CN103176036A - Device and method for monitoring alternating current entering direct current system - Google Patents

Abstract

The invention relates to a device and method for monitoring direct current insulation. The device comprises two balancing resistors respectively connected between a positive pole of a direct current bus and the ground and between a negative pole of the direct current bus and the ground, a sampling signal conditioning unit, an analog/digital (AD) converter and a processor. The sampling signal conditioning unit is used for conditioning extracted alternating current electric signals, the input end of the sampling signal conditioning unit is connected with the balancing resistors, the AD converter is used for converting conditioned alternating current simulation electric signals into digital signals, the input end of the AD converter is connected with the output of the sampling signal conditioning unit, and the processor is used for performing differential filtering operation on the digital signals output by the AD converter, extracting alternating current quantity in the AD converter, judging, giving an alarm after alternating current entering the direct current system is detected, and recording voltage waveform of the direct current bus. The device and method for monitoring the direct current insulation can monitor that the alternating current enters the direct current system, gives an alarm after alternating current entering the direct current system is detected, and can record the voltage waveform of the direct current bus.

Description

The monitoring alternating current seals in the device and method of straight-flow system

Technical field

The present invention relates to monitor the device and method that alternating current seals in straight-flow system, belong to straight-flow system and monitor the field.

Background technology

In electric system, the reliability service of direct supply plays a very important role security of system is stable, and straight-flow system is generally all installed the supervising devices such as D.C. isolation monitoring device.But, due to the wearing and tearing of AC and DC cable in long-time running, or the damage of AC and DC device components and parts, or manual operation accidentally, can cause alternating current to seal in straight-flow system.Accident in generating plant and transformer station's generation showed in recent years, after alternating current seals in straight-flow system, easily cause protective relaying maloperation or isolating switch false tripping, as " the AC in the DC loop causes the analysis of causes of switch trip " (relay, the 14th phase in 2007) the accident overview of generating plant, Xibaipo 220kV booster stations intermediate switch tripping operation introduced in a literary composition, and analyzed alternating current and seal in after DC loop the impact of relay protection, method and measure proposed; " the 220V industrial frequency AC is sneaked into the switch mis-jumping case study that DC control circuit causes " (Shandong Electric Power Group technology, the 4th phase in 2009) literary composition has been introduced the industrial frequency AC that Laiwu power plant causes due to electric arc and has been sealed in the failure condition that DC control circuit causes station-service Backup Power Switch false switching, find the reason of problem by test, inspection and analysis, and taked corresponding the processing and the precautionary measures; " analysis of straight-flow system is scurried in interchange " (direct supply technology, the 1st phase in 2011) literary composition to two power plant because the accident phenomenon that the AC in the DC system causes is analyzed and described.

Fig. 1～Fig. 3 is the circuit diagram that alternating current seals in straight-flow system, wherein, Fig. 1 is that alternating current seals in the schematic diagram of straight-flow system by dc bus positive pole and negative pole, and namely dc bus positive pole and negative pole are received respectively in the two poles of the earth of alternating current, and it shows as alternating voltage of stack on DC voltage; Fig. 2 is that alternating current seals in the schematic diagram of straight-flow system by dc bus negative pole and the earth, and it shows as alternating voltage of stack on the DC voltage between dc bus negative pole and the earth; To be alternating current by dc bus anodal and the earth seals in the schematic diagram of straight-flow system for Fig. 3, and it shows as the alternating voltage that superposes on DC voltage between dc bus positive pole and the earth.In generating plant or transformer station, because alternating current is generally ground connection or by grounding through arc, so it is comparatively common that Fig. 2 and alternating current shown in Figure 3 seal in the fault of straight-flow system.

Alternating current seals in straight-flow system and has the characteristics such as intermittence, disguise, after accident occurs, often bring comparatively serious consequence, there is no in the market and can in time detect the device that alternating current seals in straight-flow system, alternating current is sealed in straight-flow system can't monitor and report to the police.

Summary of the invention

The purpose of this invention is to provide a kind of device and method that alternating current seals in straight-flow system of monitoring, this device has alternating current and seals in the straight-flow system monitoring function, reports to the police after alternating current seals in straight-flow system detecting, and can record the voltage waveform of dc bus.

Technical solution of the present invention comprises that the monitoring alternating current seals in the apparatus and method of straight-flow system.

A kind ofly monitor the device that alternating current seals in straight-flow system, it is characterized in that comprising:

The alternating current quantity sampling circuit is used for extracting the ac signal that seals in straight-flow system; The sampled signal modulate circuit is used for the ac signal that extracts is nursed one's health, and its input connects from the output that exchanges the electric quantity acquisition circuit; AD converter, the AC analogue electric signal after being used for nursing one's health converts digital signal to, and its input connects the output of sampled signal modulate circuit; Processor is used for the digital signal of AD converter output is carried out computing, calculates and seals in alternating voltage, and judge, after alternating current being detected and sealing in straight-flow system, sends the voltage waveform of reporting to the police and recording dc bus.

Further:

Described alternating current quantity sampling circuit comprises two balance resistances, and two balance resistances are connected between dc bus positive pole and ground, between dc bus negative pole and ground.

Described alternating current quantity sampling circuit comprises two balance resistances, at least two AC signal extraction circuit that are composed in series by divider resistance and capacitance; Two balance resistances are connected between dc bus positive pole and ground and between dc bus negative pole and ground; If an AC signal is extracted circuit, this AC signal extraction circuit is connected between dc bus positive pole and the earth or is connected between dc bus negative pole and the earth; If two AC signal are extracted circuit, between dc bus positive pole and the earth and the dc bus negative pole with the earth among from being connected an AC signal extraction circuit.

Described alternating current quantity sampling circuit comprises that at least one is by the elementary AC signal extraction circuit that is composed in series of capacitance and AC voltage transformer; If an AC signal is extracted circuit, this AC signal extraction circuit is connected between dc bus positive pole and the earth or is connected between dc bus negative pole and the earth; If two AC signal are extracted circuit, between dc bus positive pole and the earth and the dc bus negative pole with the earth among from being connected an AC signal extraction circuit; Secondary and the sampled signal modulate circuit of AC voltage transformer is connected.

A kind ofly monitor the method that alternating current seals in straight-flow system, it is characterized in that comprising the following steps:

1) with following methods gather over the ground voltage U of dc bus positive pole+and over the ground voltage U of dc bus negative pole-:

If the ac frequency that may seal in straight-flow system is f, the voltage sample time interval is Δ t, and the sampling number in one-period is:

$n=\frac{1}{f\×\mathrm{\Δt}}$

Be located at the voltage that collects in first cycle and be respectively u ₁, u ₂U _n, the voltage that next cycle collects is respectively u _n+1, u _n+2U _2n, each voltage that collects is drawn the difference of each voltage and a upper voltage by following computing:

Δu ₁＝u ₂-u ₁

……

Δu _n＝u _n+1-u _n

……

Δu _2n-1＝u _2n-u _2n-1

Collecting u _n+1After namely gathering n+1 voltage, to the Δ u that calculates ₁Δ u _nCarry out following computing:

$U_{\mathrm{ac}}=A\×\sqrt{\frac{{{\mathrm{\Δu}}_1}^2+......+{{\mathrm{\Δu}}_n}^2}{n}}$

U _acBe the current effective value that seals in the alternating current of straight-flow system, wherein A is correction coefficient,

2) U to calculating _acWith the alarming value U that sets _acaCompare, if U _acGreater than the alarming value U that sets _aca, implement to report to the police, and fault waveform carried out record, otherwise continue step 3);

3) after gathering n+1 point, the difference of this point voltage and a upper voltage is a bit namely calculated in later every collection,

Gathering u _xAfter namely gathering x voltage, x is the sequence number of voltage acquisition herein, and it is worth greater than n+1, to the Δ u that calculates _x-nΔ u _xCarry out following computing:

$U_{\mathrm{ac}}=A\×\sqrt{\frac{{{\mathrm{\Δu}}_{x-n}}^2+......+{{\mathrm{\Δu}}_x}^2}{n}}$

4) in each sampling time interval Δ t, to the U that calculates _acWith the alarming value U that sets _acaCompare;

5) if U _acGreater than the alarming value U that sets _aca, implement to report to the police, and fault waveform carried out record, otherwise return to step 3).

Due to Real-time Collection dc bus positive pole of the present invention voltage and dc bus negative pole voltage over the ground over the ground, therefore the alternating current that seals in straight-flow system can in time be detected, send alerting signal, and by recording the DC bus-bar voltage waveform, for malfunction elimination provides foundation.

Description of drawings

Fig. 1 is the circuit diagram that alternating current seals in straight-flow system, and alternating current shown in this figure seals in by dc bus positive pole and negative pole.

Fig. 2 is the circuit diagram that alternating current seals in straight-flow system, and shown in this figure, alternating current seals in by dc bus negative pole and the earth.

Fig. 3 is the circuit diagram that alternating current seals in straight-flow system, and alternating current shown in this figure seals in by dc bus positive pole and the earth.

Fig. 4 is the theory diagram that monitoring alternating current of the present invention seals in the device of straight-flow system.

Fig. 5 is embodiment 1 theory diagram of the monitoring alternating current of the present invention device that seals in straight-flow system.

Fig. 6 is embodiment 2 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.

Fig. 7 is embodiment 3 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.

Fig. 8 is embodiment 4 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.

Fig. 9 is embodiment 5 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.

Figure 10 is embodiment 6 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.

Figure 11 is embodiment 7 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.

Figure 12 is that the present invention monitors the method flow diagram that alternating current seals in straight-flow system.

Embodiment

The present invention relates to monitor the apparatus and method that alternating current seals in straight-flow system.

The inventive system comprises:

The alternating current quantity sampling circuit is used for extracting the ac signal that seals in straight-flow system; The sampled signal modulate circuit is used for the ac signal that extracts is nursed one's health, and its input connects from the output that exchanges the electric quantity acquisition circuit; AD converter, the AC analogue electric signal after being used for nursing one's health converts digital signal to, and its input connects the output of sampled signal modulate circuit; Processor is used for the digital signal of AD converter output is carried out computing, calculates and seals in alternating voltage, and judge, after alternating current being detected and sealing in straight-flow system, sends the voltage waveform of reporting to the police and recording dc bus.

Method of the present invention comprises following steps:

1) with following methods gather over the ground voltage U of dc bus positive pole+and over the ground voltage U of dc bus negative pole-:

If the ac frequency that may seal in straight-flow system is f, the voltage sample time interval is Δ t, and the sampling number in one-period is:

$n=\frac{1}{f\×\mathrm{\Δt}}$

Be located at the voltage that collects in first cycle and be respectively u ₁, u ₂U _n, the voltage that next cycle collects is respectively u _n+1, u _n+2U _2n, each voltage that collects is drawn the difference of each voltage and a upper voltage by following computing:

Δu ₁＝u ₂-u ₁

……

Δu _n＝u _n+1-u _n

……

Δu _2n-1＝u _2n-u _2n-1

Collecting u _n+1After namely gathering n+1 voltage, to the Δ u that calculates ₁Δ u _nCarry out following computing:

$U_{\mathrm{ac}}=A\×\sqrt{\frac{{{\mathrm{\Δu}}_1}^2+......+{{\mathrm{\Δu}}_n}^2}{n}}$

U _acBe the current effective value that seals in the alternating current of straight-flow system, wherein A is correction coefficient,

2) U to calculating _acWith the alarming value U that sets _acaCompare, if U _acGreater than the alarming value U that sets _aca, implement to report to the police, and fault waveform carried out record, otherwise continue step 3);

3) after gathering n+1 point, the difference of this point voltage and a upper voltage is a bit namely calculated in later every collection,

Gathering u _xAfter namely gathering x voltage, x is the sequence number of voltage acquisition herein, and it is worth greater than n+1, to the Δ u that calculates _x-nΔ u _xCarry out following computing:

$U_{\mathrm{ac}}=A\×\sqrt{\frac{{{\mathrm{\Δu}}_{x-n}}^2+......+{{\mathrm{\Δu}}_x}^2}{n}}$

4) in each sampling time interval Δ t, to the U that calculates _acWith the alarming value U that sets _acaCompare;

5) if U _acGreater than the alarming value U that sets _aca, implement to report to the police, and fault waveform carried out record, otherwise return to step 3).

Describe in detail below in conjunction with accompanying drawing.

Fig. 4 is the theory diagram that monitoring alternating current of the present invention seals in the device of straight-flow system.The device that this monitoring alternating current seals in straight-flow system comprises: alternating current Acquisition Circuit, sampled signal modulate circuit, AD converter, processor.Straight-flow system anodal KM+, negative pole KM-and the earth access device enter the alternating current Acquisition Circuit, and the alternating current Acquisition Circuit is responsible for the ac signal that seals in straight-flow system is extracted, and the electric signal that extracts is inputed to the sampled signal modulate circuit; The sampled signal modulate circuit to the AC signal of extracting isolate, the processing such as amplification, filtering, ac signal is processed into the simulating signal that can be identified and process by AD converter; AD converter is the digital signal of analog signal conversion for being identified by processor of input, and inputs to processor; Processor carries out digital filtering, gets the operations such as average or effective value the digital signal of AD converter output, calculate the alternating voltage that seals in straight-flow system, and compare with the magnitude of voltage of setting, report to the police after surpassing setting voltage, and the recording voltage waveform.

Fig. 5 is the theory diagram of the embodiment 1 of the monitoring alternating current of the present invention device that seals in straight-flow system.In figure, R1, R2 are the balance resistance that is arranged in device, and balance resistance R1 one end is connected with the anodal KM+ of straight-flow system, and the other end is connected with the earth; Balance resistance R2 one end is connected with straight-flow system negative pole KM-, and the other end is connected with the earth; In general, R1=R2.After alternating current sealed in straight-flow system, an AC signal will superpose on original DC voltage.After this signals collecting, send into the sampled signal modulate circuit, by processing such as step-down, isolation, amplification, filtering, nurse one's health into the simulating signal that can be processed by AD converter, AD converter is digital signal with analog signal conversion, and be transferred to processor, processor carries out the differential filtering computing to this signal, removes DC component, extracts AC compounent, and AC compounent is carried out the root mean square computing, obtain the effective value of this electric signal.

The above-mentioned algorithm that carries out the differential filtering computing as shown in figure 12.U in figure _nThe magnitude of voltage of n the point that expression gathers, u _n+1The magnitude of voltage of n+1 the point that expression gathers, f represents to gather the frequency of AC signal, and Δ t represents two time intervals between sampled point, u _xRepresent x the magnitude of voltage of putting and x greater than n, Δ u _xRepresent the poor of x point voltage value and x-1 point voltage value, Δ U _acThe effective value that expression calculates by the difference array, U _acThe effective value of expression AC signal, A represents scale-up factor, U _acaExpression exchanges the alarm door limit value.The difference Δ u of the magnitude of voltage of the magnitude of voltage of n+1 point and n point in image data _nConsist of differential data, need to gather and consist of the difference array in first sampling period after 1/ (f * Ω t)+1 data and be respectively Δ u ₁, Δ u ₂... Δ u _n, wherein

Δu ₁＝u ₂-u ₁

……

Δu _n＝u _n+1-u _n

Then, obtain AC value U according to following computing _ac

${\mathrm{\ΔU}}_{\mathrm{ac}}=\sqrt{\frac{{{\mathrm{\Δu}}_1}^2+......+{{\mathrm{\Δu}}_n}^2}{n}}$

U _ac＝A×ΔU _ac

After gathering (n+1) individual point, effective value calculating is a bit namely carried out in every collection, is gathering u _xAfter (x is the sequence number of voltage acquisition, and it is worth greater than (n+1)), to the Δ u that calculates _x-n, Δ u _X-(n-1)... Δ u _xCarry out following computing and obtain AC value U _ac

$\mathrm{\Δ}{U}_{\mathrm{ac}}=\sqrt{\frac{{{\mathrm{\Δu}}_{x-n}}^2+{{\mathrm{\Δu}}_{x-(n-1)}}^2......+{{\mathrm{\Δu}}_x}^2}{n}}$

U _ac＝A×ΔU _ac

In each sampling time interval Δ t, to the U that calculates _acWith the alarming value U that sets _acaCompare, reach and implement after alert if to report to the police, and fault waveform is carried out record.

Calculate effective value U _ac, the sampled point of a complete cycle of needs just can carry out so the starting stage need to reach a complete sampling period; And in the later stage, because the data at least one cycle have been arranged, therefore after point of every collection (establishing sequence number is x), can delete (x-n) individual point of its front, thereby form a new complete cycle and calculate effective value, in other words, the calculating of effective value is real-time.

Fig. 6 is embodiment 2 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.In figure, R1, R2 are the balance resistance that is arranged in the D.C. isolation monitoring device, and serial connection is extracted circuit by the AC signal that resistance R 3, capacitor C 1, resistance R 4 are composed in series between dc bus negative pole and ground.Because electric capacity has the direct current of partition, passes through to exchange, the alternating current that seals in straight-flow system can be by the path that is made of resistance R 3, capacitor C 1 and resistance R 4.Resistance R 3 and resistance R 4 mainly play the dividing potential drop effect, from taking-up voltage carries out signal condition by (being R3 figure) on the lower resistance of the pressure drop after dividing potential drop, to deliver to AD converter through the voltage analog signal of conditioning, can seal in by directly adopting a calculating effective value of the alternating current of straight-flow system.

Fig. 7 is embodiment 3 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.This embodiment and embodiment 2 are basically identical, and difference is that the AC signal extraction circuit that is composed in series by resistance R 3, capacitor C 1, resistance R 4 is concatenated between dc bus positive pole and ground.

Fig. 8 is embodiment 4 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.In figure, R1, R2 are the balance resistance that is arranged in the D.C. isolation monitoring device, between dc bus negative pole and ground, serial connection is extracted circuit by the AC signal that resistance R 3, capacitor C 1, resistance R 4 are composed in series, and serial connection is extracted circuit by the AC signal that resistance R 5, capacitor C 2, resistance R 6 are composed in series between dc bus positive pole and ground.This embodiment is the cumulative form of embodiment 2, embodiment 3, and namely ac signal is by jointly taking out between straight-flow system positive pole and ground, straight-flow system negative pole and ground.

Fig. 9 is embodiment 5 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.In figure, the elementary AC signal that is composed in series of capacitor C 1 and AC voltage transformer T1 is extracted circuit and is connected between straight-flow system positive pole and ground, correspondingly, the elementary AC signal extraction circuit that is composed in series of capacitor C 2 and AC voltage transformer T2 is connected between straight-flow system negative pole and ground.The secondary sampled signal modulate circuit that is connected to of voltage transformer (VT) T1 and voltage transformer (VT) T2.After alternating current seals in straight-flow system, must be by the elementary formation loop of capacitor C 1 or C2 and voltage transformer (VT) T1 or T2, the secondary ac signal that just can induce corresponding proportion at voltage transformer (VT) T1 or T2, this electric signal by signal conditioning circuit amplify, the processing such as filtering, and will deliver to AD converter through the voltage analog signal of conditioning.

Figure 10 is embodiment 6 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.In figure, the elementary AC signal that is composed in series of capacitor C 1 and AC voltage transformer T1 is extracted circuit and is connected between straight-flow system positive pole and ground.The secondary sampled signal modulate circuit that is connected to of voltage transformer (VT) T1.After alternating current seals in straight-flow system, can be by the elementary formation loop of capacitor C 1, voltage transformer (VT) T1, the secondary ac signal that just can induce corresponding proportion at voltage transformer (VT) T1, this electric signal by signal conditioning circuit amplify, the processing such as filtering, and will deliver to AD converter through the voltage analog signal of conditioning.

Figure 11 is embodiment 7 theory diagrams of the monitoring alternating current of the present invention device that seals in straight-flow system.In figure, the elementary AC signal that is composed in series of capacitor C 2 and AC voltage transformer T2 is extracted circuit and is connected between straight-flow system negative pole and ground.The secondary sampled signal modulate circuit that is connected to of voltage transformer (VT) T2.After alternating current seals in straight-flow system, can be by the elementary formation loop of capacitor C 2 with voltage transformer (VT) T2, the secondary ac signal that just can induce corresponding proportion at voltage transformer (VT) T2, this electric signal by signal conditioning circuit amplify, the processing such as filtering, and will deliver to AD converter through the voltage analog signal of conditioning.

Claims (5)

1. monitor the device that alternating current seals in straight-flow system for one kind, it is characterized in that comprising:

The alternating current quantity sampling circuit is used for extracting the ac signal that seals in straight-flow system;

The sampled signal modulate circuit is used for the ac signal that extracts is nursed one's health, and its input connects from the output that exchanges the electric quantity acquisition circuit;

AD converter, the AC analogue electric signal after being used for nursing one's health converts digital signal to, and its input connects the output of sampled signal modulate circuit;

Processor is used for the digital signal of AD converter output is carried out computing, calculates and seals in alternating voltage, and judge, after alternating current being detected and sealing in straight-flow system, sends the voltage waveform of reporting to the police and recording dc bus.

2. monitoring alternating current as claimed in claim 1 seals in the device of straight-flow system, it is characterized in that:

Described alternating current quantity sampling circuit comprises two balance resistances, and two balance resistances are connected between dc bus positive pole and ground, between dc bus negative pole and ground.

3. monitoring alternating current as claimed in claim 1 seals in the device of straight-flow system, it is characterized in that:

Described alternating current quantity sampling circuit comprises two balance resistances, at least two AC signal extraction circuit that are composed in series by divider resistance and capacitance;

Two balance resistances are connected between dc bus positive pole and ground and between dc bus negative pole and ground;

If an AC signal is extracted circuit, this AC signal extraction circuit is connected between dc bus positive pole and the earth or is connected between dc bus negative pole and the earth;

If two AC signal are extracted circuit, between dc bus positive pole and the earth and the dc bus negative pole with the earth among from being connected an AC signal extraction circuit.

4. monitoring alternating current as claimed in claim 1 seals in the device of straight-flow system, it is characterized in that:

Described alternating current quantity sampling circuit comprises that at least one is by the elementary AC signal extraction circuit that is composed in series of capacitance and AC voltage transformer;

If an AC signal is extracted circuit, this AC signal extraction circuit is connected between dc bus positive pole and the earth or is connected between dc bus negative pole and the earth;

If two AC signal are extracted circuit, between dc bus positive pole and the earth and the dc bus negative pole with the earth among from being connected an AC signal extraction circuit;

Secondary and the sampled signal modulate circuit of AC voltage transformer is connected.

5. monitor the method that alternating current seals in straight-flow system for one kind, it is characterized in that comprising the following steps:

1) with following methods gather over the ground voltage U of dc bus positive pole+and over the ground voltage U of dc bus negative pole-:

If the ac frequency that may seal in straight-flow system is f, the voltage sample time interval is Δ t, and the sampling number in one-period is:

$n=\frac{1}{f\×\mathrm{\Δt}}$

Be located at the voltage that collects in first cycle and be respectively u ₁, u ₂U _n, the voltage that next cycle collects is respectively u _n+1, u _n+2U _2n, each voltage that collects is drawn the difference of each voltage and a upper voltage by following computing:

Δu ₁＝u ₂-u ₁

……

Δu _n＝u _n+1-u _n

……

Δu _2n-1＝u _2n-u _2n-1

Collecting u _n+1After namely gathering n+1 voltage, to the Δ u that calculates ₁Δ u _nCarry out following computing:

$U_{\mathrm{ac}}=A\×\sqrt{\frac{{{\mathrm{\Δu}}_1}^2+......+{{\mathrm{\Δu}}_n}^2}{n}}$

U _acBe the current effective value that seals in the alternating current of straight-flow system, wherein A is correction coefficient,

2) U to calculating _acWith the alarming value U that sets _acaCompare, if U _acGreater than the alarming value U that sets _aca, implement to report to the police, and fault waveform carried out record, otherwise continue step 3);

3) after gathering n+1 point, the difference of this point voltage and a upper voltage is a bit namely calculated in later every collection,

Gathering u _xAfter namely gathering x voltage, x is the sequence number of voltage acquisition herein, and it is worth greater than n+1, to the Δ u that calculates _x-nΔ u _xCarry out following computing:

$U_{\mathrm{ac}}=A\×\sqrt{\frac{{{\mathrm{\Δu}}_{x-n}}^2+......+{{\mathrm{\Δu}}_x}^2}{n}}$

4) in each sampling time interval Δ t, to the U that calculates _acWith the alarming value U that sets _acaCompare;

5) if U _acGreater than the alarming value U that sets _aca, implement to report to the police, and fault waveform carried out record, otherwise return to step 3).

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