CN204903685U - Simple and convenient direct current earth fault seeks device - Google Patents

Abstract

The utility model provides a simple and convenient direct current earth fault seeks device, includes: controllable DC power supply, a shielded conductor, shielded conductor connect controllable DC power supply's positive pole and negative pole, two weak current clamp tables of high accuracy direct current, and the data acquisition instrument ware, the weak current clamp of two high accuracy direct currents table be connected with the data acquisition instrument ware. Controllable DC power supply passes through shielded conductor output offset current, and the shielded conductor successively passes two accurate split -core type meters, and opposite direction makes two split -core type meters vise two wires of direct current system that await measuring respectively again, the direction of keeping silent for and offset current opposite direction, adjustment offset current makes the reading of split -core type meter approach zero to keep output again, two split -core type meters connect wave form acquisition and analysis instrument so that carry out the analysis. The utility model provides a not enough problem of accurate split -core type meter range, simultaneously, two split -core type meters carry out the data contrast, can measure the comparison by convenient electric current to places different on the wire. Consequently, this method finds the direct current system ground point through seeking the leakage current accuracy.

Description

A kind of easy DC ground fault searches device

Technical field

The utility model relates to the field of fault detection of electric system, and what particularly relate to the DC earthing in a kind of electric system searches device.

Background technology

DC earthing is one of common fault of electric system direct current operative power source.When straight-flow system generation one-point grounding fault (direct ground connection or insulation against ground resistance reduce); generally can not produce harmfulness consequence immediately; if but there are 2 ground connection simultaneously; then may cause the misoperation of telltale, control loop and protective relaying device; cause circuit breaker trip; or directly cause direct current operative power source short circuit, thus cause serious power system accident.Therefore, do not allow straight-flow system on one point ground connection when long-time running.Must carry out continuous print in-service monitoring to direct current operative power source, when earth fault appears in its a certain point, send alerting signal immediately, prompting staff searches and gets rid of earth fault, thus stops to cause electric power system fault because of DC system grounding.

At present, electric system extensively adopts balanced bridge to monitor straight-flow system insulation against ground, as shown in Figure 1, on load branch there is high resistance ground in A point, this earth point and balance bridge earth point have potential difference (PD), then balanced bridge earth terminal has leakage current i to flow into the earth, the upper voltage of balanced bridge R1, R2 not etc., device alarm.Due to the inconvenient power failure operation of field device, reometer can not be accessed and measure, so can only go to search earth point by some round-about ways.

Comparatively conventional DC earthing searching device has: 1. open line method, and namely by cutting off the load of each road, adopt exclusive method to draw earth point, the method needs down load, complicated operation and there is considerable risk.2. clamp on dc amperemeter mensuration, as shown in Figure 1, vise loaded line with clamp on dc amperemeter, reometer reading is leakage current I ' simultaneously, but the method Shortcomings: one, because I ' value is very little, even lower than 1mA, can measure that jaw lower than the accurate clamp on amperemeter of 1mA is very little could arrive high precision, field condition differ surely simultaneously pincers to specific two lines, or wire is too thick, cannot vise two lines simultaneously.Its two, the method can only measure the difference between current between two wires side by side, and can not measure the difference between current of a wire specifying between 2, rig-site utilization is range limited.Therefore the method searches DC earthing point and inconvenience.3. AC signal method is injected: by external about 10V ac current source, by the AC signal flow through in AC clip-on ammeter measuring circuit, earth point is differentiated with this, the shortcoming of the method is the AC signal in 110V or 220V straight-flow system China and foreign countries access 5% to 10%, potential safety hazard is brought to straight-flow system, and the industry standard of current not this aspect, producer and power supply administration all do not carry out risk assessment to it.

Utility model content

The purpose of this utility model is the deficiency overcoming above-mentioned clamp on dc amperemeter mensuration, a kind of easy DC ground fault is provided to search device, by two high-precision weak current direct current split-core type meters, clamp the diverse location at different conductor respectively, measure the difference between current between them, find out earth point quickly and easily.

The utility model is achieved through the following technical solutions above-mentioned purpose, and a kind of easy DC ground fault searches device, it is characterized in that: device comprises controllable direct current power supply, a shielded conductor, two High-accuracy direct current weak current split-core type meters, data acquisition instruments; Described shielded conductor connects positive pole and the negative pole of controllable direct current power supply, and two described High-accuracy direct current weak current split-core type meters are connected with data acquisition instrument.

Described data acquisition instrument is oscillograph.

Described controllable direct current power supply, for possessing adjustable function, can stablize the direct supply exported in 30A.

Described high-precision current split-core type meter accurately can measure the electric current of 0.1mA level.

The step that a kind of easy DC ground fault searches the using method of device is as follows:

(1) keep the line load of DC loop not suddenly change, measure the current value I of DC loop with common clamp on dc amperemeter ₁.

(2) controllable direct current power supply is then used to export offset current I by shielded conductor ₂, make Δ I=I ₁-I ₂∝ 0.Its shielded conductor is respectively by the jaw of High-accuracy direct current electric current split-core type meter a, High-accuracy direct current electric current split-core type meter b, and direction is contrary.

(3) High-accuracy direct current electric current split-core type meter a, High-accuracy direct current electric current split-core type meter b vise straight-flow system wire to be measured respectively, and adjustment jaw direction makes offset current I ₂with loop current I ₁direction is contrary.By the electric current of split-core type meter a be then: I _a=I ₁-I ₂, the electric current flowing through split-core type meter b is: I _b=I ₁-I ₂-I ', I ' be the leakage current at DC system grounding place.Adjustment offset current I ₂size, allow I _aor I _bas far as possible close to zero.

(4) two High-accuracy direct current current clamp list catenation data acquisition instruments carry out integration, and integration obtains current average divided by integral time

(5) press calculate if in calculated value I ' ± 10% scope of leakage current, be then considered as there is earth point between this two wire.

The beneficial effects of the utility model are: adopt DC earthing searching device of the present utility model to have self-compensating structure.When offset current and current in wire close to time, the electric current that split-core type meter measures just significantly reduces, and solve the problem that accurate split-core type meter range is inadequate, meanwhile, two split-core type meters carry out Data Comparison, conveniently can carry out measurement to the electric current in places different on wire and compare.Therefore, the method accurately finds DC system grounding point by searching leakage current.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of conventional clamp on dc amperemeter mensuration.

Fig. 2 is the schematic diagram that a kind of easy DC ground fault described in the utility model searches device.

Embodiment

Below in conjunction with accompanying drawing, the utility model is further illustrated.

As shown in Figure 2, a kind of easy DC ground fault searches device, and device comprises controllable direct current power supply, a shielded conductor, two High-accuracy direct current weak current split-core type meters, data acquisition instruments; Described shielded conductor connects positive pole and the negative pole of controllable direct current power supply, and two described High-accuracy direct current weak current split-core type meters are connected with data acquisition instrument.

The concrete implementation step that a kind of easy DC ground fault described in the utility model searches device is as follows:

(1) according to the upper resistance R of direct-current supervision screen ₁, R ₂measuring voltage obtain leakage current, if R ₁, R ₂voltage be respectively U ₁, U ₂, and R ₁, R ₂resistance value be R ₁=R ₂=R, then leakage current

(2) load stabilization is kept, measuring circuit electric current I ₁.

(3) by Fig. 2 wiring, I is allowed ₁, I ₂respectively in opposite directions by two split-core type meters, DC current source output current I ₂to go forward side by side Row sum-equal matrix, make Δ I=I ₁-I ₂close to zero.

(4) by the electric current of split-core type meter a be then: I _a=I ₁-I ₂, the electric current flowing through split-core type meter b is: I _b=I ₁-I ₂-I '.

(5) by I _a, I _baccess the sampling of oscillograph device respectively, in time T,

I _amean value $\stackrel{\‾}{I_a}=\left(\underset{t=0}{\overset{t=T}{\∫}}{I}_a\mathrm{dt}\right)/T=\left(\underset{t=0}{\overset{t=T}{\∫}}(I_1-I_2)\mathrm{dt}\right)/T,$

I _bmean value $\stackrel{\‾}{I_b}=\left(\underset{t=0}{\overset{t=T}{\∫}}{I}_b\mathrm{dt}\right)/T=\left(\underset{t=0}{\overset{t=T}{\∫}}(I_1-I_2-I^{\′})\mathrm{dt}\right)/T,$ The then mean value of leakage current if close to calculated value, be then considered as there is earth point between this two wire.

The utility model is not limited to above-described embodiment; the foregoing is only preferred embodiment of the present utility model; not in order to limit the utility model; all do within spirit of the present utility model and principle any amendment, equivalent to replace and improvement etc., all should be included within protection domain of the present utility model.

Claims (4)

1. easy DC ground fault searches a device, it is characterized in that: device comprises controllable direct current power supply, a shielded conductor, two High-accuracy direct current weak current split-core type meters, data acquisition instruments; Described shielded conductor connects positive pole and the negative pole of controllable direct current power supply, and two described High-accuracy direct current weak current split-core type meters are connected with data acquisition instrument.

2. a kind of easy DC ground fault according to claim 1 searches device, it is characterized in that: described data acquisition instrument is oscillograph.

3. a kind of easy DC ground fault according to claim 1 searches device, it is characterized in that: described controllable direct current power supply, for possessing adjustable function, can stablize the direct supply exported in 30A.

4. a kind of easy DC ground fault according to claim 1 searches device, it is characterized in that: described High-accuracy direct current weak current split-core type meter accurately can measure the electric current of 0.1mA level.