FIELD OF THE INVENTION
This invention relates to a new microcontroller based firing card tester for Electro
Static Precipitator power control to test a firing card.
BACKGROUND OF THE INVENTION
Electrostatic precipitator is used for collecting fly ash from flue gas in a thermal
power plant. This reduces pollution of the atmosphere. A pair of thyristors
connected back to back with a step-up transformer and rectifier is used to feed
power to an electrostatic precipitator. Firing card is a circuit (electronic card)
that is used to interface the high voltage, high current thyristors to low power
microprocessor based Electro Static Precipitator controllers. The proper
operation of the firing card is essential to avoid failure of high power thyristors
and transformer. The present invention is related to remove the above prior art
disadvantages by exhaustively testing the firing card prior to its commission and
automating the testing of the cards to reduce the testing cycle time at
manufacturing and installation stages.
DESCRIPTION OF THE INVENTION
One objective of the invention is to provide a programmed microcontroller based
tester adapted and interfaced with a developed firing card under test with a
dummy load equivalent to a typical thyristor gate current.
Another objective of the invention is to generate required input signals for firing
card under test so that it is subjected to various test conditions.
A still another objective of the invention is to check the output signal of the firing
card, given to the dummy load and validate it automatically.
A yet another objective of the invention is to safeguard the firing of thyristors
and thus to prevent failure of primary windings of a high voltage transformer
which supplies power to the electrostatic precipitator.
A still yet another objective of the invention is to develop a smart firing card
tester with programmed microcontroller to generate variable duty cycle of a
pulse width modulated signals, simulating error conditions to ensure the non-
generation of any spurious output pulses from the firing card.
According to the invention there is provided a smart firing card tester for
Electrostatic Precipitator power control to test a firing card comprising a
microcontroller to generate a pair of Pulse width modulated signals synchronous
with the mains supply and out of phase with each other, an in-built dummy load
equivalent to a typical thyristor gate current, wherein the output signals of the
firing card under test are fed back to the feedback input of the tester, the signals
of the dummy load being checked and validated by the microcontroller to
indicate various test condition through LED indicators.
The present invention will be better understood from the following description
with reference to the accompanying drawings in which
Figure 1 relates to a schematic diagram of the conventional firing card
testing arrangement with thyristor and standard Electro
Static Precipitator controller,
Figure 2 relates to smart card firing card tester
set up according to the invention and
Figure 3 shows the developed smart card tester
according to the present invention.
In the conventional method of testing (Fig. 1), the output of the firing card (04)
under test has to be verified manually to validate its proper operation. Any
intermittent or partial defect of the firing card may not be reflected in the test
results. As a result, failure in one of the two output signals (03) in the firing card
circuit, can lead to single thyristor (01) firing. This will lead to the magnetic core
saturation and heavy rush of current, which may cause failure of thyristors as
well as primary winding of the high voltage transformer that supplies power to
the electrostatic precipitator.
In the conventional method firing card test setup, standard Electro Static
Precipitator controller (05), a firing card under test (04), high power thyristors
(01) and a dummy resistive (lamp) load (02) are connected. The card is tested
by manually varying the controller knob (06) for output current from minimum to
the maximum value and observing the brightness of the brightness of the lamp
(02).
The test setup (Fig. 1) requires many discrete components to test the firing card.
Also, manual tuning of controller and observation of the output of the card is a
time consuming task.
In Figure 2 the Smart firing card tester (12) is a compact and portable device as
shown in detail in Figure 3 which is used to test firing cards exhaustively. The
tester is a microcontroller-based system that generates various test conditions
(required input signals for firing card under test) to validate the firing card. The
tester gives a pair of Pulse width modulated signals (PWM) [(14) and (15)]
synchronous with the mains supply and out of phase with each other. These
signals are fed to the firing card under test (04). With this input, the firing card
generates the triggering pulses for the thyristors. These triggering pulses (11)
are fed back to the tester. The tester has in-built dummy load (10) equivalent to
a typical thyristor gate current. A sample of the signals from the dummy load is
taken for validation of the operation of the firing card.
The microcontroller (13) in the firing card tester (12) is programmed to vary the
duty cycle of the pair of pulse width modulated signals (14) & (15) in increasing
and decreasing order in a definite duration in automatic mode. The firing card
(04) is supposed to generate the triggering pulses (11) consistent with these
input signals. This is verified by the firing card tester.
The tester also simulates error conditions by blocking PWM-1 (14) signal and
applying PWM-2 (15) to the input of the firing card under test. The firing card
(04), at this time, is expected to sense the error at the input and block both its
output pulses (11). The tester (12) verifies that there is no feedback signal from
the firing card. This test condition is repeated by blocking PWM-2 (15) and giving
PWM-1 (14).
The Smart firing card tester (12) generates another error condition by giving
both the PWM signals (14) & (15) in phase with each other and expects the firing
card to stop output pulses. It also verifies that when no input signal is given to
the firing card under test (04), it does not generate any spurious output pulses.
The tester validates the firing card under test with all the above test conditions
and gives the test result as 'PASS' if it fulfills the test requirements and TAIL'
otherwise.
The Smart firing card tester indicates the various test conditions and results with
respective LED indicators (08) via the microcontroller (13). An incandescent lamp
(09) is provided on the Smart Firing card tester (12) so that the variation in
intensity of light gives a visual indication of the operation of the firing card.
The invention as narrated herein with respect to an embodiment of the invention
should not be read and construed in a restrictive manner as various alterations,
changes and modifications are possible within the scope and limit of the
invention as defined in the encampused appended claims.
WE CLAIM
1. An automated device (12) for testing a firing card interfacing at least one
pair of high voltage, high current thyristors, the at least one pair of
thyristors connected to a step-up transformer and a rectifier for feeding
power to a plurality of low-power controllers of an Electrostatic
Precipitator, the device comprising :
- a microcontroller (13) operably connected to the firing card under
test, the microcontroller (13) is enabled to generate a pair of pulse
width modulated signals (PWM-14 and 15), with varying duty cycle
in an increasing and decreasing order at a predetermined duration,
the pair of pulse width modulated signals (PWM-14 and 15) being
synchronous with the mains supply but out-of-phase with each
other;
- the firing card receiving the input signals (PWM-14 and 15) from
the microcontroller (13) and generating triggering pulses
corresponding to the input signal;
- a dummy load (10) configured to a gate current corresponding to
that of the pair of thyristor the dummy load (10) receiving the
triggering signals (PWM-14 and 15) from the firing card and
processing the signal values in respect of those of the stored gate
current values, and feeding back to the microcontroller (13) for
validation;
- a plurality of indicators in the form of high emitting diodes (LEDs)
connected to the microcontroller (13), the LEDs receiving the
validation data from the microcontroller (13), and indicating various
test conditions and results in respect of the firing card under test.
2. The device as claimed in claim 1, wherein the various test conditions and
results generated by the microcontroller (13) in order to validate the firing
card constitute a 'PASS' or 'FAIL' indication through the LEDs.
3. The device as claimed in claim 1, wherein the microcontroller (13) is
enabled to simulate error conditions by blocking the first PWM signal
(PWM-14), and simultaneously inputting the second PWM signal (PWM-2)
to the firing card such that the firing card senses the error in the input,
and blocks both the outputable triggering signals.
4. The device as claimed in claim 1 or 3, wherein the microcontroller (13) is
further enabled to stimulate error condition by blocking the second PWM
signal (PWM-15) and simultaneously inputting the first PWM signal (PWM-
14) such that the firing card senses the error in the input, and blocks both
the outputable triggering signals.
5. The device as claimed in claim 1, wherein both the PWM signals (PWM-14
and 15) are inputted from the microcontroller (13) to the firing
card but the inputted signal being in-phase, and wherein the firing card is
enabled to sense the error in the transmitted signals and stop outputting
any triggering signals.
6. The device as claimed in any of preceding claims wherein the
microcontroller (13) is enabled to detect whether or not the firing card
erroneously generating any spurious output pulses when no input signal is
fed to the firing card under test.
7. The device as claimed in claim 1, wherein an incandescent lamp (09) is
connected to the dummy load (10) which visibly provides a varying
intensity in registration with the operating conditions of the firing card
under test.
8. An automated device for testing a firing card interfacing at least one pair
of high voltage, high current thyristor as substantially described and
illustrated herein with reference to the accompanying drawings.

This invention relates to an automated device for testing a firing card (12) which
generates the required input signal for firing card under test (04). The
preprogrammed microcontroller (13) in it provides continuous variation of input
signal [14] and [15] automatically. The output of the firing card (04) is fed to the
feedback input (11) of the smart firing card tester (12) which appears across a
dummy load (10). The microcontroller (13) checks the signal given to this
dummy load and validates it.