CN102243283A - Neutral line breakage detection method of voltage secondary loop and apparatus thereof - Google Patents
Neutral line breakage detection method of voltage secondary loop and apparatus thereof Download PDFInfo
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Abstract
Embodiments of the invention provide a neutral line breakage detection method of a voltage secondary loop and an apparatus thereof. The method comprises the following steps: monitoring third harmonic of zero sequence voltage of secondary side of a potential transformer (PT) in a protective apparatus; determining whether duration of a third harmonic amplitude that exceeds a first threshold exceeds a second threshold or not; if the duration exceeds the second threshold, determining that the neutral line between an external PT and the PT in the protective apparatus is broken. The detection apparatus comprises: a monitoring unit, which is used to monitor the third harmonic of the zero sequence voltage of the secondary side of the PT in the protective apparatus; a broken line determination unit, which is used to determine whether the duration of a third harmonic amplitude that exceeds a first threshold exceeds a second threshold or not and wherein the duration is monitored by the monitoring unit. If the duration exceeds the second threshold, the neutral line between the external PT and the PT in the protective apparatus is determined to be broken.
Description
Technical field
The invention belongs to technical field of electricity, relate in particular to a kind of broken neutral line detection method and device of voltage secondary circuit.
Background technology
The broken string of voltage secondary circuit is a kind of common faults in the electric system, in the prior art by protective device is set, can reports to the police in time and makes corresponding adjustment.Separate according to what break, the broken string of voltage secondary circuit can be divided into non-neutral line broken string (being A phase, B phase and C circuit broken string mutually) and broken neutral line (being N circuit broken string mutually).Whether present protective device can non-neutral line broken string take place according to condition judgment such as residual voltage and positive sequence voltages, but less relatively to the research of broken neutral line.When the broken neutral line that voltage transformer (VT) takes place, thereby when producing the broken neutral line of voltage secondary circuit, because the neutral point potential drifting, the phase voltage of protective device can change, thereby causes the zero-sequence direction component malfunction, causes the voltage component malfunction.
Summary of the invention
In view of this, the object of the present invention is to provide a kind of broken neutral line detection method and device of voltage secondary circuit, can detect the fault of broken neutral line in time.
For achieving the above object; one embodiment of the present of invention provide a kind of broken neutral line detection method of voltage secondary circuit; described voltage secondary circuit comprises external voltage mutual inductor and protective device; wherein the primary side of the voltage transformer (VT) in the secondary side of external voltage mutual inductor and the protective device links to each other, and this method comprises:
The third harmonic of the residual voltage of the secondary side of the voltage transformer (VT) in the monitoring and protecting device;
Whether the amplitude of judging the third harmonic of described residual voltage surpasses the duration of first threshold above second threshold value, if then judge the broken neutral line between the voltage transformer (VT) in external voltage mutual inductor and the protective device.
Preferably, described first threshold is to select according to the amplitude of the fundamental voltage of the residual voltage of the secondary side of voltage transformer (VT) in the protective device.
Preferably, described second threshold value is 10 seconds.
Preferably, described method also comprises:
Whether the duration that the amplitude of judging the third harmonic of described residual voltage surpasses first threshold surpasses the 3rd threshold value, if then carry out locking quick acting protection;
Described the 3rd threshold value is less than second threshold value.
Preferably, described the 3rd threshold value is 10 milliseconds.
On the other hand; the present invention also provides a kind of broken neutral line pick-up unit of voltage secondary circuit; described voltage secondary circuit comprises external voltage mutual inductor and protective device; wherein the primary side of the voltage transformer (VT) in the secondary side of external voltage mutual inductor and the protective device links to each other; it is characterized in that this pick-up unit comprises:
Monitoring means is used for the third harmonic of residual voltage of secondary side of the voltage transformer (VT) of monitoring and protecting device;
The broken string judging unit; whether the duration that the amplitude of the third harmonic of the residual voltage that is used to judge that described monitoring means monitors surpasses first threshold surpasses second threshold value; if then judge the broken neutral line between the voltage transformer (VT) in external voltage mutual inductor and the protective device.
Preferably, described first threshold is to select according to the amplitude of the fundamental voltage of the residual voltage of the secondary side of voltage transformer (VT) in the protective device.
Preferably, described second threshold value is 10 seconds.
Preferably, also comprise:
The protection judging unit, whether the duration that the amplitude that is used to judge the third harmonic of described residual voltage surpasses first threshold surpasses the 3rd threshold value, if then carry out locking quick acting protection; Described the 3rd threshold value is less than second threshold value.
Preferably, described the 3rd threshold value is 10 milliseconds.
According to the embodiment of the invention, the inventor has carried out after the detail analysis the feature of neutral line disconnection fault, has proposed a kind of broken neutral line detection method and device of voltage secondary circuit, can detect the fault of broken neutral line timely and accurately.
Description of drawings
In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art, to do to introduce simply to the accompanying drawing of required use in embodiment or the description of the Prior Art below, apparently, accompanying drawing in describing below is some embodiments of the present invention, for those of ordinary skills, under the prerequisite of not paying creative work, can also obtain other accompanying drawing according to these accompanying drawings.
Fig. 1 is the annexation synoptic diagram of voltage secondary circuit;
Fig. 2 is the synoptic diagram of trying to achieve the process of exciting current by graphing method;
Fig. 3 is the equivalent circuit figure of the secondary side of external voltage mutual inductor;
Fig. 4 is the wiring diagram of exciting current on the former limit of the voltage transformer (VT) of test in the protective device;
Fig. 5 is that the neutral line connects the synoptic diagram of the magnitude of voltage of passage 1 just often;
Fig. 6 is that the neutral line connects the synoptic diagram of the magnitude of voltage of passage 2 just often;
Fig. 7 is the spectrum analysis figure of passage 1 among Fig. 5;
Fig. 8 is the spectrum analysis figure of passage 2 among Fig. 6;
The synoptic diagram of the magnitude of voltage of passage 1 when Fig. 9 is broken neutral line;
The synoptic diagram of the magnitude of voltage of passage 2 when Figure 10 is broken neutral line;
Figure 11 is the spectrum analysis figure of passage 1 among Fig. 9;
Figure 12 is the spectrum analysis figure of passage 2 among Figure 10;
Figure 13 is the magnetic hysteresis loop group synoptic diagram that phase voltage is respectively 30V and 57.74V;
Figure 14 is the synoptic diagram of the broken neutral line detection method of the voltage secondary circuit in the embodiment of the invention;
Figure 15 is the synoptic diagram of the broken neutral line pick-up unit of the voltage secondary circuit in the embodiment of the invention.
Embodiment
For the purpose, technical scheme and the advantage that make the embodiment of the invention clearer, below in conjunction with the accompanying drawing in the embodiment of the invention, technical scheme in the embodiment of the invention is clearly and completely described, obviously, described embodiment is the present invention's part embodiment, rather than whole embodiment.Based on the embodiment among the present invention, those of ordinary skills belong to the scope of protection of the invention not making the every other embodiment that is obtained under the creative work prerequisite.
Voltage secondary circuit among the present invention comprises external voltage mutual inductor and protective device.Fig. 1 shows the annexation of voltage secondary circuit.In Fig. 1, external voltage mutual inductor 101 also can be described to a PT (voltage transformer (VT)), and the primary side of the voltage transformer (VT) 102 in the secondary side of external voltage mutual inductor 101 and the protective device links to each other.Because the voltage transformer (VT) 102 in the protective device is less, therefore also can be described as little PT.
The inventor has carried out the analysis of system based on the framework of above-mentioned voltage secondary circuit to the characteristics of broken neutral line, and is as follows:
Please be simultaneously referring to Fig. 1, Ua, Ub, Uc are primary voltage (being each phase voltage of the primary side of external voltage mutual inductor 101), U1a, U1b, U1c, U1n are the voltage output of the secondary side of external voltage mutual inductor 101.U2a, U2b, U2c, U2n are the secondary voltage output of the voltage transformer (VT) 102 in the protective device, calculate for protective device.
When the neutral line (U1n line) between the voltage transformer (VT) 102 in external voltage mutual inductor 101 and protective device take place breaks; because the voltage of external voltage mutual inductor 101 primary sides can not change; so the output voltage of external voltage mutual inductor 101 secondary sides can not change yet; be U1a; U1b, U1c can not change to the voltage of U1n.But U1a, U1b, whether U1c can change to the voltage of U1n ', directly has influence on U2a, U2b, U2c is to the voltage of U2n.
Because the secondary load of the voltage transformer (VT) 102 in the protective device is very big, is equivalent to be operated in light condition, so the voltage transformer (VT) 102 in the analysis protective device during in the broken neutral line feature, can be analyzed according to the phase separation transformer of YY0 connection fully.
The while inventor thinks iron circuit nonlinear, and the iron circuit of the voltage transformer (VT) 102 in the protective device is no exception, and promptly the relation of main flux in the iron core and excitation magnetic potential (or exciting current) presents saturation characteristic.
Can at first analyze the zero load of single transformer.At the standard sine wave of the former limit adding of single transformer 50Hz, analyze the characteristic of the exciting current on former limit.Because unloaded, institute's making alive on former limit approximates induced potential, promptly induced potential is sinusoidal wave.Induced potential is produced by magnetic flux so, and promptly magnetic flux also is sinusoidal wave, and magnetic flux is the exciting current generation by former limit so.If magnetic flux and exciting current are linear, then exciting current also is sinusoidal wave.But the voltage transformer (VT) in the protective device 102 is unshakable in one's determination non-linear, and exciting current has presented peaked wave.Exciting current to this peaked wave decomposes, and can obtain first-harmonic and third harmonic.That is: former limit adds the voltage of 50Hz sine wave, and first-harmonic and third harmonic will appear in exciting current.
Fig. 2 shows the process of trying to achieve exciting current by graphing method, does not wherein consider magnetic hysteresis and iron loss.The figure of left is a magnetization curve among Fig. 2, and right-hand figure is the oscillogram of magnetic flux and exciting current.
Then can analyze the three-phase transformer zero load that the neutral line does not break under the situation.
Because normal three-phase voltage mutual deviation 120 degree, wherein exciting current also differs 120 degree, and third harmonic content wherein is:
I
A_3harm＝I
3harmsin3ωt
I
B_3harm=I
3harmSin3 (ω t-120 °)=I
3harmSin3 ω t (formula 1)
I
B_3harm＝I
3harmsin3(ωt-240°)＝I
3harmsin3ωt
Therefore, i.e. the third harmonic of three-phase current same-phase in time.If the neutral line is arranged, three-phase current, promptly the triple harmonic current in the zero-sequence current can circulate by the neutral line.The exciting current of each phase is a peaked wave so, and the magnetic flux that this exciting current produces just is sinusoidal wave, thereby each phase magnetic potential is sinusoidal wave, and each phase voltage is sinusoidal wave.
At last the three-phase transformer zero load of broken neutral line situation is analyzed.If the generation broken neutral line, then the triple harmonic current in the neutral line can not circulate.Third harmonic in the exciting current of each phase can not circulate, and causes exciting current to change, and is sinusoidal wave substantially, because Nonlinear Magnetic Circuit, sinusoidal wave exciting current has produced the magnetic flux of flat-topped wave.The magnetic flux of this flat-topped wave is decomposed, can obtain the magnetic flux of first-harmonic and third harmonic.The frequency of the first-harmonic electromotive force of fundamental flux induction is 50Hz, phase lag fundamental flux 90 degree.The frequency of three electromotive forces of three flux of magnetic inductions is 150Hz, phase lag and three magnetic flux 90 degree.Synthetic first-harmonic electromotive force and three electromotive forces, obtaining the phase electromotive force is a peaked wave.So comprise first-harmonic and third harmonic in the phase electromotive force, thereby the protection secondary side has been experienced first-harmonic and third harmonic voltage.
In a word; broken neutral line will cause the third harmonic in the exciting current on former limit (i.e. the primary side of this voltage transformer (VT) 102) of the voltage transformer (VT) 102 in the protective device not have flow cycle; exciting current is sinusoidal wave substantially; because unshakable in one's determination non-linear, the magnetic flux that this exciting current produces is a flat-topped wave.The magnetic flux of flat-topped wave produces the electromotive force of peaked wave, this electromotive force is decomposed can obtain first-harmonic electromotive force and third harmonic electromotive force, and then protective device can be experienced third harmonic voltage.
Then the inventor analyzes the mechanism of production of zero sequence fundamental voltage.
In the wiring of reality, the often secondary side meeting of external voltage mutual inductor and connect multiple arrangement, its load meeting imbalance.When the laod unbalance of external voltage mutual inductor secondary side, the meeting of neutral point voltage drift.
Fig. 3 is the equivalent circuit figure of the secondary side of external voltage mutual inductor.Wherein, Zp is each phase input impedance of the secondary side of external voltage mutual inductor, should be the external voltage mutual inductor secondary side each install the parallel connection of corresponding phase of impedance.With A phase of impedance loop impedance Z s in parallel, come the fictitious load imbalance.The output voltage of case of external voltage transformer (VT) is the positive sequence voltage of standard.The nodal method of analysis according to circuit can be in the hope of U
N ' nVoltage be:
When broken neutral line, Zn is infinitely great, and Zn is the impedance between Fig. 3 mid point N and the some N ', according to formula 2, and the U of this moment
N ' nVoltage be:
So when Zs is infinity, i.e. during threephase load balance, U
N ' n=0; When Zs was 0, promptly three-phase was asymmetric fully, U
N ' n=Ua; When Zs changes between 0-∞, U
N ' nBetween 0～Ua, change.So when the laod unbalance of the secondary side of external voltage mutual inductor, can produce zero-sequence fundamental voltage, and may cause the malfunction of voltage component.When external area error takes place, or may cause the malfunction of zero-sequence direction component during disturbance.
Then, the inventor has carried out experiment simulation and data analysis.At first measure former limit (i.e. the primary side of this voltage transformer (VT) 102) exciting current of the voltage transformer (VT) 102 in the protective device.Fig. 4 is the wiring diagram of the exciting current on the former limit of the voltage transformer (VT) in the test protective device.Wherein, U1a, U1b, U1c, U1n is the Ua of OMICRON, Ub, Uc, Un output, seal in a small resistor R (being the resistance between the Ch1 two ends among Fig. 4) at A in mutually temporarily, the pressure drop on passage 1 measuring resistance, thus reflect A phase exciting current indirectly, in Fig. 4, ch1 (test channel 1) is exactly the voltage drop that is used for monitoring on this small resistor R that temporarily seals in.Ch2 (test channel 2) measures the A phase voltage on the winding, thereby reflects magnetic flux indirectly, thereby can obtain the magnetic hysteresis loop group under the different voltages.Record ripple by protective device can obtain U2a, and U2b, U2c are to the voltage of U2n, as the data of the criterion of studying protective device.In the A impedance that is in parallel, with the simulation unbalance load, the generation of checking residual voltage.Adopt following steps particularly:
(a) by measuring A phase exciting current and A phase winding voltage, can verify that working as center line connects just often, exciting current contains third harmonic, and winding voltage is sinusoidal wave; When broken neutral line, exciting current is sinusoidal wave, and winding voltage contains third harmonic.
(b) when the PT broken neutral line takes place, measure the third harmonic content of protection secondary side voltage, so that propose Practical Criteria.
(c) go up impedance in parallel mutually at A, when the PT broken string takes place, measure the zero-sequence fundamental voltage of protection secondary side.
Found through experiments, when the neutral line connects just often, the magnitude of voltage of passage 1 (reflection exciting current) as shown in Figure 5, the magnitude of voltage of passage 2 (reflection magnetic flux) is as shown in Figure 6.Voltage and phase voltage on the resistance R of test channel 1 (Ch1) test are carried out spectrum analysis, obtain the spectrum analysis figure (see figure 7) of passage 1 and the spectrum analysis figure (see figure 8) of passage 2 respectively, UR represents the voltage at the resistance R two ends of test channel 1 (Ch1) test in Fig. 8.As seen, connect just often at the neutral line, contain third harmonic in the exciting current, promptly the third harmonic in the exciting current can circulate by center line; Phase voltage is sinusoidal wave, only contains fundametal compoment.
When broken neutral line, the magnitude of voltage (reflection magnetic flux) of magnitude of voltage of passage 1 (reflection exciting current) and passage 2 is respectively as Fig. 9 and shown in Figure 10.Ohmically voltage (exciting current) and phase voltage are carried out spectrum analysis, the spectrum analysis figure (seeing Figure 11) of the passage 1 that obtains respectively and the spectrum analysis figure (seeing Figure 12) of passage 2.As seen, when the neutral line disconnected, the third harmonic in the exciting current did not have flow cycle, and then exciting current is sinusoidal wave.The phase voltage that this exciting current produces is a peaked wave, promptly contains third harmonic in the phase voltage.
The composite measurement result, as can be seen, when the neutral line connects just often, exciting current has presented peaked wave shape (see figure 5), and contains bigger third harmonic (seeing Fig. 7 and Fig. 8), and winding voltage presents standard sine wave.
When broken neutral line, the third harmonic in the exciting current does not have flow cycle, and then exciting current is sinusoidal wave, and the phase voltage that this exciting current produces is a peaked wave, promptly contains third harmonic in the phase voltage.
When broken neutral line, exciting current is sinusoidal wave (see figure 9) substantially, and winding voltage has presented the peaked wave shape, contains bigger third harmonic (seeing Figure 11 and Figure 12).Because the second harmonic winding voltage satisfies: E=4.44fN Φ
m,
On phase place, lag behind
The degree, can in the hope of
So can obtain magnetic flux Φ and exciting current
Magnetic hysteresis loop, Figure 13 shows the magnetic hysteresis loop group that phase voltage is respectively 30V and 57.74V.
As seen, under different winding voltages, can produce different magnetic hysteresis loops.Because influences such as the magnetic hysteresis of ferromagnetic material and eddy current, even maximum magnetic flux is not operated in state of saturation, exciting current and winding voltage neither linear relationships.In case the PT broken neutral line has taken place, the voltage of PT secondary side is bound to contain third harmonic.
In addition; the situation that broken neutral line takes place during also to different voltage the inventor has been carried out sunykatuib analysis; the waveform and the frequency spectrum thereof of the original edge voltage by the voltage transformer (VT) in the protective device only comprise integral frequency harmonizing wave in each phase voltage as can be known, and non-integer harmonics is very little.For integral frequency harmonizing wave, the third harmonic maximum.Therefore, when the PT broken string took place, third harmonic can appear in the voltage that enters the former limit of the voltage transformer (VT) in the protective device, and the voltage of secondary relatively is very easy to find by data, and secondary voltage has reflected really and third harmonic occurred by original edge voltage.
Following table is former limit when adding different symmetrical voltages, the third harmonic content value of secondary phase voltage.
Table 1
As seen, the size of the third harmonic content in the phase voltage is linear substantially with the voltage on former limit.So can dynamically adjust the threshold value of third harmonic according to the amplitude of fundamental voltage.
In addition; after the zero-sequence fundamental voltage of the secondary side (i.e. the secondary of this voltage transformer (VT)) of the voltage transformer (VT) in the protective device is analyzed; also can draw: the third harmonic in each phase voltage is the same substantially, and the third harmonic content maximum in the residual voltage (3U0).
Can draw from top analysis: because the third harmonic of each phase voltage same-phase in time, so the third harmonic value of residual voltage is the third harmonic value of 3 times phase voltage, its third harmonic content maximum.Can adopt the third harmonic value in the residual voltage to judge.When system normally moved, residual voltage was very little, and its third harmonic content is also very little.When earth fault took place, though residual voltage is arranged, the third harmonic content of residual voltage was generally very little.When the PT broken neutral line took place, the third harmonic in the residual voltage can be very big.
Based on top analytic process; the embodiment of the invention provides a kind of broken neutral line detection method of voltage secondary circuit; the framework that the voltage secondary circuit here adopts above-mentioned analytic process to adopt; be that the voltage secondary circuit comprises external voltage mutual inductor and protective device, wherein the primary side of the voltage transformer (VT) in the secondary side of external voltage mutual inductor and the protective device links to each other.
As Figure 14, the broken neutral line detection method of the voltage secondary circuit in the embodiment of the invention comprises the steps:
Step S1401: the third harmonic of the residual voltage of the secondary side of the voltage transformer (VT) in the monitoring and protecting device;
Step S1402: whether the amplitude of judging the third harmonic of the above-mentioned residual voltage that monitors surpasses the duration of first threshold above second threshold value, if then judge the broken neutral line between the voltage transformer (VT) in external voltage mutual inductor and the protective device.
Only surpass first threshold in the amplitude of the third harmonic of residual voltage and just judge that broken neutral line is irrational, therefore also detect the time-delay that whether also has the end time, whether the duration that promptly surpasses reaches certain degree.
The first threshold here is to select according to the amplitude of the fundamental voltage of the residual voltage of the secondary side of the voltage transformer (VT) in the protective device.
Through repeatedly experiment, inventor's discovery is best with the effect that second threshold value is chosen as 10s.
In addition,, can also increase protection mechanism, for example, when the duration that the amplitude of the third harmonic of judging residual voltage surpasses first threshold surpasses the 3rd threshold value, just carry out locking quick acting protection in order to improve the security of system.The 3rd threshold value here should be less than second threshold value.In the reality, the 3rd threshold value can be chosen as 10ms.
The method that provides by the foregoing description can detect the fault of broken neutral line rapidly and accurately, prevents misoperation further.
On the other hand, the present invention also provides a kind of broken neutral line pick-up unit of correspondent voltage secondary circuit, and as shown in figure 15, this device comprises monitoring means 1501 and broken string judging unit 1502.The third harmonic of the residual voltage of the secondary side of the voltage transformer (VT) in the detecting unit 1501 monitoring and protecting devices wherein; broken string judging unit 1502; whether the duration that the amplitude of the third harmonic of the residual voltage that is used to judge that monitoring means 1501 monitors surpasses first threshold surpasses second threshold value; if then judge the broken neutral line between the voltage transformer (VT) in external voltage mutual inductor and the protective device.
In like manner, the first threshold here also is to select according to the amplitude of the fundamental voltage of the residual voltage of the secondary side of voltage transformer (VT) in the protective device.Second threshold value is preferably elected 10s as.
In addition, can also increase protection judging unit 1503, whether the duration that the amplitude that is used to judge the third harmonic of residual voltage surpasses first threshold surpasses the 3rd threshold value, if then carry out locking quick acting protection; Described the 3rd threshold value is less than second threshold value.
The above only is a preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the principle of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.
Claims (10)
1. the broken neutral line detection method of a voltage secondary circuit; described voltage secondary circuit comprises external voltage mutual inductor and protective device; wherein the primary side of the voltage transformer (VT) in the secondary side of external voltage mutual inductor and the protective device links to each other, and it is characterized in that this method comprises:
The third harmonic of the residual voltage of the secondary side of the voltage transformer (VT) in the monitoring and protecting device;
Whether the amplitude of judging the third harmonic of described residual voltage surpasses the duration of first threshold above second threshold value, if then judge the broken neutral line between the voltage transformer (VT) in external voltage mutual inductor and the protective device.
2. method according to claim 1 is characterized in that, described first threshold is to select according to the amplitude of the fundamental voltage of the residual voltage of the secondary side of voltage transformer (VT) in the protective device.
3. method according to claim 1 is characterized in that, described second threshold value is 10 seconds.
4. according to any described method in the claim 1 to 3, it is characterized in that described method also comprises:
Whether the duration that the amplitude of judging the third harmonic of described residual voltage surpasses first threshold surpasses the 3rd threshold value, if then carry out locking quick acting protection;
Described the 3rd threshold value is less than second threshold value.
5. method according to claim 4 is characterized in that, described the 3rd threshold value is 10 milliseconds.
6. the broken neutral line pick-up unit of a voltage secondary circuit; it is characterized in that; described voltage secondary circuit comprises external voltage mutual inductor and protective device; wherein the primary side of the voltage transformer (VT) in the secondary side of external voltage mutual inductor and the protective device links to each other; it is characterized in that this pick-up unit comprises:
Monitoring means is used for the third harmonic of residual voltage of secondary side of the voltage transformer (VT) of monitoring and protecting device;
The broken string judging unit; whether the duration that the amplitude of the third harmonic of the residual voltage that is used to judge that described monitoring means monitors surpasses first threshold surpasses second threshold value; if then judge the broken neutral line between the voltage transformer (VT) in external voltage mutual inductor and the protective device.
7. the broken neutral line pick-up unit of voltage secondary circuit according to claim 6 is characterized in that, described first threshold is to select according to the amplitude of the fundamental voltage of the residual voltage of the secondary side of voltage transformer (VT) in the protective device.
8. the broken neutral line pick-up unit of voltage secondary circuit according to claim 6 is characterized in that, described second threshold value is 10 seconds.
9. according to the broken neutral line pick-up unit of any described voltage secondary circuit in the claim 6 to 8, it is characterized in that, also comprise:
The protection judging unit, whether the duration that the amplitude that is used to judge the third harmonic of described residual voltage surpasses first threshold surpasses the 3rd threshold value, if then carry out locking quick acting protection; Described the 3rd threshold value is less than second threshold value.
10. the broken neutral line pick-up unit of voltage secondary circuit according to claim 9 is characterized in that, described the 3rd threshold value is 10 milliseconds.
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| CN102998583A (en) * | 2012-11-16 | 2013-03-27 | 天津大学 | Method for judging line breaking of neutral line of voltage circuit |
| CN103969540A (en) * | 2013-01-30 | 2014-08-06 | 江苏省电力公司常州供电公司 | Method for testing wiring of secondary circuits of four-star voltage transformers |
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Application publication date: 20111116 |