ESP Transformer and control

In recent years, due to the increasing awareness towards pollution & changing norms of emissions by the Government Agencies World wide, it has become absolutely necessary to achieve higher efficiency from the Electro Static Precipitator (ESP) to reduced the emission.

In the last decade the maximum permissible emission form the power plants was 150mg/Nm3 in general. However, due to strict norms by Pollution control boards, the emission levels have come down to almost 50mg/Nm3. In European Union new norms of 25mg/Nm3 are being strictly enforced.

There are various ways to do this in Electro Static Precipitator such as increasing the number of fields, changing the fuels, changing control system of ESP, However all these things have some limitations in achieving the required result. To achieve higher efficiency beyond certain limits, one should need to increase corona power in the ESP to achieve better & better collection.

Traditionally Single Phase TR sets ae used that give high peak voltage for better charging of the particles but the corona current is less and if current is increased to increase corona, it results into heavy sparking / acting in the ESP.

Worldwide there is a change in concept of replacing single Phase TR sets in ESP by 3 phase TR sets & it has been observed that there is a substantial increase in the collection of ESP. Similarly, the emissions can be brought down substantially without any mechanical or process change in existing ESP.

The only care to be take is to ensure healthiness of the mechanical field before replacing 1 phase TR sets by 3 phase TR sets. 

• 3 Phase Mains input supply with low line voltage distortion
• Lower input inline current compared to single phase system.
• For same KVA rating input cable and switch gear sizes are reduced
• Higher transfer efficiency ratio of 95 % compared to 75 % with single phase
• Fast recovery after sparking
• Low voltage ripple higher average DC voltage
• Fast response to sparks an Arcs

Each of the above factors offers potential cost saving for both new and retrofit installation. Lower poor consumption due to the improved power factor will result in direct cost saving. There are other potential saving with the cabling and sizing of Switchgears used at the primary size as well as increase in electrode life due to improved spark control action. The product is useful for retrofitting as well as new ESP designs. It is yet to explore but ESP design can optimized in new ESP designs to reduce cost either by reducing collection area or reducing 1/2 fields, in large power plants. All ratings are available and supplied with the highest reliability product and service. Being a rugged transformer and rectifier design the life expectancy is almost 20+ years of operation. 

Control of back Corona

After certain amount of dust is collected at the collecting electrodes, there is a voltage drop in the dust layer. If the electrical resistivity of the dust, as in low Sulfur fly ash, is high, the amount of charges on the surface of the dust layer increases, and the electric field intensity in the layer becomes stronger. Eventually, the electric field intensity is greater than dielectric strength of the dust layer, and dielectric breakdown occurs. The positively charged dust particles move towards negatively charged discharge electrode thereby discharging the negatively charged dust particles moving towards collecting electrodes. This is called back corona. It affects significantly the dust collection efficiency. A high current occurs on the low voltage operation. Our controllers detect the typical current voltage characteristics associated with back corona, control it and enable the ESP to run at maximum efficiency.

Control of Sparking

An important function of ESP controllers is to detect and control sparking and keep it within operators set limit which is normally less than 10 sparks per minute. Power is removed by the controller as soon as the spark is detected to interrupt flow of current to the spark. It again powers the emitting electrodes after lapse of deionization time of flue gas. 

Rapper Control

ESP regulator detects hen dust accumulation at collecting electrodes reach a certain value. It reduces the voltage and sets rapping mechanism into motion. After cleaning cycle is over, it again increases power to the electrodes.

• Semipulse duty
• Four individual programs for different flue gases (Fuels)
• Basic energisation mode by voltage or current control
• De-ionization to re-establish proper gas condition when sparks have occurred
• Back corona control manual or automatic, to maintain best efficiency
• Voltage reduction, adjustable, can be initiated via closing contact
• Automatic saving of information and setting in EEPROM
• Display presentation of primary and secondary voltage/current characteristic
  Alarms as per block diagram below