F O R M 2

THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)

1. Title of the invention : METHOD TO DETECT PARALLEL ARCING OF A CIRCUIT BREAKER TO PREVENT RE-STRIKING

2. Applicant(s):

(a) NAME : LARSEN & TOUBRO LIMITED

(b) NATIONALITY : An Indian Company.

(c) ADDRESS : L & T House, Ballard Estate, Mumbai 400 001, State of Maharashtra, India

3. PREAMBLE TO THE DESCRIPTION

The following specification particularly describes the invention and the manner in which it is to be performed:

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to a method of circuit protection and more particularly to a method to detect parallel arcing of a circuit breaker to prevent re-striking during the opening of contacts using a numerical relay under a predefined condition.

BACKGROUND AND THE PRIOR ART

In a power system, protection relay plays an important role for proper and uninterrupted functioning of the healthy section of the system. The main objective of the protection relay is detection and tripping/blocking of the breaker, depending upon the application, in order to isolate the faulty section of the system from the healthy part.

It is very important to provide protection for parallel arcing of a circuit breaker which may result in damage to the entire circuit. There are a number of prior arts in the related field of invention as provided below:

US2008180866 (A1) provides a method for detecting electrical arcing in an alternating current power line, comprising the steps of producing a digital signal indicative of a presence of high frequency variations in the alternating current power line; analyzing the digital signal for the presence of at least two different criteria indicative of potential electrical arcing in the alternating current power line; and generating an arc fault signal when at least two of the at least two different criteria indicative of potential electrical arcing are determined to be present in the digital signal. It provides a combined arc fault circuit interrupter and leakage current detector interrupter. A current sensor, amplifier, and comparator are employed to detect the presence of leakage current in alternating current power conductors. Upon the detection of an amount of current leakage beyond a threshold level, a relay is opened, disconnecting a source of AC power from a power conductor being monitored, such as an appliance line cord. An arc sensor, envelope detector, amplifier, and microcontroller are employed to detect the presence of an arc fault in the alternating current power conductors. The arc fault detection algorithm implemented by the microcontroller is capable of discriminating between high frequency noises which is not caused by a parallel or series arc fault, with high frequency anomalies which are the result of arcing.

CA2492262 (A1) provides a system for eliminating an arcing fault of power distribution equipment, said system comprising a first switch including a first input; a circuit interrupter electrically connected in series with said first switch; a second switch including a second input, said second switch being electrically connected in parallel with the series combination of said first switch and said circuit interrupter; and a circuit adapted to detect said arcing fault and responsively output a first signal to the first input of said first switch to close said first switch and, also, responsively output after a predetermined time a second signal to the second input of said second switch to close said second switch.

US2004165322 (A1) provides for relay arcing protection arrangement for a relay of a type including an electromagnetic coil adapted to be connected to a control circuit and effect an opening or closing of at least two electrically conducting contactors in response to a transition signal from the control circuit, including electronic circuit means to detect arcing across the contactors, and to effect activation of a solid state current connection means providing a parallel current pathway to the electrical connectors when arcing is detected during such a selected period of time after activation.

US5548466 (A) is directed to a system for sensing fault current flowing through a person who touches an exposed conductor in a cable connecting a machine to a power distribution center wherein the power distribution center has a number of power cables for connecting a number of machines thereto. Each power cable has a different frequency impressed thereon by an oscillator which frequency is transmitted through an electrical path including the power center if the operator touches the fault. A sensing circuit for each cable is connected in the electrical path and tuned to only the frequency applied to that cable. When the sensing circuit detects that frequency, the sensing circuit interrupts power to the cable. If, for some reason, the sensing circuit fails to interrupt power to the cable, within a selected time interval of less than one-half second, a backup system interrupts power to the entire power center. In order to detect ground faults, the ground conductor in each cable is grounded to the power center's frame through a zener diode bank which is in parallel with a high pass capacitor connected thereto by a preventive resistor. The zener diode bank also suppresses inter-machine arcing should two machines touch or come into close proximity. In addition to ground faults, broken ground wires are detected by connecting each ground wire through a preventive resistor to a signal monitor. If a ground wire breaks, the signal monitor for that cable alerts the sensing circuit for that cable, and the sensing circuit interrupts power to the cable.

JP3098218 (A) suppress abnormal voltage generated at the time of circuit-breaking to a low level by defining a contact parting distance between a lightning electrode and a lightning movable electrode of an arrestor, kept within a certain distance for the period of time after the contact parting, while elongated long enough after that. When a fixed side arc contact and a moving side arc contact are parted with one another, and arc is generated between them, SF6 gas in a puffer cylinder is blasted to the arc, which is eliminated. At this time, between the respective contacts, abnormally high voltage of re-striking voltage is generated, which is suppressed by an arrester connected in parallel with the contacts. Since the contact parting distance B between a lightning electrode and a lightning movable electrode is set within 20mm, for the period of time from the contact parting until approximately 1/2 cycle of power source frequency passes by, surge current runs between the lightning electrode and the lightning movable electrode. After the approximately 1/2 cycle of the power source frequency passes by, the distance between the lightning electrode and the lightning movable electrode is further parted, whereby perfect circuit-breaking condition is achieved.

Although the given prior art provide method for detecting and preventing arcing, the method provided is complex and may not be accurate.

The present invention therefore provides a method to detect parallel arcing in a circuit breaker due to unhealthy condition of the breaker contacts. This document enunciates the concept of Breaker Re-strike and elucidates the settings and firmware logic to be incorporated for including the feature in the New Feeder Protection relay. This logic will be used in a numerical relay as a part of LV/MV switchboards. The algorithm will go as flow logic into the firmware build or embedded systems of the relay.

OBJECTS OF THE INVENTION

A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.

Another object of the present invention is to provide a method to detect parallel arcing of a circuit breaker to prevent re-striking during the opening of contacts using a numerical relay under a predefined condition.

Other object of the present invention is to prevent breaker re-strike under a predefined set of conditions.

Yet another object of the present invention is to provide a simple and accurate method to detect breaker re-strike condition.

These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

There is provided a method of circuit protection.

According to one embodiment of the present invention, there is provided method to detect parallel arcing of a circuit breaker to prevent re-striking during the opening of contacts using a numerical relay under a predefined condition, said method comprising the steps of: checking status of breaker re-strike function; receiving phase current as input; verifying zero cross detection for each phase current; comparing each phase current to predefined current nominal value and current pickup value; checking status for breaker tripping; verifying re-strike time delay and providing output status to breaker re-strike condition.

Other embodiment of the present invention provides for capturing current analog samples per cycle and converting into digitized form using an analog/digital converter; said digitized samples from said analog/digital converter fed to a data acquisition and metering section; output from said data acquisition and metering section further fed to a CPU controller where the protection algorithm logic is processed; said CPU controller further generating the flex logic operand.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In the appended drawings:

Fig 1 illustrates a method to detect parallel arcing of a circuit breaker to prevent re-striking during the opening of contacts using a numerical relay under a predefined condition.

Fig. 2 illustrates the protection algorithmic logic being processed in CPU controllers.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.

Reference is first invited to Fig 1 where the method to detect parallel arcing is shown. It shows different units like Data acquisition and metering section, CPU controller, Numerical relay etc.

Fig. 2 shows the processing of logic in the numerical relay. It provides different method steps used in detecting and preventing re-striking in a breaker.

The invention therefore provides a method to detect parallel arcing of a circuit breaker to prevent re-striking during the opening of contacts using a numerical relay under a predefined condition.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly the present invention provides a method to detect parallel arcing of a circuit breaker to prevent re-striking during the opening of contacts using a numerical relay under a predefined condition. It provides a method to detect parallel arcing in a circuit breaker due to unhealthy conditions of the breaker contacts.

This function is related to detection of re-striking condition in the breaker during the opening of contacts. Breaker re-strike is very critical as it can result to massive explosion of the breaker and eventually hazardous explosion in the switchboard. This logic will be used in a numerical relay as a part of LV/MV switchboards. The algorithm will go as flow logic into the firmware build or embedded systems of the relay.
This invention enunciates the concept of Breaker Re-strike and elucidates the settings and firmware logic to be incorporated for including the feature in the New Feeder Protection relay.

Figure 1 depicts the flow of the inputs /commands to the corresponding hardware of the numerical relay. There are numerous components in terms of embedded systems (hardware) in the numerical relay of which Data acquisition & metering and CPU controller are the two main sub sections of the relay. Initially the current transformer secondary inputs i.e. phase currents which are analog inputs are fed to the Analog/Digital (A/D) converter located inside the relay. The A/D converter captures the current analog samples per cycle and converts into digitized form. 64 samples / cycle are captured by the A/D converter. These digitized samples from A/D converter go into the Data acquisition and metering section of the numerical relay and further to the protection algorithm logic. The protection algorithm logic is installed in the CPU controller, in a coded form, which is embedded inside the relay. Through Data acquisition and metering section, the current inputs advance to CPU controller where the protection algorithm logic is processed.

Here in this present invention when breaker re-strike condition exists, the flex logic operand for breaker re-strike becomes high and the digital output of the relay (hardware) gives the command to the connected hardware depending upon the user and its application.
Re-strike is a phenomenon that may occur during the opening of circuit breakers. As the breaker’s electrodes separate, the dielectric medium of the circuit breaker starts to regain its strength. The withstanding voltage of the breaker is the maximum voltage that the breaker can withstand across its 2 terminals, without arcing. When the breaker contacts open its withstanding voltage increases at a near-linear rate. At the same time, the voltage across the contacts builds up in accordance with the nature of the switching event and the system characteristics. If the voltage buildup exceeds the regained withstand voltage at any instance, an inter electrode breakdown occurs, and arc current is produced, this is known as re-strike.
The withstanding voltage is assumed to be linearly increasing to the insulation level of the breaker. In case 1, the contacts voltage buildup never exceed the withstanding voltage of the breaker, thus re-strike does not occur. In case 2, the voltage buildup exceeds the withstanding voltage at time ts, and re-strike occurs. In the event of re-strikes, excessive overvoltage and high dv/dt is produced. These transients can potentially be damaging to loads, cable and equipment.

The IEEE standard for Breaker re-strike is C37:100. As per this standard, re-strike is “resumption of current between the contacts of a switching device during an opening operation after an interval of zero current of ¼ cycle at normal frequency or longer”.

Settings:-

Breaker Re-strike feature(Enabled/Disabled)
Re-strike pickup(0.05 to 2 times of the nominal current in steps of 0.01 , default=0.3)
Re-strike time delay(0 to 50 seconds in steps of 0.01 secs)
Flex logic elements needs to be added (BKR RE-STRIKE PKUP, BKR RE-STRIKE OP, BKR RE-STRIKE DPO for all 3 phases)

Inputs:-
a)Breaker status(open)
b)Phase currents(Ia,Ib,Ic)
c)Is the feature enabled ?

Outputs:-
Flex logic operand becomes high/low depending on the value of the value in the register map based on algorithm flow logic output.

If the breaker status is found to be open and if there is a detection of high frequency current for a short duration after zero crossing detection of the current waveform, the algorithm defines it as a Breaker re-strike condition.

Abbreviations used:

HMI: Human machine interface
CPU: Central processing unit
A/D: Analog to digital
BKR: breaker
PKUP: pickup
OP: operate
DI: digital input
ZCD: zero crossing detection
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

WE CLAIM

1. A method to detect parallel arcing of a circuit breaker to prevent re-striking during the opening of contacts using a numerical relay under a predefined condition, said method comprising the steps of: checking status of breaker re-strike function (Enable/Disable); receiving phase current as input; verifying zero cross detection for each phase current; comparing each phase current to predefined current nominal value and current pickup value; checking status for breaker tripping; verifying re-strike time delay and providing output status to breaker re-strike condition.

2. Method as claimed in claim 1 comprising further steps of capturing current analog samples per cycle and converting into digitized form using an analog/digital converter; said digitized samples from said analog/digital converter fed to a data acquisition and metering section; output from said data acquisition and metering section further fed to a CPU controller where the protection algorithm logic is processed; said CPU controller further generating the flex logic operand.

3. Method as claimed in claim 2 wherein said CPU controller processing protection algorithm logic providing output status for breaker re-strike operation.

4. Method as claimed in claim 1 wherein setting for breaker re-strike status, re-strike pickup time and re-strike time delay is provided to said numerical relay to detect parallel arcing.

5. Method as claimed in claim 1 further comprising a step wherein after said zero cross detection on detecting a high frequency current, output status to said breaker re-strike condition gets enabled.

6. A method to detect parallel arcing of a circuit breaker to prevent re-striking during the opening of contacts using a numerical relay under a predefined condition as herein described and illustrated with reference to accompanying drawings.