CN202735453U - Detection circuit for bus grounding in direct current system - Google Patents

Abstract

The utility model discloses a detection circuit for bus grounding in a direct current system. A positive bus is connected with three circuit branches respectively, one circuit branch is connected to a ground wire through a first resistor, another circuit branch is connected to the earth wire through a first ground resistor and a first analog switch, and a third circuit branch is connected to a power ground through a second resistor, a first potentiometer and a first sampling resistor. A negative bus is connected with three circuit branches respectively, one circuit branch is connected to the power ground, another circuit branch is connected to the earth wire through a second ground resistor and a second analog switch, and a third circuit branch is connected to a power ground through a third resistor, a second potentiometer and a second sampling resistor. According to the detection circuit for bus grounding in the direct current system, asymmetric and symmetric bridge principles are combined to detect the insulation condition of the direct current system, the values of the ground resistors of the positive and negative buses can be calculated by measuring the voltages to ground of buses, an existing problem that the condition of the positive and negative buses being simultaneously grounded cannot be monitored is solved, and at the same time, the sensitivity of direct current insulation detection is improved.

Description

Straight-flow system median generatrix grounded inspection circuit

Technical field

The utility model relates to a kind of straight-flow system median generatrix grounded inspection circuit, adopts asymmetric and symmetrical electrical bridge principle to combine to detect the insulation status of straight-flow system, belongs to the DC system insulating monitoring technical field.

Background technology

The insulating resistance value of the negative or positive electrode of straight-flow system between over the ground is reduced to a certain setting valve, perhaps is lower than a certain setting, claims that straight-flow system has positive earth fault or negative earth fault.

The generating plant, the transformer station direct current system connected equipment is many, the loop is complicated, can be because problem of aging, the equipment itself of variation, cable and the joint of the change of environment, weather etc. in During Process of Long-term Operation, and DC system earth fault inevitably occurs.Particularly in generating plant, transformer substation construction construction or enlarging process, because the variety of problems of construction and installation, the hidden danger of electric power system fault is left in the meeting that is difficult to avoid, and straight-flow system is a weak link especially.The probability of the DC system earth fault that the time of putting into operation is longer is larger.

Earth fault can produce many harm: positive ground connection may cause the isolating switch mistrip; Negative ground connection may cause the tripping operation of refusing of isolating switch; Straight-flow system can not cause the accident to two tunnel loops iff being one point earth, if 2 ground connection are arranged, malfunction or the tripping of isolating switch just may occur.Therefore, in straight-flow system, allow on one point anything but or use equipment in the situation of the long-time ground connection of multiple spot.Must carry out continuous in-service monitoring to straight-flow system, in case find that earth fault is arranged, supervisory system should be sent warning immediately, and the prompting field personnel checks and gets rid of earth fault, to avoid occuring serious electric power system fault.

Because the straight-flow system of generating plant, transformer station is huge, a complicated direct supply network, connected equipment is many, and bus, little bus distribute layer by layer, and the loop is crisscross, has objectively increased the difficulty of searching DC ground fault.

Three kinds of methods of the general employing of bus insulation monitoring: symmetrical electric bridge detection method, asymmetric electric bridge detection method and low-frequency ac detection method.

1. symmetrical electric bridge detection method

Symmetrical bridge method presets 2 over the ground divider resistance R1, R2 that resistance is identical in insulation monitoring and warning device inside, the external ground resistance R+, R-, principle such as Fig. 1.

The advantage of symmetrical bridge method is that symmetrical bridge method belongs to static measurement, and the size of dc bus ground capacitance does not affect measuring accuracy.Because be not subjected to the impact of direct earth capacitance, detection speed is fast.When shortcoming was two sides earth, measuring error was large, can not detect balanced to ground.

2. asymmetric electric bridge detection method

Insulation detection device inside arranges resistance to earth R1, the R2 that two resistances equate, the external ground resistance R+, R-, resistance to earth R1, R2 respectively through analog switch J1, J2 according to certain close, disconnected order ground connection, calculate grounding resistance, principle is seen Fig. 2.

The advantage of asymmetric bridge method is that any earthing mode can both accurately detect.Shortcoming is in measuring process, need positive and negative bus to throw over the ground respectively resistance, so bus changes to ground voltage.In order to obtain accurately measurement result, drop into needs time-delay behind the resistance at every turn, measures after Bus Voltage is stable again, and detection speed is slow than symmetrical bridge method.In addition, direct earth capacitance also affects the measuring accuracy of asymmetric electric bridge.The advantage of symmetrical bridge method is that symmetrical bridge method belongs to static measurement, and the size of dc bus ground capacitance does not affect measuring accuracy, because be not subjected to the impact of direct earth capacitance, detection speed is fast.When shortcoming was two sides earth, measuring error was large, can not detect balanced to ground.

3. low-frequency ac detection method

The low-frequency ac detection method is to inject low-frequency ac signal by device to dc bus, and low-frequency current or voltage swing are detected in device inside, differentiate the stake resistance of dc bus, as shown in Figure 3.

During normal operation, alternating current is output as low frequency signal through the rectification/voltage stabilizing of device.Low frequency signal is superimposed upon on the dc bus negative pole, if certain road dc load generation single-phase earthing, low frequency signal forms path over the ground.Flow through low-frequency current in the loop, produce a low-frequency voltage on the detection resistance R of device inside, be changed to the stake resistance of dc bus by device internal circuit dress.

The advantage of low-frequency ac detection method is to support the use with the branch road pick-up unit, and overall cost is lower.Shortcoming is that direct earth capacitance affects measuring accuracy.In addition, the low-frequency ac detection method can not be identified the polarity of ground strap.When two sides earth, measuring error is larger.

The utility model content

Technical problem to be solved in the utility model is to overcome defective of the prior art, and a kind of straight-flow system median generatrix grounded inspection circuit is provided, and can monitor the simultaneously situation of ground connection of positive and negative busbar.

For solving the problems of the technologies described above, the utility model provides a kind of straight-flow system median generatrix grounded inspection circuit, it is characterized in that, positive bus-bar connects respectively three branch roads, and first resistance of leading up to is connected to geodesic line; Another road is connected to geodesic line by the first stake resistance, the first analog switch; Leading up to the second resistance, the first potentiometer, the first sampling resistor is connected to power supply ground again;

Negative busbar connects respectively three branch roads, and one the tunnel joins with power supply ground; Another road is connected to described geodesic line by the second stake resistance, the second analog switch; Leading up to the 3rd resistance, the second potentiometer, the second sampling resistor is connected to described power supply ground again.

Gather both end voltage after the series connection of described the first potentiometer and the first sampling resistor by a single-chip microcomputer.

Gather both end voltage after the series connection of described the second potentiometer and the second sampling resistor by a single-chip microcomputer.

The resistance of the resistance of described the second potentiometer RW2, the second sampling resistor R2＜＜the three resistance.

The resistance of described the first stake resistance and the second stake resistance equates.

The resistance of described the first resistance and the 3rd resistance equates.

The beneficial effect that the utility model reaches:

Straight-flow system median generatrix grounded inspection circuit of the present utility model, adopt asymmetric and symmetrical electrical bridge principle to combine to detect the insulation status of straight-flow system, can calculate the stake resistance resistance of positive and negative busbar by measuring Bus Voltage, solved and to have monitored at present the simultaneously problem of Grounding of positive and negative busbar, can improve the sensitivity that D.C. isolation detects simultaneously.

Description of drawings

Fig. 1 is that symmetrical electric bridge detects schematic diagram;

Fig. 2 is that asymmetric electric bridge detects schematic diagram;

Fig. 3 is that low-frequency ac detects schematic diagram;

Fig. 4 is straight-flow system median generatrix grounded inspection circuit figure of the present utility model.

Embodiment

Below in conjunction with accompanying drawing the utility model is further described.Following examples only are used for the technical solution of the utility model more clearly is described, and can not limit protection domain of the present utility model with this.

In the straight-flow system median generatrix grounded inspection circuit of the present utility model, by the state control to analog switch JKC1, JKC2 on the electric bridge, measure the positive and negative busbar CM+ under several groups of states, the voltage-to-ground of CM-, thus the stake resistance resistance of positive and negative busbar when calculating positive and negative busbar and simultaneously Grounding being arranged.

Such as Fig. 4, positive bus-bar CM+ divide three the tunnel, and the excessive resistance R 2C of a-road-through is connected to geodesic line DD; Another road is connected to geodesic line DD by stake resistance R9, analog switch JKC2; Leading up to resistance R 41, potentiometer RW1, sampling resistor R42 is connected to power supply ground GND again.Single-chip microcomputer gathers the both end voltage after potentiometer RW1 part resistance and the sampling resistor R42 series connection, is designated as INM.

Negative busbar CM-divides three the tunnel, the one tunnel to join with power supply ground GND; Another road is connected to geodesic line DD by stake resistance R7, analog switch JKC1; Leading up to resistance R 1C, potentiometer RW2, sampling resistor R2 is connected to power supply ground GND again.Single-chip microcomputer gathers the both end voltage after potentiometer RW2 part resistance and the sampling resistor R2 series connection, is designated as INJ.

During detection, disconnect at first simultaneously analog switch JKC1 and JKC2, because the resistance of potentiometer RW2, sampling resistor R2 is far smaller than resistance R 1C, can ignore, then circuit forms symmetrical electric bridge, records the voltage U m between positive and negative busbar; Then disconnect analog switch JKC2, closed analog switch JKC1 records the voltage-to-ground Uj1 of negative busbar this moment; Disconnect at last analog switch JKC1, closed analog switch JKC2 records the voltage-to-ground Uj2 of positive bus-bar.And in the present embodiment, R7=R9=100K, R1C=R2C=220K establishes R7=R9=R1, R1C=R2C=R2, positive bus-bar stake resistance R+, negative busbar stake resistance R-:

$\frac{\mathrm{Um}-\mathrm{Uj}1}{\mathrm{Uj}1}=\frac{R1//\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="120727160809.png"\; state="\{\{state\}\}">R</figure-callout>}2//R+}{R1//R-}---\left(1.1\right)$

$\frac{\mathrm{Um}-\mathrm{<figure-callout\; id="2"\; label="Uj"\; filenames="120727160809.png"\; state="\{\{state\}\}">Uj</figure-callout>}2}{\mathrm{<figure-callout\; id="2"\; label="Uj"\; filenames="120727160809.png"\; state="\{\{state\}\}">Uj</figure-callout>}2}=\frac{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="120727160809.png"\; state="\{\{state\}\}">R</figure-callout>}2//R+}{R1//\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="120727160809.png"\; state="\{\{state\}\}">R</figure-callout>}2//R-}---\left(1.2\right)$

Simultaneous formula (1.1), (1.2):

$R+=\frac{(\mathrm{Uj}2-\mathrm{Uj}1)R1R2}{\mathrm{Uj}1(R1+R2)-\mathrm{Uj}2R1}---\left(1.3\right)$

$R-=\frac{(\mathrm{Uj}2-\mathrm{Uj}1)R1\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="120727160809.png"\; state="\{\{state\}\}">R</figure-callout>}2}{\mathrm{UmR}2-(\mathrm{Uj}1+\mathrm{Uj}2)(R1+R2)}---\left(1.4\right)$

Can be found out by formula (1.3), (1.4), also can be detected when positive and negative busbar simultaneously Grounding occurs, and calculate the resistance size of positive and negative busbar stake resistance.

The above only is preferred implementation of the present utility model; should be understood that; for those skilled in the art; under the prerequisite that does not break away from the utility model know-why; can also make some improvement and distortion, these improvement and distortion also should be considered as protection domain of the present utility model.

Claims (6)

1. a straight-flow system median generatrix grounded inspection circuit is characterized in that, positive bus-bar connects respectively three branch roads, and first resistance of leading up to is connected to geodesic line; Another road is connected to geodesic line by the first stake resistance, the first analog switch; Leading up to the second resistance, the first potentiometer, the first sampling resistor is connected to power supply ground again;

Negative busbar connects respectively three branch roads, and one the tunnel joins with power supply ground; Another road is connected to described geodesic line by the second stake resistance, the second analog switch; Leading up to the 3rd resistance, the second potentiometer, the second sampling resistor is connected to described power supply ground again.

2. straight-flow system median generatrix grounded inspection circuit according to claim 1 is characterized in that, gathers both end voltage after the series connection of described the first potentiometer and the first sampling resistor by a single-chip microcomputer.

3. straight-flow system median generatrix grounded inspection circuit according to claim 1 is characterized in that, gathers both end voltage after the series connection of described the second potentiometer and the second sampling resistor by a single-chip microcomputer.

4. straight-flow system median generatrix grounded inspection circuit according to claim 1 is characterized in that, the resistance of the resistance of described the second potentiometer RW2, the second sampling resistor R2＜＜the three resistance.

5. straight-flow system median generatrix grounded inspection circuit according to claim 1 is characterized in that, the resistance of described the first stake resistance and the second stake resistance equates.

6. straight-flow system median generatrix grounded inspection circuit according to claim 1 or 5 is characterized in that, the resistance of described the first resistance and the 3rd resistance equates.

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