The turn-to-turn short circuit on-Line Monitor Device of voltage transformer (VT)
Technical field
The present invention relates to a kind of turn-to-turn short circuit on-Line Monitor Device of voltage transformer (VT), be specially for high-tension electricity magnetic-type voltage transformer (VT) or power transformer, according to the magnetic potential balance principle, adopt the high-acruracy survey admittance method to detect its shorted-turn fault, belong to electrotechnical measurement and detection technique field.
Background technology
The turn-to-turn short circuit of winding class high voltage electric equipment (transformer and mutual inductor) is very serious accident.According to statistics, the transformer shorted-turn fault accounts for 50%~60% of the large-scale fault of transformer, at present both at home and abroad for the winding kind equipment turn-to-turn short circuit carried out correlative study, for transformer, following research method is arranged specifically:
Whether (1) utilize first and second winding voltage and current change quantity to monitor breaks down.During due to shorted-turn fault, former and deputy polygonal voltage and curent change value are very little, and transformer is in actual motion, load is dynamic, cause electric current also not stopping variation, and the amplitude that its amplitude of variation changes considerably beyond shorted-turn fault, therefore be difficult to reject the impact of this variation on shorted-turn fault;
While (2) utilizing transformer to be short-circuited, whether the variation of stray field is monitored and is broken down.When transformer generation shorted-turn fault, stray field changes apparent in view, utilize detector to survey the leakage flux variation and can monitor shorted-turn fault, but this method need to be put into detecting coil transformer inside, by measuring the variation of induced voltage in detecting coil, monitor the shorted-turn fault of winding, this can exert an influence to equipment performance;
(3) utilize the measurement power attenuation to monitor turn-to-turn short circuit.When winding kind equipment generation turn-to-turn short circuit, its internal power consumption can obviously increase, and utilizes voltage, the magnitude of current of each side of transformer, calculates the power of transformer, and then draws the variation of loss.Error for the current transformer of measuring electric current, voltage and voltage transformer (VT) introducing equally can be on the evaluation of impact to measurement result.
Face too such problem for electromagnetic potential transformer, after turn-to-turn short circuit occurs, due to very little to its major insulation and error effect, usually be difficult for being monitored to, in case fault enlarges, and will cause equipment major insulation to burn out, and power grid security is caused significant impact.Generally, to puncture the required time to major insulation be not wait a few minutes to tens hour from turn-to-turn short circuit occurs, and electric pressure is higher, and speed of development will be faster.
The reason that winding interturn short-circuit of electromagnetic potential transformer produces has multiple, and the method for conventional monitoring electromagnetic potential transformer state of insulation is mainly to its winding exciting curent I
1Monitor, as shown in Figure 1, in figure, sensor 1 is used for the monitoring primary current, and sensor 2 is used for insulated leakage current between monitoring first and second.Because how a lot of umber of turn of electromagnetic potential transformer is than transformer, as the 110kV electromagnetic potential transformer, its umber of turn is 33990 circles, when a winding generation turn-to-turn short circuit, winding reduces by 1 circle, on the amount of the impact order of magnitude of leakage current, is 10
-5, and the precision of general centre path current sensor is 10
-4Left and right, the voltage measuring transformer error reaches 10
-3, therefore, adopt above-mentioned three kinds of methods that detect transformer fault, the turn-to-turn short circuit that can not effectively monitor the mutual inductor kind equipment changes.
Chinese invention patent " a kind of method that realizes tranformer protection based on admittance principle " (application number: 200710119033.8 applyings date: 2007-06-18) disclosed; that the output waveform of voltage, current transformer to protected each side of transformer is sampled and obtained voltage, electric current instantaneous sampling value; calculate voltage, current amplitude phase angle information, protective device calculates the excitation admittance Z of protected transformer according to the admittance algorithm again
0, compare with set-point afterwards, to send and whether carry out guard signal, the method is quick on the draw to the transformer fault situation, and criterion nargin is large, simple, reliable.Its weak point is: the computing method of excitation impedance are complicated; Sample by electric current, voltage transformer (VT) that transformer is connected, sampling precision is the highest can only reach 10
-3Far more than transformer, during turn-to-turn short circuit, the changing value of excitation admittance is much smaller than transformer due to umber of turn of electromagnetic potential transformer, and therefore, the method can not be adapted to the protection of electromagnetic potential transformer.
Summary of the invention
The objective of the invention is the problem that proposes for background technology, the on-line monitoring electromagnetic potential transformer turn-to-turn short circuit device that a kind of precision is high, be easy to realize is disclosed, utilize the magnetic potential balance principle, an admittance of high precision monitor, reflect the electromagnetic potential transformer shorted-turn fault therefrom.
Technical scheme of the present invention is: the turn-to-turn short circuit on-Line Monitor Device of voltage transformer (VT), comprise data acquisition element, A/D conversion element, data handling system and host computer, it is characterized in that: described data acquisition element comprises sampling resistor and divider resistance, end at a high-tension coil of voltage transformer (VT), be in series with sampling resistor; On one group of low-voltage coil of secondary windings of PT, be in series with divider resistance; Sampling resistor and divider resistance are connected with respectively the A/D conversion element, the A/D conversion element that is connected with sampling resistor is connected to data handling system by optical isolation, the A/D conversion element that is connected with divider resistance is direct-connected to data handling system, and host computer is connected with data handling system.
The turn-to-turn short circuit on-Line Monitor Device principle of work of voltage transformer (VT) of the present invention is as follows:
Electromagnetic potential transformer T shape equivalent electrical circuit as shown in Figure 2, its primary circuit admittance
, be a non-linear value, relevant with impressed voltage, can calculate by the ratio of measuring electromagnetic potential transformer primary current and secondary voltage, namely
, as shown in Figure 3, Y
mThe size of value can reflect the inner magnetic potential balance of electromagnetic potential transformer accurately.When electromagnetic potential transformer generation turn-to-turn short circuit, its inner magnetic potential balance is broken, and admittance will change.
The invention has the beneficial effects as follows: utilize the magnetic potential balance principle to monitor an admittance of electromagnetic potential transformer, because sampling resistor and divider resistance are pinpoint accuracy resistance, by A/D conversion element and data handling system computing, the systematic sampling precision can reach 10
-4Above, improve the current straight-through current transformer monitoring current signal accuracy that utilizes and do not reached the shortcoming of requirement, can well reflect the electromagnetic potential transformer shorted-turn fault.
Description of drawings
Accompanying drawing 1 is traditional electromagnetic potential transformer on-line monitoring method schematic diagram;
Accompanying drawing 2 is voltage transformer (VT) T shape equivalent circuit diagram;
Accompanying drawing 3 is electromagnetic potential transformer admittance measurement schematic diagram;
Accompanying drawing 4 is embodiment of the present invention systematic schematic diagram.
Embodiment
Below in conjunction with accompanying drawing, inventive embodiments is described further:
Mark in accompanying drawing: in accompanying drawing 2, I
1-monitored electromagnetic potential transformer primary current, I
0-exciting current, I
2 '-secondary current (conversion is to primary side), U
1-primary voltage, E
1-induced potential, E
2-secondary induced potential, U
' 2-secondary voltage (conversion is to primary side), Z
1-winding equiva lent impedance, Z
m-excitation impedance, Z
' 2-Secondary Winding equiva lent impedance (conversion is to primary side), Z
' b-secondary load (conversion is to primary side).In accompanying drawing 3, U
1-primary voltage, U
2-secondary voltage, a, x-Secondary Winding terminal.In accompanying drawing 4, PT-monitored electromagnetic potential transformer, U
1-primary voltage, U
2-secondary voltage, I
1-monitored electromagnetic potential transformer primary current, k-one time winding end shield terminal, a, x-Secondary Winding terminal, R
1-sampling resistor, R
2, R
3-divider resistance, A/D1-one time A/D conversion element, A/D2-secondary A/D conversion element.
Below in conjunction with accompanying drawing, the embodiment of the present invention is elaborated.
As shown in Figure 4, electromagnetic potential transformer primary current I
1Sampling resistor R
1With electromagnetic potential transformer primary current I
1Be converted to voltage signal, and input to A/D conversion element A/D1 one time, voltage signal is converted to digital signal, then through optical isolation, transmits signals to data handling system; From divider resistance R
3With electromagnetic potential transformer secondary output voltage U
2Proportional sampling, and input to secondary A/D conversion element A/D2, voltage signal is converted to digital signal, be resent to data handling system, data handling system is by formula
Calculate admittance value of electromagnetic potential transformer, and be uploaded to host computer., at host computer,, by early warning system is set,, when admittance value floats 3 times that surpass initial value the time, be considered as electromagnetic potential transformer generation shorted-turn fault.
Generally, sustainable long time of electromagnetic potential transformer generation shorted-turn fault initial stage, when its admittance value arranges early warning value over host computer, cut off rapidly the electromagnetic potential transformer that breaks down, and it is carried out offline inspection, the dangerous generation such as can effectively prevent that electromagnetic potential transformer from blasting, ensure the power system safety and stability operation.
Because sampling resistor and divider resistance are pinpoint accuracy resistance, by A/D conversion element and data handling system computing, the systematic sampling precision can reach 10
-4Above, improve the current straight-through current transformer monitoring current signal accuracy that utilizes and do not reached the shortcoming of requirement, can well reflect the electromagnetic potential transformer shorted-turn fault.