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This configuration, sometimes referred to as a "shoebox on the wall" is the least expensive option of the three major types. It features a basic frequency inverter connected between the line and the load. Speed control is generally operator initiated either through a front panel keypad or speed potentiometer. Functionality and features on this type of frequency inverter are generally limited. It should be noted that an external disconnect is required and that this type of frequency inverter may not be suitable for filter room applications due to the harsh environment and the lack of a secondary enclosure. One major issue with this type of frequency inverter is that being the sole load driving component, a failure of the frequency inverter will bring the entire system down until the frequency inverter is removed from service for repair or replacement.
Tags: inverter, Frequency inverter
The early-break contact should break around 500ms before the main legs to be effective. Typically-available 10ms early-break aux-contact isolators are ineffective as the residual motor field will not have decayed, resulting in an inductive kick 10ms later when the 3 main legs open. Pffff! goes the frequency inverter output! It is unclear in this situation what a suitable isolator could be. The only practical solution is a lockable isolator, the expectation being that the person with the key understands the need for care.
If one is expecting a lot of switching on the input, then this could be a problem. If an early-break contact on the contactor is used to panic-stop the inverter first, then that may be okay. It depends on the timing and also how the inverter responds to this sort of treatment. Some are more tolerant than others. Consult the manufacturers of the inverter.
In the case of an emergency, nothing can stop the motor faster than the inverter itself (most inverters having an E-Stop input anyway). How the frequency inverter handles the emergency condition is usually a programmable function: ramp down at max or coast. This assumes, of course, that the inverter is undamaged, one would be wise to tie in a line or load contactor to the NO (normally open) output of the inverter-status relay. If it's an emergency, break it on the load side (inverter output). Nobody at the inquiry is going to sympathize with your concerns to pamper the thyristors when weighed against the potential risk to human life.
If one is expecting a lot of switching on the input, then this could be a problem. If an early-break contact on the contactor is used to panic-stop the inverter first, then that may be okay. It depends on the timing and also how the inverter responds to this sort of treatment. Some are more tolerant than others. Consult the manufacturers of the inverter.
In the case of an emergency, nothing can stop the motor faster than the inverter itself (most inverters having an E-Stop input anyway). How the frequency inverter handles the emergency condition is usually a programmable function: ramp down at max or coast. This assumes, of course, that the inverter is undamaged, one would be wise to tie in a line or load contactor to the NO (normally open) output of the inverter-status relay. If it's an emergency, break it on the load side (inverter output). Nobody at the inquiry is going to sympathize with your concerns to pamper the thyristors when weighed against the potential risk to human life.
Tags: inverter, Frequency inverter
Frequency inverter also known as variable frequency drive, VFD, VSD or PWM inverter, the frequency inverter provides direct control of the speed of an electric motor whilst maintaining high levels of motor torque. Frequency inverters achieve this speed control by varying the frequency applied to the motor. Using a PWM (Pulse Width Modulated) control system the output is controlled to vary the voltage and frequency to the motor.
Process automation and productivity improvements
A frequency inverter offers total control of motor speed without sacrificing torque. The speed can be controlled locally (manually), remotely or automatically using internal or external controls. The optimum speed for a process can be adjusted quickly and easily by an operator or process controller.
Energy savings and improved resource management
A frequency inverter enables a reduction in speed when operation at full power or capacity is not required. On variable torque loads such as fans and pumps a reduction in speed can result in substantial energy savings. Pumping water becomes more efficient. Energy costs and carbon footprint are reduced.
Process automation and productivity improvements
A frequency inverter offers total control of motor speed without sacrificing torque. The speed can be controlled locally (manually), remotely or automatically using internal or external controls. The optimum speed for a process can be adjusted quickly and easily by an operator or process controller.
Energy savings and improved resource management
A frequency inverter enables a reduction in speed when operation at full power or capacity is not required. On variable torque loads such as fans and pumps a reduction in speed can result in substantial energy savings. Pumping water becomes more efficient. Energy costs and carbon footprint are reduced.
Tags: inverter, Frequency inverter
Inverter is capable to smoothly starting AC motors (ramp from 0 up to 100% of the load) as well as the energy saving will be achieved, accordingly. Also may I confirmed that frequency inverter also acting as AC Motor starting means among (Star/Delta, Soft Starter, Auto Transformer, Electrolyte, series resistance - wound rotor- etc,). The starting factor of frequency inverter is usually 1 up to 1.2 with respect to the rated load current while for Direct On line about 5-6.
Moreover and as you know the inverter can control the speed of the AC motors in accordance to the formula N=120f/P rpm
where f = the supply frequency and P = number of the Poles.
According to this formula, Motor Speed can be changed either by changing/control the frequency or by changing the number of Poles of the Motor by which step changed in the RPM will be given, while the former gives continuous variable speed as per application demand.
However, as per newly developed power Semi Conductor IGCT based on PWM frequency inverter became the most smart, effective and efficient control device in Industries since is associated also with protective and monitoring means.
Moreover and as you know the inverter can control the speed of the AC motors in accordance to the formula N=120f/P rpm
where f = the supply frequency and P = number of the Poles.
According to this formula, Motor Speed can be changed either by changing/control the frequency or by changing the number of Poles of the Motor by which step changed in the RPM will be given, while the former gives continuous variable speed as per application demand.
However, as per newly developed power Semi Conductor IGCT based on PWM frequency inverter became the most smart, effective and efficient control device in Industries since is associated also with protective and monitoring means.
Noise radiated from a frequency inverter cable is proportional to the amount of varying electric current within it. As cable lengths grow, so does the magnitude of reflected voltage. This transient over voltage, combined with the high amplitudes of current associated with frequency inverters, creates a significant source of radiated noise. By shielding the frequency inverter cable, the noise can be controlled. In the tests presented in this paper, relative shielding effectiveness was observed by noting the magnitude of noise coupled to 10 ft. of parallel unshielded instrumentation cable for each frequency inverter cable type examined. The results of the shielding effectiveness testing are documented in the Figure.
As demonstrated by its trace in that figure, foil shields are simply not robust enough to capture the volume of noise generated by frequency inverters. Unshielded cables connected between a frequency inverter and a motor can radiate noise in excess of 80V to unshielded communication wires/ cables, and in excess of 10V to shielded instrumentation cables. Moreover, the use of unshielded cables in conduits should be limited, as the conduit is an uncontrolled path to ground for the noise it captures. Any equipment in the vicinity of the conduit or conduit hangers may be subject to an injection of this captured, common- mode noise. Therefore, unshielded cables in conduit are also not a recommended method for connecting frequency inverters to motors.
As demonstrated by its trace in that figure, foil shields are simply not robust enough to capture the volume of noise generated by frequency inverters. Unshielded cables connected between a frequency inverter and a motor can radiate noise in excess of 80V to unshielded communication wires/ cables, and in excess of 10V to shielded instrumentation cables. Moreover, the use of unshielded cables in conduits should be limited, as the conduit is an uncontrolled path to ground for the noise it captures. Any equipment in the vicinity of the conduit or conduit hangers may be subject to an injection of this captured, common- mode noise. Therefore, unshielded cables in conduit are also not a recommended method for connecting frequency inverters to motors.
Frequency inverters require an acceptable electrical supply for safe, successful and reliable operation.
Single phase inverters have standardized voltages of 120 and 240 volts. Three phase motors have standardized voltages of 200, 230, 460 and 575 volts.
The nominal supply voltage of the distribution system is normally higher than the inverter nameplate voltage to allow for voltage drops from the distribution transformer to the point of utilization.
Rated frequency is usually 60Hz (hertz or cycles per second) in North America.
Harmonics
Harmonic distortion of voltage and current is produced in electrical systems by non-linear loads such as frequency inverters, welders, rectifiers, Uninterruptible Power Supplies (UPS), arc furnaces etc. Harmonics cause electrical waveform distortion that can propagate through the entire power system and even outside of the plant. The source of harmonic distortion in frequency inverters is the solid-state power switching devices used to generate the varying supply frequencies.
These effects, known as "line harmonic currents", are multiples of the fundamental 60 Hz supply current. For example, a frequency of 180 Hz is called the third harmonic. These currents generate harmonic voltage distortions which often exceed acceptable levels.
For more information, refer to the CEATI Power Quality Energy Efficiency Reference Guide.
Harmonic Components
Harmonic Amplitudes
The odd harmonic amplitudes usually decrease with increasing frequency, so the lowest order harmonics are the most significant. Even numbered harmonics are not normally generated by frequency inverter systems.
Harmonics occur as long as the harmonic generating equipment is in operation and tend to be of a steady magnitude.
Harmonics may be greatly magnified by power factor correction capacitors. The supply system inductance can resonate with capacitors at certain harmonic frequencies developing large currents and voltages, which can damage equipment.
Single phase inverters have standardized voltages of 120 and 240 volts. Three phase motors have standardized voltages of 200, 230, 460 and 575 volts.
The nominal supply voltage of the distribution system is normally higher than the inverter nameplate voltage to allow for voltage drops from the distribution transformer to the point of utilization.
Rated frequency is usually 60Hz (hertz or cycles per second) in North America.
Harmonics
Harmonic distortion of voltage and current is produced in electrical systems by non-linear loads such as frequency inverters, welders, rectifiers, Uninterruptible Power Supplies (UPS), arc furnaces etc. Harmonics cause electrical waveform distortion that can propagate through the entire power system and even outside of the plant. The source of harmonic distortion in frequency inverters is the solid-state power switching devices used to generate the varying supply frequencies.
These effects, known as "line harmonic currents", are multiples of the fundamental 60 Hz supply current. For example, a frequency of 180 Hz is called the third harmonic. These currents generate harmonic voltage distortions which often exceed acceptable levels.
For more information, refer to the CEATI Power Quality Energy Efficiency Reference Guide.
Harmonic Components
Harmonic Amplitudes
The odd harmonic amplitudes usually decrease with increasing frequency, so the lowest order harmonics are the most significant. Even numbered harmonics are not normally generated by frequency inverter systems.
Harmonics occur as long as the harmonic generating equipment is in operation and tend to be of a steady magnitude.
Harmonics may be greatly magnified by power factor correction capacitors. The supply system inductance can resonate with capacitors at certain harmonic frequencies developing large currents and voltages, which can damage equipment.
Tags: inverter, Frequency inverter
Energy Savings with inverters
if you have an AC motor-driven application that does not need to be run at full speed, then you can cut down energy costs by controlling the motor with an inverter (frequency inverter, aka variable frequency drive). Inverters allow you to match the speed of the motor-driven equipment to the process requirement. There is no other method of AC motor control that allows you to accomplish this.
Example of an Excellent inverter Candidate
Example of a Decent inverter Candidate
Example of a Poor inverter Candidate
Variable Torque Versus Constant Torque
inverters, and the loads they are applied to, can generally be divided into two groups: constant torque and variable torque. The energy savings potential of variable torque applications is much greater than that of constant torque applications. Variable torque loads include centrifugal pumps and fans, which make up the majority of HVAC applications. Constant torque loads include vibrating conveyors, punch presses, rock crushers, machine tools, and other applications where the drive follows a constant V/Hz ratio.
Why Variable Torque Loads Offer Great Energy Savings
in variable torque applications, the torque required varies with the square of the speed, and the horsepower required varies with the cube of the speed, resulting in a large reduction of horsepower for even a small reduction in speed. The motor will consume only 25% as much energy at 50% speed than it will at 100% speed. This is referred to as the Affinity Laws, which define the relationships between speed, flow, torque, and horsepower. The following diagram illustrates these relationships.
if you have an AC motor-driven application that does not need to be run at full speed, then you can cut down energy costs by controlling the motor with an inverter (frequency inverter, aka variable frequency drive). Inverters allow you to match the speed of the motor-driven equipment to the process requirement. There is no other method of AC motor control that allows you to accomplish this.
Example of an Excellent inverter Candidate
Example of a Decent inverter Candidate
Example of a Poor inverter Candidate
Variable Torque Versus Constant Torque
inverters, and the loads they are applied to, can generally be divided into two groups: constant torque and variable torque. The energy savings potential of variable torque applications is much greater than that of constant torque applications. Variable torque loads include centrifugal pumps and fans, which make up the majority of HVAC applications. Constant torque loads include vibrating conveyors, punch presses, rock crushers, machine tools, and other applications where the drive follows a constant V/Hz ratio.
Why Variable Torque Loads Offer Great Energy Savings
in variable torque applications, the torque required varies with the square of the speed, and the horsepower required varies with the cube of the speed, resulting in a large reduction of horsepower for even a small reduction in speed. The motor will consume only 25% as much energy at 50% speed than it will at 100% speed. This is referred to as the Affinity Laws, which define the relationships between speed, flow, torque, and horsepower. The following diagram illustrates these relationships.
Tags: inverter, Frequency inverter
Frequency inverters are basically a green energy savings product that matches the amount of work or load on a motor to the amount of energy it needs to power that amount of work. This reduces excess energy from being wasted.
We use a lot of energy in this country and most of that energy is used to move air and water around a building. About half the electricity in commercial buildings is just used to move air and water around, so a frequency inverter is a big way to save energy there. If you look at a typical pump motor the life cycle cost of a pump, 90% of its life cycle costs is the energy it consumes and only 10% the actual cost of the pump motor… a frequency inverter can cut that in half.
Most motors are oversized to deal with your worst-case scenarios, your peak loads. A frequency inverter allows you to run that motor at the load it needs to be instead of running it at peak load all the time. Another benefit is it has a built-in soft start capability. So those combinations of things are going to give you savings; not only on energy, but also extending the life of the motor.
So what is a frequency inverter? Some of the different names that are used in the industry are a inverter, an adjustable frequency drive, a variable speed drive, or an adjustable speed drive. The technology has been around for quite a few years but only has started to make some headway in HVAC and pumping applications in the last several years. The size and cost of electronics has made frequency inverters applicable to a wider range of motors and increased the opportunity for savings.
All frequency inverters are going to take 3 phase AC power and convert that 3 phase power to DC power inside the drive and pulse it out in a simulated AC wave form to the motor. The motor still thinks it has AC power but the DC power conversion now lets us control the speed of the motor without harming it. Now we are in control to save energy and money.
The basic concept with the savings for frequency inverters is your speed and your flow are more or less proportional. But the energy consumption is cubed. If you're running your motor at full speed 60 Hertz, you don't have any savings- but any reduction pays the reduction cubed.
We use a lot of energy in this country and most of that energy is used to move air and water around a building. About half the electricity in commercial buildings is just used to move air and water around, so a frequency inverter is a big way to save energy there. If you look at a typical pump motor the life cycle cost of a pump, 90% of its life cycle costs is the energy it consumes and only 10% the actual cost of the pump motor… a frequency inverter can cut that in half.
Most motors are oversized to deal with your worst-case scenarios, your peak loads. A frequency inverter allows you to run that motor at the load it needs to be instead of running it at peak load all the time. Another benefit is it has a built-in soft start capability. So those combinations of things are going to give you savings; not only on energy, but also extending the life of the motor.
So what is a frequency inverter? Some of the different names that are used in the industry are a inverter, an adjustable frequency drive, a variable speed drive, or an adjustable speed drive. The technology has been around for quite a few years but only has started to make some headway in HVAC and pumping applications in the last several years. The size and cost of electronics has made frequency inverters applicable to a wider range of motors and increased the opportunity for savings.
All frequency inverters are going to take 3 phase AC power and convert that 3 phase power to DC power inside the drive and pulse it out in a simulated AC wave form to the motor. The motor still thinks it has AC power but the DC power conversion now lets us control the speed of the motor without harming it. Now we are in control to save energy and money.
The basic concept with the savings for frequency inverters is your speed and your flow are more or less proportional. But the energy consumption is cubed. If you're running your motor at full speed 60 Hertz, you don't have any savings- but any reduction pays the reduction cubed.
Implementing frequency inverter can pay back big benefits, and adopting them is easier than it might seem at first. You just have to follow a few basic guidelines:
- What are the torque demands of the loads or processes in your planned system? Will any of the loads be hard to start? Inverters have limited over-current capacity, so hard-to-start loads may require an over-sized unit to cover higher current demands.
- How many motors will the frequency inverter control? If it's more than one, will they start sequentially or simultaneously? Calculate the total peak currents of all motor loads under the worst operating conditions your planned system will see. Size the inverter according to this maximum current requirement.
- Will your applications require a quick start or an emergency stop of the load? If so, high currents will be demanded of the inverter. Over-sizing the frequency inverter may be necessary.
- Is motor overheating a potential concern for any of your planned inverter applications? It may be, for reduced-speed, constant-torque applications.
- What range of motor sizes will your process or processes require the inverter to handle? Remember, smaller motors aren't as efficient as larger ones, so improvements due to the inverter will likely be apparent. However, since large motors use much more power, even small increases in efficiency can produce appreciable savings over the life of the motor.
Tags: inverter, Frequency inverter
Introduction of reconstruction
1) Parameters
a. mill fan: 2
b. parameters of mill fan
Motor parameters
c. Work parameters: air flow of single fan 48000 m3/h, yearly work time 5850h. Average current is 40A when motor runs in direct on line.
d. Power price: 0.24 Yuan /kWh
2) Equipment after reconstruction
The system is composed of inverter and bypass cabinet. In above figure, QS1, QS2 and QS3 are all in bypass cabinet. QF and M are original equipment.
The system has switch function between line frequency and variable frequency. QS2 and QS3 cannot close together. They are mechanical interlock. During variable frequency operation, QS1 and QS2 close, QS3 opens. During line frequency operation, QS3 closes, QS1 and QS2 open.
3. Mill fan Technics
Mill fan is installed behind of ball mill, raw powder separator and fine powder separator. In ball mill, raw coal mixes with hot air and recycle air from outlet of mill fan. Raw coal is dried and grindered into coal powder. With negative air flow produced by mill fan, fine powder separator separates air from powder. Coal powder drops in warehouse as storage. Residual gas contains 5~10% mixture of air and powder. It is delivered to furnace as tertiary air, or mixes with coal powder left as primary air. Mixture is delivered to furnace. From above processes, we see mill fan provides negative pressure for system. After reconstruction with frequency inverter, outlet gate of mill fan is full open. Meanwhile, adjust outlet gate appropriately. It can meet requirement of providing negative pressure completely, without affection on tertiary air.
1) Parameters
a. mill fan: 2
b. parameters of mill fan
Model | M6-31No20D | Rated flow (qv, max) | 78000 m3/h |
Rated pressure (Pa) | 13235 | speed (NO) | 1450 r/min |
Motor parameters
Model | Y5601-4 | Rated voltage (UO) | 6000V |
Rated power (Pdn) | 630kW | Efficiency (η) | 96% |
Rated current (IO) | 71A | Power factor (cosФ) | 0.87 |
speed (NO) | 1485r/min | | |
c. Work parameters: air flow of single fan 48000 m3/h, yearly work time 5850h. Average current is 40A when motor runs in direct on line.
d. Power price: 0.24 Yuan /kWh
2) Equipment after reconstruction
The system is composed of inverter and bypass cabinet. In above figure, QS1, QS2 and QS3 are all in bypass cabinet. QF and M are original equipment.
The system has switch function between line frequency and variable frequency. QS2 and QS3 cannot close together. They are mechanical interlock. During variable frequency operation, QS1 and QS2 close, QS3 opens. During line frequency operation, QS3 closes, QS1 and QS2 open.
3. Mill fan Technics
Mill fan is installed behind of ball mill, raw powder separator and fine powder separator. In ball mill, raw coal mixes with hot air and recycle air from outlet of mill fan. Raw coal is dried and grindered into coal powder. With negative air flow produced by mill fan, fine powder separator separates air from powder. Coal powder drops in warehouse as storage. Residual gas contains 5~10% mixture of air and powder. It is delivered to furnace as tertiary air, or mixes with coal powder left as primary air. Mixture is delivered to furnace. From above processes, we see mill fan provides negative pressure for system. After reconstruction with frequency inverter, outlet gate of mill fan is full open. Meanwhile, adjust outlet gate appropriately. It can meet requirement of providing negative pressure completely, without affection on tertiary air.
Electrical environment
A. Prevent overvoltage in input terminal
The main circuit of the inverter is consisted of power electronic parts, these devices are very sensitive on the voltage, the over voltage on input terminal will cause permanent damage of the main components. For example, some factories have their own electricity generator, power grid fluctuation is relative high, so they should have precautions on the input voltage of the frequency inverter.
B. Prevent electromagnetic interference
The inverter main electrical components are power module and control system hardware and software circuit, If these components and software programs are impacted by a certain electromagnetic interference, it will cause hardware circuit malfunction, software program failed and then cause accident. So, in order to avoid electromagnetic interference, the variable frequency inverter needs to prevent electromagnetic interference according the electrical environment. For example: the input power cord, output motor lines, control lines shall be kept away from each other; The devices and signal lines which are easily affected, should be installed as far as possible from the frequency inverter; The critical signal lines should be shielded cable, it is recommended to use shield cable with 360° grounded.
A. Prevent overvoltage in input terminal
The main circuit of the inverter is consisted of power electronic parts, these devices are very sensitive on the voltage, the over voltage on input terminal will cause permanent damage of the main components. For example, some factories have their own electricity generator, power grid fluctuation is relative high, so they should have precautions on the input voltage of the frequency inverter.
B. Prevent electromagnetic interference
The inverter main electrical components are power module and control system hardware and software circuit, If these components and software programs are impacted by a certain electromagnetic interference, it will cause hardware circuit malfunction, software program failed and then cause accident. So, in order to avoid electromagnetic interference, the variable frequency inverter needs to prevent electromagnetic interference according the electrical environment. For example: the input power cord, output motor lines, control lines shall be kept away from each other; The devices and signal lines which are easily affected, should be installed as far as possible from the frequency inverter; The critical signal lines should be shielded cable, it is recommended to use shield cable with 360° grounded.
Constant Torque: This is where the torque required to run the load is the same no matter what speed it is running at. For example a conveyor with a 1000 lb load and a 1 foot radius head pulley would require 1000 ft. Lb. of torque at all speeds. Because these applications can be started under full load conditions the rule of thumb is to provide a frequency inverter drive with 150% overload capacity for 60 seconds in order to overcome the inertia at start up and for overload conditions. Further understanding of the application is required for situation such as an outdoor conveyor that has is fully loaded overnight with a wet gravel load which is now frozen. Starting this load might require 200% or more full load torque, current and HP just to get it running.
Variable Torque: This is where the power required to run the driven equipment increases to the cube of the speed. For example centrifugal pumps and fans. Because these applications start with no load and build up to full load they generally do not require more than 100% of full load torque, current and HP. Inverters with 110% overload capacity for 60 seconds can protect the driven equipment in the case of bearing failure etc. This is the type of application where energy savings are usually large. For example if you have a 300HP water cooling tower fan. To get the return water temperature that you desire in August may require full flow of air. In January you may only require 50% air flow and each month may be different. At 80% flow the horse power required would be about 52% providing saving of 48%.
Constant Horse Power: This is where the torque required to run the load changes with the process. An example here is a mixer used to make soap. The operator starts the mixer and has it running at full speed. He adds water, then other chemicals one after the other. As each chemical is added he reduces the speed but the soap gets thicker and thicker requiring more and more torque. Since the speed is reducing and the torque is increasing the horse power required might be constant or it might even require more horse power at the low speeds. The old variable pitch belt drives were very good for these applications because they provided constant HP from full to half speed.
Variable Torque: This is where the power required to run the driven equipment increases to the cube of the speed. For example centrifugal pumps and fans. Because these applications start with no load and build up to full load they generally do not require more than 100% of full load torque, current and HP. Inverters with 110% overload capacity for 60 seconds can protect the driven equipment in the case of bearing failure etc. This is the type of application where energy savings are usually large. For example if you have a 300HP water cooling tower fan. To get the return water temperature that you desire in August may require full flow of air. In January you may only require 50% air flow and each month may be different. At 80% flow the horse power required would be about 52% providing saving of 48%.
Constant Horse Power: This is where the torque required to run the load changes with the process. An example here is a mixer used to make soap. The operator starts the mixer and has it running at full speed. He adds water, then other chemicals one after the other. As each chemical is added he reduces the speed but the soap gets thicker and thicker requiring more and more torque. Since the speed is reducing and the torque is increasing the horse power required might be constant or it might even require more horse power at the low speeds. The old variable pitch belt drives were very good for these applications because they provided constant HP from full to half speed.
Tags: inverter, Frequency inverter