DESC:TECHNICAL FIELD

The present subject matter described herein, in general relates to circuit breakersand more particularly, to a method for protection of equipment against earth fault under noisy environment due to harmonics.

BACKGROUND

A circuit breaker is an automated switch, considered to protect a circuit from harms caused due to overload or shortcircuit. Its basic function is to sense an interrupt and fault conditions in the current flow. The circuit breakers are made from small devices and are of varying size that protects household appliances during overload or short electrical circuit. The circuit breakers are normally used in the electrical panel, and also to detect a ground fault, which provides a protection from abnormal electrical shock exposure.

The ground fault is an unwanted connection between system conductors and the ground. Undetected ground fault may be dangerous and can shut down power and damage the electrical equipments, which disrupts the flow of production leading to hours or even days of lost productivity. Ground faults can lead to safety hazards such as equipment malfunctions, fire and electric shock. The conventional circuit breakers have transformer based earth fault and harmonics detection. Harmonics are the currents having nonstop multiples of the fundamental frequency for example, of 60 Hz such as 120 Hz (2nd harmonic) and 300 Hz (5th harmonic). Generally, the harmonic currents provide current or power that cannot be used by the electrical appliances under normal conditions and also takes up electrical system capacity.

Traditionally, the earth fault detection was done through core balance current transformer (CBCT) where all the line and neutral currents would flow and current equivalent to unbalance would be produced at secondary which would be used for threshold comparison and tripping. Alternate method was to have individual samples of line and neutral currents and then taking vector addition that would result in signal equivalent to core balance current transformer method.The “insulation fault current” is measured in the neutral- earth link of the Low Voltage transformer. But in industrial application that generates lot of harmonic, above mentioned methods do not provide enough sensitivity to distinguish between fundamental and harmonic frequency content, and therefore result in nuisance trips, especially when configured for the low current level threshold. Nuisance trips will often require that an operator manually reset a breaker which is undesirable.

There are various recently proposed traditional methods for earth fault detection. The prior-art documents EP 2259402 A1and US 6546342 B1 are found to be close prior-art references. Both the patent documents consider nuisance tripping due to presence of harmonics and provide method to prevent it. Further, both patent documents include methods for accurate sensing of earth fault in presence of harmonics and issuing a trip only in case of actual fault.

In the prior-art documents fundamental as well as second harmonic component of all the three phases is needed to provide an effective solution. Further, the prior-art document uses second harmonic restraint, i.e., if ratio of summation of second harmonic components of all phases to the summation of fundamental content of all phases exceeds a particular threshold, then tripping is restrained.

Further, with an introduction of electronic trip units in circuit breakers, Micro-controller based approach is used for earth fault detection. Using microcontroller and internal ADC, line current and neutral current are sampled at interval required to detect harmonics of interest as per the Nyquist criteria.

In the view of above mentioned drawbacks, there exists a need to provide an efficient and cost-effective method for protecting the equipment against earth fault under noisy environment due to harmonics. Further, there also exists a need to device method for accurate sensing of earth fault in presence of harmonics and thereby tripping under actual fault condition and thus reducing the number of nuisance trips.

SUMMARY

This summary is provided to introduce concepts related to a micro-controller based method for protecting the equipment against earth fault under noisy environment due to harmonics. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

In one implementation,an efficient and cost-effective method for protecting the equipment against earth fault under noisy environment due to harmonics is disclosed.

In one implementation, a method for accurate sensing of earth fault in presence of harmonics and thereby tripping under actual fault condition and thus reducing the number of nuisance trips is provided.

In one implementation, individual phase fundamental components need not be extracted to provide an effective solution.

In one implementation, the proposed invention uses a digital filter used to extract the fundamental component, a delayed tripping is accomplished by using timer. Further, if the sum of squares value is greater than predefined threshold called pickup setting then timer is initiated. Further, the timer value and pickup is predetermined as per the setting from user interface. User interface with breaker could be either DIP switch or rotary switch or display or any other means.

Accordingly, a device method for accurate sensing of earth fault in presence of harmonics and thereby tripping under actual fault condition and thus reducing the number of nuisance trips is disclosed.

In one implementation, a micro-controller based accurate sensing of earth fault in presence of harmonics and thereby tripping under actual fault condition and thus reducing the number of nuisance trips is disclosed.

Accordingly, in one implementation a method for earth fault detection based on a signal received, thereby tripping said electronic tripping unit of said circuit breaker is disclosed. The method comprises of extracting fundamental components values from the signal received; calculating earth current signal using said fundamental components extracted, and initiating a timer; if sum of said earth current signal calculated exceeds a predefined threshold value, thereby tripping the said electronic tripping unit of said circuit breaker.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to refer like features and components.

Figure1 illustrates a method (200) for earth fault detection is shown, in accordance with an embodiment of the present subject matter.

Figure 2 illustrates a formula for earth fault detection is shown, in accordance with an embodiment of the present subject matter.

Figure 3 illustrates a basic block diagram of earth fault detectionsystem is shown, in accordance with an embodiment of the present subject matter.

Figure 4 illustrates a flow chart for earth fault detection is shown, in accordance with an embodiment of the present subject matter.

Figure 5 illustrates an exemplary output for earth fault detection method is shown, in accordance with an embodiment of the present subject matter.

DETAILED DESCRIPTION

Preferred embodiments of the present disclosure will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

In the embodiments provided in the present application, it should be understood that the disclosed method, device, and data frame may be implemented in other manners. For example, the described device embodiments are merely exemplary. For example, the unit division is merely logical function division and can be other division in actual implementation. For example, a plurality of units or components can be combined or integrated into another system, or some features are negligible or not performed.

When the functions are implemented in the form of a software functional unit and sold or used as an independent product, the functions may be stored in a computer-readable storage medium. Based on such an understanding, the technical solutions of the present invention essentially, or the part contributing to the prior art, or part of the technical solutions may be implemented in the form of a software product. The computer software product is stored in a storage medium, and includes several instructions for instructing a computer device (which may be a personal computer, a server, a network device, or the like) to perform all or a part of the steps of the method described in the embodiment of the present invention. The storage medium includes: any medium that can store program codes, such as a USB flash disk, a removable hard disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a magnetic disk, or an optical disk.

In one implementation, a device method for accurate sensing of earth fault in presence of harmonics and thereby tripping under actual fault condition and thus reducing the number of nuisance trips is disclosed.

In another implementation, a micro-controller based for accurate sensing of earth fault in presence of harmonics and thereby tripping under actual fault condition and thus reducing the number of nuisance trips is disclosed.

While aspects of a micro-controller based method is described for protecting the equipment against earth fault under noisy environment due to harmonics may be implemented in any number of different computing systems, environments, and/or configurations, the embodiments are described in the context of the following exemplary system.

Referring now to figure 1, a method (200) for earth fault detection based on a signal received, thereby tripping said electronic tripping unit of said circuit breaker is disclosed. The method (200) comprises of extracting (202) fundamental components values from the signal received; calculating the earth fault current using said fundamental components and initiating a timer (206), if sum of said earth fault current extracted exceeds a predefined threshold value, thereby tripping (208) said electronic tripping unit of said circuit breaker.

In one implementation, said signal received is an earth fault signal.

In one implementation, said fundamental components values are extracted using a digital filter.

In one implementation, said sum is obtained using a vector summation (204).

In one implementation, said tripping is a delayed tripping obtained by using a timer.

In one implementation, said predefined threshold is a pickup setting obtained from a user interface provided to the said circuit breaker.

In one implementation, said user interface to the said circuit breaker is selected from a group comprising of a DIP switch, a rotary switch, a display, and the combination thereof.

In one implementation, said timer has a pre-defined timer value obtained from said user interface provided to the said circuit breaker.

In one implementation, the method is a microcontroller based method for earth fault detection based on said signal received, thereby tripping said electronic tripping unit of said circuit breaker.

Referring now to figure 2, a formula for earth fault detection is shown, in accordance with an embodiment of the present subject matter.

In one embodiment, the method uses four phase input current to detect the earth fault. The method may use digital filter to extract the fundamental component of the signal received by the micro-controller. Vector summation is done using fundamental components as per the formulae in figure 2.
The formula used is as given below in equ.1:
…………. (equ. 1)
Where,
Ig indicates an Earth current
IR indicates R phase current
IY indicates Y phase current
IB indicates B phase current
IN indicates Neutral current

Referring now to figure 3 illustrates a basic block diagram of earth fault detection system, in accordance with an embodiment of the present subject matter. In one implementation, four phase current is sensed by the current sensor. Output of current sensor is given to signal conditioning circuit to adjust the gain of the input signal. Amplified signal is given to micro-controller unit. Step by step processing of these signals in micro-controller is shown in figure 4 along with its corresponding module. Output of protection unit is trip signal which is given to FSD trip circuit which in turn operates the breaker.

Referring now to figure 4 illustrates a flow chart for earth fault detection, in accordance with an embodiment of the present subject matter.

In one embodiment, the method may follow the below mentioned steps as shown in figure 4:

1. Get ADC sample of 4 phase current from the Data acquisition (DAQ) module. 4 phase current sample with harmonics is shown in figure 5. Also shown is unfilteredand filtered earth current sample.
2. Perform Vector summation on these samples using the formulae in figure 2 to get Earth current sample. Vector summation is done using individual sample summation of 4 phases and subtracting the neutral sample. The resultant value is earth current sample. These earth current samples will be unfiltered sample as shown in Figure 5.
3. Extract the fundamental components from the Earth current sample using any harmonic analysis algorithm (Digital filter) such as DFT, FFT or Goertzel algorithm. Extracted samples will be filtered earth current sample as shown in figure 5.
4. Calculate Root mean squared (RMS) value of filtered earth current sample
5. The timers are used to accomplish the delayed tripping.
6. If the RMS value is greater than predefined threshold called pickup setting then timer is initiated.
7. If the RMS value is less than predefined threshold, it is understood by the micro-controller that the current is in normal condition and no harm to the appliance will be caused due to this flow.

In another implementation, the timer value and pickup is predetermined as per the setting from user interface. User interface with breaker could be either dual in-line package (DIP) switch or rotary switch or display or any other means.

Referring now to figure 5 illustrates an exemplary output for earth fault detection method is shown, in accordance with an embodiment of the present subject matter.

Exemplary embodiments discussed above may provide certain advantages. Though not required to practice aspects of the disclosure, these advantages may include those provided by the following features:

One feature of the invention is that, the method disclosed uses four phase input current to detect the earth fault. Hence above mentioned method is faster and occupies less code size on microcontroller.

Another feature of the invention is that, the individual phase fundamental signals need not be extracted, as the traditional methods uses to follow.

Another feature of the invention is that, micro-controller based earth fault detection is disclosed.

Yet another feature of the invention is that, an individual current sampling and earth fault signal generation using vector addition is disclosed.

Yet another feature of the invention is that, a fundamental signal extraction is achieved from extracted earth fault signal.

Yet another feature of the invention is that, a configurable pickup and delay setting is possible in the disclosed invention

Yet another feature of the invention is that, the configuration through is made possible through the DIP or rotary switches, display or communication.

Still another feature of the invention is that, a delayed tripping is accomplished by using timer.

Although the device method for accurate sensing of earth fault in presence of harmonics and thereby tripping under actual fault condition and thus reducing the number of nuisance trips have been described in language specific to structural features and/or methods, it is to be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features are disclosed as examples of implementations for device method for accurate sensing of earth fault in presence of harmonics and thereby tripping under actual fault condition and thus reducing the number of nuisance trips.
,CLAIMS:1. A method (200) for earth fault detection based on a signal received, thereby tripping said electronic tripping unit of said circuit breaker, said method comprising:
extracting (202) fundamental components values from the signal received;
calculating (204) earth current signal using said fundamental components extracted; and
initiating a timer (206), if sum of said earth current signal calculated exceeds a predefined threshold value, thereby tripping (208) said electronic tripping unit of said circuit breaker.

2. The method as claimed in claim 1, wherein said signal received is an earth fault signal.

3. The method as claimed in claim 1 and 2, wherein said fundamental components values are extracted using a digital filter.

4. The method as claimed in claim 1 to 3, wherein said sum is obtained using a vector summation (204). 0

5. The method as claimed in claim 1 to 4, wherein said tripping is a delayed tripping obtained by using a timer.

6. The method as claimed in claim 1 to 5, wherein said predefined threshold is a pickup setting obtained from a user interface provided to the said circuit breaker.

7. The method as claimed in claim 7, wherein said user interface to said circuit breakeris selected from a group comprising of a DIP switch, a rotary switch, a display, and the combination thereof.

8. The method as claimed in claim 1 to 7, wherein said timer has a pre-defined timer value obtained from said user interface provided to the said circuit breaker.

9. The method as claimed in claim 1 to 8, is a microcontroller basedmethod for earth fault detection based on said signal received, thereby tripping said electronic tripping unit of said circuit breaker.