|Title of Invention||
A SYSTEM FOR DETECTION OF EARTH LEAKAGE CURRENT
|Abstract||Abstract The present invention provides a Numerical Earth Leakage Detector. This embedded system would replace the existing protection based on conventional Earth leakage measurement. The present invention would also provide additional features like field settings, time settings, Inverse curve selections, and Harmonic rejection using DFT technique, Auto/Manual Reset and test operation.|
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
NATURE OF THE INVENTION
A SYSTEM FOR DETECTION OF EARTH LEAKAGE CURRENT
A) Technical field
1. The present invention relates to a system for detection of earth leakage current.
The present invention more particularly relates to a system for detection of earth
leakage current in electronic and electrical applications.
B) Background and prior art
2. Grounding is an important feature provided with all electronic and electrical goods for the safety of user as well as for protecting the device from sudden surge in current. The magnitude of this ground fault current depends on system grounding method .For low impedance grounded system there is a high level of ground fault which requires line tripping to remove this fault, ground over current relays are the typical fault protection method for these systems.
3. In multi grounded system, this ground fault detection is difficult due to multi grounded four wire systems, in which the relay measures the ground fault current measures the ground current combined with unbalanced current generated by line phase and configuration and load balance, due to which we require ground relays with high sensitivity because the fault current is very low compared to solidly grounded systems. Most ground fault detection use fundamental frequency voltage and current components, which can also be used in high impedance grounded system.
4. US 5,920,451 describes a Earth leakage circuit breaker assembly which is a multi-
pole circuit breaker assembly for interrupting AC power to a load upon the detection of an earth leakage fault or an over current condition includes a pair of circuit breaker units mounted adjacent to an earth leakage module. The earth leakage module includes an electronic circuit that senses a current imbalance between the power line lead and the neutral line lead using a differential transformer. In response to a current imbalance greater than a predetermined value, the electronic circuit periodically energizes a switching circuit that provides power across a solenoid. The solenoid, when actuated, engages a common trip mechanism to open concurrently the contacts of the circuit breakers units. The common trip mechanism includes an elongated bar that extends through the casing of the earth leakage module and the circuit breaker units. The elongated bar engages a U-shaped trip member pivotally disposed in each circuit breaker. Each trip member has a depending member extending from a leg that trip its respective circuit breaker unit when pivoted upwardly by the solenoid.
5. US 6,262,585 depicts an apparatus for I/O leakage self-test in an integrated circuit, wherein an integrated circuit is disclosed that includes a first input/output (I/O) circuit and a leakage detection circuit coupled to the first I/O circuit. In a test mode of operation, the leakage detection circuit tests the first I/O circuit for excessive leakage current. According to another embodiment, the integrated circuit also includes a first resistor coupled between a line voltage and the first I/O circuit and a second resistor coupled between the first I/O circuit and ground. Further, the integrated circuit includes a second I/O circuit coupled to the leakage detection circuit and the first and second resistors. The leakage circuit also tests the second I/O circuit for excessive leakage current in the test mode of operation.
6. US 6,025,980 depicts an earth leakage protective relay wherein an earth fault detection circuit employs a differential current transformer and burden resistor to sample circuit current for potential earth fault current. A second order low pass
filter circuit is employed to filter out harmonics within the protected circuit and a time delay circuit is used to insure the occurrence of a true earth fault leakage condition. A circuit with an operational amplifier is used to create a symmetric power supply for the rest of the circuits from a full wave rectified AC source.
US 6,807,037 depicts an electronic earth leakage current device, comprising: a moving contact and a fixed contact which can be mutually coupled/uncoupled; and first sensor means for detecting an earth leakage current and for generating an-electric signal which is indicative of the value of the earth leakage current; and first electronic means which are electrically connected to the first sensor means in order to generate, on the basis of the electric signal which is indicative of the value of the earth leakage current, an electric tripping signal; and actuation means, operatively connected to the moving contact, in order to perform, in response to an electric tripping signal, the separation of the moving contact from the fixed contact; Its particularity consists of the fact that it comprises: second sensor means for detecting one or more physical values which are indicative of the operating condition of the electronic device for protection against earth leakage current; and second electronic means, electrically connected to the second sensor means, for receiving from the second sensor means electric signals which are indicative of the operating condition of the electronic device for protection against earth leakage current and for generating an electric tripping signal depending on the electric signals.
US 6,696,841 depicts an electric power system relay and on-line method of testing same, wherein the electric power system relay includes a simulator that substitutes test values of current and voltage for sensed values for use by relay logic to perform specified relay functions, but without loss of the relay protection functions. The sensed values of current at least are monitored even while the test values are being used by the relay logic. If the monitored sensed values exceed a
threshold value, a data switch operates to return to use of the sensed current and voltage values by the relay logic. In addition, the sensed values of current and voltage replace the test values, if a time interval longer than that required to perform the specified relay functions using the test values has expired.
US Patent application 20040196603 depicts a protective relay capable of protection applications without protection settings wherein the current differential relay operates without adjustable settings, and includes a phase current differential element with a predetermined threshold, responsive to local phase current values and remote phase current values, to detect three-phase faults and producing a first output signal if the threshold value is exceeded. Either a negative sequence current differential element or two phase current differential elements, also having predetermined threshold values and responsive to the local and remote phase currents, detect phase-to-phase faults and phase-to-phase-to-ground faults and produces a second output signal if the predetermined threshold is exceeded. A negative sequence or zero sequence current differential current element, with a predetermined threshold value is responsive to the local and remote phase currents to detect phase-to-ground faults and to produce a third output signal if the threshold is exceeded. If any one of the first, second and third output signals occur, a trip signal is generated and directed to the associated circuit breaker. The thresholds are selected to permit use of the relay in a wide range of possible applications.
US 5,508,623 provides an apparatus and method to identify harmonic producing loads on a utility electrical network. The apparatus is connected to the utility electrical network at a location adjacent to a load. The apparatus includes a network voltage node to receive a voltage signal, and a network current node to receive a current signal. The apparatus also includes harmonic filters to process the voltage signal and current signal to isolate selected harmonic voltage signals and selected
harmonic current signals. A signal processor derives a set of selected power signals from the selected harmonic voltage signals and the selected harmonic current signals. The signal processor also identifies any positive polarity signals in the set of selected power signals. In response to a positive polarity signal, the signal processor activates a sensory output device to indicate that harmonics are being produced by the load.
US 4,788,619 provides protective relays and methods for use in an electrical power system having electrical conductors which are energizable with an AC voltage. The protective relay includes a circuit for sensing the AC voltage to produce an AC output that has zero crossings and a time period between zero crossings, a circuit for supplying an electrical signal representing a pre-selected pickup value of volts-per-Hertz for the relay, and a circuit responsive to the AC output and to the electrical signal for generating an electrical level as a function of both the time period and the pickup value and for producing an output signal for the relay when the AC output exceeds the electrical level. In this way, the output signal is produced when a volts-per-Hertz value of the AC voltage exceeds the pre-selected pickup value of volts-per-Hertz for the relay. Other protective relay apparatus and methods are also disclosed.
. US Patent application 20020112075 provides a relay apparatus which is connected to a host computer through a network and transmits data received from the host computer to a device. A first basic unit and a second basic unit are provided for the relay apparatus. A common network address is set into the first and second basic units. The relay apparatus performs a relay control between the host computer and the device. A common unit makes one of the first and second basic unit operative as a present system and monitors its status. When an abnormality is detected during the monitoring operation, the relay apparatus stops the basic unit of the present system and switches it to the operation of the basic
unit of a standby system.
13. In all the previous inventions a passive unit has been used for the purpose of calculation of earth relay current. Also they are not flexible to depict various curves.
14. The present invention shows a novel method for finding the grounding earth relay current by means of a microprocessor .The invention uses a software algorithm which helps in making it highly sensitive and also it uses a digital FFT filtering .The invention is also flexible to select multiple curves ( curves IEC255 standards which is specific time delay).
C) Brief description of the drawings
15. Fig 1 depicts the block diagrammatic representation of the earth leakage detection
system of the present invention.
D) Detailed description of the invention
16. The present invention relates to a system for detection of earth leakage current in electronic and electrical applications.
17. Initially we refer to Fig 1, which depicts a block diagrammatic representation of the system of the present invention for detection of earth leakage current. The system of the present invention comprises a power supply unit, a transducer, a signal conditioning circuit, a micro-controller based processor, a plurality of DIP switches, relays operated by the switches, test button and LED indicators.
18. The power supply unit of the present invention is an SMPS (Switching Mode
Power Supply) which consist of a power handling switching components which are continuously switching in an "ON" and "OFF" state. The duty cycle, frequency or phases of these transitions are varied to control an output parameter. The high operating frequency results in a smaller size of the power supply and smaller conduction looses. This SMPS supplies an input voltage of 5 — 12 Volts. The system of the present invention is a plug-and-play device which can be inserted or plugged into any system whose earth leakage current has to be detected, thereby making it easily portable and easily installable. The transducer unit provided in the system of the present invention is a current transformer input which takes in the input current from the device whose earth leakage current needs to be detected. The analog input current which is detected by the transducer unit is then sent to an analog signal conditioner circuit in order to filter out noise and amplify the current and voltage signal sensed by the sensor unit. After the signal conditioning is performed on the analog input signal, the analog input signal is sent to the microcontroller based processor. The micro-controller based processor requires a power supply of 20-265 Volts for operation. The micro-controller based processor performs two main functions, namely digitizing the analog input signal and executing appropriate Discrete Fourier Transformation (DFT) modules (which are stored in the database unit of the micro-controller based processor) on the digitized signal. The micro-controller based processor takes in the analog input signal as the input and samples the input signal and then performs digitization of the sampled signals using 8-bit ADC. Once the signals are digitized the Discrete Fourier Transformation (DFT) module is retrieved from the database of the microcontroller based processor and executed. The micro-controller based processor also performs the task of harmonic rejection (which are worst case amplitude of all harmonically related outputs or signals relative to the carrier (fundamental frequency) power) using the DFT module. This value is then compared with the Set point provided from front panel DIP switches, further the trip time is calculated using the curves set, then the Trip signal is issued to the Relay for further
tripping the Breaker contacts.
The DFT module is a routine that calculates the Discrete Fourier Transform (DFT) of the input signal voltage whose earth leakage current has to be measured. For this action different samples of the input signal can be taken. For instance in case 32 samples of the input signal are taken for calculation. The fundamental value of the voltage is calculated. This DFT module calls for appropriate routines for the extraction of fundamental components of Cosine and Sine values.
The DFT module executes the exact Root-Mean-Square (rms) value of the input signal. The table contains the cosine and sine values of the fundamental wave at every ll:25deg. The table is used for extracting the fundamental components of the input waveform. The table shows the features related to the numerical earth leak generator. It requires [Current 1A and 5A as a Input signal] [ provides or requires , I didn't get it] a current range of lAmp and 5 Amps and a frequency range of 50 Hz with an auxiliary supply of 20V to 110V DC or 88V to 264 V AC. The various setting parameter are a current (Is) which is 1% to 16% of In [In is either 1A or 5A Factory selectable] in steps of 1%. a high set of 21s to 161s and a time multiplier of 0.1 to 1.6. The time current characteristic of the numeric earth leakage detector are a pick up current which is same as Is, a reset current which is 95% to 90% of set current Is, an operating time of four curves which are a) normal inverse 3 seconds b) normal inverse 1.3 seconds c) very inverse 1.5 seconds and d) extremely inverse 0.8 seconds , a definite time of three ranges, an accuracy which is as per error class and a reset time of less then 50 m sec. The operational indicators are provided which are time current characteristics and power ON status .This routine calls the DFT module for the two channels and also updates the DFT read pointer. In addition this routine also does the work of finding out the fundamental rms value. It compares the gain channel squared value with the predefined (calibrated vale) value.
The ADC data is stored in the following memory locations (16 samples are stored) each cycle and every time the previous cycle data (16 samples) and present cycle data (16 samples) are taken for calculation of the fundamental rms value.
The rms value of the input signal is calculated to know the exact current flowing and to determine which switch should be turned on.
The DIP-switches of the system of the present invention are the high setting DIP -switch which is switched on when there is sudden flow of earth leakage current, low setting dip switch and time multiplier dip switch. The DIP - switches basically act as a user interface in the form of a front panel DIP -switch selection which enables the users to select relay settings with high resolution. Use of this selection makes the user view it easily. The advantages of having such dip switch selection is based on simple dip switch settings, ease of setting the required setting, high resolution settings are possible, fault indications through LED is available.
In addition to the dip switches the system of the present invention also includes a third harmonic filter using DFT technique to ensure that it does not operate on spikes generated by switching of various loads.
An Auto/ Manual Reset feature is provided which allows the user to select specific reset condition to reset the fault condition. In auto mode unit itself detects the healthy condition and resets the relay, user needs to press the reset switch for manual resetting. The Trip Indication LED ensures the user that relay has tripped. The detector is mounted where TRIP relay is the final control device, which is controlled by the detector to provide open/close operation to further breaker. The detector gets Single Phase CBCT (core balanced current transformer) output as an input. When supply is connected to auxiliary input order to operate the detector, detector energies and a check for the healthy condition of the voltage connected
to the auxiliary input and subsequently when all signals are perfect it starts the detector. In the mean time, detector continuously measures the current flowing in order to determine if there is any fault condition a cutoff signal is given to the relay subsequently opening the breaker (which is the trip operation).
In addition to the above, a test button is provided which performs testing after installation of the earth leakage detector system. The test button is a push button which is pressed for more than 2 sees operates the relay & LED to confirm the operation of the system. If the test button is pressed after production only the LED glows to confirm that the relay is working. The LED trip indicator front panel glows to indicate that the relay is operated.
The micro-controller based processor is mounted inside the relay enclosure,
a. It would also provide additional features like field settings, time settings,
Inverse curve selectability, and additional features like Harmonic rejection
using DFT technique, Auto/Manual Reset and test operation, which are not
available in existing relays.
b. The front panel enables user to control and modify the settings in the field.
The compact design utilizes the minimum space with more number of
c. Wide range of AC Operating voltages gives the dynamic use in various
The Earth leakage Detector is an industrial protection system with third harmonic rejection capability. The Detector deploys a PCB mounted electromechanical relay for final making and cut-off of the Relay contacts.
The applications of the system of the present invention are in the field of electrical and electronic circuits like in transformers, generator section to detect earth leakage.
Following are the features offered in Numerical Earth Leakage Detector. Ratings
Current (In) : 1A / 5A
Frequency : 50 Hz ± 2.5Hz
Auxiliary Supply : 20V to 110V AC/DC
or : 88V to 264V AC/DC Settings
Current (Is) : 1% to 16% of In in steps of 1%
High Set (His) : 21s o 161s in steps of 21s and
Time Multiplier (TMS) : 0.1 to 1.6 in steps of 0.1
Time Current Characteristic
Pick-up Current : Same as set current Is
Reset Current : (95% - 90%) of set current Is
Operating Time : Four Curves As per
IEC60255-3 Normal Inverse 3.0s
b) Normal Inverse 1.3s.
Very Inverse.l.5s Extreme Inverse.0.8s
Definite Time :Three Ranges(lsec, lOsecs, lOOsecs)
: Trip time = TMS x Range
Offers Definite time delay starting.
Accuracy : As per error class 5, IS3231:1987
Reset time : Less than 50msec.
Highset (Instantaneous Trip)
Accuracy : As per error class 5, IS3231:1987
Operating Time : Less than 50msec for Iin : Less than 50msec for Iin (Iin = input Current)
Overload capacity CT : 2 In Continously.
: 20 In for One second.
Operation Indicators : Separate LED indication for
Time Current Characteristics.
Power ON Status. : Trip Status: When Input crosses
Contact configuration : 2 pairs of C/O contacts
E) Scope of the invention
30. A primary advantage of the present invention is to have an integrated unit which is provided with a compact design which can take care of complete Earth leakage detection.
31. Another advantage is that the earth leakage detector of the present invention is a plug and play module thereby making it convenient, easy to carry and easy to install.
Another advantage is that the earth leakage detector of the present invention is provided with a DFT module which is stored in the database unit of the processor thereby eliminating the hardware required to perform this task.
One more advantage is that a test button is provided to test the functioning of the system of the present invention.
|Indian Patent Application Number||2/CHE/2006|
|PG Journal Number||40/2013|
|Date of Filing||02-Jan-2006|
|Name of Patentee||LARSEN & TOUBRO LIMITED|
|Applicant Address||MYSORE WORKS, HAVING OFFICE AT KIADB INDUSTRIAL AREA, HEBBAL-HOOTAGALLI, MYSORE 570 018, KARNATAKA|
|PCT International Classification Number||H02H 3/00|
|PCT International Application Number||N/A|
|PCT International Filing date|