1 Introduction
Drainage pumping stations are generally used in the pump power is relatively large, in order to avoid the pump motor direct current impact generated when the impact on the power grid generally use indirect methods to start the pump. Indirect starting methods commonly used are YD starting method, autotransformer starting method and soft-start method. For these start-up modes, conventional secondary control lines are usually implemented using multiple intermediate relays and time relays. With the development of technology, many devices need to be reformed, such as the start-up method and the upgrading of components; many devices need to be adjusted in the way of remote operation and use. For example, local control is changed to remote control or computer control. For the updating of these technologies, the disadvantages of the traditional control loop design methods such as the number of components, complex wiring and poor universality, bring more difficulties to the equipment reconstruction and maintenance.
Therefore, it is necessary to improve the control circuit of the indirect starting pump to make the control circuit simple and reliable, strong adaptability and rich functions, and a novel mini programmable controller with a programmer can achieve the purpose.
2, micro programmable controller and the traditional control methods of comparison
2.1 micro programmable controller profile
Take for example the universal logic control module LOGO! Manufactured by Siemens, which is an interface between control functions, operation and display units, power supply and program modules. The basic functions that can be adjusted (such as switching on and off delay relays and pulse relays Etc.), time switch, binary indicator, text display, a variety of device types such as input / output functions in one of the micro-programmable logic controller. A standard controller has 8 digital inputs, 4 relay outputs, and its dimensions are 72x90x55mm. It is produced to save system footprint, simplify installation complexity, and facilitate system manufacturing and standardization. The user's control program can be entered, programmed and displayed by using the 6 operation buttons integrated with the controller itself and the LCD panel, or software programmed, tested, simulated and printed on the PC.
2.2 compared with the traditional control methods
Compared with the traditional way of relay control LOGO! Has many advantages:
(1) can greatly reduce the number of relays and the complexity of the circuit to simplify the installation and maintenance of equipment to improve the reliability of the system.
(2) LOGO! As the core of the pump start control circuit hardware connection has a very strong compatibility. YD start-up mode, auto-buck start mode and soft-start mode hardware only a small difference, a little change can be common to each other, help to achieve standardized design and transformation of the old equipment.
(3) The control logic of the starting control system is almost entirely implemented by LOGO! Internal program. During manufacturing and operation, the program can be modified as needed to make the system easy to use and maintain.
(4) It has the function of communication with the host computer, which lays the foundation for the pump control system to further improve the degree of automation and remote monitoring.
Although this controller has many advantages, it also has some disadvantages.
(1) Compared with the traditional relay control, the investment of LOGO! Control mode components is slightly larger.
(2) In addition to the hardware connection, the LOGO! Controller requires programming control and increases the programming and debugging workload.
(3) The number of input and output points under control is limited by the number of input / output ports of LOGO! Controller itself, which can not be used by the system with more control points.
In summary, although the LOGO! Controller has some disadvantages, its advantages are well adapted to control the start of the pump.
3, Take soft starter as an example to introduce the structure of the system
3.1 System Overview
A pump station uses three soft starter, respectively, on three rain pumps to achieve one-on-one soft-start control. Each LOGO! Controller and a soft starter installed in the pumping station control room within the pump control cabinet, the operator can be installed in the control room ultrasonic level transmitter transmitter level value control the pump start and stop . Each side of the control cabinet is divided into primary and secondary systems in two parts.
3.2 a system
The primary system electrical equipment in the cabinet includes a Siemens 3RW34 soft starter, a 3NP4070 load switch with fuses to protect the semiconductors, a set of bypass AC contactors and three current transformers. After the control side issues the order, the soft starter starts to start the water pump, by the contactor after the start completes, bypasses the soft starter automatically in order to realize the protection to the soft starter.
3.3 secondary system of each loop function
Pump soft starter system control core for the Siemens company LOGO! 230RC # micro-controller. It has 8 digital input points and 4 relay output points. The use of these input and output points to control the soft-start system, as detailed below:
The "L" and "N" terminals of the controller are the working power inputs, and the input working power is 220VAC. In order to eliminate the damage of the internal voltage components of the controller due to the peak voltage of the line, a metal oxide varistor RV needs to be connected in parallel with the "L" and "N" terminals. The operating voltage of the RV should be at least 20% of the rated working voltage.
"I1" end for the start-end, press the SA1 button to start the pump.
"I2" end for the stop, press the SA2 button to stop the pump.
"I3" side into the contactor KM work signal, used to reflect the pump into working condition.
"I4" The introduction of thermal relays and pumps integrated protector signal. Thermal relay FR indicates pump motor overload, stalling and phase failure; relay KA1 indicates submerged pump underwater seal chamber failure.
"I5" introduced ultrasonic liquid level gauge low liquid level protection switch, when the pump tank reaches or drops below the set minimum water level, control the pump down to protect the submersible pump.
"I7" introduces the soft starter working status information, to achieve the soft starter monitoring.
"I8" introduced the soft starter fault information.
"Q1" After the SA1 button is pressed, "Q1" will issue a start command to the soft starter to start the pump if no error message is input.
"Q2" When "I4", "I5" and "I8" are connected to the error message, the "Q2" relay ON indicator indicates a fault and "Q1" signals the pump stop.
"Q3" indicates the working state of the pump when the pump is working normally.
In addition, in addition to the above-mentioned input and output functions, the display unit of the controller can also realize the dynamic display of the input and output signals, and use the text / parameter display function block to make preset information texts on the LCD display unit , Running fault) real-time display.
4 Conclusion
The micro-programmable logic controller as the core pump start control circuit not only to achieve the start and stop the pump control, operation and fault monitoring and protection functions, but also reduces the number of traditional relays to use, simplifying the installation and wiring workload and improve System reliability, but also increased the teleoperation and automatic control functions. This design method has been applied in some projects.
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