Digital automatic harmonic elimination device

Abstract

The invention discloses a digital automatic harmonic elimination device which comprises a residual voltage input unit, a harmonic elimination unit, a singlechip and a display setting unit. Data collected by the residual voltage input unit collects is converted by an A/D and sent to the singlechip which calculates and obtains data larger than a fixed value given by the display setting unit and triggers a bidirectional thyristor to switch on by controlling an optocoupler; the harmonic elimination unit is switched in a PT open triangle, a voltage collecting unit for collecting the three-phase voltages of a bus is also switched in the A/D connected with a data interface of the singlechip which calculates the data collected by the voltage collecting unit, obtains a residual voltage by and compares the residual voltage with a residual voltage obtained by the open triangle; single-phase grounding occurs if a difference value is smaller than the setting value, and power frequency resonance occurs if the difference value is larger than or equal to the setting value. The invention can accurately distinguish the defaults, such as the power frequency resonance, the single-phase grounding, and the like, accurately eliminates the system resonance in time and has the functions of over-voltage protection, low-voltage protection and PT break judgment.

Description

technical field [0001] The invention belongs to the technical field of distribution network control and protection, and in particular provides a highly reliable digital automatic harmonic elimination device with overvoltage protection and low voltage protection. Background technique [0002] The neutral point in my country's medium and low voltage power distribution network is usually not grounded. In order to monitor the insulation, the busbars of power plants and substations are usually connected with electromagnetic voltage transformers with open triangles. During normal operation, the three-phase saturation degree of the electromagnetic voltage transformer is basically balanced, and the equivalent inductance of the electromagnetic voltage transformer is much larger than the line-to-ground capacitance, so a resonant circuit will not be formed. At this time, the displacement voltage of the neutral point is very small. However, after some switching operations or the ground...

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Problems solved by technology

Because the resonance is accompanied by different frequency components, although it can sometimes eliminate part of the resonance, it is not satisfactory in most cases. It is time-consuming and labor-intensive to eliminate the ferromagnetic resonance by changing the structural parameters of the system by pulling in the voltage transformer or cutting off part of the load. interruption of user power supply

Although there are currently some devices that use single-chip microcomputers to control thyristors to eliminate resonance, this device only detects resonance by collecting the zero-sequence voltage of the open triangle of the bus PT, and eliminates resonance by controlling the thyristor. When the open triangle appears When the zero-sequence voltage is 50Hz, these harmonic elimination devices can only judge the fault by comparing the zero-sequence voltage with a preset threshold inside the device, and the judgment sensitivity for resistance grounding is not high. frequency resonance

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