Hubei pilot altimeter Electric Holdings Limited to answer your questions: Insulator string voltage distribution analysis
Under the action of the operating voltage, string Insulator voltage distribution is an important issue, which is commonly available to examine this issue equivalent circuit.
We know that every Insulator is equivalent to a capacitor, so a Insulator string is equivalent to chain-shaped circuit composed of a capacitor made up of many.Since the volume resistivity and surface resistivity normally called Insulator (50Hz) is much greater capacitance, it is generally called a series of his capacity circuit.Although the capacity of each Insulator equal, but the composition Insulator strings, each sharing a voltage Insulator is not the same, mainly due to the inter-lead deposit are large stray capacitance between the metal portion of each Insulator tower (ground) (parasitic capacitance) caused.
First, to illustrate the influence of the stray capacitance between the respective metal portions Insulator string and Tower.
Insulator string voltage profile
Left panel: l-voltage distribution when considering only CZ; 2- voltage distribution when considering only Cd; voltage distribution along the string voltage distribution Lu Insulator (220KV) when considering CZ 3 and Cd
Right panel: 1- intact Insulator string; 2- # 10Insulator (0MΩ); 3- # 4Insulator (60MΩ
Insulator itself capacitance provided by C, the metal portion of the tower is a capacitance of Cz, as shown in (a),.Because of this capacitance, when the potential difference, there is a current through the current flowing through the capacitor Cz to C, respectively, so that, the closer to the wire capacitance C of the current flowing through the greater.As the opera sub-capacitance approximately equal, they are also a large voltage drop.If only consider the impact Insulator capacitance to ground, the following Insulator string voltage distribution curve in the graph shown in FIG. 1.
Next will be described the influence of stray capacitance between the conductor string Insulator.
Insulator Metal capacitance portion is provided on the wire as Cd, which equivalent circuit is shown in (b),.Both ends of each capacitor Cd has a potential difference, hence the current through the capacitor, and the circuit must be constructed by the capacitor C, and leads to more distant from a current flowing through the Insulator more, so that the voltage drop it gets.The following voltage distribution curve in the diagram shown Insulator string 2.
Since Insulator Metal capacitance Cd of the conductor portion of the capacitance to ground Cz smaller than, and thus current flows is small, so the pressure drop is relatively small.
Voltage distribution on each string Insulator Insulator actual capacitance should consider two simultaneous action, i.e., the voltage distribution along Insulator strings should be considered by the voltage obtained Cz and Cd distribution superimposed. Shown below curve 3.Seen from the figure, leaving the conductor-side ends Insulator decreased pressure drop, the voltage drop increases again when Insulator.Measured results fully proved this point (as shown below).
Studies have shown that, Insulator string longer, the more non-uniform voltage distribution, the more easily lead some parts of the dielectric breakdown, the voltage measured distribution will be more meaningful.