What is the size of the series connector compared to the coil size?

[kh2]

The series connectors are the parts that connect, in series, two coils by brazing them between (or inside)the connectors. This practice is used on the stator coil winding connections. The series connectors are carrying the same amount of current as the coils. Therefore, it is assumed to be sized the same cross section area of the coil. For example, if the cross section area of the coil is 0.5 square-inch, the series connectors are expected to be 0.5 sqare-inch. But, there are series connectors that are only 40% to 50% of the cross section area of the coil, and these are of motors and generators in service.

Could you please expalin the reason for the small cross sections.

How do you calculate the cross section area and the ampacity of the series connectors to maintain the same current of the coils?

Thank you for your input and help.

 

[edison123]

kh2,

Aren't series connections between coils taken directly from the coils themselves ? i.e. End of coil directly connected to the start of the next coil in the same group.

Do you mean group jumpers ?

 

[electricpete]

The series connector is one turn. The coils may be many turns.

For example two stands per turn, wound 4 in-hand (4 turns per coil): the series connector is two strands and the coil is 8 strands.

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[aolalde]

The series connections are those that make a grup of coils. The coils per group are the total coils divided by the product of the phases and the poles. The groups are equal to the product of the poles and phases.

As Edison123 stated for most of the motors 2400 to 13.8KV, the individual coil terminals are used as connectors. Some use a copper ring but only to hold the two terminals overlapped and ease of the brazing process. The minimum cross section area is the same as that of the coil conductor (overlap).

Very large generators with roebel transposed bars use copper plates brazed to the bar lateral faces. The cross section criterion again is to match at least the conductor area.

Note that a conductor could be composed of several strands (wires in hand). The number of turns per coil have nothing to do when the connection cross section area is considered.

The same criteria is followed to connected group to group jumpers (1 -4 or 1 -7).

It is risky (bad practice) attempt to use lower cross section area than the coil conductor area, since a potential hot spot is created.

 

[kh2]

This application is for large generators with roebel transposed bars, as aolalde explained. The series connectors are two plates with lips at one side, solid copper. The bars are brazed between the connectors, the front bar side to the back bar side. You braze at the top and at the bottom of the stator core to complete the diamond lap winding. You connect in series a group of five slots (say) and then connect the pole jumper. The bars (or multi-turn coils) are copper strands, regtangular in shape and placed between the two plates spaced about 1-2 inches apart. After brazing, the cross section of the area not occupied with the bars is about 50% of the cross section of the bar.

The manufacturer is saying that the series connectors, this way, are adequate if you take into consideration the skin effect, the current distribution, and the mechanical strength of the connectors.

Still believe that the connectors should be the same cross section of the bar to carry the same amount of current the bar was sized to carry. Or you experience overheating at this undersized area.

Can someone better informed explain the logic given by the manufacturer.

 

[Sargardani]

KH2

I know only one manufacturer (sorry cannot disclose its name) who's generators employ the series connectors you have explained above (may be there are more but at least in my limited experience I have come across only one). I am sorry I don't have all the technical details but apparently the connectors are designed to have a uniform current distribution. It was hard to accept the series connectors having cross sectional area considerably lesser than that of the conductor itself, but so far these have been working well, for the past so many years, as per claims of the supplier, with no problems of heating etc.

Sarg

 

[UKpete]

I have not seen this done (no high voltage experience), although in distribution boards I have seen busbar connections where there is a reduction in overall copper area; indeed where there are connections generally there are going to be areas of higher resistance. I think the justification is that the thermal conductivity of copper is so good that heat is easily conducted away and that there is no significant hot spot. Also, where the joint is not covered by insulation, strictly speaking it is not limited by the temperature class of the insulation.

The manufacturers explanation doesn't add up though - skin effect? surely the winding copper is sized so that this is negligible, so that the connector will be no better as regards skin effect.