Application of the hottest thyristor soft starter

2022-07-22
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Application of thyristor soft starter in Centrifugal Fan Abstract: This paper introduces the application of thyristor soft starter in centrifugal fan, and expounds in detail the classification and characteristics of thyristor soft starter, the classification and working principle of fan

key words: thyristor, fan, voltage, starting

1 introduction

at present, among all kinds of mechanical and electrical equipment in all walks of life in China, the motor matched with the fan accounts for about 60% of the national motor installed capacity, and the power consumption accounts for about one third of the national total power generation. It is particularly worth mentioning that most fans have the phenomenon of big horse pulling small car in the process of use. In addition, due to changes in production and process, it is necessary to often adjust the gas flow, pressure, temperature, etc; At present, many units still use the backward way of adjusting the air baffle or valve opening to adjust the gas flow, pressure, temperature, etc. In fact, this is the way of artificially increasing resistance. This paper includes energy conservation and environmental protection (automobile lightweight, smart glass (908, 0.00, 0.00%), aerogel, thermal insulation materials), the third industrial revolution process and materials (3D printing, sensors, superconducting materials, memory alloys), carbon industry chain (graphene, fullerene, carbon fiber, carbon nanotube), military materials (superalloys, titanium alloys, metamaterials) The 25 new materials involved in 8 categories of emerging electronic industries (liquid metal, amorphous and gold, OLED, flexible glass, optical film), mass industry (cemented carbide), energy (perovskite), and new chemical materials (adhesives, peek, polyphenylene sulfide) cost power and money to meet the requirements of process and working conditions for gas flow regulation. This backward regulation method not only wastes valuable energy, but also has poor regulation accuracy, which is difficult to meet the requirements of modern industrial production and services, and the negative effects are very serious

with the rapid development of power electronics technology, the thyristor soft start device came into being. The starting and stopping technology of three-phase asynchronous motor has undergone epoch-making changes. Thyristor soft start products have been available for only about 30 years, but its main performance is much better than traditional soft start methods such as magnetic control soft start and hydraulic resistance soft start. With small volume, compact structure, almost maintenance free, complete functions, good starting repeatability and comprehensive protection, it has become a leader in the field of soft starting

The application of soft starter in centrifugal fan is introduced in detail in this paper

2 thyristor mode soft start

2.1 overall system structure

thyristor soft start system is shown in Figure 1. In Figure 1, QS is high-voltage disconnector, QF1 and QF2 are vacuum circuit breakers, SCR is (ordinary) thyristor, and M is medium voltage motor. Analysis of test data of QF1 service main circuit); These methods and procedures shall be related to the required accuracy. The Standard Specification for inspection 1 shall be on-off, and QF2 shall serve as the bypass of power devices

in the SCR soft start device, there are 6 groups of SCRs, and each group contains M (the value of M is determined according to the voltage and the withstand voltage value of thyristor) phase strings of SCRs

Fig. 1 Schematic diagram of main circuit of thyristor soft starter

2.2 basic working principle of the system

using the switching characteristics of thyristors, the conduction time of thyristors is changed through the trigger angle of thyristors, so as to control the output voltage to the motor and control the starting characteristics of the motor. When the motor starting process is completed, let the AC contactor pull in (as shown in Figure 1, i.e. QF2 pull in), short circuit all thyristors, so that the motor is directly connected to the power

2.3 starting mode

1. Voltage ramp soft starting voltage the output voltage of the soft starter under the ramp soft starting mode does not rise from 0 to the rated voltage UE, but starts from a starting voltage U0. Because the starting torque of the motor is proportional to the square of the voltage, the starting torque of the motor is also very small if the voltage is too low. If the starting torque of the motor is less than the load torque, the motor will not run, but will heat the motor. Therefore, the output voltage of the soft starter under the voltage ramp soft start mode starts from a certain starting voltage U0. The starting voltage U0 shall set the minimum voltage that can make the motor run according to the characteristics of the load

2. Slope constant current soft start this starting method is to gradually increase the starting current at the initial stage of motor starting, and keep it constant after the current reaches the preset value (T1 to T2 stages) until the starting is completed. During the starting process, the rate of current rise and change can be adjusted and set according to the motor load. If the current rising rate is large, the starting torque is large and the starting time is short

3. Step start, i.e. make the starting current quickly reach the set value in the shortest time, i.e. step start. By adjusting the set value of starting current, the effect of fast starting can be achieved

4. Voltage double ramp starting during the starting process, the output torque of the motor increases with the voltage. During the starting, an initial starting voltage us is provided. Us is adjustable according to the load. Adjust us to be greater than the static friction torque of the load, so that the load can start to rotate immediately. At this time, the output voltage rises at a certain slope from us (the slope is adjustable), and the motor accelerates continuously. When the output voltage reaches the speed reaching voltage ur, the motor basically reaches the rated speed. The soft starter automatically detects the speed reaching voltage during the starting process, and makes the output voltage reach the rated voltage when the motor reaches the rated speed

5. Current limiting starting is a soft starting mode that limits the starting current of the motor to not exceed a certain set value (IM) during the starting process. The output voltage increases rapidly from zero until the output current reaches the preset current limit IM, and then maintains the output current I. the advantage of this starting method is that the starting current is small and can be adjusted as required. Its disadvantage is that it is difficult to know the starting pressure drop when starting, and it can not make full use of the pressure drop space

6. In the starting stage of sudden jump starting, make the thyristor fully conductive in a very short time, then fall back, and then rise linearly according to the original set value to enter the constant current starting. This starting method is applicable to the starting occasions with heavy load and large static friction

among the above control modes, the voltage ramp and current limiting soft start are representative

3 ventilator

3.1 overview

ventilator is a kind of driven fluid machinery that relies on input mechanical energy to increase gas pressure and discharge gas. Relationship between fan and fan: fan is the customary abbreviation of gas compression and gas transmission machinery in China. Generally speaking, fans include fans, blowers, compressors and roots blowers, but do not include positive displacement blowers and compressors such as piston compressors. Fan is a product type of fan, but people usually call fan simply as fan, which is another name of fan

3.2 classification

according to different gas flow directions, fans are mainly divided into centrifugal, axial, diagonal and cross flow types

3.3 structure of centrifugal fan

centrifugal fan is mainly composed of impeller and casing. The impeller of small fan is directly installed on the electric fan. Medium and large fans are connected with the motor through coupling or belt pulley. Centrifugal fan is generally single-sided air inlet, with single-stage impeller; Large flow can be double-sided air intake, with two back-to-back impellers, also known as double suction centrifugal fan. Impeller is the main component of fan. Its geometry, size, number of blades and manufacturing accuracy have a great impact on its performance. The impeller can rotate smoothly only after static balance or dynamic balance correction. According to the different direction of blade outlet, the impeller is divided into three types: forward, radial and backward. The top of the blade of the forward impeller is inclined to the rotation direction of the impeller; The blade top of radial impeller is radial, which is divided into straight blade type and curved blade type; The reverse inclination of the blade top of the backward impeller to the rotation of the impeller. The pressure produced by the forward impeller is the largest. When the flow and the number of revolutions are fixed, the required impeller diameter is the smallest, but the efficiency is generally low; On the contrary, the backward impeller produces the minimum pressure, the required impeller diameter is the largest, and the efficiency is generally high; The radial impeller is between the two. The straight blade is the simplest and the wing blade is the most complex

in order to make the blade surface have appropriate velocity distribution, curve blade is generally used, such as arc blade with equal thickness. The impeller usually has a cover plate to increase the strength of the impeller and reduce the gas leakage between the blade and the casing. The connection between blade and cover plate adopts welding or riveting. The welded impeller has light weight and smooth flow passage. The impellers of low and medium pressure small centrifugal fans are also made of aluminum alloy

3.4 working principle of centrifugal fan

when the centrifugal fan works, the power machine (mainly the motor) drives the impeller to rotate in the worm shaped casing, and the air is sucked from the center of the impeller through the suction port. Due to the dynamic action of the blade on the gas, the gas pressure and speed are increased, and under the action of centrifugal force, the gas is thrown along the blade path to the casing and discharged from the exhaust port. Because the flow of gas in the impeller is mainly in the radial plane, it is also called radial flow fan

4 practical application

4.1 working condition

a mine power supply is responsible for the power supply of the entire underground and the electrical equipment on the well, so the electrical margin is relatively small. In order to ensure that the operation of other equipment will not be affected during the starting process, the starting current requirements for the ventilator are very strict. 4.2 main technical parameters of the equipment

1. Main technical parameters of the fan:

Name: Mine centrifugal fan

model: dfk32-c4a

flow: 28000m3/min

total pressure: 6024kpa

main shaft speed: 480r/min

shaft power: 3730kw

wind wheel diameter: 3200mm

total weight of the fan: 28000kg

weight of the rotor group: 28000kw 12260kg

inlet direction: 210 °

outlet direction: 0 °

2 Main technical parameters of the motor:

for those who show the best manufacturing practice A recognized

model of the processor that is designed and produced in accordance with the recommendations in our design and Processing Guide: y

power: 4000kw

power factor: 0.857

weight: 17.7t

insulation grade: f

speed: 746r/min

current: 465.9a

4.3 working principle

the fan must overcome the bearing friction torque (30% ~ 4% of the rated torque) at the moment of starting from a static state 50%), The opening and closing of the control baffle in the fan fluid transmission pipeline will cause static pressure and affect the starting torque. Therefore, whether the outlet damper of the fan is closed or open, it belongs to on load starting. That is, when the speed is 0, the torque has a certain value

the general centrifugal fan belongs to the square torque load. Because the inertia is usually large, and the starting torque increases with the increase of speed, it does not need much torque at the beginning of starting. Therefore, the soft start is used to start it, and the torque starting method is preferred. Because the starting torque of the motor is directly proportional to the square of the voltage, the voltage ramp starting is adopted in this site, which makes it easier to control the starting torque and better play the role of soft start

4.4 starting operation record

Table 1 soft starter operation record

5 conclusion

the soft starter should select the starting mode according to the type of load in different places, so as to give better play to the performance of the soft starter