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 OF AUTORECLOSING DURING TRANSIENT FAULTS

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 electrical system protection and more particularly to a method of auto reclosing during transient faults thus improving electrical system stability using a numeric relay.

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.

Some of the prior arts in the related field of invention are as follows:

FR2700645 (A1) The electrical distribution network has a supply circuit breaker (DP) at the head of the principal lines (LP) and automatic reclose circuit breakers (DRR) at the head of the feeder lines (LD). A coordination unit (BCO) is placed between the fault detectors (DD) at the head of the principal line and the line breaker (DP).The coordination unit has a memory (MM) that retains a masking time slightly greater than the reaction and closure time of the auto-reclosing circuit breaker in the feeder, and also a masking time equal to the opening time of the auto-reclose breaker.

CN101135709 (A) The method thereof comprises: cutting off the live-line single-phase switch containing a T type wire connection mutual inductance lines to cause the phase-missing running; after load current provides the zero sequence current for the measurement 0.5-1 second, using the auto-reclosing circuitbreaker to recover the normal running of lines in order to generate the live-line measurement zero sequence heavy current; or, powering off the a certain line of the T type wire connection mutual inductance lines, and newly adding an external zero sequence voltage to provide the zero heavy current used for live-line measurement; using GRS technology to make sampling for the zero sequence voltage and zero sequence current signals from the multi-port of the T type wire connection mutual induction lines to relevant data about the zero sequence current and zero sequence voltage; ; the data collected from each measurement points are sent to the central computer to the impedance parameter.

WO2006068614 (A1) The invention relates to a method for controlled reclosing of branch elements, for example a line, in an electric power system which has been subjected to a disturbance, comprising at least one branch element and at least one circuit breaker connected thereto, and wherein the angular difference between the voltage vectors, on both sides of the circuit breaker or at the two end points of the line, is detected and compared with a comparison value, and, in dependence on the magnitude of the deviation of said angular difference from the compari not son value, said reclosing is either completed or blocked. The invention is achieved by updating the comparison value auto not matically and regularly in such a way that an adaptive value is obtained. A system according to the invention comprises means arranged to update the comparison value automatically and regularly in such a way that an adaptive value is obtained.

GB 2292249 (A) In Auto-reclosers, ie circuit breakers for use generally in remote locations, having means for reclosing automatically after tripping on detection of a fault, and wherein LiSO2 batteries are used both to energise the relay (ie the control circuit) and to power the magnetic actuator which drives the circuit breaker contacts, such batteries, in the absence of a fault, out of use for very long periods and acquiring passivation layers which reduce the available battery power, at least initially, the passivation layers are burnt off by applying a series of pulses to the opening coil of the recloser prior to making an attempt to energise the closing coil.

CN201130844 The utility model relates to an auto reclosing control device used for a low voltage circuit breaker, which comprises a signal input unit, a signal processing unit, a signal output signal, and a power supply unit; wherein, the signal input unit is connected with the low voltage circuit breaker, and the signal processing unit is connected with the signal input unit and the signal output unit; the power supply unit is connected with the signal input unit and the signal processing unit. Compared with the prior art, the auto reclosing control device has the advantages of strong versatility, high reliability, and low cost and practicality; moreover, by adding the auto reclosing control device, the automatic reclosing can be performed in case of power restoration, thus improving the reliability of power supply, and reducing the workload.

Although the cited prior arts provide for auto-reclosing but the method used is complex and may not always be accurate. The present invention therefore provides a novel method of auto-reclosing logic in a system during transient faults and blocking of the scheme under appropriate conditions. This invention is related to circuit breaker reclosing after tripping due to transient faults in the system so that the power supply is not lost during such transients and also the manual effort is reduced for the supervision of such faults which is frequent in nature. 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 of electrical system protection.

Other object of the present invention is to provide a method of auto reclosing during transient faults thus improving electrical system stability using a numeric relay.

Other object of the present invention is to provide an algorithmic logic for auto reclosing operation of breaker.

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

There is provided a method of electrical system protection.
According to one embodiment of the present invention, there is provided

Other embodiment of the present invention provides a method of auto reclosing during transient faults thus improving electrical system stability using a numeric relay, said method comprising the steps of: providing input setting for auto reclose status and breaker status; providing time settings to dead timer and reclaim timer; processing protection algorithm logic in a numerical relay, said relay giving closing command to breaker through a hardware interface; opening breaker contacts by making lockout flag high.

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.

Additionally, Auto reclosing of three phase improves stability as the power continues to get transmitted through the two healthy phases when one phase is interrupted.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig 1 illustrates a method of auto reclosing during transient faults thus improving electrical system stability using a numeric relay.

Fig 2 illustrates the flow logic for lockout.

Fig 3 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 a method of auto reclosing during transient faults thus improving electrical system stability using a numeric relay is provided. It shows different units like Data acquisition and metering section, CPU controller, Numerical relay etc.

Fig. 2 shows flow logic of lockout.

Fig. 3 shows the processing of logic in the numerical relay. It provides different method steps used in facilitating auto reclosing.

The invention therefore provides a method of auto reclosing during transient faults thus improving electrical system stability using a numeric relay.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly the present invention provides a novel method of auto-reclosing logic in a system during transient faults and blocking of the scheme under appropriate conditions. This scheme is related to circuit breaker reclosing after tripping due to transient faults in the system so that the power supply is not lost during such transients and also the manual effort is reduced for the supervision of such faults which is frequent in nature. 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 elucidates the application space and concept of Autoreclose and Lockout and illustrates the HMI settings and the firmware logic to be incorporated to include this feature in New Feeder Protection relay.
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.

The above 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 case after the procession of the logic, the digital output of the relay (hardware) gets the signal to close the breaker (with maximum of 4 shots allowed) and the close command is sent to the breaker through hardware interface. When the four attempts of closing the breaker are completed, then the lockout flag will be high and the breaker gets opened permanently.

Autoreclose as the name suggests is reclosing of circuit breaker contacts automatically once it gets tripped or opened due to any fault in the system. It is recommended to be used in the feeders where the frequency of transient faults such as insulator flash over or semi-permanent faults such as a tree branch falling on the line are more. Here in the case of semi-permanent one, the fault would not be removed by immediate tripping of the breaker but could be burnt away during a time delayed trip. Majority of overhead line faults tentatively 80% are transient in nature so autoreclosing is very beneficial in such cases as it eliminates loss of supply from such faults and also it allows a particular substation run unattended. Thus, the number of visits by personnel to reclose a circuit breaker manually, after a fault occurs, could be substantially reduced which is an important consideration for substations in remote areas. For feeders where a significant portion of faults are permanent for e.g. broken conductors, transformer faults, cable faults or machine faults autoreclosing is not a good idea since reclosing on to a faulty cable is likely to aggravate the damage.

On HV/MV distribution networks, auto-reclosing is applied mainly to radial feeders where system stability problems do not generally arise. The system conditions to be met for closing are that the system voltages are in synchronism or dead line/live bus or live line/dead bus conditions exist, indicated by the internal check synchronizing element and that the circuit breaker closing spring, or other energy source, is fully charged. Auto reclosing may be single phase or three phase type. Mostly single phase auto reclosing breakers are preferred as most of the transmission faults are single phase to ground faults.
Auto reclosing of three phase improves stability as the power remains transmitted through the two healthy phases when one phase is interrupted.

In the present invention Dead timer provides the time between the breakers tripping and reclosing again. This time should be sufficient enough to be allowed after tripping for the fault arc to de-energize prior to reclosing otherwise the arc will re-strike. The dead time depends on the line voltage, breaker and type of fault occurring in the line frequently.

Reclaim timer provides the time delay which is given once the breaker closes and it should be in excess of the time delayed protection operating time to ensure that the protection can operate before the autoreclose function is reset. During this time, if the breaker is tripped due to protection or manually, the Autoreclose (A/R) either advances to the next shot (if it is programmed for multi-shots), or goes to lockout if all programmed reclose attempts have been made. The reclaim timer starts once the CB has physically closed. If there is no trip before the reclaim timer expires, the A/R function resets at the end of the timer.

Further Lockout provides for the permanent opening of breaker and autoreclose is blocked. It can be set either manually or get sets after all the A/R shots are completed. It is necessary to reset from lockout to reset the autoreclose function. Reset Lockout is of two types: Hand reset & Software reset.

Settings:-

Autoreclose feature (Enabled/Disabled)
Dead timer ( 0 to 100 seconds in steps of 0.1 sec)
Reclaim timer (0 to 100 seconds in steps of 0.1 sec, default= 1 sec)

Inputs

Status of feature (Enabled/Disabled)
Breaker status (Open/Closed)
Autoreclose initiate( due to trip from any protection function)

Outputs

Algorithm triggers a reclose command and the Flex logic operand goes high/low depending on the algorithm output.

Abbreviations used:

HMI: Human machine interface
CPU: Central processing unit
A/D: Analog to digital
HV/MV: High voltage/Medium voltage
A/R: Autoreclose
CB: Circuit breaker

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 of auto reclosing during transient faults thus improving electrical system stability using a numeric relay, said method comprising the steps of: providing input setting for auto reclose status and breaker status; providing time settings to dead timer and reclaim timer; processing protection algorithm logic in a numerical relay, said relay giving closing command to breaker through a hardware interface after the expiration of said dead timer and increasing the counter of autoreclose attempts; starting the reclaim timer to reset the autoreclose flag once the reclaim timer expires if no fault exists; opening breaker contacts by making lockout flag high once all the pre-specified number of attempts to reclose the breaker are over .

2. Method as claimed in claim 1 wherein said timing setting for said dead timer provide for fault arc to de-energize prior to reclosing.

3. Method as claimed in claim 1 wherein said timing setting for reclaim timer is provided such that the protection can operate before the reclose function is reset.

4. Method as claimed in claim 1 wherein during said lockout breaker gets opened and said auto reclose is further blocked once all the pre-specified number of attempts to reclose the breaker are over.

5. Method as claimed in claim 1 comprising the 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.

6. Method as claimed in claim 5 wherein said the protection algorithm logic is processed by said CPU controller and providing close command to said breaker.

7. A method of auto reclosing during transient faults thus improving system stability using a numeric relay as herein described and illustrated with respect to the accompanying drawings.

Dated this 23rd day of February 2012

Abhishek Sen
Of S. Majumdar & Co.
(Applicant’s Agent)