working in variable speed (among other parameters). This is definition used in all topical discussion on this paper. A basic VFD system generally consists of an AC motor, a controller, and an operator interface.
How are water pump motors actuated?
In order to realize the variable flow technology, the water pump motors are actuated by the variable frequency drives. For this reason the mathematical model of the pump with new features would be more complicated.
How to understand the characteristics of a water pump?
To understand the characteristics of the pump, establishment of mathematical model of water pump is the premise. Formula (1) and formula (2) illustrate the pump performance and they are basic equations for pump without inverts . We can derive mathematical model of water pump with variable frequency drive by combining the basic formula with the pump law of hydraulic similarity.
Why is the pump head overloaded?
From the discussion, one may conclude that the most important reason which causes overload is pump head exceeds the pipeline system requirement. For those multiple-pump systems, this problem occurs often when only a fraction of pumps are put into operation. Variable frequency technology is a valid method of overcoming overload. Method of calculating operating frequency is more complex and the article illustrates calculation method with an example. This method needs not only the mathematical formulas but also actual performance parameters of pump.
What are the parameters of a water pump?
The basic parameters of water pump include the pump flow and pump head. Under normal conditions we can use the pump characteristics curve to express the model of water pump. The Figure 1 sketches the relationship between pump head with pump flow, the single pump characteristics curve is illustrated with curve 1 and the curve 2 illustrates two parallel pumps characteristics curve in Figure 1. The curve 3 in Figure1 illustrates the pipe system head curve.
Why is my water pump overloaded?
As mentioned above, one of the main cause that cause pump overload is unreasonable operation regulation, the heating or air conditioning water system adopt variable flow technology. The flow rate needs to be regulated by changing numbers of operating pumps or pump operating frequency when the building heating or cooling load changes, especially for those multiple-pumps system.
What is a synchronous variable frequency drive converter?
Synchronous variable frequency drive converter is a good technology to meet the needs of the water system with variable flow; it also can effectively avoid the water pump and variable frequency drive overload. This technique is suitable for the water system with the small number of pumps. However, when the water system with large number of pumps needs smaller flow, Add-Sub pumps control technology is a better choice. Then it is a viable technology to change the number of running pumps, but this approach applied inappropriately would lead to water pumps and variable frequency drives overload. How can we avoid this? Let us take Figure 4 as an example to analyze.
What is the operating point of a water pump union?
The water pump union operating point is point A under designed operating condition, and operating point of the single pump is point C, Figure 1 below sketches these relationships. When the two pumps all put in operation, the total flow is 2Q 0 (Q 0 is rated flow of single pump) and flow rate provided by each pump is Q 0. We can also use formula to express mathematical model without variable frequency drive of water pump:
Why do we need a VFD?
Summary. VFD’s are an increasingly common technology that is applied to simplify pumping systems and maximize system efficiency. Understanding the most common reasons why VFD’s are used will enable you to provide intelligent assistance to pump system designers in selecting the right pumps for the job.
Why do we use VFDs?
Another reason someone might employ VFD’s is to maximize system efficiency. It’s no secret that pumps operate most efficiently within a small portion of their total potential operating range. This range has been dubbed the “Preferred Operating Range” and formally defined by the Hydraulic Institute Standards and the American Petroleum Institute. In most cases the POR extends from 70% to 120% of the flow at the best efficiency point on the pump performance curve. VFDs are often employed to adjust the number of pumps in operation and their operating speed to keep pumps operating as close to the POR as possible as system demands change.
How many GPM does a pumping system need?
So let’s say a pumping system needs to produce a total flow of 10,000 GPM. However, it is also expected to operate regularly at flows of 2,500 GPM and 5,000 GPM. Easy enough right? Just size four pumps for 2,500 GPM each and run 1, 2, or 4 pumps depending on the system requirements! Not so fast.
Why do you need variable frequency pumps?
There are two primary reasons why someone might consider operating pumps on variable frequency drives: To simplify the pumping system by minimizing the different sizes of pumps needed. To ensure the pumps operate as efficiently as possible. Lets explore each of these reasons independently.
How does a pump control speed?
It is increasingly common for pumps to be operated by motors that are controlled by variable frequency drives (VFDs). VFDs control motor speed by varying the frequency of the power being sent to the motor. So a 60 Hz motor operating at 1800 RPM will reduce to 1500 RPM if the frequency is varied down to 50 Hz. There are two primary reasons why someone might consider operating pumps on variable frequency drives:
What is the downside of a pump?
The downside is that when one pump is in operation it will produce a flow far larger than 2,500 GPM. Also, because the pump will be operating beyond the end of the published performance curve there is a serious risk of significantly diminishing the life of the pump. The pumps could be different sizes.
What is pump 101?
This article is part of Pumps 101, an eleven-part series of articles designed as an introduction to the fundamentals of centrifugal pump design, selection, and application. To get the most out of Intro to Pumps check out the full series:
Why use a VFD for a motor?
Because of the VFDs optimal control of the motor’s frequency and voltage, the VFD will offer better protection for your motor from issues such as electro thermal overloads, phase protection, under voltage, overvoltage, etc.. When you start a load with a VFD you will not subject the motor or driven load to the “instant shock” of across the line starting, but can start smoothly, thereby eliminating belt, gear and bearing wear. It also is an excellent way to reduce and/or eliminate water hammer since we can have smooth acceleration and deceleration cycles.
What is a VFD?
A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. Other names for a VFD are variable speed drive , adjustable speed drive , adjustable frequency drive , AC drive , microdrive, and inverter.
How to reduce motor frequency to 30 Hz?
If we want to reduce the motor frequency to 30 Hz, then we simply switch the inverter output transistors more slowly. But, if we reduce the frequency to 30Hz, then we must also reduce the voltage to 240V in order to maintain the V/Hz ratio (see the VFD Motor Theory presentation for more on this). How are we going to reduce the voltage if the only voltage we have is 650VDC?
How to get rid of ripple on DC bus?
We can get rid of the AC ripple on the DC bus by adding a capacitor. A capacitor operates in a similar fashion to a reservoir or accumulator in a plumbing system. This capacitor absorbs the ac ripple and delivers a smooth dc voltage. The AC ripple on the DC bus is typically less than 3 Volts. Thus, the voltage on the DC bus becomes “approximately” 650VDC. The actual voltage will depend on the voltage level of the AC line feeding the drive, the level of voltage unbalance on the power system, the motor load, the impedance of the power system, and any reactors or harmonic filters on the drive.
How many diodes are in a VFD?
The first stage of a Variable Frequency AC Drive, or VFD, is the Converter. The converter is comprised of six diodes, which are similar to check valves used in plumbing systems. They allow current to flow in only one direction; the direction shown by the arrow in the diode symbol. For example, whenever A-phase voltage (voltage is similar to pressure in plumbing systems) is more positive than B or C phase voltages, then that diode will open and allow current to flow. When B-phase becomes more positive than A-phase, then the B-phase diode will open and the A-phase diode will close. The same is true for the 3 diodes on the negative side of the bus. Thus, we get six current “pulses” as each diode opens and closes. This is called a “six-pulse VFD”, which is the standard configuration for current Variable Frequency Drives.
What is the frequency of a motor?
Frequency (or hertz) is directly related to the motor’s speed (RPMs). In other words, the faster the frequency, the faster the RPMs go. If an application does not require an electric motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements change, the VFD can simply turn up or down the motor speed to meet the speed requirement.
What is PWM in water?
This is called Pulse Width Modulation or PWM. Imagine that we could control the pressure in a water line by turning the valve on and off at a high rate of speed. While this would not be practical for plumbing systems, it works very well for VFD’s. Notice that during the first half cycle, the voltage is ON half the time and OFF half the time. Thus, the average voltage is half of 480V or 240V. By pulsing the output, we can achieve any average voltage on the output of the VFD.
Re: How Do VFDs Work in Pumps?
Simple. As the load on the pump increases the current the pump draws also increases.
Re: How Do VFDs Work in Pumps?
"But I want to know how these VFD's senses the variation in pump load and changes the frequency/power input to the motor?"
Re: How Do VFDs Work in Pumps?
I read the data sheet on the link that you posted, and I see your confusion. This PARTICULAR system is custom designed to work with THEIR pump specifically. Here is what they say:
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Why use a VFD pump?
In the case of an oversized pump, using a VFD allows for the use of a larger pump to meet future or periodic high flow requirements without wasting energy during the majority of operation. And unlike the limitations created by a trimmed impeller, the use of a VFD preserves the ability to increase the speed of the pump in the future when expanded flow and pressure are needed.
How does a pump motor work with a VFD?
There is a common misperception that pairing a pump motor with a VFD simply moves the operating point up and down the pump curve. In reality, for every 0.1 hertz (Hz) of speed regulation, a new pump curve is developed, resulting in an infinite number of pump curves generated by varying the speed of a pump. But the system curve stays the same, so as speed is varied the flow in the pumping system is also varied, dropping the amount of frictional head pressure as flow decreases. The pumping system did not change, so the system curve is still valid as speed varies in the pump, with the operating point simply sliding up and down the system curve.
How to balance pump flow?
Some of the common, more rudimentary methods of achieving this balance include oversizing the pump to ensure maximum flow at all times or controlling flow with a throttling valve, a bypass valve or by trimming the impeller. More recently, controlling the flow by pairing the pump motor with a variable frequency drive (VFD) has emerged as a more viable solution in many cases. In order to appropriately examine these methods in more detail, it is important to consider the value of system curves and pump curves in understanding the relative merits of each option.
Why are VFDs important?
Another major benefit of VFDs is in mitigating stress on an aging pump system infrastructure. In many municipalities where the piping system is old and decaying, a full voltage start of the pumps across the line could cause damage to pipes, pumps and motors, and increase expenditures required to maintain the system.
What is a pump curve?
Typically provided by a pump manufacturer, a pump curve describes the relation between the flow rate and the head for the actual pump (essentially data about a given pump’s ability to produce flow against certain head). It is only good for one specific pump, with one impeller diameter, operating at one speed and has one best efficiency point (BEP).
What is the head of a hydraulic pump?
A system curve graphically defines the amount of head pressure required to move a fluid through a hydraulic piping system as a function of flow rate. Head, which is measured in meters or feet, is the maximum height (pressure) a pump can achieve. In wastewater applications this is the vertical lift from the inlet of the pump to the discharge of the pipe. Flow is measured in gallons per minute.
How does efficiency decrease with flow?
As head increases from the BEP, efficiency decreases as the operating point moves up the pump curve toward shutoff head. As flow increases (which means head has decreased) from the BEP, efficiency decreases as the operating point moves down the pump curve. If a valve is installed to restrict flow or use a bypass to restrict head pressure, the pump curve does not change and the operating point simply moves up and down the pump curve.
Why do engineers want to vary the speed of a pump?
Many engineers want to vary the speed of the pump because it is easier, or they don't know how to properly design and size a pump system. Make no mistake about it, most are lying about VFD's to line their own pockets. These Variable Speed type pumps do not save energy, and do not make pumps last longer. To the contrary, varying the speed of these ...
What is CSV pump?
The CSV is a disruptive product. It really does make pumps last longer and use smaller pressure tanks. The CSV really does eliminate cycling and water hammer. The CSV really does save you money, which is why it is disruptive to the pump industry. Don't let a fast talking salesperson force you into a money pit.
Why is a CSV valve disruptive?
The CSV is disruptive to the pump industry because, it may well be the last time you need spend any money on your water system.
How many hours does a pool pump run?
A pool pump only needs to run 6 to 8 hours a day. If you can't turn the pump off, of course a VFD is going to show $2,000 a year savings. But slowing the pump down with a VFD is not doing any good.
Can you slow down a pump with a VFD?
But slowing the pump down with a VFD is not doing any good. At really low flow rates the skimmers don't skim, the vacuum won't vacuum, and the filter won't filter. Turning a standard pump off with a timer, instead of letting a VFD run it slowly all day, WILL save thousands of dollars a year.
Does a VFD reduce RPM?
Still others will make a big deal about how the motor amps are reduced as the RPM is reduced with a VFD. However, they conveniently forget to mention that the flow is reduced 5 times faster than the amps, which makes the VFD cause 500% more energy use per gallon.
Do variable speed pumps save energy?
These Variable Speed type pumps do not save energy, and do not make pumps last longer. To the contrary, varying the speed of these type pumps can increase the energy used by as much as 500% per gallon produced. Likewise, varying the speed increases the heat in motors, causes excessive vibration, and shortens the life of motors from other undue ...
