Device for measuring the capacity of a network with isolated neutral

 

(57) Abstract:

The invention relates to electrical engineering, in particular to devices for measurement and compensation of capacitive currents of single-phase earth fault in electric networks with isolated neutral voltage 6 - 35 kV, and can be used to accurately measure the capacity of network phases to earth for further resonance settings arc suppression reactors. The technical result is to increase the measurement accuracy of network capacity, expanding the functionality of the device and reduces power consumption by the power supply circuits. In the device for measuring capacitance network with the creation of neutral artificial potential non-industrial frequency as the source for non-industrial use frequency periodic discharge to the signal winding of the pre-charge capacitor, and the signal is directly proportional to the capacity of the phases of the network with isolated neutral, receive at the time of discharge on the output winding of the voltage transformer connected in open triangle, with the help of series-connected two differentiating sections, the amplitude detector and the divider, and the time of each discharge of the capacitor through block cinemoi the invention relates to the field of electrical engineering, in particular to devices for measurement and compensation of capacitive currents of single-phase earth fault in electric networks with isolated neutral voltage 6...35 kV, and can be used to accurately measure the capacity of network phases to earth for further resonance settings arc suppression reactors (DR).

There are a large number of methods and devices for measuring the capacity of a network with isolated neutral and automatic tuning arc suppression reactors [1] . In most practical systems compensation is used pre-resonance tuning compensating devices without direct measurement of the capacity of the network, when the arc suppression reactors are adjusted until the occurrence of a ground fault on either natural or artificially created offset voltage of the neutral network. In these cases, according to the EMP, you must enter the detuning compensation not less than 5% of the resonance, which reduces the accuracy of compensation and, accordingly, increases the residual current in place of the circuit. Moreover, such methods are not applicable for new type of arc suppression reactors, in particular, the magnetically controlled that require quick and accurate settings the bone network.

Closest to the proposed device is a way of measuring the capacity of a network with isolated neutral, which consists in creating a neutral artificial potential by introducing a neutral source of non-industrial frequency signal through the winding arc reactor or through a separate transformer and the voltage measurement bias neutral on an open winding of the transformer voltage [1]. This is also connected to the signal winding of the reactor sine wave signal generator of non-industrial frequency, for example, increased 100 Hz or lower 16,6 Hz. In normal operation, the network generator continuously provides the offset of the neutral, which depends on the capacity of the network phases to earth and is fixed on the output winding of the voltage transformer connected to the open triangle. Such devices operate successfully and provide a measure of network capacity for the subsequent resonance settings arc reactor, however, this measurement method has several disadvantages, which reduces the measurement accuracy in the presence of natural bias voltage neutral or parallel-connected DR and continuous losses, svjazanno as non-industrial source frequency is suggested to use the periodic discharge to the signal winding of the pre-charged capacitor, when this signal is inversely proportional to the capacity of the network phases on land allocated by means of an amplitude detector at the output of the differentiating element, connected to the output winding of the voltage transformer connected to the open triangle. The more network capacity, the constant charge capacitor proportionally less than the charge rate capacity of the network and, accordingly, the amplitude of the derivative of the voltage of the charge capacity of the network at the output of the differentiating element connected to the winding of the voltage transformer connected to the open triangle. To get instead of the inverse proportional dependence on network capacity enough to take the reciprocal of the signal at the output of the amplitude detector using a divider or similar element, which provides the inverse function 1/X.

However, in this case at significantly smaller losses on the measurement and the lack of influence paralleled DR and other inductances (due to the low duration and high is equivalent to the frequency of the pulse capacitor discharge) this device may have significant error in significant size bias voltage neutral, which Pets and really destinating circuit, when the displacement of the neutral corresponds to the phase voltage (100%). Therefore, the proposed scheme must be supplemented by the synchronization unit, ensuring the discharge of the capacitor at the moment of passing the natural bias voltage neutral (voltage noise) through zero.

The aim of the invention is to improve the accuracy of the device for measuring the capacity of the network, expanding its functionality and reduced losses in the measurement mode.

This goal is achieved by the fact that the device for measuring the capacity of a network with isolated neutral, containing connected in the neutral of the network through the signal winding of the arc reactor or a separate transformer non-industrial source frequency and the standard voltage transformer winding connected in open Delta, non-industrial source frequency contains the charging unit and connected to its output capacitor through a managed switch periodically discharged to the signal winding of the arc reactor or a separate winding of the transformer, and the signal proportional to the capacity of the network, obtained from the output winding of the voltage transformer connected to the open triangle is laudry detector and the divider when this synchronization unit connected to an input of the second differential element, and the output is with a managed switch, provides a capacitor discharge through a managed switch in the time of the transfer bias voltage of a neutral position and its second derivative crosses zero.

To explain the principle of the drawing shows one possible structural schemes of the device.

The schema contains the charging unit 1, is connected by its input to mains 220 V, 50 Hz, capacitor 2, is connected via a managed switch 3 to the signal winding arc reactor 4, which in turn is connected to the network 6...35 kV through the supply transformer, the standard voltage transformer IOIE or US 5, the first differentiating element 6 connected to the winding of the voltage transformer connected to the open triangle and block synchronization, control and measurement 7, through which the synchronization unit (BS) controls the discharge of the capacitor and records the measured value of the capacitance network output contained in the serial chain from the second differentiating element (DZ) 2, the amplitude detector (BP) and denominator (D).

The scheme works following logicheskie is charged by the charging unit 1 to a fixed value and is discharged through a managed switch 3 to the signal winding of the reactor 4. Each capacitor discharge is accompanied by the appropriate charge capacities of the phases of the network and by the shift of the neutral, which is converted at the output of the voltage transformer 5 through the differential element 6 in the derived voltage neutral. The application of the second differential element, consisting, as before, in the simplest case of the RC - chain, allows to obtain the second derivative of this voltage, after which the amplitude detector is allocated its maximum, and the divisor is calculated counter value is directly proportional to the size of the containers phases to earth. Thus, any change in capacitance of the phases of the network caused by operational switches, respectively, changes the speed of their charge, its derivative and the amplitude of the voltage at the detector output, the inverse value of which in the scale corresponds to the capacitive current or conduction network.

In case of significant bias neutral due to the asymmetry of the phases of the network or in the single-phase circuit is the bias voltage will be superimposed on measured voltage transformer signal, and the discharge voltage of the capacitor 2 through the transformation of the bias voltage in centervideo link error of the measurement result will be approximately the voltage value of the natural bias neutral.

In order to eliminate the influence of the transformed signal in the winding bias voltage on the discharge capacitor 2, the synchronization unit monitors this bias voltage and provides a discharge of the capacitor at the moment of transition bias voltage through zero. Moreover, the control of the transfer voltage through zero is playable with voltage transformer, and the signal winding of the reactor, and the second derivative of the voltage passing through zero at the same time.

However, at the time of discharge the first derivative of the voltage offset at the output of the first differentiating element will have a maximum and from the useful signal, and the voltage from the natural bias neutral (when a sinusoidal bias voltage passes through zero, its derivative has a maximum). The overlay gives the same error, and the selection of the useful signal on the background of significant interference is a serious hardware problems.

But if this second derivative is obtained at the output of the second differentiating element, free from interference, because the second derivative of the neutral voltage passes through zero simultaneously with the transition through zero a "natural" sinusoidal napraslina less than one millisecond, freely received and processed by the block 7 by differentiating sections, the amplitude detector and divider irrespective of voltage level shift the neutral frequency and multiples of harmonic.

Thus, the synchronization unit BS and the second differentiating element DZ 2 exclude errors from the influence of bias voltage neutral frequency and higher harmonics, allowing essentially to measurement mode single-phase earth fault. The divisor D provides obtaining the magnitude is inversely proportional to the second derivative of the output of the amplitude detector HELL and is directly proportional to capacitance, the capacitive current and capacitive conduction network (the higher the capacity of the network and its conductivity, the smaller the measured signal from the voltage transformer and the speed of its rise, but the more its inverse value of the output of the divider).

Thus, in principle, no matter what standard is achieved by means of the momentum transfer capacitor discharge in a neutral network and get feedback from the voltage on the neutral. In the absence of this resonance or signal winding it pulsed source of non-industrial h is entrusted with the corresponding wiring diagram. The transformer voltage can be any value, including members of the group phase.

The proposed device for measuring the capacity of a network with isolated neutral was implemented by the author in the mock-up samples and tested in conjunction with the network. Tests showed a high accuracy of measurement of capacitance and confirmed the described characteristics. The implementation of the present invention is not straightforward as discrete semiconductor and digital hardware components.

Bibliography

1. A. A. Chernikov. "Compensation of capacitive currents in networks with ungrounded". - M.: Energy, 1974, S. 83-84.

Device for measuring the capacity of a network with isolated neutral, containing connected in the neutral of the network through the signal winding of the arc reactor or a separate transformer non-industrial source frequency and voltage transformer with a winding connected in open triangle, characterized in that the non-industrial source frequency contains a charging unit, charging connected to its output capacitor through a managed switch periodically discharged to the signal winding of the arc reactor or is the transformer voltage, connected in open triangle, connected in series through the first differentiating element, a second differentiating element, the amplitude detector and the divider, and the synchronization unit connected to an input of the second differential element, and the output is with a managed switch, provides a capacitor discharge through a managed switch in the time of the transfer bias voltage of a neutral position and its second derivative crosses zero.

 

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