CN204855699U - Direct current earth fault detection circuitry - Google Patents

Abstract

The utility model provides a direct current earth fault detection circuitry, including direct current partial pressure unit, voltage detection unit and processing unit, direct current partial pressure unit includes a divider resistance, first relay, the 2nd divider resistance, the second relay, a divider resistance and first relay concatenate jointly between positive direct current input and earthing terminal, the 2nd divider resistance and second relay concatenate jointly between burden direct -current input end and earthing terminal, direct current partial pressure unit still includes an absorption capacitors who connects in parallel with first relay and the 2nd absorption capacitors who connects in parallel with the second relay. The utility model discloses when two relays of disconnection, because absorption capacitors's characteristic, the voltage on the electric capacity can not suddenly change, and the switching voltage of two relays will reduce by a wide margin, and the less relay of switching voltage can be chooseed for use to the relay, and this type of relay volume is very little, low cost, further, when absorption capacitors was great, multiplicable current -limiting resistor avoided the exoelectric heavy current of absorption capacitors to burn out relay contact points.

Description

DC ground fault testing circuit

Technical field

The utility model relates to DC Line Fault detection field, more particularly, relates to a kind of DC ground fault testing circuit.

Background technology

At present, the detection method of domestic and international DC ground fault has a lot, compares and common are Low frequency signal injection method, frequency variation signal injection method, electric resistance partial pressure method.

There are some shortcomings in these methods, such as: Low frequency signal injection method injects a pair low frequency signal by two capacitances to bus, although this low frequency signal opposing busbars voltage is compared very little, but still to bring unsafe factor the system high concerning security requirement, and the system larger to distributed capacitance is difficult to accurately detect; Frequency variation signal injection method can solve the impact of Low frequency signal injection method distributed capacitance in theory, but during practical application, Detection results is unsatisfactory, and said method implements more complicated; Electric resistance partial pressure method implements fairly simple, also more accurate detection can be realized, but when this detection method is applied to the detection of high voltage direct current earth fault, need to use the very high DC relay of switched voltage access dividing potential drop impedance and be separated, cause that testing circuit volume is large, cost is high.

Utility model content

The technical problems to be solved in the utility model is, the above-mentioned accuracy of detection for prior art is not high, volume compared with the defect of macrostructure complexity, provide a kind of and realize simple, accuracy of detection compared with DC ground fault testing circuit high, that volume is little, with low cost.

The utility model solves the technical scheme that its technical matters adopts: construct a kind of DC ground fault testing circuit, comprise the DC partial voltage unit be connected with direct-current input power supplying, the voltage detection unit be connected with described DC partial voltage unit and the processing unit be connected with described voltage detection unit, described DC partial voltage unit comprises the first divider resistance, first relay, second divider resistance, second relay, described first divider resistance and the first relay are serially connected with between positive direct-current input end and earth terminal jointly, described second divider resistance and the second relay are serially connected with between negative direct-flow input end and earth terminal jointly, described DC partial voltage unit also comprises first Absorption Capacitance in parallel with described first relay and second Absorption Capacitance in parallel with described second relay.

In DC ground fault testing circuit described in the utility model, described DC partial voltage unit also comprises the first current-limiting resistance and the second current-limiting resistance, described first current-limiting resistance is common in parallel with described first relay after connecting with described first Absorption Capacitance, and the second current-limiting resistance is common in parallel with described second relay after connecting with described second Absorption Capacitance.

In DC ground fault testing circuit described in the utility model, described voltage detection unit comprises at least two: the first voltage power detection circuit, the second voltage power detection circuit, tertiary voltage power detection circuit in following three piezoelectric sensing circuitry; Described first voltage power detection circuit is in parallel with described first divider resistance, second voltage power detection circuit is in parallel with described second divider resistance, described tertiary voltage power detection circuit is in parallel with described direct-current input power supplying, and described first voltage power detection circuit, the second voltage power detection circuit, tertiary voltage power detection circuit are connected to described processing unit respectively.

Implement DC ground fault testing circuit of the present utility model, there is following beneficial effect: in the utility model when disconnection two relays, due to the characteristic of Absorption Capacitance, the voltage of electric capacity can not suddenly change, the switched voltage of two relays will significantly reduce, so relay can select the relay that switched voltage is less, this type of relay volume is very little, with low cost, whole testing circuit can not by the coupling influence of other testing circuits, the detection that can realize degree of precision; Further, when Absorption Capacitance is larger, the big current discharged for avoiding Absorption Capacitance burns out relay contact, during by increasing by two current-limiting resistances to avoid relay closes, electric current is excessive causes relay contact adhesion, and select suitable resistance value, realize reducing the switched voltage of relay, make the relay selected be volume relay very little, with low cost.

Accompanying drawing explanation

Below in conjunction with drawings and Examples, the utility model is described in further detail, in accompanying drawing:

Fig. 1 is the circuit theory diagrams of the embodiment one of the utility model DC ground fault testing circuit;

Fig. 2 is the circuit theory diagrams of the embodiment two of the utility model DC ground fault testing circuit.

Embodiment

In order to there be understanding clearly to technical characteristic of the present utility model, object and effect, now contrast accompanying drawing and describe embodiment of the present utility model in detail.

As shown in Figure 1, be the circuit theory diagrams of embodiment one of the utility model DC ground fault testing circuit;

DC ground fault testing circuit of the present utility model, for all kinds of earth-free photovoltaic generating system to the detection of photovoltaic arrays earth fault, and the detection of the DC bus earth fault of other straight-flow systems, comprise: DC partial voltage unit 100, voltage detection unit 200 and processing unit 300, DC partial voltage unit 100 is connected with direct-current input power supplying, voltage detection unit 200 is connected with described DC partial voltage unit 100, and processing unit 300 is connected with described voltage detection unit 200.

Direct-current input power supplying; comprise positive direct-current input end and negative direct-flow input end; namely the present embodiment is be described for photovoltaic cell as direct-current input power supplying: DC+, DC-in figure represent positive direct-current input end, negative direct-flow input end respectively; PE represents earth terminal; namely the utility model is for calculating DC+ or DC-to the impedance ground Rg existing for PE; and when Rg is less than certain value, can think that existence needs the earth fault carrying out protecting.

DC partial voltage unit 100, comprise divider resistance R1, divider resistance R2, relay K 1, relay K 2, Absorption Capacitance C1, Absorption Capacitance C2, described divider resistance R1 and relay K 1 are serially connected with between positive direct-current input end DC+ and earth terminal PE jointly, described divider resistance R2 and relay K 2 are serially connected with between negative direct-flow input end DC-and earth terminal PE jointly, Absorption Capacitance C1 is in parallel with described relay K 1, and Absorption Capacitance C2 is in parallel with described relay K 2.

Voltage detection unit 200, comprises following three piezoelectric sensing circuitry: the first voltage power detection circuit, the second voltage power detection circuit, tertiary voltage power detection circuit; Described first voltage power detection circuit is in parallel with described divider resistance R1, second voltage power detection circuit is in parallel with described divider resistance R2, described tertiary voltage power detection circuit is in parallel with described direct-current input power supplying, and described first voltage power detection circuit, the second voltage power detection circuit, tertiary voltage power detection circuit are connected to described processing unit 300 respectively.

Wherein, the first voltage power detection circuit, the second voltage power detection circuit, tertiary voltage power detection circuit are respectively used to detect DC voltage U1, the DC voltage U2 on divider resistance R2 on divider resistance R1, the DC voltage Udc on DC bus (i.e. the voltage of direct-current input power supplying).For convenience of calculating, as in figure, the impedance in the first voltage power detection circuit, the second voltage power detection circuit, tertiary voltage power detection circuit represents with Z1, Z2, Z3.

It should be explicitly made clear at this point, due to Udc=U1+U2, so three piezoelectric sensing circuitry only can select wherein two and dispense another one.

Testing process is: before detection, and two relay K 1, K2 all disconnect, and when testing circuit is started working, relay K 1, K2 adhesive, complete after detecting and calculating, relay K 1, K2 disconnect.

Principle of work: in relay K 1, K2 handoff procedure, if there is no Absorption Capacitance C1, C2, if DC-is to PE short circuit, so relay K 1 is when disconnecting, voltage in relay K 1 is about Udc, when adhesive, voltage in relay K 1 is about 0, when carrying out relay type selecting, need to select switched voltage to be more than or equal to the DC relay of Udc, and when Udc is higher, the DC relay of this high pressure is incited somebody to action very expensive and volume is very large, if switched voltage is selected too small, very easily in relay disconnection process, produce arcing and burn relay.And the utility model is at increase Absorption Capacitance C1, after C2, before testing circuit is started working, relay K 1, K2 disconnects, Absorption Capacitance C1, voltage sum on C2 equals Udc, when entering detection, relay K 1, the moment of K2 adhesive, Absorption Capacitance C1, C2 is by relay K 1, K2 discharges, processing unit 300 calculates actual impedance ground Rg by the steady state voltage that detection three testing circuits detect, after completing calculating, disconnect K1, during K2, due to the characteristic of electric capacity itself, Absorption Capacitance C1, voltage on C2 can not suddenly change, therefore relay K 1, the switched voltage of K2 is about 0.

The calculating of impedance ground Rg: due to divider resistance R1, electric resistance partial pressure relation is met between voltage on R2 and photovoltaic cell input, so when there is earth fault, due to the change of DC+ and DC-equiva lent impedance over the ground, divider resistance R1 during stable state, voltage on R2 also changes, according to the resistance R1 that three voltage detecting circuits detect, voltage on R2 and the relation of DC input voitage, the size of impedance ground can be calculated by processing unit 300, when DC+ exists less impedance to PE, or DC-to PE exist less impedance time, the utility model can detect, computation process is as follows:

Impedance ground Rg is present in less one of the voltage of DC+ and DC-, and suppose that the voltage of DC+ is less, then DC+ exists impedance ground to PE is Rg, then, after relay adhesive, DC+ to the equiva lent impedance of PE is:

$Rp=\frac{1}{\frac{1}{Rg}+\frac{1}{R1}+\frac{1}{Z1}}$

DC-to the equiva lent impedance of PE is:

$Rn=\frac{1}{\frac{1}{R2}+\frac{1}{Z2}}$

Can U1, U2, Udc be obtained, according to electric resistance partial pressure relation by three voltage detecting circuits:

$\frac{U1}{U2}=\frac{Rp}{Rn}$

Because Z1, Z2 are different with the difference of testing circuit, but for the testing circuit determined, Z1, Z2 are known, solve, just can draw the size of Rg so combine above three equations.Can judge whether to need to protect this earth fault according to the size of Rg.

With reference to figure 2, be the circuit theory diagrams of the embodiment two of the utility model DC ground fault testing circuit.

Be from the different of embodiment one, in the present embodiment, by Absorption Capacitance C1, C2's current-limiting resistance R3 has respectively connected, R4, because relay K 1, after K2 adhesive, Absorption Capacitance C1, C2 is respectively via relay K 1, K2 discharges, when voltage is certain, if electric capacity is larger, electric charge then on electric capacity is more, discharge current is larger, so as Absorption Capacitance C1, when C2 is larger, series limiting resistor R3 can be distinguished, R4 carries out current limliting, switched voltage when then relay K 1 closes is 0, switched voltage during disconnection approximates (R3*U+)/R1+R3, wherein U+ is the voltage of DC+ to PE, switched voltage when relay K 2 closes is 0, switched voltage during disconnection approximates (R4*U-)/R2+R4, wherein U-is the voltage of PE to DC-, as long as so the choosing value of R1, R2, R3, R4 is suitable, can realize small voltage equally to switch, such as, R1, R2 get larger value, R3, R4 get less value, then the value of (R3*U+)/R1+R3, (R4*U-)/R2+R4 can be made to reduce as far as possible.

In sum, implement DC ground fault testing circuit of the present utility model, there is following beneficial effect: in the utility model when disconnection two relays, due to the characteristic of Absorption Capacitance, the voltage of electric capacity can not suddenly change, and the switched voltage of two relays will significantly reduce, so relay can select the relay that switched voltage is less, this type of relay volume is very little, with low cost, and whole testing circuit can not by the coupling influence of other testing circuits, the detection that can realize degree of precision; Further, when Absorption Capacitance is larger, the big current discharged for avoiding Absorption Capacitance burns out relay contact, by increasing by two current-limiting resistances, and select suitable resistance value, realize reducing the switched voltage of relay, make the relay selected be volume relay very little, with low cost.

By reference to the accompanying drawings embodiment of the present utility model is described above; but the utility model is not limited to above-mentioned embodiment; above-mentioned embodiment is only schematic; instead of it is restrictive; those of ordinary skill in the art is under enlightenment of the present utility model; do not departing under the ambit that the utility model aim and claim protect, also can make a lot of form, these all belong within protection of the present utility model.

Claims (3)

1. a DC ground fault testing circuit, comprise the DC partial voltage unit be connected with direct-current input power supplying, the voltage detection unit be connected with described DC partial voltage unit and the processing unit be connected with described voltage detection unit, described DC partial voltage unit comprises the first divider resistance, first relay, second divider resistance, second relay, described first divider resistance and the first relay are serially connected with between positive direct-current input end and earth terminal jointly, described second divider resistance and the second relay are serially connected with between negative direct-flow input end and earth terminal jointly, it is characterized in that, described DC partial voltage unit also comprises first Absorption Capacitance in parallel with described first relay and second Absorption Capacitance in parallel with described second relay.

2. DC ground fault testing circuit according to claim 1, it is characterized in that, described DC partial voltage unit also comprises the first current-limiting resistance and the second current-limiting resistance, described first current-limiting resistance is common in parallel with described first relay after connecting with described first Absorption Capacitance, and the second current-limiting resistance is common in parallel with described second relay after connecting with described second Absorption Capacitance.

3. DC ground fault testing circuit according to claim 1, it is characterized in that, described voltage detection unit comprises at least two: the first voltage power detection circuit, the second voltage power detection circuit, tertiary voltage power detection circuit in following three piezoelectric sensing circuitry; Described first voltage power detection circuit is in parallel with described first divider resistance, second voltage power detection circuit is in parallel with described second divider resistance, described tertiary voltage power detection circuit is in parallel with described direct-current input power supplying, and described first voltage power detection circuit, the second voltage power detection circuit, tertiary voltage power detection circuit are connected to described processing unit respectively.