Method, device and equipment for detecting transformer based on ethylene signal and storage medium

文档序号：1919787 发布日期：2021-12-03 浏览：21次中文

阅读说明：本技术 基于乙烯信号的变压器检测方法、装置、设备和存储介质 (Method, device and equipment for detecting transformer based on ethylene signal and storage medium ) 是由曹旺胡边万元潘平衡刘章进唐伟于 2021-08-31 设计创作，主要内容包括：本申请涉及一种基于乙烯信号的变压器检测方法、装置、计算机设备和存储介质。该方法包括：往怀特池中通入已知浓度的乙烯气体,计算得出乙烯的二次谐波气体吸收峰的峰值与浓度之间的一次关系；将变压器中的分离出溶解在油中的乙烯气体,利用TDLAS技术对乙烯气体的浓度进行检测,根据二次谐波气体吸收峰的峰值与浓度关系反推乙烯气体浓度；根据推算的乙烯气体浓度,确定变压器的故障信息。提供将巴特沃斯滤波器与TDLAS的信号处理相结合,降低二次谐波中噪声对吸收峰的影响。使得对最终乙烯的检测变得十分精确,进而使得变压器的故障分析更加合理,同时避免了机械检测对变压器的正常运行进行的干扰。(The application relates to a transformer detection method and device based on an ethylene signal, computer equipment and a storage medium. The method comprises the following steps: introducing ethylene gas with known concentration into the white pool, and calculating to obtain a first relation between the peak value and the concentration of a second harmonic gas absorption peak of the ethylene; separating ethylene gas dissolved in oil from the transformer, detecting the concentration of the ethylene gas by using a TDLAS technology, and reversely deducing the concentration of the ethylene gas according to the relation between the peak value of a second harmonic gas absorption peak and the concentration; and determining fault information of the transformer according to the estimated ethylene gas concentration. A Butterworth filter is combined with signal processing of TDLAS, and the influence of noise in a second harmonic on an absorption peak is reduced. The detection of the final ethylene becomes very accurate, so that the fault analysis of the transformer is more reasonable, and the interference of mechanical detection on the normal operation of the transformer is avoided.)

1. A method for detecting a transformer based on an ethylene signal, the method comprising:

introducing ethylene gas with known concentration into the white pool, and calculating to obtain a first relation between the peak value and the concentration of a second harmonic gas absorption peak of the ethylene;

separating ethylene gas dissolved in oil from the transformer, detecting the concentration of the ethylene gas by using a TDLAS technology, and reversely deducing the concentration of the ethylene gas according to the relation between the peak value of a second harmonic gas absorption peak and the concentration;

and determining fault information of the transformer according to the estimated ethylene gas concentration.

2. The method for detecting the transformer based on the ethylene signal as claimed in claim 1, wherein the step of introducing the ethylene gas with the known concentration into the white cell and calculating the first relation between the peak value and the concentration of the second harmonic gas absorption peak of the ethylene comprises:

respectively introducing high-concentration ethylene and low-concentration ethylene into the white pool, and respectively extracting second harmonic waves;

carrying out spectrum analysis on the second harmonic, selecting the frequency corresponding to the ethylene gas, and calculating the frequency according to the width of an absorption peak of ethylene under the condition of high concentration;

and determining the ethylene frequency according to the fact that the amplitude corresponding to the high-concentration gas frequency is larger and the amplitude corresponding to the low-concentration gas frequency is obviously reduced in the frequency spectrum.

3. The method for detecting the transformer based on the ethylene signal as claimed in claim 2, wherein the step of introducing the ethylene gas with the known concentration into the white cell to calculate the first relation between the peak value and the concentration of the second harmonic gas absorption peak of the ethylene further comprises:

designing a Butterworth filter in a filter design tool in MATLAB according to the determined ethylene frequency;

extracting filter coefficients according to parameters of a Butterworth filter, such as passband frequency, stopband frequency, passband attenuation and stopband attenuation;

filtering by using the determined ethylene frequency as a passband frequency in a dual filtering mode of firstly passing through a high-pass filter and then passing through a low-pass filter;

and according to the second harmonic extracted by the phase-locked amplifier, the second harmonic passes through a Butterworth high-pass filter and a low-pass filter to obtain the filtered second harmonic.

4. The method of claim 1, wherein determining fault information of the transformer according to the estimated ethylene gas concentration comprises:

obtaining the aging condition of insulating oil and solid insulating materials in a transformer under the action of temperature, electric field and oxidation environmental factors;

and determining the corresponding transformer fault information of the ethylene under different concentrations according to various running states of the transformer under different types of mixed gas of the ethylene.

5. A transformer detection system based on ethylene signals, comprising:

the relationship determination module is used for introducing ethylene gas with known concentration into the white pool and calculating to obtain a first relationship between the peak value and the concentration of the second harmonic gas absorption peak of the ethylene;

the concentration calculation module is used for separating ethylene gas dissolved in oil from the transformer, detecting the concentration of the ethylene gas by using a TDLAS technology, and reversely deducing the concentration of the ethylene gas according to the relation between the peak value of a second harmonic gas absorption peak and the concentration;

and the fault analysis module is used for determining fault information of the transformer according to the calculated ethylene gas concentration.

6. The ethylene signal-based transformer detection system of claim 5, wherein the relationship determination module comprises a frequency processing unit configured to:

respectively introducing high-concentration ethylene and low-concentration ethylene into the white pool, and respectively extracting second harmonic waves;

7. The ethylene signal-based transformer detection system of claim 6, wherein the relationship determination module further comprises a filter optimization unit configured to:

designing a Butterworth filter in a filter design tool in MATLAB according to the determined ethylene frequency;

extracting filter coefficients according to parameters of a Butterworth filter, such as passband frequency, stopband frequency, passband attenuation and stopband attenuation;

filtering by using the determined ethylene frequency as a passband frequency in a dual filtering mode of firstly passing through a high-pass filter and then passing through a low-pass filter;

8. The ethylene signal-based transformer detection system of claim 5, wherein the fault analysis module comprises a gas evaluation unit configured to:

obtaining the aging condition of insulating oil and solid insulating materials in a transformer under the action of temperature, electric field and oxidation environmental factors;

9. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the steps of the method of any of claims 1 to 4 are implemented when the computer program is executed by the processor.

10. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 4.

Technical Field

The present application relates to the field of power equipment, and in particular, to a method and an apparatus for detecting a transformer based on an ethylene signal, a computer device, and a storage medium.

Background

With the rapid development of the power industry and the expansion of the scale of the power grid, higher requirements are put on the safe operation and the power supply reliability of the power system, and the transformer plays a very important role in the power system, is one of the most important electrical equipment in the power system, and the safe reliability of the operation of the transformer is directly related to the safety and the stability of the power system. In recent years, a plurality of transformer accidents also sound the alarm clock for the power system in China. Therefore, the improvement of the operation reliability of the transformer, particularly the large-scale power transformer, has very important significance on the safe and reliable operation of the whole power grid.

The operation states of the insulating oil and various insulating materials of the transformer have important influence on the transformer, when the operation temperature rises, the insulating oil and the insulating materials of the transformer are aged to a certain degree and gas volatilizes, the aging life reduction of the transformer is accelerated, and how to calculate the operation state of the reverse transformer according to the volatilized gas cannot be overcome by the prior art.

Disclosure of Invention

In view of the foregoing, it is desirable to provide a transformer detection method, apparatus, computer device and storage medium based on ethylene signals.

In a first aspect, an embodiment of the present invention provides a method for detecting a transformer based on an ethylene signal, where the method includes the following steps:

and determining fault information of the transformer according to the estimated ethylene gas concentration.

Further, the step of introducing ethylene gas with a known concentration into the white cell, and calculating a first relation between a peak value and a concentration of a second harmonic gas absorption peak of ethylene comprises:

respectively introducing high-concentration ethylene and low-concentration ethylene into the white pool, and respectively extracting second harmonic waves;

Further, the step of introducing ethylene gas with a known concentration into the white cell, and calculating a first relation between a peak value of an absorption peak of second harmonic gas of ethylene and the concentration further includes:

designing a Butterworth filter in a filter design tool in MATLAB according to the determined ethylene frequency;

extracting filter coefficients according to parameters of a Butterworth filter, such as passband frequency, stopband frequency, passband attenuation and stopband attenuation;

filtering by using the determined ethylene frequency as a passband frequency in a dual filtering mode of firstly passing through a high-pass filter and then passing through a low-pass filter;

Further, the determining fault information of the transformer according to the estimated ethylene gas concentration includes:

obtaining the aging condition of insulating oil and solid insulating materials in a transformer under the action of temperature, electric field and oxidation environmental factors;

On the other hand, the embodiment of the invention also provides a transformer detection system based on ethylene signals, which comprises:

and the fault analysis module is used for determining fault information of the transformer according to the calculated ethylene gas concentration.

Further, the relationship determination module includes a frequency processing unit, and the frequency processing unit is configured to:

respectively introducing high-concentration ethylene and low-concentration ethylene into the white pool, and respectively extracting second harmonic waves;

Further, the relationship determination module further includes a filtering optimization unit, and the filtering optimization unit is configured to:

designing a Butterworth filter in a filter design tool in MATLAB according to the determined ethylene frequency;

extracting filter coefficients according to parameters of a Butterworth filter, such as passband frequency, stopband frequency, passband attenuation and stopband attenuation;

filtering by using the determined ethylene frequency as a passband frequency in a dual filtering mode of firstly passing through a high-pass filter and then passing through a low-pass filter;

Further, the fault analysis module includes a gas evaluation unit for:

obtaining the aging condition of insulating oil and solid insulating materials in a transformer under the action of temperature, electric field and oxidation environmental factors;

The embodiment of the present invention further provides a computer device, which includes a memory, a processor, and a computer program stored in the memory and capable of running on the processor, and when the processor executes the computer program, the following steps are implemented:

and determining fault information of the transformer according to the estimated ethylene gas concentration.

An embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the following steps:

and determining fault information of the transformer according to the estimated ethylene gas concentration.

The method, the device, the computer equipment and the storage medium for detecting the transformer based on the ethylene signal comprise the following steps: introducing ethylene gas with known concentration into the white pool, and calculating to obtain a first relation between the peak value and the concentration of a second harmonic gas absorption peak of the ethylene; separating ethylene gas dissolved in oil from the transformer, detecting the concentration of the ethylene gas by using a TDLAS technology, and reversely deducing the concentration of the ethylene gas according to the relation between the peak value of a second harmonic gas absorption peak and the concentration; and determining fault information of the transformer according to the estimated ethylene gas concentration. The Butterworth filter is combined with the TDLAS signal processing, the advantages of flatness in a pass band and high attenuation speed in a stop band of the Butterworth filter are utilized, a double filtering mode of high pass and low pass is adopted, and the influence of noise in second harmonic on an absorption peak is comprehensively reduced. The second harmonic wave filtered by the Butterworth filter does not have phenomena of aliasing peak, interference peak and the like, is very beneficial to the feature extraction of the absorption peak, and the stability is obviously enhanced. The detection of the final ethylene becomes very accurate, so that the fault analysis of the transformer is more reasonable, and the interference of mechanical detection on the normal operation of the transformer is avoided.

Drawings

FIG. 1 is a schematic flow diagram of a method for detecting a transformer based on an ethylene signal according to an embodiment;

FIG. 2 is a schematic flow chart of the determination of ethylene frequency in one embodiment;

FIG. 3 is a schematic flow chart illustrating a process for filter optimization of a gas in one embodiment;

FIG. 4 is a schematic flow diagram illustrating fault evaluation based on ethylene in one embodiment;

FIG. 5 is a block diagram of an embodiment of a system for detecting a transformer based on an ethylene signal;

FIG. 6 is a diagram illustrating an internal structure of a computer device according to an embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In one embodiment, as shown in fig. 1, there is provided a method for detecting a transformer based on an ethylene signal, comprising the steps of:

step 101, introducing ethylene gas with known concentration into a white cell, and calculating to obtain a first relation between the peak value and the concentration of a second harmonic gas absorption peak of ethylene;

102, separating ethylene gas dissolved in oil from the transformer, detecting the concentration of the ethylene gas by using a TDLAS technology, and reversely deducing the concentration of the ethylene gas according to the relation between the peak value of a second harmonic gas absorption peak and the concentration;

and 103, determining fault information of the transformer according to the estimated ethylene gas concentration.

Specifically, the scenario of the present embodiment is a transformer oil spectrum online monitor, which heats oil in a transformer, separates gas dissolved in the oil (ethylene is one of the gases), measures the concentration of the gas by using a TDLAS technology, and estimates a possible hidden fault of the transformer through the gas concentration. The TDLAS technique is a technique for calculating the component and state information of a gaseous substance by applying a tuning signal to a diode laser to scan the wavelength and obtain the absorption spectrum of the gaseous substance, and is widely applied to gas detection in the industrial and environmental fields. In the actual detection process, the peak-to-peak value of the gas absorption peak in the second harmonic is usually used as the basis for concentration calculation, and the first-order relationship between the peak-to-peak value and the concentration of the gas absorption peak in the second harmonic is calculated by introducing gas with known concentration into the white cell. When the gas with unknown concentration needs to be measured, the second harmonic peak value and the relation are calculated, and the concentration can be reversely deduced. Therefore, the accurate finding of the gas absorption peak in the TDLAS realization process is the first priority of accurate concentration measurement.

In addition, the Butterworth filter is combined with the TDLAS signal processing, the advantages of flatness in a pass band and high attenuation speed in a stop band of the Butterworth filter are utilized, a double filtering mode of high pass and low pass is adopted, and the influence of noise in second harmonic on an absorption peak is comprehensively reduced. The second harmonic wave filtered by the Butterworth filter does not have phenomena of aliasing peak, interference peak and the like, is very beneficial to the feature extraction of the absorption peak, and the stability is obviously enhanced. The detection of the final ethylene becomes very accurate, so that the fault analysis of the transformer is more reasonable, and the interference of mechanical detection on the normal operation of the transformer is avoided.

In one embodiment, as shown in fig. 2, the process for determining ethylene frequency comprises:

step 201, respectively introducing high-concentration ethylene and low-concentration ethylene into a white pool, and respectively extracting second harmonics;

step 202, performing spectrum analysis on the second harmonic, selecting a frequency corresponding to ethylene gas, and calculating the frequency according to the width of an absorption peak of ethylene under the condition of high concentration;

and step 203, determining the ethylene frequency according to the fact that the amplitude corresponding to the high-concentration gas frequency is larger and the amplitude corresponding to the low-concentration gas frequency is obviously reduced in the frequency spectrum.

Specifically, high-concentration ethylene and low-concentration ethylene are respectively introduced into the white pool, and second harmonics are respectively extracted. The second harmonic obtained is subjected to spectral analysis, the frequency corresponding to ethylene is selected, and the approximate frequency can be calculated from the width of the absorption peak of ethylene at high concentration. To ensure that the selected ethylene frequency is accurate, multiple tests can be performed to observe that, from the spectrum, a high concentration of a certain frequency corresponds to a larger amplitude, and a low concentration of the certain frequency corresponds to a significantly reduced amplitude, so that the certain frequency is determined to be the ethylene frequency.

In one embodiment, as shown in fig. 3, the process of performing the filter optimization process on the gas includes:

step 301, designing a butterworth filter in a filter design tool in MATLAB according to the determined ethylene frequency;

step 302, extracting filter coefficients according to parameters of a Butterworth filter, such as passband frequency, stopband frequency, passband attenuation and stopband attenuation;

step 303, filtering the determined ethylene frequency as a passband frequency in a dual-filtering mode of firstly passing through a high-pass filter and then passing through a low-pass filter;

and 304, according to the second harmonic extracted by the phase-locked amplifier, enabling the second harmonic to pass through a Butterworth high-pass filter and a low-pass filter to obtain the filtered second harmonic.

Specifically, in order to improve the waveform of the second harmonic in the case of low concentration, so that the peak-to-peak value is easy to find and stable, the present embodiment proposes a method of combining a butterworth filter with TDLAS digital signal processing. The traditional filter is usually realized by hardware, the processing speed is high, but the flexibility of the filtering is not enough. Digital filtering, also known as software filtering, is a data processing process that uses mathematical calculations to suppress or remove noise in a digital signal, leaving valid signals. The low-pass filter allows only signal components below the cut-off frequency to pass through, and signal components above the cut-off frequency are suppressed. The low pass filter is the basis of the filter design, and the high pass, band pass and band stop filters can be obtained by frequency conversion of the low pass filter.

Wherein A is_passThe passband attenuation is called the maximum attenuation of the passband, and has a conversion relation with the passband ripple as follows:

A_pass＝-20lg(1-δ_pass)

A_stopfor stopband attenuation, the overall stopband minimum attenuation, in dB, is related to the stopband ripple as follows:

A_stop＝-20lg(δ_stop)

δ_passis the passband ripple, δ_stopThe stopband ripple is the range of fluctuation of the ripple, namely the amplitude-frequency characteristic.Ω_passThe amplitude-frequency characteristic value at the boundary frequency of the passband is 1-delta_pass。Ω_stopThe stopband cutoff frequency is the frequency at which the amplitude characteristic is equal to the stopband ripple.

In a low-pass digital filter, the amplitude of the fluctuation of the amplitude-frequency response in the pass band is determined by the pass-band ripple delta_passIs determined. Passband ripple delta_passThe smaller the amplitude-frequency response of the filter in the pass band is, the closer the amplitude-frequency response is to 1, and the smaller the loss of the amplitude of the signal in the pass band is when the signal passes through the filter. Stop band ripple delta_stopThe smaller the amplitude-frequency response of the filter in the stop band is, the closer the amplitude-frequency response is to 0, the more the attenuation of the signal in the stop band is when the signal passes through the filter, and the better the suppression effect on the interference signal is. The amplitude-frequency characteristic in the transition band is monotonously decreased, and the smaller the bandwidth, the closer to an ideal filter is. In the process of determining the ethylene frequency, the ethylene frequency is taken as a passband frequency, and filtering is performed in a dual filtering mode of firstly passing through a high-pass filter and then passing through a low-pass filter; and finally, according to the second harmonic extracted by the phase-locked amplifier, enabling the second harmonic to pass through a Butterworth high-pass filter and a low-pass filter to obtain the filtered second harmonic.

In one embodiment, as shown in FIG. 4, performing fault assessment based on ethylene includes:

step 401, acquiring the aging condition of insulating oil and solid insulating materials in a transformer under the action of temperature, electric field and oxidation environmental factors;

step 402, determining transformer fault information corresponding to ethylene under different concentrations according to various running states of the transformer under different types of mixed gas of ethylene.

Specifically, the faults in the operation of the transformer mainly include three types, namely mechanical faults, electrical faults and thermal faults, wherein the electrical faults and the thermal faults are mainly used. At present, most transformers of domestic power systems adopt insulating oil for insulation and heat dissipation. With long-term operation, the insulating oil and the solid insulating material in the transformer are gradually aged under the action of temperature, electric field, oxidation and other factors, and a small amount of H2 and low molecular hydrocarbon gas such as CH4, C2H6, C2H4 and the like are generated. The CO and the CO2 are generated by the overheating decomposition of the fixed insulating material, and the generation of the C2H2 represents the transmission discharge fault of the transformer, so the potential fault of the transformer can be obtained by analyzing the dissolved gas in the oil. Therefore, according to the different running states of the transformer and the ethylene in different types of mixed gas, the corresponding transformer fault information of the ethylene in different concentrations is determined, and further the accuracy and the stability of the measurement of the C2H4 directly influence the result of transformer fault identification.

It should be understood that, although the steps in the above-described flowcharts are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least a portion of the steps in the above-described flowcharts may include multiple sub-steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the order of performing the sub-steps or the stages is not necessarily sequential, but may be performed alternately or alternatingly with other steps or at least a portion of the sub-steps or stages of other steps.

In one embodiment, as shown in fig. 5, there is provided a transformer detection system based on ethylene signals, including:

a relation determining module 501, configured to introduce ethylene gas with a known concentration into the white cell, and calculate a first relation between a peak value and a concentration of a second harmonic gas absorption peak of ethylene;

a concentration calculation module 502, configured to separate ethylene gas dissolved in oil from the transformer, detect the concentration of the ethylene gas by using a TDLAS technology, and reversely estimate the ethylene gas concentration according to a relationship between a peak value of a second harmonic gas absorption peak and the concentration;

and a fault analysis module 503, configured to determine fault information of the transformer according to the estimated ethylene gas concentration.

In one embodiment, as shown in fig. 5, the relationship determination module 501 includes a frequency processing unit 5011, the frequency processing unit 5011 is configured to:

respectively introducing high-concentration ethylene and low-concentration ethylene into the white pool, and respectively extracting second harmonic waves;

In one embodiment, as shown in fig. 5, the relationship determination module 501 further comprises a filter optimization unit 5012, the filter optimization unit 5012 being configured to:

designing a Butterworth filter in a filter design tool in MATLAB according to the determined ethylene frequency;

extracting filter coefficients according to parameters of a Butterworth filter, such as passband frequency, stopband frequency, passband attenuation and stopband attenuation;

filtering by using the determined ethylene frequency as a passband frequency in a dual filtering mode of firstly passing through a high-pass filter and then passing through a low-pass filter;

In one embodiment, as shown in fig. 5, the fault analysis module 503 includes a gas evaluation unit 5031, and the gas evaluation unit 5031 is configured to:

obtaining the aging condition of insulating oil and solid insulating materials in a transformer under the action of temperature, electric field and oxidation environmental factors;

For specific limitations of the transformer detection system based on ethylene signals, reference may be made to the above limitations of the transformer detection method based on ethylene signals, and details are not repeated here. The modules in the above-mentioned transformer detection system based on ethylene signals can be implemented in whole or in part by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.

FIG. 6 is a diagram illustrating an internal structure of a computer device in one embodiment. As shown in fig. 6, the computer apparatus includes a processor, a memory, a network interface, an input device, and a display screen connected through a system bus. Wherein the memory includes a non-volatile storage medium and an internal memory. The non-volatile storage medium of the computer device stores an operating system and may further store a computer program, which, when executed by the processor, may cause the processor to implement the method for detecting a transformer based on an ethylene signal. The internal memory may also have a computer program stored therein, which when executed by the processor, causes the processor to perform a method for detecting a transformer based on an ethylene signal. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, a key, a track ball or a touch pad arranged on the shell of the computer equipment, an external keyboard, a touch pad or a mouse and the like.

Those skilled in the art will appreciate that the architecture shown in fig. 6 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.

In one embodiment, a computer device is provided, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, the processor implementing the following steps when executing the computer program:

and determining fault information of the transformer according to the estimated ethylene gas concentration.

In one embodiment, the processor, when executing the computer program, further performs the steps of:

respectively introducing high-concentration ethylene and low-concentration ethylene into the white pool, and respectively extracting second harmonic waves;

In one embodiment, the processor, when executing the computer program, further performs the steps of:

designing a Butterworth filter in a filter design tool in MATLAB according to the determined ethylene frequency;

extracting filter coefficients according to parameters of a Butterworth filter, such as passband frequency, stopband frequency, passband attenuation and stopband attenuation;

filtering by using the determined ethylene frequency as a passband frequency in a dual filtering mode of firstly passing through a high-pass filter and then passing through a low-pass filter;

In one embodiment, the processor, when executing the computer program, further performs the steps of:

obtaining the aging condition of insulating oil and solid insulating materials in a transformer under the action of temperature, electric field and oxidation environmental factors;

In one embodiment, a computer-readable storage medium is provided, having a computer program stored thereon, which when executed by a processor, performs the steps of: