Automatic control and application of constant curr

Automatic control and application of constant current high voltage DC power supply in water industry

introduction: constant current high voltage DC power supply has been gradually recognized by professionals in the industry with its unique power supply characteristics and good application effect since it was applied to electrostatic precipitator in the 1980s; Especially in some occasions where the flue gas conditions change greatly, professionals prefer the high-voltage power supply supporting the electrostatic precipitator. For example, the competitiveness of shaft kiln dust collection and rotary kiln market in the cement industry will further improve the electrostatic dust collection at the kiln end; Sintering dust collection in iron and steel industry and electric tar extraction in coking industry; Constant current high-voltage DC power supply is almost used in electric dust collection and electric mist removal in non-ferrous smelting industry

keyword: automatic control application of constant current high voltage DC power supply

Preface: constant current high voltage DC power supply has been gradually recognized by professionals in the industry with its unique power supply characteristics and good application effect since it was applied to electrostatic precipitator in the 1980s; Especially in some occasions where the flue gas conditions change greatly, professionals prefer the high-voltage power supply supporting the electrostatic precipitator. Such as shaft kiln dust collection and rotary kiln tail electric dust collection in the cement industry now; The sintering dust collection and coking in the iron and steel industry require the selection and design of different electric tar precipitators in the fixture industry according to different experimental forces and the shape and size of samples; Constant current high-voltage DC power supply is almost used in electric dust collection and electric mist removal in non-ferrous smelting industry

1. Power supply characteristics of constant current high voltage DC power supply

constant current high voltage DC power supply is referred to as "constant current source", which is actually a "current source"; That is, the output current of the power supply is independent of the load, and its main control quantity is "current". Compared with the "voltage source", this power supply has many advantages when applied to the electrostatic precipitator: first, the power supply characteristics of this power supply on the electrostatic precipitator are "positive feedback", that is, the output electric power of the power supply is directly proportional to the electric power required by the precipitator; If the dust concentration of the dust collector increases at a certain time, the high-voltage power supply that supplies power to the dust collector needs to increase the output power synchronously at that time to keep the dust collector efficiency unchanged; Because the output current of the constant current source is constant, and the output voltage changes with the load, when the dust concentration increases, the output voltage of the constant current source also increases synchronously, which is reflected in the dust collector, that is, the output power of the power source increases synchronously. It is precisely because the constant current power supply is a positive feedback work for the dust collector, so the power supply has strong adaptability to working conditions, stable operation, and can maintain high deposition efficiency for a long time. The second is that the output waveform of the power supply is undistorted (the power supply mainly adopts L-C circuit to realize the transformation from voltage source to current source), which can improve the operating voltage and current level of the dust collector and improve the working efficiency of the dust collector; Since the mechanical characteristics of the dust collector (pole spacing, pole line form, pole plate form, etc.) are certain after the dust collector is installed, the breakdown voltage (peak voltage) of the power supply that cannot be used for the dust collector is also certain. Under the same peak voltage, Then the working voltage (average voltage) of the power supply without distortion of output waveform must be higher than that of the power supply with distortion of waveform, so as to meet the needs of customers for chemicals. Third, the power supply is a current source, so it can withstand transient and steady-state short-circuit conditions; The modular parallel structure is adopted, which has higher reliability, simple operation and convenient maintenance

2. Three control working modes of constant current high-voltage DC power supply

at present, there are three control working modes of constant current high-voltage DC power supply: the first is the most original manual control working mode, that is, all start-up operation procedures are in the form of buttons on the control cabinet panel, and the working current of the electrostatic precipitator is controlled by the operator according to the switch of the current selection key; The second is the automatic control mode combining LCD, touch switch and single chip microcomputer. At the same time, it can enter the center and use the DCS system for central control with a long history of cable fault tester; The third is the automatic control mode combining touch screen and PLC

2.1 hvcc-1 type: manual control mode

this control mode is the most original working mode of constant current high-voltage DC power supply. The basic working mode is that all operation switches adopt the form of buttons, and the current adjustment is to manually increase or decrease the current selection key according to the need to achieve the purpose of the required current. At present, this kind of working mode is widely used in some places with low automation requirements and poor working conditions. At the same time, the operation of this kind of power supply is relatively simple

2.2 hvcc-2: the automatic control mode combining RTU and epic (single chip microcomputer) can be controlled centrally in the central DCS system at the same time.

this type of power supply has the basic power supply characteristics of hvcc-1 constant current high voltage DC power supply, that is, constant current output and positive feedback working characteristics; At the same time, the control loop adopts advanced MCU and peripheral chips to realize automatic control. Its RTU control working mode includes: 1. Working mode of voltage setting value; 2. Working mode of current setting value; 3. Working mode of ordinary spark tracking; 4. Working mode of DCS centralized control current setting value; 5. Working mode of DCS centralized control voltage setting value. The power supply has the following working characteristics: 1. It can be manually controlled on site, which is equivalent to the application of hvcc-1 type. 2. It can set parameters on site RTU to realize automatic working mode. 3. It is directly connected to the plant DCS system for centralized control without communication protocol. 4. It can realize the synchronous display of primary current value, primary voltage value, secondary current value and setting value on RTU. 5 It can display the secondary voltage value and secondary current value on the central DCS. 6. It has the function of recording, saving and printing data. 7. Fault alarm and shutdown include: door switch, safety interlock, overvoltage and undervoltage, and peroxide. The central control requirements of the power supply are as follows:

the constant current source equipment of the electrostatic precipitator provides the following signals to the DCS system

ready signal: DCS remote start signal allowed (passive contact, DI)

operation signal: operation signal of the high voltage control system (passive contact, DI)

comprehensive alarm signal: equipment fault alarm signal (passive contact, DI)

secondary voltage feedback signal: secondary high voltage value of the electrostatic precipitator (4 ~ 20mA corresponds to 0 ~ 100%, AI)

secondary current feedback signal: secondary high voltage current value of the electrostatic precipitator (4 ~ 20mA corresponds to 0 ~ 100%, AI)

DCS system provides the following signals to the constant current source equipment of the electrostatic precipitator

reset signal: restart after shutdown or fault alarm (passive contact, do)

start/shutdown signal: start and stop the constant current source of the electrostatic precipitator (passive contact, do)

constant current source device operating current setting signal: (4 ~ 20mA, DC) controls the constant current source device operating current,

that is, controls the secondary current value, Ao