CN102998529A - Insulation resistance testing method - Google Patents

Abstract

The invention discloses an insulation resistance testing method. A first switch, a second switch and a resistor are used in the insulation resistance testing method. The insulation resistance testing method includes the steps: S101: enabling the first switch and the second switch to be in open circuit, and detecting a first voltage between an anode direct-current bus and a cathode direct-current bus; S102, enabling the first switch to be in open circuit and the second switch to be switched on, and detecting a voltage to ground of a second end; S103, enabling the first switch to be switched on and the second circuit to be in open circuit, and detection another voltage to ground at the second end; and S104, computing insulation resistance of the anode direct-current bus and the cathode direct-current bus according to the first voltage, the voltage to ground and the another voltage to ground. A detection circuit of the direct-current buses is changed by switching of the two switches, so that the insulation resistance of the direct-current buses is computed accurately.

Description

The method of testing of insulation resistance

Technical field

The present invention relates to a kind of method of testing of insulation resistance, particularly relate to a kind of method of testing that detects the dc bus insulation resistance of photovoltaic power generation grid-connected inverter.

Background technology

The method of the insulation resistance of present existing detection dc bus mainly contains three kinds, is respectively that balanced bridge detects, low frequency detects and high pressure detects.

Wherein the principle that detects of traditional balanced bridge as shown in Figure 1, wherein resistance 11 and resistance 21 are respectively the insulation resistance of anodal dc bus and negative pole dc bus, the resistance 111 and 211 that described resistance is identical is in parallel with described resistance 11 and resistance 21 respectively.Thereby resistance 11,21,111,211 has consisted of an electric bridge as shown in Figure 1.After this detect the voltage V between anodal dc bus and the negative pole dc bus _B, i.e. voltage V on described resistance 11 and the resistance 21 _B, and detect voltage V on the described resistance 211 _a, and pass through V _BAnd V _aJudge the variation of the insulation resistance of described anodal dc bus and negative pole dc bus, but when the insulation resistance of described anodal dc bus and negative pole dc bus reduced simultaneously in proportion, described balanced bridge detection method can't detect the variation of described insulation resistance.

Described low frequency detection method is a kind of new method that is widely adopted in recent years, but the stake resistance that it can detect is subjected to the over the ground restriction of distributed capacitance of dc bus, and low-frequency ac signal is subjected to extraneous interference easily, the low-frequency ac signal that injects has in addition increased the ripple coefficient of voltage of dc bus, as seen, there are some defectives that are difficult to overcome in the low-frequency acquisition method.

Described high-voltage detecting method is a kind of detection method of off-line in addition, namely must be with the equipment under test dump before measurement, and the shorted to earth discharge, never allow equipment live to measure, to guarantee the safety of the person and equipment.To inducing the equipment of high-tension electricity, after this possibility of necessary elimination, just can measure.Contact resistance will be cleaned and reduce in the measured object surface, thereby guarantee the correctness of measurement result.And to check also whether megohmmeter is in normal operating conditions before measuring.And described megohmmeter should be placed on when using steadily and be firmly local, and away from external current conductor and external magnetic field.This shows, accurately measure insulation resistance, need the correct megohmmeter that uses.But in Blast Furnace Top Gas Recovery Turbine Unit (TRT), especially the insulation resistance of photovoltaic DC-to-AC converter also needs on-line measurement, so the mode of inapplicable offline inspection.

Summary of the invention

The technical problem to be solved in the present invention is in order to overcome the inaccurate defective of the insulation measurement of dc bus in the prior art, a kind of method of testing of insulation resistance is provided, switching by two switches changes testing circuit, thereby can calculate exactly the insulation resistance of described dc bus.

The present invention solves above-mentioned technical matters by following technical proposals:

The invention provides a kind of megger test method, be characterized in that described megger test method utilizes one first switch, a second switch and a resistance, wherein said the first switch is connected with an anodal dc bus, described second switch is connected with a negative pole dc bus, and described the first switch and second switch are connected in a first end; Described anodal dc bus and described negative pole dc bus are connected in one second end, and described resistance string is connected between described first end and the second end, and wherein said megger test method may further comprise the steps: S ₁₀₁, described the first switch and second switch all open a way, and detects the first voltage between described anodal dc bus and the negative pole dc bus; S ₁₀₂Described the first switch open circuit, described second switch is closed, then detects a voltage-to-ground of described the second end; S ₁₀₃, described the first switch closure, then described second switch open circuit detects another voltage-to-ground of described the second end; S ₁₀₄, calculate the insulation resistance of described anodal dc bus and negative pole dc bus according to described the first voltage and a described voltage-to-ground and another voltage-to-ground.

Preferably, described step S ₁₀₄In further comprising the steps of:

S ₁₀₄₁, calculate the insulation resistance of described anodal dc bus according to following formula:

$R+=\frac{V_{a2}-V_{a1}}{V_{a1}}R$

Wherein R+ is the resistance of the insulation resistance of described anodal dc bus; V _A1During for described the first switch open circuit and described second switch closure, a voltage-to-ground value of described the second end; Described V _A2During for described second switch open circuit and described the first switch closure, another voltage-to-ground value of described the second end; Described R is the resistance of described resistance.

Preferably, described step S ₁₀₄In further comprising the steps of:

S ₁₀₄₂, calculate the insulation resistance of described negative pole dc bus according to following formula:

$R-=\frac{V_{a2}-V_{a1}}{V_B-V_{a2}}R$

Wherein R-is the resistance of the insulation resistance of described negative pole dc bus; V _A1During for described the first switch open circuit and described second switch closure, a voltage-to-ground value of described the second end; Described V _A2During for described second switch open circuit and described the first switch closure, another voltage-to-ground value of described the second end; Described R is the resistance of described resistance, described V _BBe the first magnitude of voltage between described anodal dc bus and the described negative pole dc bus.

Positive progressive effect of the present invention is:

The method of testing of insulation resistance of the present invention is by two switches of access and a resistance in dc bus, and the switching by described two switches changes the testing circuit of dc bus test, thereby can calculate exactly the insulation resistance of described dc bus.

In addition, the method for testing of insulation resistance of the present invention does not need equipment under test outage in test process, thereby has reduced the problem that the production efficiency that causes of stopping work reduces.And insensitive to external signal, so can guarantee accuracy and the precision of megger test.

Description of drawings

Fig. 1 is the schematic diagram that balanced bridge detects in the prior art.

Fig. 2 is the schematic diagram of the preferred embodiment of megger test method of the present invention.

Fig. 3 is the process flow diagram of the preferred embodiment of megger test method of the present invention.

Embodiment

Provide preferred embodiment of the present invention below in conjunction with accompanying drawing, to describe technical scheme of the present invention in detail.

The test philosophy of the method for testing of the insulation resistance of present embodiment as shown in Figure 2, wherein said anodal dc bus and described negative pole dc bus are electrically connected on a first end 8, described anodal dc bus also is electrically connected with described switch 5, described negative pole dc bus also is electrically connected with described switch 4, described switch 4 and switch 5 are electrically connected on one second end 9, and described resistance 3 is electrically connected on described first end 8 and the second end 9.

And resistance 11 is the equivalent insulation resistance of described anodal dc bus, and described resistance 21 is the equivalent insulation resistance of described negative pole dc bus.E+ end and E-end are respectively the power supply on described anodal dc bus and the negative pole dc bus.

Calculate the resistance value of described resistance 11 and resistance 21 in the present embodiment according to the voltage-to-ground of the voltage between described E+ end and the E-end and described first end 8, namely calculate the insulating resistance value of described anodal dc bus and negative pole dc bus.

The principle of work of present embodiment is as follows:

As shown in Figure 3, may further comprise the steps in the flow process of the megger test method of present embodiment:

Step 101, then the described switch 4 among Fig. 2 and switch 5 open circuits detect the voltage V that described E+ end and E-hold _B

Step 102, described switch 5 open circuits, then described switch 4 closures detect the voltage-to-ground V of described first end 8 _A1

Step 103, described switch 5 closures, described switch 4 is opened a way, and then detects the voltage-to-ground V of described first end 8 _A2

Step 104 is according to the resistance R+ of the described resistance 11 of following formula 1 calculating.

$R+=\frac{V_{a2}-V_{a1}}{V_{a1}}R$ Formula 1

Wherein said R is the resistance of described resistance 3.

Then the described resistance R-that calculates again described resistance 21 according to following formula 2.

$R-=\frac{V_{a2}-V_{a1}}{V_B-V_{a2}}R$ Formula 2

Wherein said R also is the resistance of described resistance 3.

After this only need to repeat the insulation resistance that above-mentioned steps just can detect described anodal dc bus and negative pole dc bus in real time.

Change the testing circuit of dc bus test in the present embodiment by the switching of described switch 4 and switch 5, thereby can calculate exactly insulation resistance R+ and the R-of described dc bus.

So do not need equipment under test outage in the megger test process in the present embodiment, thereby reduced the problem that the production efficiency that causes of stopping work reduces.And insensitive to external signal, so can guarantee accuracy and the precision of megger test.

Although more than described the specific embodiment of the present invention, it will be understood by those of skill in the art that these only illustrate, protection scope of the present invention is limited by appended claims.Those skilled in the art can make various changes or modifications to these embodiments under the prerequisite that does not deviate from principle of the present invention and essence, but these changes and modification all fall into protection scope of the present invention.

Claims (3)

1. megger test method, it is characterized in that, described megger test method is utilized one first switch, a second switch and a resistance, wherein said the first switch is connected with an anodal dc bus, described second switch is connected with a negative pole dc bus, and described the first switch and second switch are connected in a first end; Described anodal dc bus and described negative pole dc bus are connected in one second end, and described resistance string is connected between described first end and the second end, and wherein said megger test method may further comprise the steps:

S ₁₀₁Described the first switch and second switch are all opened a way, and detect the first voltage between described anodal dc bus and the negative pole dc bus;

S ₁₀₂Described the first switch open circuit, described second switch is closed, then detects a voltage-to-ground of described the second end;

S ₁₀₃Described the first switch closure, described second switch is opened a way, and then detects another voltage-to-ground of described the second end;

S ₁₀₄Calculate the insulation resistance of described anodal dc bus and negative pole dc bus according to described the first voltage and a described voltage-to-ground and another voltage-to-ground.

2. megger test method as claimed in claim 1 is characterized in that, described step S ₁₀₄In further comprising the steps of:

S ₁₀₄₁, calculate the insulation resistance of described anodal dc bus according to following formula:

$R+=\frac{V_{a2}-V_{a1}}{V_{a1}}R$

Wherein R+ is the resistance of the insulation resistance of described anodal dc bus; V _A1During for described the first switch open circuit and described second switch closure, a voltage-to-ground value of described the second end; Described V _A2During for described second switch open circuit and described the first switch closure, another voltage-to-ground value of described the second end; Described R is the resistance of described resistance.

3. megger test method as claimed in claim 2 is characterized in that, described step S ₁₀₄In further comprising the steps of:

S ₁₀₄₂, calculate the insulation resistance of described negative pole dc bus according to following formula:

$R-=\frac{V_{a2}-V_{a1}}{V_B-V_{a2}}R$

Wherein R-is the resistance of the insulation resistance of described negative pole dc bus; V _A1During for described the first switch open circuit and described second switch closure, a voltage-to-ground value of described the second end; Described V _A2During for described second switch open circuit and described the first switch closure, another voltage-to-ground value of described the second end; Described R is the resistance of described resistance, described V _BBe the first magnitude of voltage between described anodal dc bus and the described negative pole dc bus.

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