Primary dispositions

The smallest single sunstation has one transformer which is a forking from a transmission line, that is the T Forking disposition. It is rare on high voltage but exist some on 120 kV. Mostly all mid voltage transformer poles and houses use this disposition. On the transformer pole the fuse works as the breaker, the line switchgear is on the previous pole and there are not measuring transformers.

The small substations use the PI disposition with only two (cut up a transmission line and put here the two ends) lines and two transformers. It has the highest working safety for the small substations but it is not able for expanding. If a line get fault, that line and transformer turns off but the transformer's fault can't turn off the lines. Some 220 kV substations have this disposition and lot of 120 kV ones.

The H disposition is able for expanding but it needs 12 switchgears and have difficult handing. It is cheaper than the PI disposition, this discosition begans be common of the small 120 kV substations. You can buy 10 switchgears for a breaker's price..

The One Busbar substations are the easiest and the cheapest substation disposition. There is one busbar, there do fields of the forkings. This disposition has the lowest working safety, if a breaker is wrong or a fault is on the busbar, all of the substation will turn off. This disposition is on small 120 kV or smaller middle voltage substations with 2-3 forkings or 2 lines and one transformer.

The Two Busbars disposition has double working safety than the last one. Every forkings have two busbar switchgears the either one is norally open. If a busbar has fault, the half of the substation will turn off, and the operator can put the off switched forkings onto the living busbar. The busbar bridge has supply function, if a busbar lost the supply, the bridge will make the supply, that is normally close. The bigger 120 kV substations and mostly the all middle voltage (20 ,10 kV) substations have this disposition.

The Aux Busbar substations have higher working safety because if a field need servicing, the operator have not to turn off the forking, that forking can get the supply from the aux busbar. Only the line forkings have aux busbar switchgear and only one forking can get supply from the aux busbar at one time. On the last two dispositions the forking doesn't works at the time of the servicing. The big 120 and the 220 kV substations have this dispositions.

The big substations need high working safety. If a busbar gets fault, the half of the busbar,the 1/4 part of the substation will turn off. If a busbar switchgear need servicing, the half of the busbar is enough for grounding. If there is aux busbar, it has a halfing switchgear, there are two aux busbar supply fields because of it two forkings can get aux supply at one time. It needs high current breakers and switchgears, this disposition is expensive but the high working safety of the big substations need this investments.

The Polygon disposition has higher working safety and cheaper than the Two Busbars but it can serve only 4-5 forkings and the forking expanding is difficult. It is cheap because one forking has one breaker. It has high working safety because all forking have two foots by two breakers, if the either foot gets fault the forking stays in work.

The Modified Poligon disposition has the highest working safety, the expanding is easy but it is the most expensive substation type: all forkings have two breakers. If a busbar grets fault neither forkings will turn off. This disposition is rare.

The base grid need high working safety and cheaper substations with easy expanding. Open the Modified Polygon substation, use make hybrid from two forkings, you get the 1.5 Breakers disposition: one field has two forkings, 3 breakers ergo one forking has 1.5 breakers. That is cheaper than the Modified Poligon but it has same working safety: All forkings have two supplies, if a busbar gets fault, the forking stays under voltage. If both busbar gets fault, the forkings stays under voltage by the central breaker independent from the substatipon. This disposition is the best for the base grid, the switching freedom is high, in Hungary all 400 kV, big 220 kV substations have this disposition. Here can be busbar breaking too if that substation is big and important

If you don't want buy the 2nd breaker for busbar breaking or you don't want breaker you can use switchears. It don't has so high working safety than the two breakers but it is higher than there is not busbar breaking. That is the switchgear busbar cutting and the combinated busbar breaking.