FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A system and method for a maintenance-free point-on-wave circuit breaker
APPLICANT (S):
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR (S):
Vaidya Tushar and Namjoshi Yogendra; both of Crompton Greaves Ltd, CG Global R & D Center, Crompton Greaves Limited, Kanjur Marg, Mumbai 400 042, Maharashtra, India; both Indian Nationals.
PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION:
This invention relates to the field of electrical and electronics engineering.
Particularly, this invention relates to the field of switchgear equipment and controllers, thereof.
More particularly, this invention relates to a system and method for a maintenance-free point-on-wave circuit breaker.
BACKGROUND OF THE INVENTION:
The term 'switchgear', used in association with an electric power system, or grid, refers to a combination of electrical disconnects, switches, isolators, and/or circuit breakers used to isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults. This type of equipment is important because it is directly linked to the reliability of electricity supply and electrical load.
An effective form of switchgear is gas insulated switchgear (GIS). In a GIS, there are a plurality of electrical components where the conductors and contacts are insulated by pressurized sulfur hexafluoride gas (SF6).
Circuit breakers are one type of switchgear component. A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to interrupt continuity upon detection of a fault condition to immediately discontinue electrical flow. The circuit breaker must react to a fault condition; in low-voltage circuit breakers this is usually done within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged with pilot devices to sense a fault current and to operate a trip opening mechanism. The trip coil that releases the latch is usually energized by a separate battery, although some high-voltage circuit breakers are self-contained with current transformers, protection relays, and an internal control power source.
Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit; some mechanically-stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts. Small circuit breakers may be manually operated; larger units have coils to trip the mechanism, and electric motors to restore energy to the springs.
A trip coil is a type of solenoid in which the moving armature opens a circuit breaker or other

protective device when the coil current exceeds a predetermined value. A closing coil is adapted to shut the circuit breaker completely.
In its working mode, if a power surge occurs in the electrical system, the breaker will trip. This means that a breaker that was in the "on" position will flip to the "off' position and shut down the electrical power leading from that breaker. Essentially, a circuit breaker is a safety device. When a circuit breaker is tripped, it may prevent a fire from starting on an overloaded circuit; it can also prevent the destruction of the device that is drawing the electricity.
The aim of point-on-wave switching is to actuate the circuit breaker at a pre-determined point on a voltage waveform. This point-on-wave switching aims to minimize switching transients, over-voltages and current surges, thereby reducing the stress on equipment insulation. To achieve this, it requires a control device that receives a random command for circuit breaker operation, and synchronizes it with a reference signal, such that the circuit breaker operates at a specified point-on-wave (POW). This is achieved with the help of an electronic device i.e. controller along with circuit breaker.
The point-on-wave switching is also called as controlled switching or synchronous switching.
For achieving point-on-wave switching, according to the prior art, compensation resulting from: 1) DC voltage parameters; 2) mechanical switching time parameters; 3) SF6 pressure parameters; 4) air pressure parameters; 5) temperature parameters - are to be taking into consideration.
The values of supply sources may be different at a different instants, thereby resulting in aberrant point-on-wave switching, if the controller is not able to deduce the exact compensation calculation parameters. Thus, there may be possible loss of point-on-wave target under circumstances wherein parameters are not being exactly sensed or predicted or computed or retrieved.
Similar aberrations could occur even during close operation resulting in inaccurate point-on-wave switching.
Therefore, there is a need for a circuit breaker and associated controller which obviates the limitations of the prior art.
Power circuit breakers; typically, SF6 circuit breakers constitute a major business in the power systems' business. Other electrical equipment include transformer - power, instrumental and distribution along with isolators and other switches. Power is typically flown through transmission

lines at higher voltages to avoid losses starting from 400kV, 765kV, and now 1200kV. Transmission and distribution - both require switching (CLOSING and TRIPPING) of a circuit breaker. It is not preferred to have random switching - meaning closing or tripping of a circuit breaker at an unknown point on the waveform. For minimal transients on the system, the circuit breakers are to be used with point on wave functionality. For capacitive effects in transmission lines, the circuit breaker with said functionality also removes the requirement of pre-insertion impedances or PIR on the breaker.
Point-on-wave circuit breakers are installed with an electronic device that monitors the health of the circuit breaker and takes in the command from a user in order to CLOSE or TRIP the breaker on the point-on-wave of a reference voltage or current. The point-on-wave is also called as synchronous switching of controlled switching.
The point-on-wave controllers bank on data required to compensate the parameters, disclosed earlier. An SF6 circuit breaker is operated, typically, through a DC coil that acts as a trigger to the circuit breaker mechanism. Typically, there are two trip coils and one close coil per each circuit breaker pole or per phase. All the coils are driven by DC voltage source. This DC voltage source determines the time required by DC coil to activate the mechanism and hence the total time predictable to CLOSE or TRIP a breaker's pole.
The SF6 circuit breaker is also dependant on the pressure of two gases - Air and SF6. Based on the pressure, its mechanism requires certain amount of time for actuation. Furthermore, the switching phenomenon is largely based on the angles at which the phases are CLOSED or TRIPPED. This means that the sequence and angles of switching of phases for a specific load is important. As discussed, the capacitive load requires closing on the voltage peak when the current is zero per each phase. New applications are being researched that adapt to different angles, dynamically, based on load type. Thus, the overall circuit breaker for point-on-wave switching is largely dependent on parameters such as DC voltage for coil, SF6 pressure, air pressure, load type, frequency of the reference phase, and the like.
One of the challenges relates to manual calibration for compensation factors. The manual calibration of a circuit breaker erected on a shop floor followed by calibration on site is done in existing controllers. The controller without signal processing relies on X-Y linear calibration. The linearity of the circuit breaker against a single parameter is itself not repeatable across different circuit breakers. Hence, manual calibration does not really guarantee point-on-wave switching on future commands.

Also, the manual calibration is further affected because of spikes during changeovers (switching of current / voltage) and is generally taken as first spike for close and last spike for open as gold standard. The method of calibration of compensation tables is discussed below. The parameter, say P, affects the breaker in its nominal range in positive slope or negative slope as far as the linear calibration process is concerned. For example, the parameter PI which is instantaneous DC voltage of the coil under operation rates from 75% up to 120% of the operating voltage. Approximately, 4-5 values are used in the prior art that states the voltage on X-axis and corresponding time required to switch the breaker on Y-axis. This is depicted in Table 1. Similarly, other parameters are input keeping the rest maintained. This takes a long time for calibration and is sometimes approximate in nature. It is notable that each circuit breaker mechanism and material, that may be supplied by different vendors following different manufacturing processes, may have slightly varying characteristics. However, this slight difference is large enough for an accuracy window of+1 msec point-on-wave switching.
Table 1: DC Voltage Compensation

Sr. No. Voltage Close Coil (Vdc) R close (msec) Y close (msec) B close (msec)
1 154 82 83 79
2 195 81 82 78
3 220 80 82 77.5
4 240 79 81 77
The data shows that calibration of compensation parameters records the circuit breaker timing of make and break. Hence, for measuring this time, it is required to find the reaction of breaker to a trigger command. The trigger command is fed through the controller or the electronic device to the coil. Typically, this is a pulse of around 100 to 300 msec. The start of the pulse is recorded on an oscillogram (trigger) and changeovers of the current signal on respective phases are determined to be fed into compensation tables.
Figure 1 of the accompanying drawings illustrates voltage and current waveforms operated through a point-on-wave switching 400kV SF6 SP-PN circuit breaker: (a) shows the closing of the breaker on the voltage peak -ve; (b) shows the tripping of the break on voltage '45deg as required by a reactor load.
One of the challenges relates to harmonics on site. The circuit breaker also needs to be manually calibrated for the compensation and other parameters on the site. However, by and large, it has been observed that the source of three phase voltage and currents may have harmonics that impose multiple zero crossings that create hassles to a service team that services circuit breakers. Therefore, they resort

on standard three phase voltage sources such as Omicron ® that generates different voltage / current 3-phase 4-wire supply from a single phase voltage input. These wires also need to be tied put to the circuit breaker removing the existing connections through ground switches. Thus, such operation takes time and skilled labour efforts on the site which needs to be repeated, again, during planned annual calibration. Figure 2 shows the harmonics found during a testing on the shop floor while the crane was operated upon the same supply as that of the reference. There are multiple zero crossings in the waveform apart from absence of a fundamental frequency.
One of the challenges relates to idle time compensation. The compensations, as said earlier, also depends on the idle time of the circuit breaker. Typically, the circuit breaker can have spread of about 0.2msec of opening time over 65 days. This idle time needs calibration on the fly rather than waiting for annual maintenance. For this, adaptive technologies are developed that calculates the next probable point of closer / opening based on idle time if it occurs through auxiliary feedback contacts. However, it is required to analyse the breaking and making point of the breaker from the command that was issued.
OBJECTS OF THE INVENTION:
An object of the invention is to provide controlled switching or point-on-wave switching of circuit breaker.
Another object of the invention is to provide controller point-on-wave tripping of trip coils of circuit breaker.
Yet another object of the invention is to provide controller point-on-wave closing of close coils of circuit breaker
Still another object of the invention is to provide a fail-safe controlled switching of circuit breaker.
An additional object of the invention is to provide accurate command in relation to point-on-wave switching, taking into account various parameters that influence delays in command receipt and actual physical actuation of the circuit breaker.
Another additional object of the invention is to provide a controller with a circuit breaker, which controller provides accurate commands in relation to point-on-wave switching, taking into account various parameters that influence delays in command receipt and actual physical actuation of the circuit breaker.

Yet an additional object of the invention is to provide a power system with improved stability.
Still an additional object of the invention is to provide an adaptive controller adapted to compute and learn data in relation to delay in time of actuation of circuit breaker with respect to receipt of signal in order to achieve accurate point-on-wave switching.
Yet an additional object of the invention is to provide a controller which removes harmonics.
Still an additional object of the invention is to provide a controller wherein noisy reference inputs which results in multiple zero crossing and hence failures in point-on-wave switching are obviated.
Another additional object of the invention is to provide a controller which detects a phase that is available and uses it intelligently to achieve point-on-wave switching.
Yet another additional object of the invention is to provide a controller which has a capability to achieve point-on-wave switching and which controller reduces stresses in an unbalanced grid.
Still another additional object of the invention is to provide a controller which has a capability to achieve point-on-wave switching and which controller reduces stresses in a noisy grid.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a system for a maintenance-free point-on-wave circuit breaker, said circuit breaker comprising a plurality of parameters per at least a pole, said circuit breaker comprising a controller adapted to provide at least a control signal for actuation of said circuit breaker, said control signal being adapted to compensate for at least a computed switching time difference, system comprises:
a. a parameter defining module adapted to define parameters which affect said circuit breaker
actuation timings in response to said at least a control signal;
b. a pole defining means adapted to define number of poles and to identify each pole in relation to
said circuit breaker, each pole being affected by each of said defined parameters;
c. an acquisition module adapted to acquire time delays in relation to each selected parameter per
defined pole;
d. a current sensing means and a voltage sensing means adapted to sense current values and
voltage values, respectively, across said controller and further adapted to store sensed current
values and sensed voltage values as a function of time;

e. a wavelet transformation means adapted to apply wavelet transform method to sensed current
values (as a function of time) and sensed voltage values (as a function of time) in order to
obtain wavelet transformed current values (as a function of time) and wavelet transformed
voltage values (as a function of time), respectively;
f. plotting means adapted to plot graphs in relation to: said sensed current values (as a function of
time); said sensed voltage values (as a function of time); said wavelet transformed current
values (as a function of time); and said wavelet transformed voltage values (as a function of
time);
g. acquisition module further comprising a changeover detecting means adapted to detect at least
a current changeover value (as a function of time), which value is the value determined by a
first major intersection of plotted sensed current values (as a function of time) and plotted
wavelet transformed current values (as a function of time);
h. acquisition module further comprising a peak and zero detecting means adapted to detect at least a voltage peak value (as a function of time), which value is the value determined by the first major intersection of plotted wavelet transformed voltage values (as a function of time) and plotted current waveform (as a function of time); and
i. computation means adapted to compute switching time difference by computing a difference in values of said current changeover value (as a function of time) and said voltage peak value (as a function of time).
Typically, said system comprises a parameter defining module adapted to define at least a parameter selected from a group of parameters consisting of DC voltage parameter; SF6 pressure parameter; Air pressure parameter; ambient temperature parameter; frequency parameter; and the like.
Typically, said system comprises a first selection means adapted to select one parameter at a time, for use by said system.
Typically, said system comprises a second selection means adapted to select one pole at a time, for use by said system.
Typically, said plotting means comprises further means adapted to plot said graphs per parameter per pole or per selected parameter per selected pole.
Typically, said system comprises a database means adapted to store: said sensed current values (as a function of time); said sensed voltage values (as a function of time); said wavelet transformed current

values (as a function of time); said wavelet transformed voltage values (as a function of time); said current changeover value(s) (as a function of time); and said peak voltage value(s) (as a function of time); each of said values adapted to be recalled during issuance of control signal by said controller.
Typically, said system comprises a polynomial curve fitting means adapted to provide curve fitting of at least a 4th order for each of said values in order to have plotted values in order to increase accuracy of said.
Typically, said system comprises an iteration means adapted to read each of said values at pre-defined intervals, which values are correlated to time delay per parameter per pole.
Typically, said system comprises a harmonics' removal means adapted to remove harmonics from said sensed current values and a current waveform, thereof, and from said sensed voltage values and a voltage waveform, thereof before being processed upon by said wavelet transformation means.
Typically, said system comprises a harmonics' removal means adapted to remove harmonics from said sensed current values and a current waveform, thereof, and from said sensed voltage values and a voltage waveform, thereof before being processed upon by said wavelet transformation means, said harmonics' removal means comprising: j. a transformation means for converting co-ordinate axis from a three phase axis to a two phase
axis; k. a filter means for allowing only 0 Hz signal (and corresponding values) to pass through its
output, thereby obtaining a harmonic's removed signal (and corresponding values);
1. an inverse transformation means for converting co-ordinate axis from a two phase axis to its
original three phase axis.
Preferably, said system comprises a harmonics' removal means adapted to remove harmonics from said sensed current values and a current waveform, thereof, and from said sensed voltage values and a voltage waveform, thereof before being processed upon by said wavelet transformation means, said harmonics' removal means comprising: m. a Park transformation means for converting co-ordinate axis from a three phase axis to a two
phase axis; n. a Low Pass filter means for allowing only 0 Hz signal (and corresponding values) to pass
through its output, thereby obtaining a harmonic's removed signal (and corresponding values);
and

o. an inverse Park transformation means for converting co-ordinate axis from a two phase axis to its original three phase axis.
Typically, said system comprises a harmonics' removal means adapted to remove harmonics from said sensed current values and a current waveform, thereof, and from said sensed voltage values and a voltage waveform, thereof before being processed upon by said wavelet transformation means, said harmonics' removal means comprising a synchronous reference frame transform means.
Preferably, said wavelet transformation means is adapted to apply wavelet transform method to sensed current values (as a function of time) and sensed voltage values (as a function of time) in order to obtain wavelet transformed current values (as a function of time) and wavelet transformed voltage values (as a function of time), respectively, further comprises use of Mexican Hat wavelet of 6th order for wavelet transform of said sensed current values (as a function of time) for achieving a first predominant zero crossing that is equal to a current changeover value.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:
Figure 1 of the accompanying drawings illustrates voltage and current waveforms operated through a
point-on-wave switching 400kV SF6 SP-PN circuit breaker: (a) shows the closing of the breaker on
the voltage peak -ve; (b) shows the tripping of the break on voltage 45deg as required by a reactor
load;
Figure 2 shows the harmonics found during a testing on the shop floor while the crane was operated upon the same supply as that of the reference;
Figure 3 shows the currents of R, Y, B phases switched in a sequence that is required by a Reactor load;
Figure 4 of the accompanying drawings illustrates a denoising application of wavelet transform in case of CLOSE of circuit breaker pole (current changeover);
Figure 5 illustrates an application of continuous wavelet transform to B phase current and checking the first transition of current at the second dominant zero crossing of transformed signal;
Figure 6 illustrates an application of continuous wavelet transform to B phase current and checking the first transition of current at the second dominant zero crossing of transformed signal followed by

finding the nearest peak of the voltage to find the error;
Figure 7 illustrates an application of continuous wavelet transform to B phase current and checking the first transition of current at the second dominant zero crossing of transformed signal followed by finding the nearest peak of the voltage to find the error;
Figure 8 illustrates a schematic of the system and method for a maintenance-free point-on-wave circuit breaker;
Figure 9 illustrates a post signal processing tool (POS) of the system and method of Figure 8; and Figure 10 illustrates a schematic block diagram for the harmonics' removal means.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a system and method for a maintenance-free point-on-wave circuit breaker. The system and method of this invention is a part of a controller of the circuit breaker which provides control signals for actuation of the circuit breaker. A circuit breaker may be a single pole circuit breaker, a double pole circuit breaker, or a multi-pole circuit breaker.
Typically, a circuit breaker is dependent on various parameters which contribute towards time delay of actuation, which time delay is the difference in signal reception and physical actuation of circuit breaker components in terms of its intended action of closing or tripping. Particularly, this time delay may have two components: 1) rated time delay; and 2) instantaneous time delay. This instantaneous time delay is dependent on the various parameters which include the following:
1) DC voltage parameter;
2) SF6 pressure parameter;
3) Air pressure parameter;
4) ambient temperature parameter;
5) frequency parameter; and the like.
Hence, there is provided a controller, according to this invention, in order to compensate for the time delay by sensing / computing / predicting the time delay based on empirical data and to issue a command signal (upon detection of fault) to a circuit breaker having compensated for the time delay.
Figure 8 illustrates a schematic of the system and method for auto-calibration of a circuit breaker for point-on-wave switching. Figure 9 illustrates a post signal processing tool (POS) of the system and method of Figure 8.

In accordance with an embodiment of this invention, there is provided a parameter defining module (PRDM) adapted to define parameters which affect circuit breaker actuation timings in response to controller signals which are adapted to actuate the circuit breaker. The various parameters include the following:
1) DC voltage parameter;
2) SF6 pressure parameter;
3) Air pressure parameter;
4) ambient temperature parameter;
5) frequency parameter; and the like.
Each parameter is a dimension which has its own effect over circuit breaker. Each parameter affects each pole of a circuit breaker.
Typically, there is provided a first selection means (SMI) adapted to select one parameter at a time, for use by the system and method of this invention.
In accordance with another embodiment of this invention, there is provided a pole defining means (PLDM) adapted to define number of poles and to identify each pole in relation to the circuit breaker. Each pole of the circuit breaker is affected by the defined parameters. Hence, calibration of each pole needs to be done, continuously, in order to judge time delays in actuation and receipt of control signal.
Typically, there is provided a second selection means (SM2) adapted to select one pole at a time, for use by the system and method of this invention.
In accordance with yet another embodiment of this invention, there is provided an acquisition module (AQM) adapted to acquire time delays in relation to each selected parameter per defined pole. The acquisition module further comprises a current sensing means (CSM) and a voltage sensing means (VSM) adapted to sense current values (CV) and voltage values (VV), respectively, across the controller and store sensed current values and sensed voltage values as a function of time.
In accordance with still another embodiment of this invention, there is provided a wavelet transformation means (WTM) adapted to apply wavelet method to sensed current values (as a function of time) (CV) and sensed voltage values (as a function of time) (VV) in order to obtain wavelet transformed current values (as a function of time) (TCV) and wavelet transformed voltage values (as a function of time) (TVV).

The wavelet transform of the wavelet transformation means (WTM) is a signal post-processing tool (POS) for detection of edges, changeovers, sharp patterns, performing denoising of the signal, removal of slow moving offsets, compression of the signal for transmission and storage and many more. All of them are required in the current invention of a point-on-wave switching, because the acquired waveform has a lot of switching noise and may have DC offset at the time of switching. All time domain signal processing methods prove less beneficial due to noise and DC offset. The promise of a wavelet is based on transforming the signal into a domain that has interpolation along with time resolution. This is otherwise called as multi-resolution analysis (MRA) and is more efficient than a single domain signal processing such as Fast Fourier Transform (FFT).
Another benefit of the transform is because of its simple mathematics nature that is based on interpolation and can be incorporated in the digital signal processor (DSP) of the electronic device.
Figure 4 of the accompanying drawings illustrates a denoising application of wavelet transform in case of CLOSE of circuit breaker pole (current changeover).
The acquisition module (AQM) further comprises a plotting means (PM) adapted to plot graphs in relation to: 1) sensed current values (as a function of time); 2) sensed voltage values (as a function of time); 3) wavelet transformed current values (as a function of time); and 4) wavelet transformed voltage values (as a function of time). These graphs are plotted per parameter per pole or rather per selected parameter (by means of SMI) per selected pole (by means of SM2).
The acquisition module (AQM) further comprises a changeover detecting means (CDM) adapted to detect at least a current changeover value (as a function of time) (CCV), which value is the value determined by the first major intersection of plotted sensed current values (as a function of time) and plotted wavelet transformed current values (as a function of time). The current changeover value is
tjnstant-
The changeovers in the current waveform (sensed current values) are majorly affected with DC offset and spikes although may be minimum because of the point-on-wave switching. A sample data of different phase current signal via a non-serviced SF6 circuit breaker is taken up just to simulate the case. Figure 3 shows the currents of R, Y, B phases switched in a sequence that is required by a Reactor load.
The clean changeover can be easily detected ideally by dA/dT method where dA is the change in the

current over the samples or sample time dT. However, this method process is inefficient in noisy conditions leading to detection of multiple changeovers. Furthermore, an intelligent system and method needs to be appended to the dA/dT signal that may be cumbersome.
Figure 5 illustrates an application of continuous wavelet transform to B phase current and checking the first transition of current at the second dominant zero crossing of transformed signal.
Inside the wavelets there are many methods to detect changeovers and patterns. The continuous wavelet transform in 1-dimension is particularly useful as it speaks about the time resolution of the transformed signal using analyzing wavelet. The system and method of this invention has utilized the continuous wavelet transform of a current signal using Mexican Hat wavelet of 6th order which provides a first predominant zero crossing that is equal to the changeover. This post processing enables non real-time comfort zone. Ideally, a power circuit breaker does not switch again in few milliseconds, unless it is a protection trip which is either bypassing the point-on-wave switching or the controller itself.
The acquisition module (AQM) further comprises a peak and zero detecting means (PZDM) adapted to detect at least a voltage peak value (as a function of time) (VPV), which value is the value determined by the first major intersection of plotted wavelet transformed voltage values (as a function of time) and plotted current waveform (as a function of time). The voltage peak value is tactual.
The error in the point-on-wave switching is the time difference between the changeover instant of the current i.e. the instant at which the current starts or stops and the angle on the voltage waveform of the respective phase. This means if the breaker needs to CLOSED at the voltage peak (positive or negative) the current must start at this point in time resolution. With a reactive load, the current is normally at zero when there is a voltage peak. The important performance criterion of the point-on-wave switching circuit breaker is achieving + lmsec. This needs to be measured and stored on every switching event For this, the voltage zero/peak and further the angle required needs to be processed to find the exact error. The wavelet transform helps here with its inherent properties of finding the zero crossing or peaks (slope zero). The system and method of this invention use odd Gaussian wavelet of the 6th order and the same continuous wavelet transform to find the zero and peak of the voltage signal. After finding a peak or zero, respective time is added or subtracted to get the instant ( tideal) on which the current is supposed to make a changeover. The sample instant at which the changeover (tactual) takes place gives the error during the switching event.

Figure 6 shows how two transforms can be used to find the t ideal and tactual as shown as marked. The Mexican Hat wavelet (pink waveform) helps to get the changeover instant (current changeover value) and the odd Gaussian wavelet help to get the peak of the voltage (voltage peak value) and hence the ideal instant. The sampling time of the signal can be further increased to decrease the resolution error after the transformation.
Figure 6 illustrates an application of continuous wavelet transform to B phase current and checking the first transition of current at the second dominant zero crossing of transformed signal followed by finding the nearest peak of the voltage to find the error.
Figure 7 illustrates an application of continuous wavelet transform to B phase current and checking the first transition of current at the second dominant zero crossing of transformed signal followed by finding the nearest peak of the voltage to find the error.
In accordance with an additional embodiment of this invention, there is provided a computation means (CPM) adapted to compute switching time difference. The time difference between tactual and ttrigger gives the switching time for the breaker CLOSE or TRIP based on the compensation parameters that may be changed. The switching time difference is calibration data per compensation parameter per pole. Multiple such calibration data is taken and stored and later retrieved during actual control signal command by the controller. The complete record is stored and Table 1 can be populated by modifying DC voltages to the system. Minor addition hardware is required to regulate the parameters that are required to be populated. Any hardware design can take care of modifying these parameters.
In accordance with yet an additional embodiment of this invention, there is provided a database means (DB) adapted to store: 1) sensed current values (as a function of time); 2) sensed voltage values (as a function of time); 3) wavelet transformed current values (as a function of time); 4) wavelet transformed voltage values (as a function of time); 5) current changeover value(s) (as a function of time); and 6) peak voltage value(s) (as a function of time). This results in a set of values to be recalled during issuance of control signal by the controller.
In accordance with still an additional embodiment of this invention, there is provided a polynomial curve fitting means (PCFM) adapted to provide curve fitting of at least a 4th order to the read values in order to have plotted value in order to increase accuracy of the system and method of this invention. The polynomial curve fitting means is adapted to plot corresponding curves for the values of the database means.

In accordance with an additional embodiment of this invention, there is provided an iteration means (IM) adapted to read values at pre-defined intervals, which values are correlated to time delay per parameter per pole. The iteration means further learns, iteratively, and stores the values in the database means (DM), in an updated manner.
In accordance with still an additional embodiment of this invention, there is provided a harmonics' removal means (HRM) adapted to remove harmonics from the current waveform and the voltage waveform before being processed upon by wavelet transformation means (WTM). Fourier transform based techniques provide one method for individual harmonic isolation, but it requires a minimum of two cycles of data for the analysis, and does not perform well in the presence of sub-harmonics which are not integral multiples of the fundamental frequency and most importantly introduces phase shifts. A phase delay is not allowable in the application where the accuracy of point-on-wave switching is of the levels of +1 msec. For this purpose, it is required to involve synchronous reference frame transform that will rotate the internal vector with the fundamental frequency without any delay. The synchronous reference frame transform further improves the auto-calibration of the system and method of this invention.
Figure 10 illustrates a schematic block diagram for the harmonics' removal means (HRM).
The harmonics' removal means (HRM) comprises a transformation means (TM), typically a Park transformation means, for converting co-ordinate axis from a three phase axis to a two phase axis. It also provides a "rotating" reference frame, which is tuned at the system frequency.
The harmonics' removal means (HRM) further comprises a filter means (FM), typically a Low Pass Filter means, for allow only 0 Hz signal to pass through its output. Harmonics are thus removed and a clean signal is obtained.
The harmonics' removal means (HRM) comprises an inverse transformation means (ITM), typically an Inverse Park transformation means, for converting co-ordinate axis from a two phase axis to its original three phase axis.
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. A system and method for a maintenance-free point-on-wave circuit breaker, said circuit breaker comprising a plurality of parameters per at least a pole, said circuit breaker comprising a controller adapted to provide at least a control signal for actuation of said circuit breaker, said control signal being adapted to compensate for at least a computed switching time difference, system comprising:
a. a parameter defining module adapted to define parameters which affect said circuit
breaker actuation timings in response to said at least a control signal;
b. a pole defining means adapted to define number of poles and to identify each pole in
relation to said circuit breaker, each pole being affected by each of said defined
parameters;
c. an acquisition module adapted to acquire time delays in relation to each selected
parameter per defined pole;
d. a current sensing means and a voltage sensing means adapted to sense current values and
voltage values, respectively, across said controller and further adapted to store sensed
current values and sensed voltage values as a function of time;
e. a wavelet transformation means adapted to apply wavelet transform method to sensed
current values (as a function of time) and sensed voltage values (as a function of time) in
order to obtain wavelet transformed current values (as a function of time) and wavelet
transformed voltage values (as a function of time), respectively;
f. plotting means adapted to plot graphs in relation to: said sensed current values (as a
function of time); said sensed voltage values (as a function of time); said wavelet
transformed current values (as a function of time); and said wavelet transformed voltage
values (as a function of time);
g. acquisition module further comprising a changeover detecting means adapted to detect at
least a current changeover value (as a function of time), which value is the value
determined by a first major intersection of plotted sensed current values (as a function of
time) and plotted wavelet transformed current values (as a function of time);
h. acquisition module further comprising a peak and zero detecting means adapted to detect at least a voltage peak value (as a function of time), which value is the value determined by the first major intersection of plotted wavelet transformed voltage values (as a function of time) and plotted current waveform (as a function of time); and

i. computation means adapted to compute switching time difference by computing a difference in values of said current changeover value (as a function of time) and said voltage peak value (as a function of time).
2. The system as claimed in claim 1, wherein said system comprising a parameter defining module adapted to define at least a parameter selected from a group of parameters consisting of DC voltage parameter; SF6 pressure parameter; Air pressure parameter; ambient temperature parameter; frequency parameter; and the like.
3. The system as claimed in claim 1, wherein said system comprising a first selection means adapted to select one parameter at a time, for use by said system.
4. The system as claimed in claim 1, wherein said system comprising a second selection means adapted to select one pole at a time, for use by said system.
5. The system as claimed in claim 1, wherein said plotting means comprising further means adapted to plot said graphs per parameter per pole or per selected parameter per selected pole.
6. The system as claimed in claim 1, wherein said system comprising a database means adapted to store: said sensed current values (as a function of time); said sensed voltage values (as a function of time); said wavelet transformed current values (as a function of time); said wavelet transformed voltage values (as a function of time); said current changeover value(s) (as a function of time); and said peak voltage value(s) (as a function of time); each of said values adapted to be recalled during issuance of control signal by said controller.
7. The system as claimed in claim 1, wherein said system comprising a polynomial curve fitting means adapted to provide curve fitting of at least a 4th order for each of said values in order to have plotted values in order to increase accuracy of said.
8. The system as claimed in claim 1, wherein said system comprising an iteration means adapted to read each of said values at pre-defined intervals, which values are correlated to time delay per parameter per pole.

9. The system as claimed in claim 1, wherein said system comprising a harmonics' removal means adapted to remove harmonics from said sensed current values and a current waveform, thereof, and from said sensed voltage values and a voltage waveform, thereof before being processed upon by said wavelet transformation means.
10. The system as claimed in claim 1, wherein said system comprising a harmonics' removal means adapted to remove harmonics from said sensed current values and a current waveform, thereof, and from said sensed voltage values and a voltage waveform, thereof before being processed upon by said wavelet transformation means, said harmonics' removal means comprising:
j. a transformation means for converting co-ordinate axis from a three phase axis to a two
phase axis; k. a filter means for allowing only 0 Hz signal (and corresponding values) to pass through its
output, thereby obtaining a harmonic's removed signal (and corresponding values); and 1. an inverse transformation means for converting co-ordinate axis from a two phase axis to
its original three phase axis.
11. The system as claimed in claim 1, wherein said system comprising a harmonics' removal
means adapted to remove harmonics from said sensed current values and a current waveform,
thereof, and from said sensed voltage values and a voltage waveform, thereof before being
processed upon by said wavelet transformation means, said harmonics' removal means
comprising:
m. a Park transformation means for converting co-ordinate axis from a three phase axis to a
two phase axis; n. a Low Pass filter means for allowing only 0 Hz signal (and corresponding values) to pass
through its output, thereby obtaining a harmonic's removed signal (and corresponding
values); and o. an inverse Park transformation means for converting co-ordinate axis from a two phase axis
to its original three phase axis.
12. The system as claimed in claim 1, wherein said system comprising a harmonics' removal
means adapted to remove harmonics from said sensed current values and a current waveform,
thereof, and from said sensed voltage values and a voltage waveform, thereof before being

processed upon by said wavelet transformation means, said harmonics' removal means comprising a synchronous reference frame transform means.
13. The system as claimed in claim 1, wherein said wavelet transformation means being adapted to apply wavelet transform method to sensed current values (as a function of time) and sensed voltage values (as a function of time) in order to obtain wavelet transformed current values (as a function of time) and wavelet transformed voltage values (as a function of time), respectively, further comprises use of Mexican Hat wavelet of 6th order for wavelet transform of said sensed current values (as a function of time) for achieving a first predominant zero crossing that is equal to a current changeover value.