The invention relates to "an apparatus for producing controlled sparks to ignite
efficiently fuels used in industries.
FIELD OF INVENTION
The apparatus described here as the present invention will be employed for
efficient light-up of liquid/gas fuels fired in the furnace of a boiler and other
similar applications. In particular, the present invention relates to employing a
high frequency switching converter technology to generate high voltage required
for producing sparks at variable energy levels and sparking rates suitable for
different fuels. More particularly, the present invention relates to using a high
frequency converter circuitry to reduce the size and weight of the ignition
apparatus. The apparatus described here also details an electronically operated
switch to control the sparking rate and energy instead of a self-actuating spark
gap, as a variant.
BACKGROUND OF THE INVENTION
Boilers are employed worldwide by thermal power plants, refineries and many
other industries to produce steam for their operation. Many of the boilers are
designed for firing fuel oil and / or fuel gas as support fuel and / or load carrying
fuel. In all these boilers, suitable type of apparatus (igniters) have to be used to
light-up the fuel in burners.

After ensuring proper conditions for firing the fuel, the fuel is admitted into the
furnace of the boiler. At the same time, electric power supply is given to the
ignitors to produce sparks in the vicinity of burning zone. The fuel gets lighted-
up by the heat energy provided by the sparks. Lighting the fuel automatically in
the first attempt itself is considered important in any boiler furnace. The heat
energy provided by the sparks from igniters play an important role in this aspect.
This invention relates to an improved method of producing and controlling sparks
in electric igniters.
Presently available igniters work on the principle of producing high voltage in the
order of 2500 V DC from 230 V AC (or 110 V AC), charging capacitors to this
high voltage and discharging them with a suitable spark gap. The stored energy
of the capacitor is released in sparks. Conventionally designed igniters use a line
frequency operated step-up transformer, the secondary of which is connected to
a voltage doubter circuit and high voltage capacitors. A self-triggering, voltage
activated spark gap is used, to discharge the high voltage capacitor to produce
the sparks at the tip of the ignitor which ignite the fuels.
Since the high voltage circuitry employed in presently available igniters, are
operated with line frequency step-up transformer, the spark generator box is
heavy and bigger in size. The output of the spark generator box is connected to
a flexible rod assembly. The rod assembly is advanced into the furnace during
light up of fuel and subsequently retracted after ignition. A pneumatic actuator
operates it. Due to its weight and size, the spark generator box cannot be
mounted on the actuator. Therefore the spark generator box is mounted
separately and a flexible high voltage cable gives the high voltage connection to
the spark tip.

GB 1262610 describes an ignition pulse generating electric circuit for generating
pulses for supply to ignition means in a furnace comprises an ignition
transformer having an input winding, and a series path comprising only the input
winding, a capacitor and a semiconductor switching means, the two ends of the
series path being respectively connected in use to the two poles of an alternating
current supply. The semiconductor switching means is a controllable rectifier.
The diode may be replaced by another controllable rectifier. The two controllable
rectifiers may be replaced by a TRIAC. The semiconductor switching means may
comprise a Zener diode or a double avalanche diode.
GB 875640 discloses a control system for arc furnace in which the electrodes are
positioned by a fluid servomotor which is controlled by a combined valve and
hydraulic amplifier. The operative members comprises two differentially wound
coils to which are applied voltages proportional to the arc current and voltage
respectively. The coil is supplied by a current transformer by way of a bridge
rectifier and a switch, in the "AUTO" position, a variable resistor being supplied
for adjustment of the electrode current. The coil is supplied by a secondary
winding of a transformer by way of a bridge rectifier and a switch in the "AUTO"
position, a variable resistor being supplied for adjustment of the voltage across
the arc.

GB 929008 discloses a protective arrangement for an induction furnace
comprising a fault-detecting circuit including an auxiliary supply, the primary
winding of a transformer, a series resistor and an indicator and/or relay
responsive to voltage drop across the resistor, the secondary winding of the
transformer being connected in series with a rejector circuit between the furnace
circuit or a shield for the furnace coil. A conductor connecting the furnace charge
to earth, the rejector circuit being turned to the frequency of the furnace circuit
and limiting the current through the rejector circuit to a value below that which is
dangerous when passing through a human body. A device may indicate the state
of the tuning of the rejector circuit. The secondary winding of the transformer
may be connected between the rejector circuit and the conductor by a bridge
rectifier with a shunt spark gap. In a further arrangement the rejector circuit
may be connected to both conductors n the furnace circuit by means of a centre-
tapped potentiometer.

OBJECTS OF THE INVENTION
It is therefore, an object of the invention to achieve controlled spark energies
and sparking rate by employing an electronically controlled switching circuitry -
This enables the ignitor suitable for different types of fuels.
Another object of the invention is to reduce the size and weight of the
apparatus, so that it can be housed in compact housing and can be directly
mounted on the pruematic actuator, thereby eliminating a flexible cable required
when the ignitor box is mounted separately.
SUMMARY OF THE INVENTION
Accordingly, there is provided an apparatus for controlling spark and energy
level of each spark to efficiently ignite fuel in a boiler furnace, comprising an
input system connected to the Power Supply line of 220/110 AC, the output of
which is connected to a primary side of a high frequency transformer (Block 3);
a high frequency rectifier unit (Block 4) connected to a secondary side of said
transformer; a high voltage capacitor bank (C 5) connected to said high
frequency rectifier unit and to a high voltage electronic switch (Block 6)
connected to a spark tip (7) of the ignitor, characterized in that the triggering

circuit comprising a digital counter and a transistor is disposed in a trigger circuit
for triggering a silicon controlled rectifier or a light activated silicon controlled
rectifier, the controller (EM 2) is presettable to control the charge rate of said
high voltage capacitor bank (C 5), and in that the controller is enabled to
generate switch-on pulses based on the charge-rate being measured by the
counter for driving the transistor which disables or enables the transformer
based on the charge rate data from the controller to control the energy level of
each spark.
The innovative aspect of this invention is that the apparatus is based on
employing an electronically controlled switching circuitry to achieve controlled
spark energies and sparking rate. The switching circuitry consists of ferrite core
set-up transformer and a high frequency switching device. Another innovative
aspect of the invention is the compact design of exciter with reduced weight and
size.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
A block diagram of the ignitor is given in the Figure - la.
Figure lb - shows the alternate method of High Voltage switching.

Figure 2a, Figure 2b and Figure 2c - shows the various configuration for
Electronic switch Q1.
Figure 3a, Figure 3b and Figure 3c - illustrates the different circuits for triggering.
Figure 4 - shows the Spark tip.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF
THE INVENTION
The overall block diagram is given in the Figure - la.
The line commutated rectifier unit (Block 1) of Figure la, consists of four diodes
D1 to D4. It is so arranged that 110 V AC input voltage can be given between
terminals A&B and 220 V AC input voltage can be given between terminals A&C.
In either case, the output DC rectified voltage will remain the same. In the case
of 110 V AC input, the diodes D1 and D4 act as voltage doubter charging the
series connected capacitors C1 & C2. In the case of 220 V AC the diodes D1 to
D4 act a bridge rectifier to charge the capacitors C1 & C2. The resistors R1 & R2
are included to reduce the switch-on current during power-up of the system.
The electronic switch module (Block 2) of Figure la consists of a driving circuit to
drive Q1. The driving circuit consists of reduced voltage power supply given by
the combination of the resistor R3, zener diode ZD1 and capacitor C3. The zener
diode clamps the voltage to a fixed value and the resistor R3 limits the current.

The electronic module EMI generates the switching-on pulses, the frequency of
which is set by the resistor R4 and capacitor C4. These pulses are applied to the
gate of MOSFET Q1, which switches on and off the primary coil of the high
frequency transformer TRl. The resistor R5 develops a voltage proportional to
the current flowing through the primary of the transformer when Q1 is switched
on. This voltage decides the current level at which Q1 is switched off by the
electronic module EM1. The Electronic switch Q1 is configured on either by
Power MOSFET or IGBT or Darlington pair. This invention covers all the
variations. Figure 2a illustrates Q1 with IGBT. Figure 2c illustrates Q1 with

Darlington pair .
High frequency transformer TRl (Block 3) of Figure - la is made up of Ferrite
core material suitable for efficient operation at high frequency. The turn's ratio
between the primary and the secondary is 1:N, the value of N being decided by
the step up voltage requirement. It can be any value between 5 to 20. The
transformer TRl has sufficient leakage reactance provided by air gap envisaged
in the construction of the core. This leakage reactance helps in reducing the
short circuit current of the transformer.
High Frequency Rectifier unit (Block 4) of Figure - la, charges the High voltage
capacitors (Block 5) of Figure - la, connected across the secondary during
switch off time of the electronic switch Ql. This mode of operation is called as
fly back mode. During 'ON' time of the electronic switch Ql, the current flowing
through the primary of TRl causes magnetization of the ferrite core and the
energy is transformed to the secondary of TRl by mutual reactance during %OFF'
time of electronic switch Ql.

The high voltage capacitor bank C5 (Block 5) of Figure - 1a gets charged
progressively. The energy stored in the capacitor is given by the equation
CV2/ 2. Depending upon the energy requirement, the charging voltage of the
capacitor can be varied. The energy stored is in the order of 6 to 18 joules. This
energy is transferred to the spark tip (Block 7) and the capacitor is discharged
through high voltage electronic switch (Block 6.).
The high voltage electronic switch (Block 6) of Figure - 1a consists of a Silicon
Controlled Rectifier D7 (SCR) and a diode D6 connected anti parallel to the SCR.
The SCR can be triggered-ON either by light (light activated SCR) or by a trigger
pulse at the gate terminal. Three options are considered for the selection of
trigger circuit. Various types of trigger circuits are illustrated. This invention
also covers various methods of configuration of trigger circuit for controlling
SCR/LASCR. Figure 3a illustrates circuit for triggering LASCR using photo
coupler. Figure - 3b illustrates circuit for triggering conventional SCR through
Pulse transformer Figure - 3c illustrates triggering LASCR using photo coupler
through Fibre optic cable.
Spark tip (Block 7) of Figure - 1a is elaborated in Figure - 4. It consists of a
cylindrical metal body and a central conductor insulated from the body by
ceramic insulating tubes. The outer body of the spark tip is connected to the
inner Conductor positive terminal of the high voltage. At the end face, metallic
conductor is at the center and the outer body is concentric to it. These two are
separated and supported by insulated ceramic tubes. At the end face, the
ceramic tube is coated with a special material. When the electronic switch
connects high voltage to the spark tip, surface discharge takes place between

the tip and outer body. This surface discharge further develops into spark
discharge by subsequent heating and ironizing of the surrounding air. The
special coating material initiates the surface discharge.
The invention also has a provision to control the number of sparks produced and
the energy of each spark. This is achieved by the circuitry shown in Figure -3a.
A digital counter counts the switch-on pulses produced by the Electronic Module
EM-2, which is preset to a value of N. The output of this counter drives a
transistor Q2 that either switches on the light emitting diode (LED) in the case of
LASCR or pulse transformer. The charge rate of high voltage capacitor C5 can
be controlled by setting appropriate preset value in Electronic Module EM-2. The
charge ratio indirectly controls the energy level of each spark from 6 to 18
joules.
In Figure - 1b alternate method of High Voltage switching (Block 6) is employed
replacing SCR with Spark Gap. Except this, all other methods adopted are same.
The Spark Gap acts as a switch, when the ionizing potential is reached between
electricals resulting in breakdown of medium and thereby causing current flow.
The Spark Gap being self triggered high voltage switch, the representation of
Figure - 2a, 2b and 2c are not applicable for system function described above.

We claim:
1. An apparatus for controlling the number of spark and energy level of each
spark to efficiently ignite fuel in a boiler furnace, comprising an input system
connected to the Power Supply line of 220/110 AC, the output of which is
connected to a primary side of a high frequency transformer (Block 3); a high
frequency rectifier unit (Block 4) connected to a secondary side of said
transformer; a high voltage capacitor bank (C 5) connected to said high
frequency rectifier unit and to a high voltage electronic switch (Block 6)
connected to a spark tip (7) of the ignitor, characterized in that the triggering
circuit comprising a digital counter and a transistor for triggering a silicon
controlled rectifier or a light activated silicon controlled rectifier, the controller
(EM 2) is presettable to control the charge rate of said high voltage capacitor
bank (C 5), and in that the controller is enabled to generate switch-on pulses
based on the charge-rate being measured by the counter for driving the
transistor which disables or enables the transformer based on the charge rate
data from the controller to control the energy level of each spark.

2. The ignitor as claimed in claim 1, wherein the input system comprising a
line-commutated rectifier unit (1) and an electronic switch module (2).
3. The ignitor apparatus as claimed in claim 1, wherein the high frequency
set up transformer (3) is a ferrite core transformer.
4. The ignitor as claimed in claim 1, wherein the high frequency rectifier unti
(4) consists of H F and H V diodes.
5. The ignitor as claimed in claim 1 wherein the capacitor bank (5) is
charged by said high frequency rectifier unit (4).
6. The ignitor apparatus as claimed in claim 1 wherein said electronic switch
(6) controls the discharge of the capacitor bank (C 5).
7. The ignitor apparatus as claimed in claim 6 wherein the controlled
discharge is supplied to the spark tip (7) which generates sparks of controlled
rate and variable energy based on types of fuels.

8. The ignitor apparatus as claimed in any of claims 1 to 7, optionally
comprising a dual power supply input of either 110 VAC/220 VAC which can be
housed in a compact housing and mounted directly on the pruematic actuator of
the ignitor without any flexible cable.
9. A process of achieving controlled spark rate and energy in an improved
ignitor apparatus of a boiler furnace as claimed in any of claims 1 to 7.
10. An improved ignitor apparatus for achieving controlled spark rate and
energy in a boiler furnace as substantially described and illustrated in the
specification and drawings.

An apparatus for controlling the number of spark and energy level of each spark
to efficiently ignite fuel in a boiler furnace, comprising an input system
connected to the Power Supply line of 220/110 AC, the output of which is
connected to a primary side of a high frequency transformer (Block 3); a high
frequency rectifier unit (Block 4) connected to a secondary side of said
transformer; a high voltage capacitor bank (C 5) connected to said high
frequency rectifier unit and to a high voltage electronic switch (Block 6)
connected to a spark tip (7) of the ignitor, characterized in that the triggering
circuit comprising a digital counter and a transistor for triggering a silicon
controlled rectifier or a light activated silicon controlled rectifier, the controller
(EM 2) is presettable to control the charge rate of said high voltage capacitor
bank (C 5), and in that the controller is enabled to generate switch-on pulses
based on the charge-rate being measured by the counter for driving the
transistor which disables or enables the transformer based on the charge rate
data from the controller to control the energy level of each spark.