Transformer core right grounding mode of 4-2019
30 15:05:21 transformer is one of the core equipment of power system, play an important role in the supply enterprise, once the transformer fails, will greatly influence the safe and stable operation of the system.
Transformer core earth fault is one of the common faults of transformer, this paper analyses how grounding transformer core is right.
Transformer core multipoint earthing faults will directly result in transformer core overheating, burning coil.
Because of iron core multipoint earthing, will form the circulation on these points, produce local overheating, long running core fever, transformer therefore only one-point earthing.
The iron core multipoint earthing is divided into two kinds, one is instability core multipoint earthing, stability is a kind of iron core multipoint earthing.
Here is how to analyze the transformer core grounding is correct.
During normal operation of transformer, electric winding and fuses with the fuel tank for the non-uniform electric field, consisting of an electric field between core and other metal components in the electric field.
Between low voltage winding and high voltage winding, between low voltage winding and iron core, iron core with the earth (
Transformer oil tank)
There are between parasitic capacitance, electric winding will through the parasitic capacitance coupling effect makes the core to produce certain potential, often referred to as suspended potential.
Because of iron core and other metal component's position is different, have suspended potential is different also, when the potential difference between two points to breakdown in the insulation, then produce the spark discharge.
This is intermittent discharge, discharge after two potential;
But the discharge stop immediately, and then generate an electrical potential difference, and then discharge & hellip;
Intermittent discharge of transformer oil is decomposed as a result, over time, gradually make the transformer solid insulation damage, leading to the accident, obviously is not allowed.
To avoid the above situation happened, gb regulation, transformer core and large metal parts shall be reliable grounding through the fuel tank, and above 20000 kva transformer, the core should be through the casing from the tank top and reliable grounding.
Specific approach is to connect the transformer core and main substation system and reliable.
In this way, the parasitic capacitance between the core and the earth is short, make the iron core is at zero potential, then flows in the ground just charged winding parasitic capacitance current of iron core.
For three-phase transformer, due to the basic symmetric structure of three phase, three-phase voltage is symmetrical, so the sum of three-phase winding capacitance current of iron core is almost equal to zero.
At present, the widespread adoption of the way to put a copper grounding between core silicon steel sheet.
Despite insulating film between each piece, is still considered to be the iron core is grounded.
From core ends can be measured the resistance value, the resistance is generally small, for only a few to dozens of Europe, in the high voltage electric field can be regarded as pathway, therefore only one-point earthing iron core.
Transformer to ensure that core point ground, usually the core of grounding method has four kinds: 1, when there is between the tie rod or pulling plate and insulation, grounding copper connected to the clamp piece, again by the clip pieces by lifting the core screw grounding;
2, up and down is not insulated, grounding copper from pieces of the anchor bolt under;
3, when the upper and lower clamp pieces of insulation, up and down in the symmetry of iron yoke position of insert a copper grounding clip, clip on piece by iron chips to under ground again, is the purpose of the grounding position of symmetry in order to avoid the iron core is two-point grounding;
4, when using grounding casing, iron core through the ground lug first clamp and grounding casing connection.
Grounding transformer core either way, it is to make sure that the transformer can be normal and stable operation.
Therefore, at the time of application doesn't have to struggle on the use which kinds of means, the four ways are correct, we need to ensure that the transformer can be normal and stable work, and not out of order.