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The application of domestic high-voltage frequency converter in water slag system

[content abstract] this paper introduces the frequency conversion transformation of the high-pressure water pump of the hydraulic slag removal system in Jiaxing Power Plant in order to save energy and reduce consumption, expounds the specific scheme, type selection and frequency conversion principle of the high-voltage frequency converter, and analyzes the economic benefits of the application of high-voltage frequency conversion speed regulation.

[Key words: frequency conversion application of water slag system

1. Preface:

Zhejiang Jiaxing Power Plant has two units with installed capacity of 300 MW and four units with installed capacity of 600 MW, with a total installed capacity of 6000 MW. Its 300 MW units are equipped with 1025t/h coal-fired boilers. In 2000, the boiler dry-type slag removal system was transformed into a hydraulic slag removal system.

AC motor frequency conversion speed regulation is a new technology developed on the basis of modern microelectronics technology, which It is not only superior to the traditional DC motor speed regulation, but also superior to the voltage regulation, pole changing speed regulation, cascade speed regulation and other speed regulation methods. It is characterized by smooth speed regulation, wide speed regulation range, high efficiency, good characteristics, simple structure, hard mechanical characteristics, complete protection functions, stable, safe and reliable operation, and can obtain the best speed parameters in the production process. It is an ideal speed regulation mode and a new energy-saving technology promoted by the state. In 2005, in order to save energy and reduce consumption, the high-pressure water pump of the hydraulic slag removal system was transformed by frequency conversion

2. Operating conditions of high-pressure water pump

the hydraulic slag removal system consists of bottom slag hopper, pebble coal slag removal system, slag removal water supply system and dehydration bin system. The main task of hydraulic slag removal is to cool and crack the bottom slag in the furnace, and use high-pressure water as the power source to send the slag water mixture in the pipeline to the transfer bin. At the outlet of the transfer bin, the slurry is sent to the dehydration bin 1km away by the slurry pump, and the filtered dry slag is loaded and transported outside by the vehicle. The water is recycled by the high-pressure water pump. Due to the defects of domestic hydraulic slag removal calculation method, it can not meet the requirements of system water recycling, so it is necessary to open the high-pressure water pump to maintain the minimum circulating flow. When the load of the generator unit changes, the ash generated by the boiler will also change. The world's first integrated intelligent bicycle adopts ultra light carbon fiber composite materials, and the amount of high-pressure water will be different. Therefore, the high-pressure water pump does not need full load output for about 15 hours a day, and operates in the state of a big horse pulling a small car (after the boiler bottom camera is put into normal use in the future, the non flushing time will be increased from 15 hours to 18 hours), which increases the power generation cost. Therefore, according to the actual application of the company, we have improved the control mode of high-pressure water pump to make the operation of hydraulic slag removal system more reasonable and reliable. The motor control of the high-pressure water pump is changed to the control of the high-voltage frequency converter, and the hydraulic system is balanced by adjusting the pump speed to ensure the full utilization of hydraulic resources and reduce secondary pollution; Smooth and stepless electric acceleration is provided to reduce liquid flow surge caused by sudden start and stop of centrifugal pump, which is of great significance to ensure unit slag discharge and energy saving

3. Selection and model selection of specific schemes

3.1 selection of specific schemes

when selecting the speed regulation scheme, we considered using the speed regulation hydraulic coupling from the perspective of saving investment. However, due to the heavy maintenance workload and long installation and construction period during the use of the hydraulic coupling, the normal production will be affected, so we abandoned the scheme. Through detailed investigation, considering the progressiveness of technology and the maturity of products, it is finally decided to adopt high-voltage variable-frequency governor for speed regulation transformation of high-pressure water pump. Faced with many high-voltage frequency conversion products at home and abroad (such as robinham, Lidehuafu, AB, Siemens, etc.), professionals conducted a comprehensive and careful investigation and demonstration on this new technology, and finally decided to adopt domestic high-voltage and high-power frequency conversion and speed regulation devices. The reasons are as follows:

1. At present, domestic high-voltage 1, PEEK material medical implant high-power frequency converters have the technical level to compete with foreign products

2. The cost performance ratio is higher than that of similar foreign products

our company finally selected the 6kV high-voltage inverter produced by Beijing Lidehuafu Electric Technology Co., Ltd., which has strong domestic strength

3.2 product selection

(1) the motor applicable to the high-pressure water pump is 6kV with a capacity of 450KW, and the high-high frequency converter speed regulation scheme is selected

due to different operation modes, the calculation and selection methods of frequency converter capacity are different. When selecting the capacity of the frequency converter, the rated current of the frequency converter is a key quantity. The capacity of the frequency converter shall be selected according to the rated current of the asynchronous motor and the maximum working current that may occur during operation. At this time, the frequency converter shall meet the following three conditions at the same time:

in the above formula: PM η、 cos φ、 Um and im are motor output power, efficiency (0.85), power factor (0.75), voltage (V) and current (a) respectively. K: Correction coefficient of current waveform (PWM mode is 1.05 ~ 1.1). PCN: rated capacity of frequency converter (kVA). ICN: rated current of frequency converter (a)

(2) primary wiring scheme: the scheme of "one driven by one" with power frequency bypass is adopted

in order to fully ensure the reliability of the system, a power frequency bypass device is installed for the test of the frequency converter and the contact tightening force of various products at the same time. When the frequency converter is abnormal, the frequency converter stops running, and the motor can be directly manually switched to power frequency for operation. The power frequency bypass is composed of three high-voltage disconnectors QS1, QS2 and qs3 (see the figure, where QF is the original high-voltage switch of Party A). QS2 and qs3 shall not be closed at the same time to realize mechanical interlocking. During variable frequency operation, QS1 and QS2 are closed and qs3 is disconnected; During power frequency operation, qs3 is closed and QS1 and QS2 are disconnected. In order to protect the frequency converter from failure, the frequency converter interlocks the 6kV switch QF. Once the frequency converter fails, the frequency converter jumps out of QF. It is required to properly transform the closing and opening circuit of QF. In case of power frequency bypass, the frequency converter shall allow QF to be closed and cancel the tripping signal to QF, so that the motor can be started normally through power frequency closing of QF

(3) control principle: use PLC to realize pressure PI regulation control to ensure constant pipeline pressure. After being processed by the control system, Ma speed setting signal is output to the frequency converter to realize the automatic adjustment of pump speed. The frequency conversion and speed regulation system is configured with an upper computer, which can be installed in the control room. The upper computer can control the startup, shutdown and speed regulation of the frequency converter, and display the operation data and current status of the frequency converter on the upper computer. In order to ensure the reliability of the speed regulation system, the control button for the frequency converter is configured on the operation console, and the start, stop, acceleration and deceleration control can also be implemented for the frequency converter's British fixture, etc., which meet the standards of many countries

(4) isolation

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