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1) Reliability of components: LV is
better than MV. Mature product is better than the immature. For the same
component, the better can be chosen according to the brand and class.
2) Reliability of main circuit structure: for the requirement of reducing waste of transmitting power, most big capacity motors are medium voltage motor. Voltage class is most 6kV and 10kV.
There are several modes for inverter to output medium voltage. For high-high mode, the reliability of power cells seriers-connecting is better than direct-connecting of components. Medium-low mode or medium-low-medium mode is only temporary solution in development and they should disappear in market. Some experts believe motors of 1.7 kV, 2.3 kV, 3.3 kV, 4.16 kV should be researched or change connecting mode of motor coil and add a transformer ahead of inverter to match inverter, which acts in a procrustean way.
3) Reliability during operation: power plant has following requirements for inverter to ensure generator units safefy: continue derating operation with several cells broken; can be transferred to direct on line state when inverter is broken; inverter does not stop during instant power-fault; equip UPS for controller; power source of 380V fan is supplied by inverter.
2) Reliability of main circuit structure: for the requirement of reducing waste of transmitting power, most big capacity motors are medium voltage motor. Voltage class is most 6kV and 10kV.
There are several modes for inverter to output medium voltage. For high-high mode, the reliability of power cells seriers-connecting is better than direct-connecting of components. Medium-low mode or medium-low-medium mode is only temporary solution in development and they should disappear in market. Some experts believe motors of 1.7 kV, 2.3 kV, 3.3 kV, 4.16 kV should be researched or change connecting mode of motor coil and add a transformer ahead of inverter to match inverter, which acts in a procrustean way.
3) Reliability during operation: power plant has following requirements for inverter to ensure generator units safefy: continue derating operation with several cells broken; can be transferred to direct on line state when inverter is broken; inverter does not stop during instant power-fault; equip UPS for controller; power source of 380V fan is supplied by inverter.
Tags: inverter, Medium voltage inverter
This application is about China-made cell-cascade multi-level
medium-voltage frequency inverter system on 2 # Unit Condensate water
system, makes a comparison of energy saving before and after the reform.
The results showed that the main auxiliary equipment in power plant
using medium-voltage inverter system is feasible, with quick pay-back
and other characteristics. Inverter has a positive significance to
reduce power consumption.
Preface
A Chinese factory has two units of air-cooling system of 300MW. Inverter is manufactured by Shenzhen Gozuk Co., Ltd. Pump adopt mode of "one work, one standby". Water level of deaerator is adjusted by damper. We have a discussion about inverter application according to the actual situation of # 2 Unit condenser Pump reform in the plant.
Operating Conditions
To ensure continuous and stable operation of condenser pump is an important factor of power generating units security.
Condenser system is shown in following:
Preface
A Chinese factory has two units of air-cooling system of 300MW. Inverter is manufactured by Shenzhen Gozuk Co., Ltd. Pump adopt mode of "one work, one standby". Water level of deaerator is adjusted by damper. We have a discussion about inverter application according to the actual situation of # 2 Unit condenser Pump reform in the plant.
Operating Conditions
To ensure continuous and stable operation of condenser pump is an important factor of power generating units security.
Condenser system is shown in following:
Tags: inverter, water supply
Frequency inverters have a great of prospect in application because the
inverter can save a large amount of electric energy when they are used
for fans.
Capacity of the Power Generation is 110MW. After reconstruction of 1# dedust fan, the power of fan increases 525kW. Variable frequency technology is an effective method to save energy. Variable frequency can realize soft start, reduce impact on equipment. In addition, inverter installation is very easy. It only series connects between breaker and motor. No need to change load and motor. It is necessary to use inverter to save energy for ID fan.
Inverter reform
Air flow is controlled by damper in 1# system. Big redundancy power and damper adjusting mode cause high power consumption.
Motor parameters ID fan parameters
model: Y560-8 Y4-73-11-27D
power: 1000kW flow:425700m3/h
voltage: 6kV pressure: 5064Pa
current: 118.6A media ℃: 90℃
frequency: 50HZ
speed: 744r/min
According to practical operation, inverter current can be 100A, 18.6A less than motor rated current 118.6A. After research market, we finally choose Gozuk inverter. The inverter current is 105A.
Bypass cabinet is installed to ensure system stability. When the frequency inverter is broken, motor can be switched to direct on line manually. Bypass circuit is composed of 3 breakers QS1, QS2 and QS3. QS2 and QS3 are interlocked. In variable frequency state, QS1 and QS2 close, QS3 opens. In direct on line state, QS3 closes, QS1 and QS2 open.
In order to protect inverter, we design link lock with QF. Once the inverter is broken, inverter switches off QF. In direct on line state, inverter cancels signal of QF trip-off to make motor run in direct on line.
Frequency inverter can also be equipped with upper PC. The PC is installed in control room. User can start/stop, set speed through PC. PC can show operation data and current state. User can also control inverter through operation platform.
Capacity of the Power Generation is 110MW. After reconstruction of 1# dedust fan, the power of fan increases 525kW. Variable frequency technology is an effective method to save energy. Variable frequency can realize soft start, reduce impact on equipment. In addition, inverter installation is very easy. It only series connects between breaker and motor. No need to change load and motor. It is necessary to use inverter to save energy for ID fan.
Inverter reform
Air flow is controlled by damper in 1# system. Big redundancy power and damper adjusting mode cause high power consumption.
Motor parameters ID fan parameters
model: Y560-8 Y4-73-11-27D
power: 1000kW flow:425700m3/h
voltage: 6kV pressure: 5064Pa
current: 118.6A media ℃: 90℃
frequency: 50HZ
speed: 744r/min
According to practical operation, inverter current can be 100A, 18.6A less than motor rated current 118.6A. After research market, we finally choose Gozuk inverter. The inverter current is 105A.
Bypass cabinet is installed to ensure system stability. When the frequency inverter is broken, motor can be switched to direct on line manually. Bypass circuit is composed of 3 breakers QS1, QS2 and QS3. QS2 and QS3 are interlocked. In variable frequency state, QS1 and QS2 close, QS3 opens. In direct on line state, QS3 closes, QS1 and QS2 open.
In order to protect inverter, we design link lock with QF. Once the inverter is broken, inverter switches off QF. In direct on line state, inverter cancels signal of QF trip-off to make motor run in direct on line.
Frequency inverter can also be equipped with upper PC. The PC is installed in control room. User can start/stop, set speed through PC. PC can show operation data and current state. User can also control inverter through operation platform.
Tags: inverter, Power Generation
This application introduced Gozuk inverter Power Plant, made comparison for energy saving, explained application prospect of variable frequency drive.
Energy saving effect
1) inverter parameter
2) motor parameter
3) Calculation
For fan and pump: Q∝n ,H∝n2,P∝n3
n---speed;
Q---flow;
H---pressure;
P—shaft power
When motor speed decreases to 80% of rated speed, input power of system (inverter + motor) decreases to 51% of that in rated speed. Thus, energy saving effect is more obvious when speed is low.
Make comparison in same working conditions:
The reconstruction cost can be recovered within 18 months.
Energy saving effect
1) inverter parameter
Model |
Gozuk Inverter |
Input vlotage | 6kV |
Rated current | 130A | Rated power | 1000kW |
2) motor parameter
Rated power | 1000kW | Rated voltage | 6kV |
Rated speed | 990rpn | Rated current | 118.8A |
3) Calculation
For fan and pump: Q∝n ,H∝n2,P∝n3
n---speed;
Q---flow;
H---pressure;
P—shaft power
When motor speed decreases to 80% of rated speed, input power of system (inverter + motor) decreases to 51% of that in rated speed. Thus, energy saving effect is more obvious when speed is low.
Make comparison in same working conditions:
Load | inverter before | inverter after | Energy saving rate |
125MW | 70A | 48A | 25% |
100MW | 55A | 29A | 40% |
The reconstruction cost can be recovered within 18 months.
Frequency control is widely used in several fields for its superiority
in energy-saving, adjustment precision, adjustment range and easy to
communicate with automatic control system. This text is aiming to
illustrate its broad prospects by introducing and concluding several
success cases.
1. Frequency control of boiler's fan
1.1 Application of the boiler's SA fan
The boiler is circulation boiler which is equipped with ID fan, PA fan, SA fan. The parameters as below:
As is known in boiler's regular service, there are considerable variety in fuel composition, heat load, power load, and seasons. Thus, the air for the boiler varies greatly. However, the fan of boiler is designed according to the maximum air flow in full load. In the mean time, there is certain redundancy for air flow in case of boiler's accident. Generally the power of fan is large. From the statistic, average opening of the wind shield in normal condition, 48% in ID fan, 45% in SA fan. Adjusting shield causes a large quantity of energy waste on overcoming the shield resistance. Plant efficiency is low.
At the end of 2000, we planned to choose SA fan of #1 to reform. Considering the fan redundancy, we purposely chose inverter of 132kW to control the fan of 160kw. The inverter started to run in January 2001. By a long term running, the current of the fan reduces from 135A to 75A, which reaches obvious energy saving and meets the requirement of boiler operation. According to the ammeter, energy saving rate is 45% and the cost is recovered in one year. Furthermore, the motor is improved in thermo of start-up, adjustment, controlling and operation. For the perfect benefit, we reform the fans in the other unit later. In design of bypass circuit, we choose double-throw switch in manual as its low-cost, good performance, easy to connect and install and high reliability. The circuit is below:
1. Frequency control of boiler's fan
1.1 Application of the boiler's SA fan
The boiler is circulation boiler which is equipped with ID fan, PA fan, SA fan. The parameters as below:
- ID fan: Y400-6, 400kW, 6kV, 47.3A
- PA fan: Y355-4, 250kW, 6kV, 29.3A
-
SA fan: Y315L1-4, 160kW, 380V, 289A
Average current |
Average opening |
Maximum opening |
Maximum current |
Minimum current |
PA Fan |
||||
21 A |
50% |
55% |
23 A |
20 A |
ID Fan |
||||
25 A |
48% |
50% |
28 A |
24 A |
SA Fan |
||||
135 A |
45% |
50% |
140 A |
130 A |
As is known in boiler's regular service, there are considerable variety in fuel composition, heat load, power load, and seasons. Thus, the air for the boiler varies greatly. However, the fan of boiler is designed according to the maximum air flow in full load. In the mean time, there is certain redundancy for air flow in case of boiler's accident. Generally the power of fan is large. From the statistic, average opening of the wind shield in normal condition, 48% in ID fan, 45% in SA fan. Adjusting shield causes a large quantity of energy waste on overcoming the shield resistance. Plant efficiency is low.
At the end of 2000, we planned to choose SA fan of #1 to reform. Considering the fan redundancy, we purposely chose inverter of 132kW to control the fan of 160kw. The inverter started to run in January 2001. By a long term running, the current of the fan reduces from 135A to 75A, which reaches obvious energy saving and meets the requirement of boiler operation. According to the ammeter, energy saving rate is 45% and the cost is recovered in one year. Furthermore, the motor is improved in thermo of start-up, adjustment, controlling and operation. For the perfect benefit, we reform the fans in the other unit later. In design of bypass circuit, we choose double-throw switch in manual as its low-cost, good performance, easy to connect and install and high reliability. The circuit is below:
Tags: inverter, Power Plant
Normal start
At normal start status, inverter will start and operate at given frequency in open loop mode, or operate at the expected value of the controlled object in closed loop mode.
Soft start
At soft start status, inverter will start and accelerate to the frequency of power grid regardless of the given frequency. When the output frequency of inverter reaches the frequency of power grid (set in main interface), then the output of inverter will become 0, at the same time inverter sends 'transfer to power grid' command. This command can make the control circuit to transfer the power supply of the motor from inverter to the power grid. During the transient transfer, there is a big inrush current.
For synchronous transfer (OPTIONAL FUNCTION, synchronous transfer reactor is required), both inverter and power grid will supply the power to the motor during the transient transfer, there is very small inrush current.
At normal start status, inverter will start and operate at given frequency in open loop mode, or operate at the expected value of the controlled object in closed loop mode.
Soft start
At soft start status, inverter will start and accelerate to the frequency of power grid regardless of the given frequency. When the output frequency of inverter reaches the frequency of power grid (set in main interface), then the output of inverter will become 0, at the same time inverter sends 'transfer to power grid' command. This command can make the control circuit to transfer the power supply of the motor from inverter to the power grid. During the transient transfer, there is a big inrush current.
For synchronous transfer (OPTIONAL FUNCTION, synchronous transfer reactor is required), both inverter and power grid will supply the power to the motor during the transient transfer, there is very small inrush current.
Tags: inverter, Definition
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
Quality inverters incorporate either an AC Reactor or DC Reactor (choke). Their inclusion in the basic design of the inverter allows the design engineer to maximize the advantages of the choke. Their function is to reduce the current distortion caused by the input stage rectifiers by slowing the rate of change of current, and thus charging the internal capacitor at a slower rate over a longer time.
Some inverters allow aftermarket fitment of DC chokes but access to the DC bus is required. While it is easy to add AC chokes to the input stage, there is a disadvantage of voltage drop to the inverter that may have to be considered.
The Harmonic Distortion caused by an inverter is related to its size & load, choke size, and the supply network parameters.
With no AC Reactor or DC Choke, the harmonic distortion will be greater.
Some inverters allow aftermarket fitment of DC chokes but access to the DC bus is required. While it is easy to add AC chokes to the input stage, there is a disadvantage of voltage drop to the inverter that may have to be considered.
The Harmonic Distortion caused by an inverter is related to its size & load, choke size, and the supply network parameters.
With no AC Reactor or DC Choke, the harmonic distortion will be greater.
Tags: inverter, Accessories
1 phase inverter normally is for small power electric AC motor speed control applications, with single phase 220V to 240V input and output 3 phase voltage (lower than input voltage), due to the compact design, this type inverter can be installed in a small space easily.
Single phase inverter specification:
Single phase inverter specification:
- Power range: 0.4kW to 2.2kW
- Input voltage: 220V, 230V, 240V fluctuate rate 15% plus-minus
-
Output voltage: 0 to rated input voltage, three phase
- Sensorless vector control inverter
- Output high torque under very low frequency
- Rich fault protection function to monitor operation record
- Dynamic torque control, rapid response according to load's change
- Built-in braking unit to allow accurate control
- Provide RS-485, Modbus-RTU to communicate with PLC
- Simple PLC control with multi-step program terminals function
- Check & modify inverters parameter online
- Built-in PID for close loop control mode
- 32 bit high speed CPU in fast calculation
From a manufacturing economics standpoint, there is often a trade off in the decision to add a DC bus choke or not based on its ability to reduce the DC bus ripple. This is because it can reduce the DC bus capacitance necessary to present a clean DC source to the transistors. For some frequency inverter manufacturers who have the internal capability to wind their own component chokes, this often represents a component cost benefit compared to buying capacitors from outside vendors and being more subject to market volatility. On the other hand if the inverter manufacturer IS also a manufacturer of capacitors, it works exactly the other way around.
I believe this is why we often see small component class drives being made without DC chokes primarily by companies, mostly in Asia, for whom capacitors are a very low cost commodity. When EU and US manufacturer make larger inverters, it's usually less expensive for them to wind chokes, but that option is often perceived to be too physically large for component class drives so they farm out their designs and production to Asian manufacturers. Ironically then, users will add an external AC reactor anyway, but fail to observe that the overall footprint is now larger than it would have been with a DC choke.
I believe this is why we often see small component class drives being made without DC chokes primarily by companies, mostly in Asia, for whom capacitors are a very low cost commodity. When EU and US manufacturer make larger inverters, it's usually less expensive for them to wind chokes, but that option is often perceived to be too physically large for component class drives so they farm out their designs and production to Asian manufacturers. Ironically then, users will add an external AC reactor anyway, but fail to observe that the overall footprint is now larger than it would have been with a DC choke.
An inverter can operate down to its minimum designed frequency, however the motor design and load characteristics determine the minimum PRACTICAL frequency. If the motor is force cooled and the frequency inverter is operated in vector mode, as long as there is encoder feedback, and the load is not excessive, it is possible to achieve 100% torque at zero frequency.
Tags: inverter, Definition