Application of the hottest high voltage frequency

2022-08-16
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Application of high voltage frequency converter in energy saving transformation of high temperature fan

the air pressure control of the original high-temperature fan is adjusted by the hydraulic coupler, and after being adjusted by the high-voltage frequency converter, the defects of high mechanical and hydraulic faults are eliminated, the operation rate is improved, and the maintenance cost is reduced; The vibration and noise of motor operation are significantly reduced; The motor does not need long-term high-speed operation, and the power saving effect is remarkable, with the power saving rate of more than 20%

high voltage AC variable frequency speed regulation technology is a new type of electric drive speed regulation technology that developed rapidly in the 1990s. It is mainly used for variable frequency speed regulation of AC motor. Its technology and performance are far better than the previous speed regulation methods (such as cascade speed regulation, hydraulic coupling speed regulation, rotor water resistance speed regulation, etc.). High voltage inverter has been recognized by the majority of users for its remarkable energy-saving benefits, high speed regulation accuracy, wide speed regulation range, perfect protection function and convenient communication function. Now it has become the preferred scheme for motor energy conservation in enterprises. However, around 2000, since high-voltage converters were monopolized by foreign brands and most of them were expensive, there were not many users of high-voltage converters in cement enterprises. With the maturity of domestic high-voltage variable-frequency speed regulation technology, since 2005, Shanshui group has adopted high-voltage variable-frequency converters for all high-power fan equipment in all new production lines. At the same time, it has also implemented the transformation of high-voltage variable-frequency converters for all high-power fan equipment in the original production lines, with a total of nearly 100 units, and achieved good economic and social benefits

in the transformation process, the high-temperature fan has high power and remarkable power saving effect, but the process and equipment conditions are relatively complex. During the transformation of high-voltage frequency conversion technology, we have some successful experience in the determination of technical scheme, equipment selection, installation and commissioning, etc. here is an introduction for peer reference

technical principle of frequency conversion and energy saving

in the early stage of construction, in the application design of fans, the power of fans is selected according to the maximum demand, and there is a large margin. In actual production, the required air volume cannot be in the maximum state for a long time, and it should be changed frequently, so there is a situation of "big horse pulling small car", which needs to be adjusted, and the adjustment method is usually achieved by adjusting the opening of the baffle and valve on the pipeline

for centrifugal fans, fluid mechanics has the following principles: the output air volume q is proportional to the speed n; Output pressure h is proportional to the square of speed n: output shaft power P is proportional to the cubic of speed and Z; Namely:

q1/q2=n1/n2 (1)

h1/h2= (n1/n2) 2 (2)

p1/p2 = (n1/n2) 3 (3)

when the fan air volume needs to be changed, if the way of adjusting the opening of the damper is adopted, a large amount of electric energy will be wasted on the valve resistance. If frequency conversion speed regulation is adopted to adjust the air volume, the shaft power can be greatly reduced with the decrease of flow. During variable frequency speed regulation, when the fan is lower than the rated speed, the theoretical power saving is:

e= [1- (n ′/N) 3] × P × T (KWH) (4)

where: n-rated speed

n '- actual speed

p- motor power at rated speed

t- working hours

it can be seen that if the fan is transformed by frequency conversion, the air volume is adjusted by adjusting the speed, which has great energy-saving potential. The above formula provides a sufficient theoretical basis for frequency conversion energy saving

working condition introduction

the rotary kiln is a cylindrical material with a certain inclination. The homogenized raw material enters the kiln from the kiln tail after preheating. With the help of the rotation of the kiln, the materials are stirred in the rotary kiln to make the materials mix and contact each other for reaction. The materials move forward in the kiln depending on the inclination of the kiln shell and the rotation of the kiln. At the same time, appropriate air pressure and temperature are required to make the pulverized coal have a certain suspension time for full combustion, Raw materials can be calcined well in the kiln to form high-quality clinker products. Because the accumulation of materials in the kiln changes greatly, the instantaneous air pressure changes frequently. On the one hand, the high-temperature fan at the kiln tail is used to adjust the air pressure in the kiln, on the other hand, the waste gas (including dust) generated during calcination in the rotary kiln is led out, and then the waste gas is discharged into the atmosphere after the dust is treated in the dust collector. At present, Shandong cement plant of our group has two new dry process production lines with daily output of 1700t and 2300t respectively, and has a 7.5mw medium and low temperature waste heat generator set, and the high-temperature fan motor is configured with 6kV and 1250KW. Between the motor and fan of the high-temperature fan, a hydraulic coupler is equipped to regulate the speed of the fan. The whole process is mainly to adjust the speed of the hydraulic coupler through the control of DCS, so as to adjust the air volume of the fan and control the negative pressure in the kiln. In production, the air volume is adjusted by fan baffle

the hydraulic coupler transfers the energy of the motor and changes the output speed by controlling the change of the momentum moment of the working oil in the working chamber. The motor drives its driving working wheel through the input shaft of the hydraulic coupler to accelerate the working oil. The accelerated working oil then drives the driven working turbine of the hydraulic coupler to transfer the energy to the output shaft and load. In this way, The torque of the output shaft can be controlled by controlling the amount of working oil involved in energy transmission in the working chamber, so as to achieve the goal of controlling the speed of the load. Therefore, the hydraulic coupling can also realize stepless adjustment of load speed. However, due to the slip power loss, volume loss and mechanical loss generated by the hydraulic coupler in the adjustment process, the generated heat needs the auxiliary operation of oil pump and cooling water, and the failure rate is high. Especially in summer, due to the large heat generated by the coupler, four groups of oil coolers need to be added to cool down with circulating water, which leads to large water consumption and serious waste of resources

high temperature fan frequency conversion transformation scheme

through the statistics of the original system, during the production process, the opening of the fan baffle is mostly about 80%. According to formula (4), it can be seen that there is a large space for power saving, so we decided to carry out frequency conversion transformation of the original system, and change the wind pressure control from the original hydraulic coupling regulation to frequency converter regulation: cancel the original hydraulic coupling, A connecting shaft is used to replace the hydraulic coupling between the motor and the hydraulic coupling to increase taxes and the employment of college students, and the frequency converter is used to regulate the speed of the motor itself. Finally, the pressure of the kiln preheater (high-temperature fan population) is adjusted as the required value of the working condition; The frequency converter equipment is connected between the high-voltage switch on the fan side and the motor to be transformed, and the frequency converter control is connected to the original DCS system. The original equipment is still used for motor and high-voltage circuit breaker. In order to fully ensure the reliability of the system, the frequency converter is equipped with a power frequency bypass device, and the baffle (valve) on the original pipeline is retained. In this way, when the frequency converter fails, the motor can be switched to the power frequency state for operation, and the air volume can still be adjusted by using the damper

according to the load parameters and operating conditions, we have configured HIVERT series high-voltage frequency converter for high-temperature fan. Its main parameters are: the model of frequency converter hivert-y06/173, the capacity of isolation transformer 1800 KVA, and the capacity of bypass switch cabinet 400 a

transformation process

in order to install the frequency converter, the special room for the frequency converter must be redesigned. According to the site environment, we choose to build another special room for frequency converter next to the high-voltage distribution room, which is close to the high-voltage room and convenient for power cable laying

due to the large amount of dust on the site and the forced air cooling of the frequency converter, the air circulation in the equipment is large. In order to ensure that the frequency converter is as little as possible affected by external dust, two large-area special air intake windows are designed in the room ventilation design, and the room is basically closed without other windows. The ventilation window is filtered with special filter cotton, so that the air entering the inverter room is filtered through the ventilation window, and the dust entering the inverter room is greatly reduced

due to the large power of the frequency converter, in order to ensure sufficient ventilation and cooling effect, an integral hood is installed on the top of the transformer cabinet and the power cabinet separately, which is connected with their respective air outlets to form a so-called "air duct" to ensure the overall cooling and ventilation requirements of the frequency converter. Even in the high-temperature season in summer, it is not necessary to turn on the air conditioner to cool down

in order to reduce the installation cost, the power cable retains the cable from the original high-voltage cabinet to the motor. The original wiring of the cable is led from the high-voltage cabinet to the frequency converter, and then a power cable is laid from the high-voltage cabinet to the frequency converter. Because the frequency converter room is close to the high-voltage room, the cable length is short

after the frequency conversion transformation, due to the need to cancel the original hydraulic coupling, we designed and manufactured a set of direct connection shafts according to the connection size of the hydraulic coupling to replace it. The installation size of the base of the connecting shaft, the size of the shaft connection center, the size of the shaft diameter, and the connecting coupling between the shaft and the motor and the fan side are consistent with the original hydraulic coupler. During installation, it is only necessary to remove the original hydraulic coupling and replace the hydraulic coupling with the connecting shaft. Only a small amount of adjustment on site can meet the installation requirements, without any adjustment to the fan and motor. The installation is convenient and fast

install high-voltage frequency converter, short circuit the slip ring of the original wound motor, abolish the raw water resistance starter, reduce the maintenance of carbon brushes, water resistance starter and motor every year, and greatly reduce the comprehensive cost. In addition, the starting time of high-voltage frequency converter can be adjusted arbitrarily, so as to realize smooth startup and good protection for equipment operation

effect of frequency conversion transformation

our company began to apply high-voltage frequency converter to kiln head induced draft fan and high-temperature jaw fan with poor quality in 2006. There is no such counterpart specialty in China, such as raw mill circulating fan and other high-power fan motors. The average power saving is more than 20%, and remarkable economic benefits have been achieved. Table 1 shows the data comparison between the two high-temperature fans before and after the installation of high-voltage frequency converter

we have the following experience and experience in the formulation of technical scheme, equipment selection, installation and commissioning of high-power fans such as high-temperature fans in cement clinker production line:

(1) before formulating the scheme, we should fully understand the production process and operation process, understand the adjustment mode of air volume and pressure, and do a good job in various process parameters (set hour, air volume, air pressure, etc.) before the transformation The statistical work of equipment parameters (valve opening, operating current, etc.) provides basic data for the estimation of energy-saving effect and the formulation of technical schemes

(2) understand the operating load status and characteristics, and determine the type selection of frequency converter. For the high-temperature fan and other equipment of cement clinker line, it is recommended that the frequency converter should be of voltage source type and high one high structure, which can eliminate the output step-up transformer; For capacity selection, it can be appropriately amplified by one level

(3) due to the relatively large dust in the cement industry, the special filter cotton filter of the ventilation window needs to be cleaned frequently, so it is recommended that the cooling mode of the frequency converter adopt the air-water cooling mode, which can greatly reduce the indoor and outdoor air circulation, which can not only ensure the cleanness of the indoor air, but also ensure the operating temperature required by the frequency converter

4) practice has proved that there are few opportunities for the frequency converter to need power frequency bypass operation. The bypass device can be completely removed to save space in the power room and reduce investment, so as to further remove the valve support in the pipeline and reduce the pipeline resistance

(5) after using the frequency converter, the system is stable and reliable, the hydraulic coupling speed regulation is canceled, the defects of high failure rate of machinery and hydraulic pressure are eliminated, the operation rate is improved, and the maintenance cost is reduced; Motor running vibration and noise

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