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4# boiler (75t) of coal gangue plant of circulating flow bed boiler. Technics of boiler is following: burning is low temperature burning. Fuel is delivered to boiler chamber by coal feed system. Primary air entrances to fire box from air distributor bottom, ensuring material fluidization. The secondary air entrances along height class, increasing oxygen to ensure full burning. Materials of fire box vibrate intensively by fluidization air action. Part of solid materials are brought to boiler chamber by high speed air flow. Some big granules flow along chamber inside by gravitation. Some small granules entrance material separator following flue gas. Gas and solid are forming inside chamber. After separation of solid and gas, granules left return to fire box. Gas separated leaves boiler. Because boiler has separator of high efficiency, granules left return to chamber. Ash concentration of chamber is high. Circulating flow bed boiler differs from common boiler which only has radiation heat transfer. Circulating flow bed boiler also has other heat transfer modes such as convection, which heightens heat transfer coefficient of chamber greatly, ensures boiler to reach rated output. Circulating flow bed boiler has low requirement for coal quality. Its pollution material discharging is very low. So it is boiler of environmental protection which is promoted widely by state.
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.
For any high Torque applications like Jaw Crusher, V/F (being a scalar control) is never a right Torque control selection mode for inverters. Frequency inverter will obviously trip on over current faults whenever sudden dynamic response or Torque demanded is seen from the Load.
Also, if you operate a constant Torque application at low speed typically less than 30Hz in V/F control, inverter will trip on over current as it cannot provide the required Torque demanded by Load. V/F is best suited for variable Torque applications like Fan and pump.
The best selection in my understanding would be a modern Vector control inverter operated in vector mode. Many modern inverters have some best Torque Control features like FORCE (Field Oriented Control) that gives excellent Dynamic response, Torque control and are designed to run such application smoothly.
FORCE can provide control similar to that of a DC inverter by separating Flux and Torque producing components and controlling them individually to achieve best Torque and speed control results.
Also, if you operate a constant Torque application at low speed typically less than 30Hz in V/F control, inverter will trip on over current as it cannot provide the required Torque demanded by Load. V/F is best suited for variable Torque applications like Fan and pump.
The best selection in my understanding would be a modern Vector control inverter operated in vector mode. Many modern inverters have some best Torque Control features like FORCE (Field Oriented Control) that gives excellent Dynamic response, Torque control and are designed to run such application smoothly.
FORCE can provide control similar to that of a DC inverter by separating Flux and Torque producing components and controlling them individually to achieve best Torque and speed control results.
Tags: inverter, Vector control
Scheme selection
In order to save cost, we considered to use hydraulic coupling ever. But we finally gave up this method as its much maintenance, long installation period. After research, considering advanced technology and mature product, we decide to use medium voltage inverter. In several inverter brands such as ABB, Gozuk, Siemens, we decide to use Gozuk inverter because of its advanced technology and the cost-effective.
Model selection
1) Motor is 6kV/450kW. The frequency inverter current is a key parameter. The inverter capacity is designed according to motor rated current and max current. So inverter should meet following conditions:
η: efficiency 0.85
cosφ: power factor 0.75
Um: voltage
Im: current
K: revised coefficient of current waveform (1.05~1.1).
Pcn:inverter capacity (KVA). Icn:inverter rated current(A).
2) connecting method: one drive one bypass circuit
3) Control principle: PLC implements pressure PI control, ensures pipe pressure constant, outputs 4~20mA signal to inverter to implement auto control of speed. Equip upper PC on inverter. Install upper PC in control room, start/stop, adjust inverter through upper PC. Frequency inverter data and state shows in upper PC.
4) Link lock protection of isolator, inlet valve, outlet valve and pump fault.
5) Set over current protection, low speed protection.
6) Protection action: by PLC.
In order to save cost, we considered to use hydraulic coupling ever. But we finally gave up this method as its much maintenance, long installation period. After research, considering advanced technology and mature product, we decide to use medium voltage inverter. In several inverter brands such as ABB, Gozuk, Siemens, we decide to use Gozuk inverter because of its advanced technology and the cost-effective.
Model selection
1) Motor is 6kV/450kW. The frequency inverter current is a key parameter. The inverter capacity is designed according to motor rated current and max current. So inverter should meet following conditions:
Pcn≥(KPm)/(ηcosφ) (KVA)Pm: output power
Icn≥KIm (A)
Pcn≥K√3UmIm*10-3 (KVA)
η: efficiency 0.85
cosφ: power factor 0.75
Um: voltage
Im: current
K: revised coefficient of current waveform (1.05~1.1).
Pcn:inverter capacity (KVA). Icn:inverter rated current(A).
2) connecting method: one drive one bypass circuit
3) Control principle: PLC implements pressure PI control, ensures pipe pressure constant, outputs 4~20mA signal to inverter to implement auto control of speed. Equip upper PC on inverter. Install upper PC in control room, start/stop, adjust inverter through upper PC. Frequency inverter data and state shows in upper PC.
4) Link lock protection of isolator, inlet valve, outlet valve and pump fault.
5) Set over current protection, low speed protection.
6) Protection action: by PLC.
Scheme selection
By looking through relevant material and inquiry from other power plants, our plant put forward to adopt variable frequency adjustment. Existing practice proves that this method has considerable effect of energy saving. We also made comparison and analysis between variable frequency adjustment and hydraulic coupling adjustment. We went to Haikou Power Plant and asked for information, finding following disadvantages of hydraulic coupling: complicated system, low reliability, much maintenance labour. Its advantages is low price and low cost. Through analysing actual state, the plant did not have enough installation space for hydraulic coupling. So we gave up hydraulic coupling and decided to use variable frequency adjustment.
Introduction of variable frequency adjustment
With consecutive development, variable frequency technology has reached a high level and has applied in several industries and civil facilities, such as civil variable frequency air conditioner. Its character is to utilize open/close loop control. Power cells of inverter output power required through AC-DC-AC single phase inverter circuit. Frequency inverter makes output frequency meet technics requirement, thereby reaching goal control and purpose of energy saving.
The plant selected and purchased Gozuk inverter at last. The inverter is high-high voltage source inverter, adopting cell-cascaded and multi level technology, with advantages of less harmonic, better output waveform.
Reform implementation
Because 6kV switch room has no enough installation space, plant decided to install one inverter for each surplus heat boiler. Frequency inverter has function of "one drive two". It can drive P1, P2, and has bypass function. Two boilers use two inverters. The two inverters drive four pumps.
Reconstruction began in August, 2004. The whole installation and commissioning finished within a week.
Introduction of operation mode
For above reasons, we must adopt special operation mode to ensure safe operation of water feeding system. We selected following mode eventually.
During normal operation, variable frequency pump works. System adopts HP steam drum close loop control. Water feeding governing valve is in manual control and full open. Standby pump in direct on line does not join link start, which can prevent trip-off resulted from high water level of HP steam drum when personnel does not take measure in time.
In the case of failure of inverter or running pump, it stops automatically or by manual. Personnel should start standby pump manually and adjust appropriate opening of valve as per load of that time. Exit HP steam drum three low value protection, avoid tripping caused by lag control. The gist is that surplus heat boiler has capacity of dry burning. Anyway, these ask for high requirement to personnel. When the frequency inverter is broken, original running pump can use line power to become as standby pump, thereby making high serviceability of water feeding system, reducing probabilities of stop farthest.
By looking through relevant material and inquiry from other power plants, our plant put forward to adopt variable frequency adjustment. Existing practice proves that this method has considerable effect of energy saving. We also made comparison and analysis between variable frequency adjustment and hydraulic coupling adjustment. We went to Haikou Power Plant and asked for information, finding following disadvantages of hydraulic coupling: complicated system, low reliability, much maintenance labour. Its advantages is low price and low cost. Through analysing actual state, the plant did not have enough installation space for hydraulic coupling. So we gave up hydraulic coupling and decided to use variable frequency adjustment.
Introduction of variable frequency adjustment
With consecutive development, variable frequency technology has reached a high level and has applied in several industries and civil facilities, such as civil variable frequency air conditioner. Its character is to utilize open/close loop control. Power cells of inverter output power required through AC-DC-AC single phase inverter circuit. Frequency inverter makes output frequency meet technics requirement, thereby reaching goal control and purpose of energy saving.
The plant selected and purchased Gozuk inverter at last. The inverter is high-high voltage source inverter, adopting cell-cascaded and multi level technology, with advantages of less harmonic, better output waveform.
Reform implementation
Because 6kV switch room has no enough installation space, plant decided to install one inverter for each surplus heat boiler. Frequency inverter has function of "one drive two". It can drive P1, P2, and has bypass function. Two boilers use two inverters. The two inverters drive four pumps.
Reconstruction began in August, 2004. The whole installation and commissioning finished within a week.
Introduction of operation mode
For above reasons, we must adopt special operation mode to ensure safe operation of water feeding system. We selected following mode eventually.
During normal operation, variable frequency pump works. System adopts HP steam drum close loop control. Water feeding governing valve is in manual control and full open. Standby pump in direct on line does not join link start, which can prevent trip-off resulted from high water level of HP steam drum when personnel does not take measure in time.
In the case of failure of inverter or running pump, it stops automatically or by manual. Personnel should start standby pump manually and adjust appropriate opening of valve as per load of that time. Exit HP steam drum three low value protection, avoid tripping caused by lag control. The gist is that surplus heat boiler has capacity of dry burning. Anyway, these ask for high requirement to personnel. When the frequency inverter is broken, original running pump can use line power to become as standby pump, thereby making high serviceability of water feeding system, reducing probabilities of stop farthest.
I have a 100 HP (75 kW) 1500 RPM motor in a sugar mill, operating a TurboRotor. The motor is oversized due to the large torque it needs to apply to start the turbo rotor, there is no solution to this problem because the motor was sold integrated in the machinery.
However, the motor can be equipped with an inverter because the load of sugar is intermittent. When the silo needs sugar a valve opens and feeds the turbo rotor, during which the electric motor consumes 40,5 kW, when the silo is full the valve closes and the motor keeps operating in "No Load" consuming 33,8 kW. It isn't profitable to turn off the motor because it takes too long to start and it would result in damage to it.
Therefore I decided to use an inverter to control the speed for the "Load- no Load" problem. Can you help me with the detailed energy savings part, because I am used to calculating for Pumps but this is a different situation.
However, the motor can be equipped with an inverter because the load of sugar is intermittent. When the silo needs sugar a valve opens and feeds the turbo rotor, during which the electric motor consumes 40,5 kW, when the silo is full the valve closes and the motor keeps operating in "No Load" consuming 33,8 kW. It isn't profitable to turn off the motor because it takes too long to start and it would result in damage to it.
Therefore I decided to use an inverter to control the speed for the "Load- no Load" problem. Can you help me with the detailed energy savings part, because I am used to calculating for Pumps but this is a different situation.
At one of my work site there is a inverter which is running a motor coupled to conveyor belt
Power dips of duration 1s is somewhat frequent at site
due to this power fluctuation the frequency inverter earlier tripped, after enabling the auto restart and flying restart option in the parameter, now the inverter is not tripping but during the power dip the motor slows down and once the dip gone ramps up back. since the motor is loaded the dc link capacitor is discharging quickly
I want to avoid this speed variation occurring
so one solution which I sort out is to add additional dc link capacitor to existing so as to hold as much energy to withstand the power dip occurring
I don't know how practical it would be. And if this possible what all are the design/selection criteria, also I would like to know other alternative solution.
The inverter is Micromaster mm430 [siemens make]
Power dips of duration 1s is somewhat frequent at site
due to this power fluctuation the frequency inverter earlier tripped, after enabling the auto restart and flying restart option in the parameter, now the inverter is not tripping but during the power dip the motor slows down and once the dip gone ramps up back. since the motor is loaded the dc link capacitor is discharging quickly
I want to avoid this speed variation occurring
so one solution which I sort out is to add additional dc link capacitor to existing so as to hold as much energy to withstand the power dip occurring
I don't know how practical it would be. And if this possible what all are the design/selection criteria, also I would like to know other alternative solution.
The inverter is Micromaster mm430 [siemens make]
Tags: inverter, Troubleshooting
Both IGBT and MOSFET are the best as per application.
I am designing high efficiency grid inverter for PV with dual buck topology for 300 watt system. During my simulation I saw that the body diode of two Mosfet switches getting turning on and this switches running on grid frequency (50 Hz). And other two Mosfet's body diode of the inverter are silent during operations. And that is running at PWM frequency. One option I feel that I could replace igbt that will switch on grid frequency or else in the mosfet switch I could put an inductor to avoid the diode getting turning on. but if choose igbt i will get high on state losses compare to mosfet due to small current I= 1.30 rms and mosfet fits for that.
I am designing high efficiency grid inverter for PV with dual buck topology for 300 watt system. During my simulation I saw that the body diode of two Mosfet switches getting turning on and this switches running on grid frequency (50 Hz). And other two Mosfet's body diode of the inverter are silent during operations. And that is running at PWM frequency. One option I feel that I could replace igbt that will switch on grid frequency or else in the mosfet switch I could put an inductor to avoid the diode getting turning on. but if choose igbt i will get high on state losses compare to mosfet due to small current I= 1.30 rms and mosfet fits for that.
Tags: inverter, Grid inverter
This paper makes a comparison between the inverter and hydraulic coupling by introducing the methods and principles of inverter, analyses the situation of fans and pumps in term of energy saving. We think the inverter control program is matured, its energy saving is obviously. Inverter will be widely used in various power plants.
Variable frequency control inverter is a new electric drive and it has rapid development in twentieth century, mainly used in AC motor speed control. Its technology and performance are better than any other kind of speed control mode (such as: Voltage Step-down speed control, pole changing speed control, slip speed control, internal feedback cascade speed control and hydraulic coupling). The inverter speed control has a great acceptance in broad users as its remarkable energy saving, high-precision speed control, wide adjustment range,faultless power electronics protection, as well as easy implementation of the automatic communication function. Inverter also brings great convenience to user in safe operation, reliable installation, maintenance etc, which makes domestic and foreign enterprises adopt best choice of energy-saving method for motor.
Principle
As we know, the relationships of speed (N), flow(Q), pressure(H) and power(P) is as follows:
Variable frequency control inverter is a new electric drive and it has rapid development in twentieth century, mainly used in AC motor speed control. Its technology and performance are better than any other kind of speed control mode (such as: Voltage Step-down speed control, pole changing speed control, slip speed control, internal feedback cascade speed control and hydraulic coupling). The inverter speed control has a great acceptance in broad users as its remarkable energy saving, high-precision speed control, wide adjustment range,faultless power electronics protection, as well as easy implementation of the automatic communication function. Inverter also brings great convenience to user in safe operation, reliable installation, maintenance etc, which makes domestic and foreign enterprises adopt best choice of energy-saving method for motor.
Principle
As we know, the relationships of speed (N), flow(Q), pressure(H) and power(P) is as follows:
Q1/ Q2=n1/n2From above, if other operating conditions remain unchanged, through reducing motor speed, energy-saving effect is very remarkable. For example, working condition only demands 50% flow, personnel can adjust speed to half of rated. Power consumption is only 12.5% of rated value, that is, theoretically, energy saving rate can reach to 87.5%.
H1/ H2=(n1/n2)2
P1/ P2=(n1/n2)3
IGBT die are most commonly designed without an integral (monolithic) anti-parallel diode because they can be better optimized for particular forward parameters that way. Separate antiparallel diode die can then co-packaged for topologies that require it. This makes it easier to fully optimize the forward and reverse characteristics of the compound device. The disadvantage is that the co-packaging takes-up some extra room, and the wirebonds add a small amount of parasitic inductance. But co-packaged IGBTs like this are still the dominant devices used in motor drives and other inverter applications. One additional benefit of IGBTs is that they can be designed to survive a direct short-circuit across the bus, for several microseconds (Short Circuit SOA capability), versus Superjunction FETs do not have this capability.
Superjunction FETs on the other hand have a parasitic body diode (like all vertical FETs), whether you like it or not. The advantage of the superjunction process is that it can produce a very low ON resistance at high voltage using less silicon area than other methods. However, the big disadvantage of superjunction is that the body diode dynamic performance is poor. Even with special doping and irradiation - it might get a little better, but it is in a completely different league compared to an optimized fast diode or SiC Schottky.
Superjunction FETs on the other hand have a parasitic body diode (like all vertical FETs), whether you like it or not. The advantage of the superjunction process is that it can produce a very low ON resistance at high voltage using less silicon area than other methods. However, the big disadvantage of superjunction is that the body diode dynamic performance is poor. Even with special doping and irradiation - it might get a little better, but it is in a completely different league compared to an optimized fast diode or SiC Schottky.
Tags: Definition, inverter
We can six stepped for higher power motor like >50KW, where inverter switches doesn't respond too fast for the digitally modulated PWM (Space vector or Sine wave PWM) using a DSP or a controller or even a FPGA.
In high power applications, six stepped modulation has higher advantages to motor like:
1, Higher average starting torque output (irrespective of construction of the motor - Axial magnets or radial magnetic field)
2, Can be used easily for high speed motors where any modulation technique cannot be used.
And for de-merits, I think everyone knows the de-merits since he final output is not sinusoidal and it is just near sinusoidal.
Just be careful about the harmonic current at the output of inverter that is too dangerous as I2R losses increase as a function of harmonic current.
In high power applications, six stepped modulation has higher advantages to motor like:
1, Higher average starting torque output (irrespective of construction of the motor - Axial magnets or radial magnetic field)
2, Can be used easily for high speed motors where any modulation technique cannot be used.
And for de-merits, I think everyone knows the de-merits since he final output is not sinusoidal and it is just near sinusoidal.
Just be careful about the harmonic current at the output of inverter that is too dangerous as I2R losses increase as a function of harmonic current.
Tags: inverter, Sine wave inverter
Variable frequency speed adjustment: it adopts advanced
power and electronic technology, computer control technology and
communication technology. So it has advantages over other adjustment
modes.
So the plant selects the most advanced adjustment mode---variable frequency adjustment. By evaluating numerous inverter manufacturers, the plant decided to use Gozuk inverter. The frequency inverter has following advantages:
- The inverter has LCD interface and touch screen panel which can show voltage, current, frequency, speed at any time. Personnel can observe motor state at any time.
- High frequency resolution and adjustment precision meet technics requirement completely.
- The inverter has universal external ports which can connect to PLC and control machine, and also can connect to original control circuit, composing close loop system, such as data exchange and linkage with original DCS.
- The inverter has local control and remote control through internet.
- The inverter has power protection and electric protection which ensure inverter and motor reliable during normal operation and failure.
- Motor can realize soft start/stop. Start current is smaller than rated current of motor. Start time can be adjusted continuously, reducing affection on power grid.
- The inverter reduces wear and tear on auxiliary components, prolongs equipment lifetime and heightens production efficiency.
So the plant selects the most advanced adjustment mode---variable frequency adjustment. By evaluating numerous inverter manufacturers, the plant decided to use Gozuk inverter. The frequency inverter has following advantages:
- Gozuk takes the biggest market share in China. System runs reliably.
- It has perfect HMI.
- It has distinct technology predominance at reliability and safety.
- Inside PLC changes control logic easily, applicable to site need.
Tags: inverter, Power Plant