- Bus-type current transformer and pillar-type current transformer
Transformer
I was asked a question by someone the day before, what is the difference between a bus-type current transformer and a pillar-type current transformer? At that time, there was some confusion, let alone the difference. I still don’t have any idea what these two forms look like. After checking the materials, I found that they were all common machinery and equipment.
Bus-type current transformers are sometimes called through-core current transformers. The electric conductor is used as the primary winding through the core through the current transformer. The core of the transformer and the secondary winding are cast into a whole with insulating layer material. It is often used in the busbar bridge or the part where the high voltage switch cabinet is worn.
Pillar current transformer, the core of the transformer and the insulating layer material for primary and secondary winding are cast into one body. In addition to the role of a transformer, it also doubles as a support for the insulating layer of the primary conductor.
- Some key differences between the two
- The primary and secondary windings of the bus-type current transformer are not together, and there is air isolation in the middle, so the probability of insulating layer problems between the primary and secondary windings is very low. The primary and secondary windings of the pillar current transformer are coiled and cast together on a transformer core, and the insulation between the primary and secondary windings may be destroyed.
- In the initial stage, the transformation ratio of the pillar-type current transformer can be very large. If the current transformer with a large transformation ratio is necessary, the bus-type current transformer can only be used. But now the transformation ratio of pillar current transformers is gradually becoming larger.
- The primary current of the pillar current transformer passes through the transformer itself, so there are problems of dynamic stability and thermal stability. The primary current of the bus-type current transformer does not pass through the transformer itself, and there is no problem of dynamic stability and thermal stability.
- The pillar current transformer has 2 terminals and passes through the primary current, so it is likely to have heat problems caused by poor contact.
- The volume of bus-type current transformers is generally larger than that of pillar-type current transformers, so pillar-type current transformers are more used in equipment with limited space.
- The space between the two terminals of some pillar current transformers is not large. When a short-circuit fault occurs in the adjacent space, the electric isolation is likely to cross the two terminals, which causes the current transformer to be short-circuited at one time, and the current transformer It is invalid and affects the correct operation of related relay protection.
- There are solid insulation and gas insulation between the primary winding and the secondary winding of the bus-type current transformer. The common raw material for solid insulation is epoxy resin. The circuit between the primary and secondary windings is equivalent to two capacitors connected in series.
Because the relative dielectric constant of epoxy resin is greater than that of air, air bears more voltage than epoxy glue. In addition, because the compressive strength of air is not as good as the compressive strength of epoxy resin, this kind of bus bar current transformer is very prone to corona discharge during operation if certain effective measures are not taken. The general practice is to coat the semiconductor layer on the inner wall of the transformer and paste the equipotential connecting line, and the other section of the equipotential line is connected to the primary bus groove through the core. Then the capacitor corresponding to the air gap will not be available, and the problem of corona discharge will be solved.
