Common faults and maintenance methods of transformer core

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What is the core of a transformer?

The iron core is the mechanical skeleton of the entire transformer and the main part of the transformer. In addition, it also has the function of providing a magnetic circuit. After the winding is energized, a magnetic field is generated, and the magnetic lines of force pass through the core to form a magnetic circuit, maximizing the magnetic field intensity of the entire magnetic circuit and avoiding magnetic leakage losses. It can be said that the core is one of the most important components in the transformer

Common faults of transformer core

Core multi-point ground fault

1. The insulating cardboard between the clamp feet of the iron core and the rails fell off or was damaged, causing the laminations at the iron chokes of the feet to collide and cause grounding.

2. Due to the wear of the submersible pump shaft, metal powder enters the oil tank and accumulates under the oil tank, forming a bridge under the action of electromagnetic force. The lower iron roller is connected to the pad feet or the bottom of the tank to form a multi-point grounding.

3. The thermometer seat cover on the fuel tank cover is too long and collides with the upper clamp or the edge of the iron yoke or side pillar, forming a new grounding point.

4. When the wooden pad between the lower clamp and the iron ladder is damp or the surface is not clean, and there is a lot of sludge on it, which reduces the insulation resistance value to zero, it forms a multi-point grounding;

5. Metal foreign objects such as iron nails and welding rod heads falling into the oil tank cause the core lamination to communicate with the box body, forming a grounding

6. After the transformer is installed, the positioning pins used for transportation on the top cover of the oil tank are not turned over or removed, resulting in multi-point grounding.

Core overheating and ground fault

1. There are many causes of faults that cause overheating of the transformer core: such as winding short-circuit and overload operation, poor or abnormal grounding of the core itself, short circuit between core sheets or partial short circuit of the core, grounding of the choke screw, magnetic leakage of the core, partial short circuit of the core, power supply The voltage is high, the iron core cooling oil passage is clogged, etc. In addition to the above, poor oil circulation or low oil volume in the tank, oil deterioration, large burrs around the core laminations, and uneven gaps when stacking the core laminations may cause core overheating failure.

2. The core’s local overheating faults are basically located on the core and clamps. If the core of a running transformer overheats, especially if a local overheating failure occurs, characteristic gases H2, CH4, C2H2, and C2H6 will be produced. Chromatographic analysis found that the content of dissolved gas components in the oil exceeds the standard.

Transformer core inspection and repair methods

1. Use a clean, lint-free white cloth to wipe away the oil and impurities on the surface of the iron core.

2. If the silicon steel sheet has curling, warping, etc., use a mallet to repair it carefully. 3) Check that the core oil passage pads should be arranged neatly, and there should be no looseness when tapping the oil passage pads; check that there should be no foreign matter in the core oil passage.

3. Check that there should be an obvious and even gap between the pressure plate and the upper iron choke; check that the ground plate bolts of the steel pressure plate should not be loose; the insulation pressure plate should remain intact, without damage or cracks, and have appropriate tightening

5. Use a 1000V insulation resistance meter to measure the insulation resistance between the iron core, the core screw, and the steel strap. There is no significant change compared with previous tests.

6. Open the connecting piece between the upper clamp and the iron core and the connecting piece between the steel pressure plate and the upper clamp. Use a 2500V insulation resistance meter to measure the insulation resistance of the iron core to the clamp and the ground. The insulation resistance should be no less than 100M ohms. After the measurement, connect Chip reset is reliable.

7. Use wrenches and torque wrenches to tighten the upper and lower clamps, upper beams, side beams, pads, pressure nails, and core screw fasteners one by one.

8. Check the iron core electrical shielding condition. Use a 1000V insulation resistance meter to measure the insulation resistance of the iron core electrical shielding to the ground. The insulation resistance should be greater than 100M ohms.

9. Check the connection and insulation of the iron core grounding piece. The iron core is only allowed to be grounded at one point. The grounding piece is generally a copper piece with a thickness of 0.5mm and a width of not less than 30mm. It is inserted between the 3rd and 4th grade iron cores. The insertion depth of the large transformer is Not less than 80mm, the leakage part should be wrapped with insulation to prevent short circuit of the core.

Leilang Electrical Appliances: Choose high-quality cores

Leilang Electric uses 0.23mm, 0.27mm, and 0.3mm brand new low iron loss and high magnetic permeability cold-rolled oriented/non-oriented high-quality silicon steel materials as the core of the transformer. Silicon steel sheets have high mechanical strength, strong magnetic permeability and accurate cutting dimensions, which can effectively improve the performance of transformer products. You can see the real materials. Welcome to come and buy!

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