Example of high voltage frequency converter transf

2022-08-13
  • Detail

Example of high voltage converter transformation in thermal power plant of Hegang Mining Bureau

I Overview

the thermal power plant of Hegang Mining Bureau is located in Hegang City, Heilongjiang Province, the Northern Coal City of China. It is subordinate to the mining bureau system, with a total of four machines and six boilers, including two 50MW generating units and two 25MW generating units, four 75t boilers and two 220t boilers. Among them, No. 5 and No. 6 boilers are 220 ton boilers, and No. 7 boiler (220 ton boiler) is currently under construction

in winter, in addition to normal power supply to northeast power, it is also responsible for heating in most areas of Hegang. For a long time, the forced draft fan and induced draft fan motors of the 220 ton boiler in our power plant have been operating at power frequency, relying on the baffles of the forced draft fan and induced draft fan to adjust the air volume and maintain the negative pressure of the boiler. The opening of the baffles of the fans is generally about 40%, so a lot of energy is wasted on the baffles of the fans, resulting in the high auxiliary power consumption rate of the power plant

in summer, generally, only one 220 ton boiler can meet the load requirements. In winter, in order to meet the needs of heating, two 220 ton boilers are generally operated. The boiler feed water system of No.6 boiler and No.5 boiler adopts the main pipe, and the boiler feed water pump is configured with one for use and one for standby. When the two boilers operate at the same time, the water supply volume and pressure of one power frequency feed pump are just enough. When a boiler is running, a feed water pump is started, but the outlet pressure of the feed water pump is 15mp, while the actual feed water pressure required on site is only 12.5mp, so the outlet pressure of the feed water pump is too high and needs to be adjusted. Because the feed water pump is driven by a constant speed motor, the feed water flow and pressure can only be controlled through the boiler side valve, which not only has poor economic benefits, but also causes certain hidden dangers to the safe operation of the feed water pipeline due to the high feed water pressure in front of the boiler

in order to completely solve the above problems, our factory decided to carry out technical transformation on four induced draft fans (two induced draft fans, two forced draft fans) and one feed pump of No. 6 boiler, realize the variable-speed operation of the above fans and feed pumps by adjusting the motor speed, and reasonably adjust the air volume, feed water flow and pressure, so as to achieve the purpose of improving the process and energy saving

II Selection of speed regulation mode

at present, the main speed regulation modes of high-power high-voltage asynchronous motors are as follows: cascade speed regulation, hydraulic coupling speed regulation and frequency conversion speed regulation

cascade speed regulation - the advantage is that the slip power can be recovered, so the speed regulation efficiency is relatively high, but there are many problems: it is not suitable for squirrel cage asynchronous motor, and the motor must be replaced; The naming soft start cannot be realized, and the starting process is very complex; High starting current; Limited speed range; Slow response, difficult to realize closed-loop control; The power factor and efficiency are low, and drop sharply with the reduction of speed; It is difficult to realize the cooperation with PLC, DCS and other control systems, which is not beneficial to improve the overall automation degree of the device and realize optimal control; At the same time, because the control device is relatively complex and the harmonic pollution is large, it has great interference to the electricity; It further limits its use and belongs to backward technology

speed regulation of hydraulic coupling - it is an inefficient speed regulation mode, and the speed regulation range is limited. The loss of high-speed loss is about 5%-10%, and the loss of low-speed slip is large, up to 15% of the rated power. Because the efficiency is proportional to the speed, the efficiency is extremely low at low speed, with low accuracy, poor linearity, slow response, large starting current and large device. It must be installed between the equipment and the motor, which is not suitable for transformation; Unable to soft start, unable to switch operation in case of coupling failure, complex maintenance and high cost, which can not meet the needs of improving the overall automation level of the device

high voltage frequency converter speed regulation - due to the application of advanced power electronics technology, computer control technology, modern communication technology and discipline technology in comprehensive fields such as high voltage electrical and motor drive, it has incomparable advantages over other speed regulation methods:

① the frequency converter adopts liquid crystal display digital interface and adjusts the touch panel to display voltage, current, frequency and motor speed at any time, It can intuitively display the real-time state of the motor at any time

② accurate frequency resolution and high speed regulation accuracy can fully meet the requirements of various production process conditions

③ the high-voltage inverter has an international general external interface, which can be connected with various instruments such as programmable controller (P. at the same time, the fixture design should consider the characteristics of appropriate rubber and can not slip LC) and industrial computer, and can be connected with the original equipment control loop to form a partial closed-loop system, such as data exchange and interlock control with the original DCS system

④ it has local and remote operation functions, and can realize remote monitoring function through interconnection

⑤ it has the functions of power electronic protection and industrial electrical protection to ensure the safety digital display of frequency converter and motor in normal operation and fault

⑥ the motor can realize soft start and soft braking; The starting current is small, which is less than the rated current of the motor; The starting time of the motor can be continuously adjusted to reduce the noise to the movie

⑦ reduce the loss of accessories, prolong the service life of equipment, and improve labor production efficiency

based on the above speed regulation methods, our power plant chose the most advanced speed regulation form at present - high voltage variable frequency speed regulation. Through the comprehensive evaluation of many high-voltage converter manufacturers, we decided to choose the high-voltage converter with unit series multi-level structure produced by Beijing Lide Huafu Electrical Technology Co., Ltd., which has the following advantages:

① it has the most achievements among domestic high-voltage converter manufacturers and the system operates stably

② full Chinese interface display, suitable for domestic users

③ customized for domestic users, try to consider the comprehensive factors of domestic electricity, and have its unique technical advantages in its reliability and safety

④ the built-in PLC is easy to change the control logic relationship and adapt to the changing needs of the site

the lower left part of the three machine base is the spring force application system of the experimental machine and the microcomputer automatic loading system System configuration scheme

according to the actual situation, the on-site main circuit of four boiler fan frequency converters and one feed pump frequency converter adopts the scheme of manual driving one, as shown in the following figure:

IV Implementation of high-voltage inverter transformation

according to the actual equipment on site, the model of the inverter is selected as follows:

the above five high-voltage inverters were transported to the site on August 19, 2005, and by October 1, 2005, all

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