FIELD OF THE INVENTION
The invention relates to controlling the charging of electrodes and rapping
process in Electrostatic precipitator used for air pollution control. More
particularly, the invention relates to a system for controlling rapping motor of an
electrostatic precipitator (ESP).
BACKGROUND OF THE INVENTION
Electrostatic precipitation is one of the most effective processes to control air
pollution generated by industrial emissions. This technique, which has proven to
be highly effective in controlling air pollution, is used for removal of undesirable
particulate matter from a gas stream by electrostatic precipitation. Electrostatic
precipitator (hereafter referred as ESP) is an air pollution control device designed
to electrically charge and collect particulates generated from industrial processes,
such as those occurring in power plants, cement plants, pulp and paper mills and
utilities etc. The electrically charged particles are attracted towards electrode
plates, viz., and discharge electrode and collection plate electrode.
Electrostatic precipitator uses electrostatic forces for collection of dust particles
by applying very high voltage by using rectifier transformer to produce
electrostatic forces between positive and negative electrodes. The dust particles
between electrodes get ionized and get collected in electrode plates. The
collected dust particles are dislodged from electrode plates using tumbling
hammer mechanism. Electronic controller operates rapping Motors, when
necessary. The rapping motors drive the hammer system. The hopper at the
bottom of electrostatic precipitator collects the dust particle during rapping.

An ESP installation consists of a plurality of fields. A field is considered healthy as
long as it is charged with sufficient voltage and current between its discharge
and collection plate. For a typical larger ESP, there will have around 8 pass's and
each pass will have around 10 fields and 10 to 20 numbers of hoppers depending
on the ESP design based on inlet dust burden ash evacuation system. During
continuous operation of an electrostatic precipitator, the dust from collector
plates & discharge electrodes must be periodically removed for further collection
of dust.
Typically, energizing ESP field requires a very high voltage to the tune of 40KV to
90KV DC to be generated from the available AC sources. This involves stepping
up of AC voltage and rectifying to produce such a very high voltage. Also, the
generated high voltage shall be maintained and controlled during the operation
of the ESP field. This is generally being achieved by High Voltage Rectifier with
electronic controllers (EC-HVR). Energisation of the rapping motors is done by a
microcontroller through an output card and the motor running feedback is
obtained through an input card. The sequence of rapping are critical to the
performance of the ESP as a low frequency of rapping will permit accumulation
of large amount of ash on the electrodes and a high frequency will cause
frequent re-entrenchment of dislodged ash into the gas stream.
In the prior art, the control of high voltage rectifier is achieved through
independent controller. There will as many EC_HVR controllers as the no of ESP
fields. However, controlling Rapper motors has few varieties depending on
requirement of system. The Rapper Motors are either controlled by same EC-HVR
controller or by a separate Rapper Controller, which controls the rapper motors
of entire PASS. For increasing its availability, additional redundant or Standby

Rapper Controllers for each individual Rapper Controller are also provided.
However, for such cases, the total no of Rapper Controller will be doubled.
In the prior art, there exists no Rapper controller configuration exists, through
which the entire rapper motors of a PASS can be controlled by a single EC-HVR
Controller. Also, there is no method exist to increase the availability of Rapper
Controller for the Entire ESP using a single standby Rapper Controller avoiding
doubling the number of Rapper Controller.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a system for controlling
rapping motor of an electrostatic precipitator (ESP), having a group of EC-HVR
controllers in one pass with one EC-HVR controller acting as Master for handing
rapping operation of entire fields in a pass and other controller in a group
operating as slave for rapping function.
Another object of the invention is to propose a system for controlling rapping
motor of an electrostatic precipitator (ESP), in which EC-HVR controllers have
intelligence to switch over between Master Controller and slave controller in case
of failure of the Master controller and ensure sustained Rapping operation of
entire fields of a Pass.
A still another object of the invention is to propose a system for controlling
rapping motor of an electrostatic precipitator (ESP), in which each of the EC-HVR
controller has ability to act as master controller but only one controller can act as
master at a time for rapping functioning of the system.

Yet another object of the invention is to propose a system for controlling rapping
motor of an electrostatic precipitator (ESP), in which all the EC-HVR controllers
have same parameter back up and user settings similar to the master controller
for functioning of the system during failure of the Master controller.
A further object of the invention is to propose a system for controlling rapping
motor of an electrostatic precipitator (ESP), in which an EC-HVR controller to
perform HVR controlling based on ESP flow parameter's and alarm conditions in
addition to Master detection logic for high voltage rectifier transformer
controlling operation.
A still further object of the invention is to propose a system for controlling
rapping motor of an electrostatic precipitator (ESP), in which the user of the
Master controller can give rapper commands for the entire field's in that pass as
per user requirements.
Another object of the invention is to develop to propose a system for controlling
rapping motor of an electrostatic precipitator (ESP), which can display the
rapping and alarm status of the rapper motor in each of the controller connected
in a pass for the user interface.
Another object of this invention is to propose a system for controlling rapping
motor of an electrostatic precipitator (ESP), which is configurable as per the
power plant requirement such as number of fields to suit same hardware for all
functional area.
Another object of the invention is to propose a system for controlling rapping
motor of an electrostatic precipitator (ESP), which is an embedded device having
advanced communication system such as RS485, CAN for faster, error free
transmission of the data to ESP single point controlling system and plant
Distributed control system (DCS).

SUMMARY OF THE INVENTION
The invention provides a system for controlling and monitoring of rapping motor
operation of an electrostatic precipitator (ESP), in which a group of EC -HVR
controllers of a pass are connected over a common RS 485 communication
channel, to facilitate rapping operation of the pass in addition to HVR
transformer controlling. An input card is used for reading Motor ON/OFF
feedback and output cards are used for giving Motor ON/OFF commands. All the
controllers in the pass and cards are connected by a common RS485
communication channel functioning on MODBUS protocol.
The invented system has in-built intelligence to handle the communication over
the bus as master and slave controller mode. The Pass master logic approach
based controllers, software receive and process the data over the two wire
RS485 communication channel over MODBUS protocol, Process it and assign self
as Master/ Slave controller and also update the rapping status on each
controller of the pass in addition to functioning as high voltage transformer
controller.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1 - shows a block diagram a system for controlling rapping motor of an
electrostatic precipitator (ESP) system for ESP.
Figure 2 - shows the internal block diagram of an Electronic controller.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The hardware block diagram of the control system having a group of electronic
controllers in one pass of an ESP , in which one of the controllers acts as a
Master at a time, based on Pass Master logic module, as is shown in figure 1.
In Fig (1), blocks [1] to [7] form a group for electronic controller for one pass of
the ESP [8] having Pass master control logic module to assign one as Master in
the group and others as slaves. Block [9] is a RS 485 communication channel,
which connects all the controllers of the pass [8], a pair of output cards, i.e., an
active output card [10] and a redundant output card [11] and an input card [14].
The pair of output cards (10) also has a separate RS485 link [13] between them.
A plurality of HVR controllers having Pass Master logic are located in the
electronic controller panel room, which controls the high voltage rectifier
transformer and its auxiliary output card and input card are located in the motor
switch gear control panel. The output cards are used for giving Rapper Motor
ON/OFF commands, and Input card is used for reading the feedback.
The hardware block diagram of an Electronic controller is shown in (Fig (2). In
Fig (2) block (14) is the power supply unit for the controller. In Fig (2) block (15)
is the RS 485 communication interface connecting all the controllers , input
card and output card and the ESP to operate as a single point controlling
system. In Fig (2) block (16) is a central processor (Micro controller) which
executes the software execution. It has inbuilt memory to store the program. In
Fig (2) block (17) is a liquid crystal display for display the status and other
parameters.

Each of the EC-HVR controllers has separate setting for its address, Pass name
as well as field number. Controller address is unique and it is used for
establishing communication with remote access point. The Pass master control
logic module works based on the field number assigned to the controller forming
the pass. Once the controllers in a pass are energized, the controller having the
highest field number will send command in the common communication channel
[9] which links all the controllers, input card, output card and wait for reply, if
reply from the output card is received, it will act as the master and take over the
function of controlling the rapping mechanism of the pass. Other controllers
assign self as slave as long as they receive reply from output cards. The Pass
Master controller communicates the user commands to other slave controllers in
the pass, hence the rapping commands given by the user is updated in all the
controllers in the Pass. Hence all the controllers keep the track of rapping
sequence and other related parameters set by the operator or from the
centralized monitoring and control system.
The Pass master control logic module is having in-built intelligence to assign only
one controller as pass Master at a time in a pass. Suppose if there are N fields in
a pass then there will be N numbers of controllers having field number setting 1
to N. The time delay assigned for each controller for assigning self as master of
the system is calculated by subtracting N (No of Fields in a Pass) with field
number assigned to that particular controller. Obviously it will be zero for the
controller having last field number, i.e, N. It will become 1, 2 3, 4, 5, 6, 7, 8 time
units for successive controllers. Hence once the pass is energized controller
having highest field setting will command first in the common RS 485
communication bus. If it fails the next controller having lowest time delay will
command and assumes as master and it can control rapping operation of a pass
in addition to HVR transformer control and all other as slaves take care of

charging of HVR transformer of field to which it is connected. The slave
controllers continuously monitor the healthiness of the Master controller based
on the commands reception from the Pass master controller and reply from relay
cards over common RS 485 communication link [9]. If slave controller doesn't
receive any command from master controller it detects as master controller
failure, the controller having lowest time delay will automatically assumes as
Pass master. In Pass master based rapping system have XN' levels redundancy
(Where N is the no of the field) i.e., if any one of pass master fails , next
controller having minimum time delay will automatically pick up as Pass master,
and control and monitor rapping system of the Pass. Since all the controllers
having the same track of rapping records, the failure of one controller will not
affect the system.
Indication is available in controller to identify which controller is acting as the
pass master at a particular time. The Pass Master controller is the Master
controller, which can control the different modes of operation of motors such as
Manual Mode- for Manual ON/OFF operation, Auto- for Automatic operation
based of pre-defined time table available in controller as well as STOP mode to
permanently switch OFF rapping motor. The pass master controller co-ordinates
the rapping process based on the raping sequence programmed in it. The
rapping motor associated with various fields of the ESP are switched ON/OFF at
optimum periodic intervals based on the input provided by the operator on pass
master controller or by a centralized monitoring system of the ESP.

In this system, the motor ON / OFF information is transmitted to the output card
as well as to other slave controllers over the serial communication link [9] using
standard Modbus protocol. The output card [10] as well as the other slave
controllers decodes this packet. Subsequently output card [10] switches ON /
OFF the relay based on the information from Pass Master. The same time slave
controllers update its own data base to maintain same track of record. The
redundant output card [11] keeps track of the healthiness of the active output
card[10] and on its failure , takes over the as active output card without
hindering the rapping operation. Rapping motor ON/OFF feedback is received at
input card [12], which transmits this information to all the controllers over the
serial communication link[9], using standard MODBUS Protocol. Each controller
receives the data packet over RS485 communication link, and updates its LCD
display module available in controller. Each controller in a Pass can display the
rapping motor running status of the Field for which it is assigned. The same time
Pass master can display the rapping status of motors of the Entire Pass of ESP.

WE CLAIM :
1. A system for controlling and monitoring rapping motors of an electrostatic
precipitator ESP (8), comprising a plurality of fields, generated and
maintained by high-voltage rectifier transformer controlled by EC-HVR
Controllers; and a plurality of rapper motors controlled by group of EC-
HVR Controllers, of the same pass (1 to 7) connected by a common
communication link (9), along with an active output card (10), a
redundant output card (11) an input card (12), wherein the Pass master
control Logic is enabled in each of EC-HVR Controllers to assign one of
said plurality devices (1 to 7) to act as a master controller, and the
remaining of the devices to act as a slave controller in a single pass of the
ESP (8), wherein the output cards (10,11) are connected through a
second communication link (13) for redundant operation, and wherein the
controllers have in-built Pass Master Logic intelligence, to switch over from
the role-of Slave Controller to Master controller and assign it as master in
case of failure of the master controller to continue rapping operation of
entire fields of a Pass.
A system as claim (i) in which each of the controller have ability to act as
master controller but only one controller as master at a time for proper
rapping functioning of the system.
2. A system as claimed in claim 1, wherein all the controllers have same
parameter back up and user settings for functioning of the system during
the failure of an arranged Master controller.

3. The system as claimed in claim 1, wherein the HVR transformer
controlling based on ESP flue gas flow and other parameters is performed
by the controllers in addition to function as the master controller for
rapper control.
4. A system as claimed in claim 1, wherein all the electronic control units [1]
to [7] are enabled to switch ON/OFF the rapping motors at optimum
periodic intervals.
5. A system as claimed in claim 1, wherein the actuation of the rapping
motor is performed through a plurality of relays located on the output
card [10], the redundant output card [11] and the feedback read through
input card [12].