After adding current-limiting resistor, the grounding current of iron core 2 or 3 to about 34 mA, clip pieces of earth current is "big small" (see figure 2), the change rule of between mA range from 10.7 to 10.7 A.
According to the fundamental core earth current 2 and 3 is equal to infer and clamp grounding current transformer may be the cause of the problem is: the iron core is between 2, 3, due to run vibration insulation board damaged, core sub between 2, 3, cause iron core multipoint earthing, and destroyed the clip pieces and insulation between the iron core.
n September, when the transformer is out of power, the insulation resistance of each part of the core is obtained by using 2500V megohm meter as shown in table 2. When all grounding wires are open for testing, the insulation resistance between core 23 is zero. When the ground wire is opened successively, the core 23 has zero ground insulation resistance, which proves the inference of short connection between iron core 2 and 3.
As can be seen from the photos taken during the internal inspection (as shown in figure 3), the distance between the 23 ends of the iron core is obviously too close, which indirectly proves the inference of short connection. According to manufacturer technical staff analysis, core ends up and down as the insulation vulnerabilities, caused by core between 2, 3, short answer the multipoint earthing of circulation, the insulation of the inconsistency between core and clip a reversible damage, cause is when the earth current big small anomalies. ,
Conditions are not due to the site for the repair, maintenance cost is higher, returned to the factory and transformer core 2, 3, has formed a short meet, decided to open the iron core 2 grounding line, to form core 2, 3, only one place, to avoid more ground, at the same time ensure the core and the clip pieces of insulation is not damaged.
According to statistics, the ground fault of iron core and clamping parts has become one of transformer frequent faults. When there is a core multipoint earthing faults, want to make a comprehensive measurement and comprehensive analysis, after checking it again according to the condition of site specific treatment scheme choice, must not blindly to discharge impact electric welding or burning, lest cause insulation damage, extend the fault.