Application of the hottest high voltage frequency

2022-08-13
  • Detail

The application of high-voltage inverter in gas presser

1 preface

the technological requirements of the 80000 gasholder outgoing gas presser in Hebei Handan Iron and steel plant are to proportioning converter gas to the western gas pipe of Handan Iron and steel plant. After mixing, the gas is supplied to the Third Steelmaking Plant, gas power generation, blast furnace, medium plate and other places at the same time. There are many users and the demand changes greatly. At the same time, it is limited by the supply of coke oven gas, Make the adjustment amount of the presser more frequent

the original design of the converter gas recovery 80000 gasholder 1 #, 2 # pressurizer system at the Third Steelmaking Plant of Han steel adopts the traditional method, that is, the fan operates at a constant speed, and the air volume and pressure are adjusted through the fan baffle. Its disadvantages are mainly as follows: (1) the pressure difference before and after the baffle is increased, the working safety characteristics are deteriorated, and the pressure loss is serious, resulting in increased energy consumption; (2) The fan operates at a constant speed, the baffle adjustment throttle loss is large, the outlet pressure is high, and the system efficiency is low, resulting in a waste of energy; (3) The air duct pressure is too high, threatening the sealing performance of the system equipment; (4) The long-term opening of 40-70% accelerates the wear of the baffle itself, realizes the intelligent manufacturing of extrusion molding, and leads to the deterioration of the control characteristics of the baffle; (5) The equipment has short service life, large amount of daily maintenance and high maintenance cost, resulting in a waste of various resources; (6) The starting impulse current of the equipment is large, so it is necessary to increase the capacity of the distribution equipment and increase the investment; (7) It can not cooperate with DCS directly, so it is difficult to realize automatic control and operation

for this reason, Handan thermal power plant adopted two sets of powersmarttm-- high-voltage variable-frequency speed control devices produced by Harbin Jiuzhou Electric Co., Ltd. on November 20, 2005 to control the gas recovery of 80000 gasholder gas 1 # and 2 # pressurizer groups of converter gas in No. 3 steelmaking plant, and adjust the air volume and air pressure of the fan by changing the motor speed

2 adjustment mode and existing problems before the transformation

before the transformation, it was realized by adjusting the rear baffle of the machine. When the baffle was adjusted to less than 50%, due to uneven air flow, the pipeline would surge, and the vibration of the pipeline would increase. Therefore, when the rear baffle of the machine was opened to a certain opening, the return baffle must be opened to make some gas flow back to the gas tank, which would waste some electric energy; At the same time, when the baffle is used to adjust the flow, the pipe resistance is artificially increased, and part of the electric energy will be consumed

3 features of variable frequency speed regulation device

3.1 the variable frequency speed regulation device changes the speed of the motor by changing the frequency of the motor power supply, so that the motor operates at different frequencies. (1) the speed regulation range is wide, and it can be smoothly adjusted from zero speed to power frequency speed; (2) The soft start of small current can be realized on the large motor, and the start time and start mode can be adjusted according to the on-site working conditions; (3) The frequency adjustment is to output the voltage and frequency according to the voltage frequency ratio coefficient of the motor at low frequency. At low speed, the motor not only has low heating capacity, but also has low input voltage, which will reduce the insulation aging speed of the motor

3.2 novel technology

the application of series multiple superposition technology realizes the real high-high power transformation without step-down and step-up transformation, reduces the loss of the device, improves the reliability, and solves the difficulties of high-voltage power transformation. The application of series multiple superposition technology also opens up a new way to realize pure sine wave and eliminate electric harmonic pollution. Fontface= blackbody 3.3 high performance index (1) high power factor, up to more than 0.95, without additional power factor compensation device, avoiding the loss caused by reactive power; (2) The efficiency is high, up to more than 96%, which is much higher than the high-power speed regulating device of thyristor; (3) Meet the strict requirements of IEEE standards, do not generate harmonic pollution, and do not need any filter devices; (4) It does not produce harmonic pollution to the motor, effectively reduces the heating capacity of the motor, and the noise is similar to that when using power frequency power supply; (5) The torque pulse is very low, which will not cause the resonance of mechanical equipment such as motor, and also reduce the wear of transmission mechanism; (6) The output waveform is perfect, and the distortion is less than 1%; (7) The electric stress intensity of the motor is similar to that of the power frequency power supply, so it is not necessary to be equipped with a special motor; (8) The connection with the motor is not limited by the cable length

3.4 high scientific and technological content

(1) the large-scale gate array CPLD circuit is adopted to realize the high real-time, rapidity and accuracy of PWM control; (2) The two optical "decrypted" EEG signals "command" the robot fiber real-time transmission technology, which has won the national invention patent, making the communication between the control unit and the power unit more rapid and reliable; (3) The specially designed H-bridge inverter circuit has obtained the national patent, which provides a guarantee for the reliability of the system; (4) The perfect power unit bypass technology has obtained the national patent, which further improves the reliability of system operation; (5) The control part adopts high-performance DSP and FPGA chip, which greatly improves the performance of the control system, realizes constant v/f and constant torque control, and the lifting characteristics can be set arbitrarily to meet the requirements of various mechanical start-up and operation; (6) The excellent mathematical model of DSP software greatly improves the real-time and efficiency of the system

4 powersmarttm high voltage variable frequency speed control device system technical scheme

4.1 system composition

powersmarttm series high voltage variable frequency speed control system is mainly composed of phase-shifting dry-type transformer cabinet, power unit cabinet, control unit cabinet, remote control operation box, bypass switch cabinet and other components. Fontface= bold 4.1.1 phase-shifting dry-type transformer phase-shifting dry-type transformer is the input equipment of frequency converter, which is generally composed of iron core, input winding, shielding layer, output winding, cooling fan, overheat protection, etc. In order to meet the requirements of safety, dust prevention, maintenance and aesthetics, it is generally installed in the cabinet

the transformer selected for powersmarttm series high-voltage frequency converter has an insulation grade of H pole, and the insulation materials are imported high-quality products of DuPont company of the United States, with a temperature rise of 150 ℃; Vacuum impregnation, maintenance free. The primary side of the transformer is star connected, which is at the innermost side. The secondary side is on the outside, which is connected along the side triangle. According to different voltage levels, there are generally 9, 18 or 27 three-phase secondary side windings. Another grounding shielding layer is set between the primary and secondary windings. The three-phase windings on the secondary side can be divided into three groups, which are respectively supplied to the three phases in the power unit cabinet. The output voltage amplitude of each three-phase small winding in each group is the same, and the phase shift between them is 20 °, 10 ° or 6.6 °. The transformer cabinet is also equipped with a temperature monitoring device, which can provide overheating warning signal and overheating fault signal when the winding temperature exceeds the warning temperature. An induced draft fan is installed on the top of the transformer cabinet to discharge the heat generated by the transformer during operation. The cabinet door is installed with dust-proof

4.1.2 control unit cabinet

control unit cabinet is mainly composed of main controller, temperature controller, fan protector, man-machine interface (digital tube and color touch screen optional), PLC, embedded microcomputer, switching power supply, EMI module, isolation transformer, air switch, contactor, relay, analog quantity module, switching quantity module, etc

the main controller is composed of bus board, power unit, CPU unit, interface unit, three phase control units and input and output sub modules of switching and analog quantities. It is the control core of the frequency converter, which is composed of two DSPs, multiple FPGA, clpd, etc. the PWM signal is transmitted to the power unit through high-quality optical fiber, so as to achieve high reliable control

the temperature controller can be connected with three temperature sensing probes to test the temperature of the splitting transformer and provide alarm or protection nodes

there are 3 fan protectors, which are used to monitor the lack of phase, overcurrent, etc. of the fan. Among them, 2 are connected to the power unit cabinet and 1 is divided into transformer cabinet

plc, with built-in PID adjustment module and program, can realize closed-loop control. It also contains analog quantity and switching quantity modules, and the number of channels can be customized according to user requirements

the man-machine interface is set on the front door of the control unit cabinet to provide setting, monitoring, switching and other operations

it has two modes: digital tube mode and color touch screen mode, which can be selected according to user needs, as shown in Figure 3 and Figure 4 respectively

4.1.3 power unit cabinet

power unit cabinet is generally composed of 1 ~ 2 cabinets, mainly composed of power unit, current transformer, output voltage detection unit, air duct wind pressure detection device and high-voltage cable

There are 27 power units in the

10kv system, which belong to 3 phases (U, V, w respectively from top to bottom). Each phase has 9 head and tail phase strings, and the phases are connected by stars. There are two current transformers used for current acquisition, processing, monitoring and current closed loop, which are respectively connected in series to u phase and W phase at the star point connection of the power unit. The input terminal of the output voltage detection unit is respectively connected to the three phase terminals of the star connection. Used to detect output voltage and other information. The air duct air pressure detection device is used to detect whether the cooling air duct is unblocked in real time. The air pressure can be displayed dynamically in real time. It, together with the fan computer protector and temperature controller, forms a cooling monitoring system of the frequency conversion system, which further enables the heat of the frequency converter to be transmitted out in time to ensure the reliable operation of the frequency converter

for frequency converters with different power and voltage levels, the type of power unit adopted is strengthened, and the research and development entity number of technical support and guarantee for major national strategic tasks and key projects is different

4.2 working principle

the working principle of the frequency converter is shown in Figure 5

as shown in Figure 6, the power unit module is a PWM voltage source inverter with three-phase low-voltage input and one-phase low-voltage output, which is composed of rectifier diodes and insulated gate bipolar thyristors (IGBT). Due to the independence of the secondary winding of the transformer, the main circuit of each power unit is relatively independent, similar to the conventional low-voltage converter

The

powersmarttm series high-voltage inverter adopts the unit series multiplex technology, which belongs to the voltage source high-high high-voltage inverter. It uses the low-voltage single-phase inverter in series with each other to make up for the lack of the withstand voltage ability of the power device IGBT. The so-called multiplicity means that each phase is composed of several low-voltage power units in series, and each power unit is independently powered by a multi winding phase-shifting isolation transformer. Taking 10kv High-voltage Inverter as an example, 10kV series has 27 power units, and every 9 power units are connected in series as one phase (see Figure 6). The input voltage of each unit is three-phase 650V, and the output is single-phase 650V. After the units are connected in series, the phase voltage can be output 5850v. When the output frequency of the frequency converter is 50Hz, the phase voltage is 19 step wave, as shown in Figure 7. Ua1... UA9 in Figure 7 are the output voltages of 9 power units of phase a respectively, and the superimposed output voltage of phase a of the frequency converter ua0. Figure 7 shows the A-phase reference voltage UAR used when generating PWM control signal, and it can be seen that ua0 is very close to UAR. UAF is the fundamental component of phase a output voltage

since the midpoint of the frequency converter is not connected with the neutral point of the motor, the output of the frequency converter is actually a line voltage, and the UAB output line voltage generated by the output voltage of phase A and phase B can reach more than 10000v, which is 37 step wave. As shown in Figure 7, it is the stepped waveform of the output line voltage and phase voltage. UAB not only has sinusoidal waveform, but also the number of steps increases exponentially, so the harmonic component and dv/dt are small. The three-phase voltage output by the frequency converter is added to the motor to generate current to rotate the motor. The voltage and current (measured waveform) of the motor during rated operation are shown in Figure 8. It can be seen that the motor current is close to the sine wave because the harmonic of the output voltage is very small

the voltage and current (measured waveform) of the motor during rated operation adopt the method of multiple superposition, so that the output voltage of the frequency converter is

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