Contemporary Approach to Power of Electrostatic Precipitators XII International Scientific – Professional Symposium INFOTEH®-JAHORINA 2013 Contemporary Approach to Power of Electrostatic Precipitators DSP control Željko V.Despotović- Mihajlo Pupin Institute, University of Belgrade, Serbia, zeljko.despotovic@pupin.rs Slobodan N.Vukosavić-Scholl of Electrical Engineering, University of Belgrade, Serbia, boban@etf.rs Mladen Terzić -Scholl of Electrical Engineering, University of Belgrade, Serbia

INTRODUCTION The power management method of electrostatic precipitators (ESP) significantly affect on the separation efficiency of fly ash and fine particles from smoke gases that through the funnel drainage into the atmosphere as a specific unwanted product of electric energy production In previous decades ESP in TPP were supplying by SCR controlled devices having a high degree of reliability, but with relatively low collection efficiency, hence requiring large effective surface of the collection plates and a large weight of steel construction. The collection and energy efficiency of the ESP can be increased by applying multiresonant high frequency high voltage (HFHV) power supply.

THE CONVENTIONAL ESP POWER SUPPLY The ESP power supply and controls are traditionally based on one pair of anti parallel connected thyristors T1 and T2, which alter the amplitude of the primary AC voltage. The primary supply is usually single-phase, 400V, 50Hz. By changing the firing angle, the voltage is being changed in the range from 0 to 400 V and brought to the primary of the line frequency power high voltage transformer (HVT) whose secondary voltage reaches 45 kV to 90 kV.

High Voltage Rectifier (HVR) The high voltage rectifier (HVR) made out of the great number of series connected diodes is placed in the oil-filled container, along with the transformer itself. The transformer and the diode rectifier are denoted as transformer – rectifier (T/R) set. One T/R set provides the DC output voltages from 50 kV to 100 kV and currents from 1А-2А. The supply of larger filter section is achieved by putting several T/R units in parallel.

SCR 50Hz POWER SUPPLY - PROBLEMS Considering the occurrence of sparks and short circuits in ESP circuit, it is necessary to foresee the short circuit current limitation measures. The switched on thyristor cannot be switched off before the expiration of the current half-period of the mains. Erosion of electrodes system Hence, the short circuit current is limited by the series reactance Lo only. The short circuit reactance of single phase HVT is relatively small and insufficient for the proper limitation of the short circuit current. Eventual design of dedicated transformer with increased leakage flux would increase the losses as well as the size and weight of the HVT. Very poor power factor and unfavorable waveform of electric currents and voltages

50Hz ESP Supply - VOLTAGES and CURRENTS The thyristor commutation creates harmonic distortion, while the presence of relatively high series reactance along with phase delays due to thyristor firing angle create substantial reactive power. Electrode voltage has a large pulsating component at the fundamental frequency of 100 Hz, which causes a decrease in the average voltage. Characteristic voltage and current waveforms obtained with the T/R power supply; (a)-Input characteristic, (b)-Output characteristic

CORONA and PRECIPITATION EFFICIENCY Namely, the peak voltage must not be higher than breakdown voltage Ubd. For that reason, the average voltage must be significantly lower. If the voltage waveform is such that the pulsing component at 100 Hz has an amplitude of, the average voltage across the electrodes must be less than or equal to Ubd -∆U . As a consequence, the electric current density is lowered as well as the precipitation efficiency. Hence, for the given gas flow and specified precipitation efficiency, it is necessary to foresee the electrode system with increased surface and weight. Such an increase raises the weight, size and cost of the ESP. EFFICIENT CORONA Ubd

Why do High Frequency High Voltage (HFHV) POWER SUPPLY? It is possible to provide more precise control of the ESP parameters such as the output voltages and currents. It is also possible to make a rapid increase or decrease in voltage and to effectuate a very fast response to load changes

Why do High Frequency High Voltage (HFHV) POWER SUPPLY? Due to previously advantages it is possible to suppress the supply quickly in the case of sparking, reducing the spark energy and the quantity of ionized gasses produced by the electric arc. Reduction in the spark energy is up to 10 times compared to conventional thyristors solution. This means that the erosion of the electrode system is significantly reduced, and that the quality of the collection plates is preserved for much longer periods. At the same time, lower quantity of ionized gasses produced by the spark contributes too much shorter de-ionization intervals, required to quit sparking and evacuate charged particles in order to reinstate the voltage and proceed with the operation.

High Frequency High Voltage (HFHV) Power Supply COST SAVINGS!!!!!!! In addition, HFHV power supply provides a significant reduction in size and weight of the complete ESP installation, hence reducing the tons of steel that has to be built in. Therefore, the HFHV power supply may be the key instrument to reducing the cost of the dedusting ecological equipment. Besides, size and weight reduction leads to cost savings of installation and maintenance. According to estimates, savings in steel may reach 30%, contributing to the overall cost savings of roughly 20%.

THE PROBLEMS OF EXISTING SOLUTIONS OF HFHV ESP POWER SUPPLY The problems encountered in the HF ESP power supply exploitation are frequently reflected in : breakdown of semiconductor power switches in the primary circuit secondary circuit insulation breakdown problems of EM noise and control

HVHF POWER SUPPLY-bridge topology The primary voltages and currents within HF power supply assume values next to 600V and 300А. Therefore, the semiconductor power switches to be used are the IGBT devices. In addition to their favorable characteristics, IGBT-s also has their commutation losses which limit the maximum switching frequency. The recommended switching frequency for IGBT power switches depends on the rated current, and it is lower as the current rating increases. For transistors of 300А, commutation and conduction losses are equal at the frequencies between 2 kHz and 5 kHz, which represents the technical optimum for their operation.

RESONANT TOPOLOGIES-the best solution!!!!! Therefore, it is necessary to utilize resonant topologies in high frequency range, enabling the semiconductor power switches to operate without commutation losses. This enables the elimination or at least a significant decrease in commutation losses.

THE SERIES RESONANT LINK TOPOLOGY NWL technology (power converter+HVHF transformer+control) RESONANT TANK-LC is the HIGH GABARITE!!!! SERIES CONECTED CAPACITOR Cr!!! HIGH CURRENT (200-300A) RESONANT CAPACITOR Cr!!!

THE PARALLEL RESONANT LINK TOPOLOGY PARALLEL RESONANT TANK-LC is the HIGH GABARITE!!!!

BASIC TOPOLOGY OF THE NEW MULTI-RESONANT ESP POWER SUPPLY HVHF topology are dominant two distributed parasites transformer capacitance C1 and, C2 on the primary and secondary side, respectively. This capacitances with corresponding inductance, Ls, L1 and L2, with capacitance in HVHF rectifier- and ESP plate capacitance CESP, form multi resonant circuits. Distributed multiresonant converter topology enables ZCS commutation of IGBT power switches, significantly reduce commutation losses and the insulation stress, hence suppressing the catalytic effects of the electric field high speed changes and preventing chemical reactions leading to accelerated dielectric aging.

HIGH VOLTAGE HIGH FREQUENCY(HVHF) TRANSFORMER CONSTRUCTION FERRITE CORE

THE MULTIRESONANT TOPOLOGY- SIMULATION CIRCUIT 1:120 I II III Multi resonant topology of HFHV power supply-simulation scheme ESP parameters -PWM voltage source (duty cycle and frequency control) -three resonant circuit I, II,III -HV rectifier -model ESP (Oglesby)

SIMULATION RESULTS-open circuit (no load) Simulation results of multi-resonant power converter for open-circuit (OC) to a load at varying of duty cycle δ; (a) δ=12.5%, VESP=30kV, (b) δ=25%, VESP=60kV

SIMULATION RESULTS-short circuit Simulation results of multi-resonant power converter for short-circuit (SC) i.e. VESP=0V, to a load at duty cycle δ=15%

SIMULATION RESULTS-rated load Simulation results of multi-resonant power converter for rated load RESP=68kΩ at duty cycle δ=98%; VESP=68kV, IESP=1A.

FIELD OF APPLICATION OF MULTIRESONANT TOPOLOGY HVHF Power Supply AR70/1000 The developed a solution can be applied in integrated systems for the removal of air pollution at thermal power plants and heating plants Specifically, this solution has been applied to TPP "Morava", and is currently under putting into operation six such units in the HF plant of TPP "Nikola Tesla" at block A1 Since 2008-2010, the testing took place at TPP “Morava”, equipped with AR70/1000 units

HVHF Power Supply AR70/1000 TOPOLOGY GABARITES THERMAL VISION

APPLICATION on TPP “Morava” TPP “Morava” Svilajnac Block diagram of ESP plant with the possible comparison conventional 50Hz and multi resonant HFHV power supply system

THE MULTIRESONANT TOPOLOGY -EXPERIMENTAL RESULTS In next slides will be presents the experimental results obtained during the verification and testing HFHV power supply AR70/1000. Testing and experimental verification was conducted in the various load regimes: open-circuit (no load), short-circuit, and the rated load.

EXPERIMENTAL RESULTS-open circuit(no load) Oscilloscopic records of voltage and current of IGBT converter (CH1 and CH2); 30kV output voltage of HFHV power supply AR70/1000 (CH3) Oscilloscopic records of voltage and current of IGBT converter (CH1 and CH2); 60kV output voltage of HFHV power supply AR70/1000 (CH3)

EXPERIMENTAL RESULTS-short circuit Oscilloscopic records of voltage and current of IGBT converter (CH1 and CH2); Short circuit of HFHV power supply AR70/1000; "duty cycle” δ = 15%

EXPERIMENTAL RESULTS-rated load Oscilloscopic records of voltage and current of IGBT converter (CH1 and CH2); full load 70kV/1000mA of HFHV power supply AR70/1000

THE COMPARISON of SCR 50Hz and HVHF Power Supply/criterion: input current from the mains power PF=0.3 PF=0.9 PF - POWER FACTOR

THE COMPARISON of PARTICLE EMISSION for HFHV supply AR70/1000 and SCR 50 Hz supply (in the time interval of four hours)

CONCLUSIONS It was presented new multiresonant topology of HFHV power supply of ESP’s. For the same operating conditions was confirmed by good correlation of simulations and experimental results. HFHV power supply AR70/1000 is in the exploitation conditions proved very successful. The multi resonant power converter topology enables ZCS commutation of IGBT power switches, significantly lowering the overall converter losses. Voltage and current control includes the possibility controlling the number of sparks per minute

ACKNOWLEDGEMENTS The proposed multiresonant topology represents the basis of power supply AR70/1000 developed in the framework of scientific cooperation between the School of Electrical Engineering, the University of Belgrade and Mihajlo Pupin Institute, Belgrade This investigation has been carried out with the financial support of the Serbian Ministry of Science- Project No: TR33022

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