Network protection from third harmonics current effects

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering and may be used for hardware designing to improve quality and reduce voltage and electric power losses, when such power is transmitted in three-phase four-wire electric networks due to reduction of anharmonicity and asymmetry. Protection device generates 150 Hz frequency current from phase currents. This current is immediately introduced to harmonics 3 current of neutral working wire in opposite phase.

EFFECT: compensating highest current harmonics flowing along neutral conductor.

2 cl, 2 dwg

 

The invention relates to electrical engineering and can be used to improve quality and reduce power loss by reducing nonsinusoidal current curve and unbalance in three-phase four-wire electric networks with earthed neutral.

It is known device [1], containing three transformer windings of which are included in the star schema with zero - triangle". For longitudinal insertion of such a transformer in the electrical network, the third harmonic currents close in the windings, connected in a "triangle", and are not in the line currents on the side of the transformer with windings connection to the "star".

The disadvantage of this device are large consumption of materials and incomplete compensation of the third harmonic with an unbalanced load in the network phases, which reduces the efficiency of suppression of the current third harmonic distortion sinusoidally voltage network.

The known method, which is implemented device adopted for the prototype [2], consisting of a transformer, the higher harmonics analyzer, filter, first harmonic, filter higher harmonics controlled semiconductor Converter and rectifier.

The disadvantages of this device include its large consumption, complexity and low reliability at first the voltages, arising in the primary electrical network.

The task of the claimed invention is to reduce material consumption device, increasing its reliability while maintaining the accuracy of the compensation of the third harmonic current component.

This technical result is achieved that the device protecting the network from the effects of third harmonic currents, containing the first measuring transformer and rectifier, entered three transformer reactor, the primary winding of which is unipolar included in rassechku linear wire network, and the beginning of their secondary windings form with the end of the secondary winding of the first transformer common point, the ends of the secondary winding of the three transsectoral through a rectifier and a capacitor connected to the beginning of the secondary winding of the first transformer, the primary winding of which is included in the neutral wire network unipolar with respect to the three mentioned transsectoral, with the first measuring transformer made by transformer reactor and rectifier three - phase.

In addition, all four transformer reactor completed magnetic circuit with break-type clamp.

The inventive device network protection from the effects of currents of the third harmonic is shown in figure 1, figure 2 charts harmonic the ski components of voltages and currents for continuous operation.

Device protecting the network from the effects of third harmonic currents contains included in the neutral N and phase conductors L1-L3 transrectal 1, 2, 3, 4, to the secondary windings of which are connected three-phase rectifier 5 and the capacitor 6 (figure 1). The three-phase diode rectifier 5 their anodes form a common point with one of the terminals of the capacitor 6. The second output capacitor 6 is connected with the beginning of the secondary winding of the transformer reactor 1.

Transrectal 1-4 as part of the device protecting the network from the effects of third harmonic currents have the same transformation ratio.

Device protecting the network from the effects of third harmonic currents operates as follows.

Single-phase nonlinear load currents and magnetization step-down transformers cause the flow in the phase and neutral wire networks of non-sinusoidal currents, predominantly third harmonic. Under the action of stresses UL1UL2and UL3(2) in the secondary windings of transsectoral 2, 3, 4 three-phase rectifier diodes are switched alternately by 1/3 period of industrial frequency. The talk will be held in the rectifier diode, the potential of the anode of which is relatively common point of transsectoral 2, 3, 4 higher than other diodes. Switching diodes occurs at points in time corresponding to the intersection points is sinusoid phase voltage, therefore, the curve of the rectified voltage Udhas the form of the envelope of the sinusoid phase voltages, currents running through the secondary windings of transsectoral (figure 2). The curve of the rectified current idrepeats the curve of the rectified voltage. The frequency of pulsations of the rectified current flowing in the secondary winding of the current transformer 1 with respect to the fundamental frequency of the primary network, is equal to three.

For compensation arising by straightening the constant component of Edput the capacitor 6. The value of the capacitance of the capacitor is selected from the conditions of compensation of the inductive resistance of the secondary electrical circuit at a frequency of 150 Hz(where L is the total inductance of the secondary winding transsectoral). In the result, the current flowing through the transformer reactor 1 current iinfrequency of 150 Hz will not contain a permanent part of Id(figure 2), and the secondary winding transsectoral will not be additionally warm.

Thus, decreases the intensity of electromagnetic compensator increases the reliability and accuracy of the compensation of the third harmonic current component, which improves the quality of electric energy, reduces loss of active power and voltage losses in all network elements from the current third harmonic component.

Sources in the information

1. Briskin DE Electric machine. In 2 hours Part 1 / Daibouken, Aesoteric, Vshost. - M.: Higher school, 1987. - s.

2. Patent RU 2294044, CL H02J 3/01, H02J 3/26, 2007, BI 5 - prototype.

1. Device protecting the network from the effects of third harmonic currents, containing the first measuring transformer and rectifier, characterized in that it introduced three transformer reactor, the primary winding of which is unipolar included in rassechku linear wire network, and the beginning of their secondary windings form with the end of the secondary winding of the first transformer common point, the ends of the secondary winding of the three transrectal through a rectifier and a capacitor connected to the beginning of the secondary winding of the first transformer, the primary winding of which is included in the neutral wire network unipolar with respect to the three mentioned transsectoral, with the first measuring transformer made by transformer reactor and rectifier three - phase.

2. Device protecting the network from the effects of third harmonic currents according to claim 1, characterized in that all four transformer reactor completed magnetic circuit with break-type clamp.



 

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