The capacity of medium and high voltage (3-10KV) motors is relatively large, generally above 200KW. In recent years, as China's industrialization process has accelerated, the production capacity of many industries has become larger and larger, and the drive motors for its production equipment are also growing. For example, in the steel and chemical industries, the use of motors above 10,000 KW has become more and more important. many. Comparison of starting methods for very large motors Packing & Finishing Panels In Perth
Packing & Finishing Panels In Perth,Packing And Finishing Panels,Glossy Panel,Finishing Panels For Sale, Wall End Panel Kitchen
Fully assembled – No assembly required
Save time and Installation Costs
Designed for easy installation
FSC approved, eco-friendly E1 quality board
Durable white high gloss finish on all sides
Constructed from a high moisture resistant 16mm board
Painted with a polyurethane 2-pack High gloss finish
Bright white interior
Soft closing drawers and doors
Quick release hinges to all doors and full extension drawer runners to all drawers
Stylish chrome handles
Solid 16mm backing board and drawer bases
Top-quality premium cabinet
I. Overview
The capacity of medium and high voltage (3-10KV) motors is relatively large, generally above 200KW. In recent years, as China's industrialization process has accelerated, the production capacity of many industries has become larger and larger, and the drive motors for its production equipment are also growing. For example, in the steel and chemical industries, the use of motors above 10,000 KW has become more and more important. many.
With the large use of ultra-large motors (10000KW-50000KW), the above problems have become more and more serious. Pumped storage power stations generally have several generating motors of 40,000 to 300,000 KW. According to China's recent development plan, there are more than a dozen tons of steel companies and millions of tons of ethylene projects. There are also many pumped storage power station projects to be launched. If coupled with other industries, the number of ultra-large high-voltage motors is considerable. Therefore, the problem of starting the super motor is mentioned on the agenda.
In the past, there were not many applications for super-large motors, and there were fewer people studying the starting method. For the super-large motors, some disadvantages of decompression starting became prominent. Therefore, the decompression starting was applied to more than 10,000 kW to 20,000 kW motors. If it is larger, it will be less used. For ultra-large motors of more than 20,000 kW, if you want to soft start, you only need to buy high-voltage inverters at a high price. Because of its high price, people often abandon the soft start and use independent transformers directly.
Full-pressure starting, which is a last resort choice after weighing all aspects, is not the preferred method, because the danger of direct full-pressure starting becomes more prominent for very large motors.
Second, the direct danger of the motor direct pressure start and soft start benefits
1. Impact on the grid
1 The impact of the large current on the grid is almost similar to the impact of the three-phase short circuit on the grid, which often causes power oscillations and makes the grid unstable.
2 The starting current contains a large number of high-order harmonics, which will cause high-frequency resonance with the grid circuit parameters, causing malfunctions such as relay protection malfunction and automatic control failure.
2. Damage motor insulation and reduce motor life
The Joule heat generated by a large current repeatedly acts on the outer insulation of the wire to accelerate the aging of the insulation and reduce the life.
The mechanical force generated by the 2 large currents causes the wires to rub against each other, reducing the insulation life.
3 The jitter of the contact when the high voltage switch is closed will generate an operating overvoltage on the stator winding of the motor.
3. Electric power damage to the motor
The large current generates a large impact force on the stator coil of the motor and the squirrel cage of the rotor, which may cause failures such as loose clamping, deformation of the coil, and breakage of the squirrel cage.
4. Damage to mechanical equipment " target=_blank> mechanical equipment
The starting torque at full pressure direct start is about twice the rated torque. Such a large torque is suddenly added to the stationary mechanical equipment "target=_blank> mechanical equipment, which will accelerate gear wear and even toothing, accelerate belt wear and even Pull the belt off, accelerate the fatigue of the blade and even break the blade.
When the decompression start is adopted, the above hazard is only reduced to a certain extent; when the soft start is adopted, the above hazard almost completely disappears; the direct start of the independent transformer power supply mode can only alleviate the fluctuation of the grid voltage, and other hazards are all Still exist.
Very large motors are of high value and play a central role in production. A little fault will cause great economic losses, and it is necessary to adopt perfect protection.
Third, a comparison of several starting methods
1. Autotransformer decompression start
I. The motor is connected to the low voltage side of the transformer when starting. Therefore, the primary current is small, which can reduce the line voltage drop to a certain extent and reduce the impact on other equipment.
But there are the following disadvantages:
1 Impact: During the starting process, the voltage is switched 2~3 times, so the torque will have 2~3 times of mutation, which is very unfavorable for the more precise mechanical equipment "target=_blank> mechanical equipment; in electrical aspects If the self-deformation is relatively high, the impact on the power grid is also large.
2 Reliability: Due to the large current during switching, induced overvoltage will occur on the autotransformer winding, which will sometimes damage the winding insulation and reduce the service life.
This method is often used on motors of 10,000 to 20,000 kW, and it has rarely been used when the motor is large.
II. Reduced decompression start
The so-called reduced-pressure decompression starting method is a traditional self-depressing transformer decompression starting, and a high-voltage power capacitor that outputs a capacitive current is added to the secondary side of the self-twisting transformer, which is to solve the situation of starting a large motor in a small-capacity power grid. Inductive current when starting the motor is less likely to flow into the grid. However, this method does not reduce the starting current of the motor itself, and the impact of the starting current on the motor and the load is still large (for example, in some cases, the starting current of the motor circuit is 4.8 Ie).
The use of capacitors to reduce the inductive current flowing into the grid is a well-known method. For the starting of the motor, there are several problems that the author is concerned about:
1 The higher harmonics in the sudden change of current at the start of the motor will affect the life of the capacitor.
2 When the capacitor is closed, a large inrush current is generated, making this method unsuitable for frequent starting.
3 If the motor trips due to an accident during the starting process, motor oscillation may occur, which seriously endangers the safety of mechanical equipment "target=_blank> mechanical equipment.
4 When the motor starts near the end, the current will drop. At this time, the capacitor should be removed in time, otherwise there will be over-compensation, which will greatly increase the voltage fluctuation rate.
2. Independent transformer power supply direct full pressure start (TD group)
This method is essentially a direct full pressure start. Only a high-impedance transformer is used to isolate the effects on other consumers, while the high impedance of the transformer is used to reduce the current in the line and the starting circuit. However, the damage to the motor and the mechanical equipment "target=_blank> mechanical equipment still exists. In addition, compared with the case of the shared power grid, a considerable amount of power loss is required.
Take the 20000kW/10kV motor as an example. When using the independent transformer power supply mode, the primary system is generally as shown in Figure 1:
T1 is the three-winding main transformer. The 10kV winding supplies power to other loads; the 35kV winding supplies power to the T2-D. The capacity of D is generally around 0.6 of the T2 capacity.
figure 1
If motor D is operated in common with other loads, the primary system is shown in Figure 2. The main transformer can be selected as a double winding transformer.
figure 2
The following data can be found from the national standard for three-phase oil-immersed power transformers:
Comparing Fig. 1 and Fig. 2, it can be seen that the increase of the TD group startup mode compared with the common network mode is mainly composed of two parts: 1 The loss difference of the main transformer. 2 T2 power loss. The power loss of T2 is mainly composed of iron loss and copper loss. Because of the load, the copper loss is smaller than the full load, and the copper loss is proportional to the square of the current. The copper loss at this time is equivalent to the full load. We assume that the iron loss at full load is equal to the copper loss, so we can get the following multi-energy calculation: large motors are generally continuous working system, assuming that the calculation is 0.5 yuan / kWh, the annual electricity consumption (10,000 yuan)
That is to say, due to the use of independent transformer power supply, it consumes 1.16 million kWh per year and costs 580,000 yuan for electricity. If one transformer T2 is used in consideration of the operation of the common network, a cost can be saved in the capital investment, and the economic benefit is considerable.
3. Using static inverter mode
Using static frequency conversion device for soft start, its performance is the best in the current soft start mode: large output dynamic torque, starting within rated current, mechanical equipment "target=_blank> mechanical equipment smooth and no impact operation. But static frequency conversion The technology is still in the development stage, the switching loss of the device is still relatively large, and the reliability of the frequency conversion device is not very high. Unexpected failures often occur. The control technology is also quite complicated, and it is difficult for general technical workers to cope with professional management and Maintenance personnel. The starting time is long, especially in the application of pumped storage units, the starting time can even reach 3 to 5 minutes, which is very unfavorable for the quick response of the energy storage station that needs to be peak-filled.
Large-capacity static frequency conversion devices are currently not produced in China, mainly relying on imports. The key technologies are monopolized by a few foreign companies, and their prices are very expensive. In addition, the cost of maintenance services after operation is also very high.
4. Switching transformer type high voltage motor soft starter
The soft starter of the switching transformer is another device that has recently adopted the switching characteristics of the thyristor to continuously adjust the output voltage of the transformer, thereby realizing the soft start of the high voltage motor. It is an improvement on the thyristor series soft starter. It replaces the thyristor string with the high voltage winding of the switching transformer (TK), and places the thyristor on the low voltage side of the switching transformer (as shown in Figure 3). The thyristor does not need to be connected in series, and the reliability is greatly improved; and due to the filtering effect of the leakage resistance of the switching transformer, the harmonics applied to the power supply are greatly reduced. Other aspects: voltage and current can be adjusted in full range; can output arbitrary waveform; can form closed-loop control, small time constant, rapid response; as long as the motor power increases, only increase the capacity of the power device; and the loss during startup is small, continuous Starting; because it is a purely regulated soft start, the capacity of the motor can be far apart for a long time. All of this makes the switch-transformer high-voltage motor soft starter the soft-starter of the high-voltage motor with the highest current/price ratio.
The switch-transformer high-voltage motor soft starter can be used to start any large-capacity motor as long as the capacity of the main circuit power component is properly selected. 
image 3
With the switching transformer technology, soft start can be applied to any large-capacity motor. For example, the current capacity of a pumped-storage power station is 300,000 kW, and it is soft-started when it is used as a pump. At present, static frequency conversion is used, and the invisible killer of high harmonics will affect the service life of the motor. This problem can be effectively solved if a switching transformer type high voltage motor soft starter is used.
Fourth, the application of soft starter of switching transformer in catalytic cracking unit of a large petrochemical enterprise
1. 12000kW high voltage motor and load related parameters:
Motor: rated power 12000kW, rated current 1322A, rated voltage 6kV. (Producted by Jiamusi Motor Factory)
Fan: AV-50 series axial compressor. (Shaanxi Blower Group Co., Ltd.)
Power grid: transformer-motor unit power supply, 20000kVA transformer, voltage class 35kV/6kV
2. Starting situation
At 10:05 am on April 11, 2007, the optical axis started the 12000kw motor. The maximum starting current was 3000A (2.27 times rated), the starting time was 10.4 seconds, and the 6kV bus voltage dropped by 15%. The starting curve is shown in Figure 4: 
Figure 4
On April 16, 2007, the light load starting load vane opening degree was 22 degrees, the maximum starting current was 2850A (2.16 times rated), the starting time was 40s, and the maximum voltage drop of the 6kV busbar grid was 25%. Figure 5 shows: 
Figure 5
The successful operation of the device marks the birth of a new generation of ultra-large capacity soft starter with independent intellectual property rights. Since then, our country has its own soft starter for ultra-large capacity motors.
V. Conclusion
Ultra-large high-voltage motors are expensive and play a central role in the production operations of various industries. It is necessary to carry out multi-party care. Although the soft starter has a short working time, its important achievements cannot be ignored, and should be highly valued by electrical technicians and managers. From the point of view of energy saving of the motor system, the use of soft start can eliminate the independent power supply transformer, which has a significant energy saving effect. It has practical practical significance in today's Dali advocating energy saving and emission reduction.
The ultra-large high-voltage motor soft starter is a major technical equipment product. At present, it mainly relies on imports and is expensive. The switch-transformer high-voltage motor soft starter has advanced technical performance, high reliability and low price, which provides a new way for us to choose the soft-start mode of ultra-large capacity motor. Http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
Packing & Finishing Panels In Perth,Packing And Finishing Panels,Glossy Panel,Finishing Panels For Sale, Wall End Panel Kitchen
Duraplex Limited , https://www.fsduraplex.com