Power transformer core structure / installation protection / grounding protection

Transformer core structure

The iron core is composed of silicon steel sheets. In order to reduce the eddy current, there is a certain insulation resistance between the sheets (generally only a few ohms to several tens of ohms). Since the inter-chip capacitance is extremely large, it can be regarded as a path in the alternating electric field, and thus the iron core The stack of iron core laminations can be clamped to ground potential with a single grounding.

The iron core is the main magnetic circuit part of the transformer. It is usually made up of hot-rolled or cold-rolled silicon steel sheets with a high silicon content and a surface coated with insulating varnish. The iron core and the coil wound thereon form a complete electromagnetic induction system. The amount of power transmitted by the power transformer depends on the material and cross-sectional area of ​​the core.

Transformer installation protection points

(1) Separately set a grounding lead wire for the iron yoke clamp. Because if the iron core hits the upper clamp and causes multiple ground faults, the ground current only flows inside the core clamp, and no current flows through the core ground lead, which may cause the staff to mistake the core for failure; After setting, no matter where the iron core hits the clip, it will form a loop through two grounding outer leads, so that the ground current can be detected correctly on the outside.

(2) The core grounding piece is placed in the middle of the cross section of the iron yoke. In this way, no matter where the iron yoke pulls the insulating bolt and where the fault grounding point is, the maximum induced voltage of the loop is only 1/4 of the 匝 voltage. At this time, the maximum ground current is only a few amps or so. The grounding lug is much smaller when placed in other locations.

(3) If it is necessary to place the core grounding piece in other positions due to problems such as inconvenient installation on site, the insulating bolt of the yoke pull strap and the grounding lug should be placed diagonally to prevent large currents from being generated.

Core protection grounding in power transformer

When the transformer is working, an uneven electric field is generated around the winding, and a floating induced voltage is generated on the iron core and other metal members. When the voltage difference between the floating potentials exceeds the insulation voltage, internal discharge or ground discharge occurs. Therefore, it is necessary to make a reliable grounding at a certain point on the transformer core to vent the floating induced voltage of the iron core and protect the transformer.

Power transformer core material

Power transformer core material is generally selected from silicon steel laminated core

Silicon steel has a high magnetic permeability, so it is widely used in the manufacture of motors and transformers. Because the whole ferromagnetic material will generate a large eddy current inside, it is unfavorable for the transformer. To reduce the eddy current (the eddy current has a skin effect), it is necessary to form the ferromagnetic material into thin sheets and stack them into the required ones. Cross-sectional area.

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