In recent years, the domestic many substation due to lightning formation expand accidents, the majority of Grounding resistance unqualified related to ground network plays the role of working grounding and protection grounding, grounding resistance is too large when: a ground fault occurs, so neutral point voltage offset increases may sound phase and neutral point voltage is too high and cause damage to the equipment exceeds the level of insulation required. Lightning or lightning wave attack, due to the current very high residual pressure, so that the threat of the nearby equipment subjected to counterattack, and reduce the ground grid protection equipment (overhead transmission line and substation electrical equipment) live conductors Ray resistance level, less than the design requirements and damage to equipment. Grounding resistance of the grounding system of qualified directly related to the the substation operating personnel, the substation maintenance personnel personal safety; but because the soil has a corrosive effect on the grounding device, along with a longer running time, the grounding device already corrosion, impact the safety of the substation run; therefore, must vigorously strengthen the network to be regular monitoring of the grounding resistance; running substation network grounding resistance measurement, the larger the system interference net current inflow as well as test the interference between the lead line, so that the test results error. Especially large grounding resistance is small (generally in 0.5Ω less), even subtle interference test results will have a huge impact; inaccurate to network ground resistance testing, not only damage the equipment, but will also cause such ground network mistakenly transformation unnecessary losses, combined with my Grounding impedance test method are summarized as follows:
Second, ground resistance testing principles and methods:
Test the grounding means grounding impedance when the current electrode to be arranged as far as possible the normal current pole and the distance from the edge of the test grounding device dcG should test grounding device maximum diagonal length D 4 to 5 times (parallel wiring Act), 2-fold or more (triangle wiring method desirable areas of uniform soil resistivity), the voltage lead length is 0.618 times the length of the current leads (flat-line wiring method) or equal to the current line (triangle wiring method).
1, E pole in the use of the three-pole measurement must be shorted together with P1, small local network grounding resistance, the local network grounding resistance is small (≤ 0.5Ω), in order to improve the measurement accuracy, reduce the instrument and ground network measurements lead resistance and contact resistance measurement results can be untied EP shorting; reduce contact resistance errors caused separately lead connected to the ground network test points.
Note:
1, E - then be measured network;
2, P1 - then be measured network;
3, P2 - then measuring the voltage line (0.618 times the length of the current line length);
4 C - connected to a measuring current line (its length taken ground network, the diagonal length of 4 to 5 times);
Third, testing considerations and significance
Most of the characteristic parameters of the grounding device is closely related to soil moisture, ground assessment of the state of the device and the acceptance testing should be carried out as far as possible in the dry season and the soil is not frozen, should not be in the thunder, rain, snow, or rain and snow after carried out immediately. Actual measurements provide a reliable basis for our rectification. The proposed rectification optimization on Substation Grounding condition, so that the grounding resistance of the grounding grid to meet the requirements, so as to effectively prevent the equipment insulation damage caused by the step voltage to cause personal injury or equipment damage. Play to ensure the safe operation of the electrical equipment for the substation staff to create a safe and secure work environment.
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