The Application of Frequency Converter in the Control System of the Dust Pump in Banshan Power Plant
Abstract: This article describes the process of Mid-mortar pump system power plant, describes the functions of the drive in the system, the mortar pump to achieve a frequency regulation while retaining the power frequency operation, based on improved production efficiency, reduce equipment wear , And to achieve the remote control.
1 Introduction
Hangzhou Banshan Power Plant Co., Ltd. has four old coal-fired plants in the old factory area, equipped with two sets of gray-frequency pumps running at a designed frequency of 760m3 / h. The gray water produced by the operation of the unit is delivered to dehydration silos and clarifiers in the company. The closed circulation of slag water is realized. After the large slag is dehydrated for comprehensive utilization, the slag water is clarified and then returned to the boiler through a backwater pump to be reused for slag flushing. At the same time due to environmental needs, put into operation the sewage treatment system, in order to prevent the gray water spill, does not affect the normal operation of the sewage treatment system, the original discharge into the slag ditch boiler feed, induced draft fan and air preheater and other equipment cooling water The diversion and recycling.
As a large amount of cooling water is recovered and reused, the level of water in the forehearth of the mortar pump is often too low, causing the mortar pump to be emptied. In order to prevent this phenomenon, by adjusting the mortar pump outlet control valve to control the amount of slag water, the normal operation of the control valve opening is too small (usually only about 15%), causing the valve and the import and export pipe wear and tear worse, the normal situation In the next two to three months on the need to replace the control valve; the same time due to throttling losses to control the flow, the pump motor must be maintained at a higher speed operation, resulting in a waste of energy. In addition, if the air pump is prevented by replenishing industrial water, not only the water resource is wasted, but also the gray water spills and the sewage treatment system can not operate normally. In order to save maintenance cost and water resources, reduce energy consumption, adopt the inverter as the core to realize the control of mortar pump.
2 system components and inverter characteristics
The composition of the mortar pump control system shown in Figure 1, leaving the two mortar pump parallel operation in the form of only # 1 mortar pump frequency control, the use of ultrasonic water level gauge to achieve automatic adjustment of mortar pump before the pool level; while design bypass Control function, in the case of inverter failure to achieve # 1 mortar pump power frequency operation, to ensure the safe operation of mortar pump system. # 1 mortar pump motor model Y355M3-6, rated power of 200KW, working voltage of 380VAC, rated current of 374A, speed of 990rpm.
According to the working characteristics of # 1 mortar pump motor, the mortar pump inverter selects ABB company's ACS807 Guiji, ACS807 Guiji designed a complete ventilation and cooling system and dust-proof features, the specific technical indicators are as follows:
Model: ACS800-07-0260-3 + P901;
Rated output power: 200kW;
Rated output current: 445A;
Recommended maximum motor cable length: 300 m;
Environment: temperature 0 ~ 50 ℃, relative humidity 5 ~ 95% (no condensation), pollution level, not allowed to have conductive dust.
According to the ACS807 output current over-temperature derating characteristics: rated current limit of the ambient temperature is 40 ℃, more than 40 ℃, the ambient temperature for each additional 1 ℃, the rated output current decreased by 1.5%, when the ambient temperature reaches the inverter temperature limit 50 ℃ , The rated current reduced by 15%, down to 378A, to meet the gray pump motor current 374A requirements.
3 inverter control and bypass control mode switch
In the composition of mortar pump system, # 1 mortar pump under normal circumstances by the inverter control to achieve frequency control operation of the water level, in order to ensure the safety of mortar pump system in the case of inverter failure, the mortar pump power frequency operation is still retained capacity , Through the bypass control to maintain the safety of the system. Therefore, in the control system must be achieved by the inverter control and bypass control mode switching, switching control mode.
Control mode by two knife switch hard hand toggle switch, each knife switch has three groups of contacts, two states. When the two knife switches are hit to the lower side, the power signal coming from the motor control center is directly connected to the # 1 mortar pump motor, the inverter is bypassed to realize the power frequency operation of the mortar pump; when both the knife switches are hit To the upper side, the motor control center over the power signal is connected to the inverter, the inverter output signal connected to the # 1 mortar pump motor, mortar pump inverter control, to achieve variable frequency operation; when the two knife switch in a different Direction, the entire system power supply circuit is disconnected, you can not achieve any control.
4 operation control function to achieve
In the mortar pump system, the control circuit includes motor control center (the original mortar pump control cabinet) and inverter control two parts, of which the motor control center part of the system to achieve the transformation of the control, including mortar pump power supply closing and tripping to achieve mortar pump Power frequency operation. Inverter part is divided into start-stop control and speed control, inverter start-stop control, including local and remote operation of two modes, you can choose the local switch settings. Inverter control part of the local control cabinet for signal synthesis, as shown in Figure 3, resulting in power switch, power trip, the inverter starts and inverter stop four signals. In variable frequency mode of operation, the power switch, the power trip in the motor control center for power transmission to the inverter, under normal circumstances through the power switch so that the # 1 mortar pump in the hot standby state, such as to run # 1 mortar Pump, you must form # 1 Mortar pump drive start-up command either locally or remotely, while the drive stop signal is used to stop the # 1 Mortar pump operation; if # 1 Mortar pump drive is in operation, a shutdown fault occurs Mortar pump for the power frequency operation, the power switch formed by the control cabinet, power trip signal changed to # 1 mortar pump start / stop instructions.
Inverter speed control, including manual adjustment and automatic control of the inverter in two ways, manual mode is divided into local analog adjustment, local switching and inverter operation panel adjustment, manual and automatic mode selection from the local operation The external digital signal from the controller to the inverter can be set by remote control. The selection of operating mode in manual mode must be set in the inverter properly.
â— Inverter automatic control is the main control mode, the ultrasonic level meter measured mortar pump pool level signal input to the inverter, at the same time in the inverter panel, enter the target value of the water level, the use of inverter built-in PID regulator Automatic adjustment, speed control, to maintain the water within the normal range of deviation.
â— Local analog adjustment is the main mode of operation in manual mode. An analog signal of 4 ~ 20mA is given from the remote control room or local operator, which is used as the manual speed command of the inverter.
â— Local switch adjustment is a backup method of analogue adjustment. When there is a fault on the local analog channel (such as AO fault, power loss, disconnection), step-by-step adjustment can be realized by using the local increase / decrease button to prevent Inverter out of control, to ensure the operation of mortar pump.
â— Adjusting the inverter operation panel is the last resort of control. Use the operation buttons on the panel to realize the control.
5 Summary
The application of frequency changer in the mortar pump system has changed the way of adjusting the water level of the mortar pump before using the throttling method and obtained obvious economic benefits:
â— Reduce or even substantially eliminate the wear and tear of the regulating valve and the inlet and outlet pipes caused by throttling, prolong the service life of the regulating valve and save a large amount of equipment costs (a valve is nearly 30,000 yuan);
â— To achieve the purpose of automatic control of the water level to improve the level of automation of the system to maintain the water level in the mortar pump before the pool within the normal range to avoid or significantly reduce the possibility of cavitation pumps caused by the water level cavitation pump cavitation may pole The earth reduces maintenance costs;
â— reduce the number of frequent start or stop mortar pump, mortar pump to improve the service life;
â— Reduce the power consumption of the gray slurry pump, reduce the waste of electric energy and improve the efficiency of the system. Before and after the transformation, the current value of the gray slurry pump runs at an average of 320A; after using the inverter, the current at the maximum speed The value is 300A, the lowest speed when the current value of 50A, the operator calculated an average of 175A, the average current reduced by 45%;
â— The remote control is realized, which creates the preconditions for integrating the mortar pump and the forecourt water level into the DCS of the unit unit in the future.
The author of this innovation: In the use of frequency converter to achieve the foreshore pond water level automatic control at the same time, the maintenance of the mortar pump frequency running circuit, in a convenient and efficient way to achieve frequency and power frequency mode switching, and to achieve the inverter Of the distance control, improve the economy of system operation, achieve the purpose of reducing the manpower and increasing efficiency.
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