2 phase bridgeport on 3 phase power

[unitedmachineworks]

hi we recently joined this forum. We have a question we hope you could help us with:
We recently purchased a bridgeport milling machine that runs on 240/2 phase. we have 240/3 phase. could we run it on the 3 phase or do we need a transformer of some sort???

thanks in advance for taking the time out to answer our question.
Edward & Heather ZOll

http://www.UnitedMachineWorks.com

 

[busbar]

It may be possible. Can you post the nameplate data on the motor(s)?

 

[G1ZFS]

Hello
That seems an unusual specification, although I realise things are different in the states from the uk.

As well as the rating plate details the other gentleman has asked for, how many motors does the machine have ?

Can you see any variable speed controllers ?

If for example you only have one motor, and it is dc, it would be quite common for the "drive" to be a two phase 415 Vac supply device.

If however you have more than one motor, even if they are supplied by two phase drives, I would expect them to be balanced across all three phases.

I look forward to your reply.

Best wishes

Nigel

Arvor engineer

 

[jbartos]

Suggestion: The 240V/2 phase machine can run on 240V/3phase (two phase wires instead of three phase wires will be connected to the 3 phase supply) providing that the
240V/3phase is sufficiently rated to power 240V/2
phase machine.

 

[busbar]

If the 3ø service is 240/120V 4w, a 208—120/240V 1ø transfomer may do it.

 

[busbar]

Apparently there is some 2ø service in the Philadelphia area. PECO lists 120/240V 2ø 5-wire service at

http://www.exeloncorp.com/peco/library/documents/1999tariff.doc

 

[ScottyUK]

Hi Busbar,

There is some 2ø service in Northumberland, UK, or there was until recent years. It was on the MV network though, not at final distribution voltage.

Edward / Heather,

Do you know where the machine originated? If it is a UK machine (do Bridgeport have a US manufacturing facility?), it is very probably 240V 1ø rather than 240V 2ø. In this case, you can either run it from a transformer as you suggest, or you can replace it with a 3ø motor. The 3ø motor will be smaller, give better starting charateristics, and you can go to fully variable speed at a later date if you by a VSD. Worth considering IMHO.


Hope this helps.


Scotty.


-----------------------------------

Start each new day with a smile.

Get it over with.

 

[cbarn24050]

Come on guys, he obviously means 240v single phase, get a grip your meant to be experts!

 

[ScottyUK]

Well cbarn, there are some old motors (and I mean old) still around which are very definitely designed to work with 2 phases in quadrature. Bridgeport's machines used to be built to very high standards and consequently last a long time. It wouldn't be surprising if the machine in question dates back to the early part of the previous century when 2ø power was in use.

Maybe it isn't quite so obvious?



-----------------------------------

Start each new day with a smile.

Get it over with.

 

[Skogsgurra]

Yes,

The first asynchronous induction motors were actually two phase motors. It was Nicolas Tesla that invented the motor and the reason for using two phases was simple, he had learnt in school that a sine and a cosine signal combined would produce a circular and rotating pattern.

By changing that to a three-phase system, Westinghouse and Wenstrom introduced the modern asynchronous induction motor that utilised the wires and the motor better than did the two-phase system.

 

[aolalde]

jbartos:

Please explain how to get “two phases” 220 V from a 220 V three wire three phase system. To me it looks like 220 V singlephase.

 

[busbar]

Historical aside — Apparently around the beginning of the last century, CF Scott came up with his transformer-based 3ø-2ø conversion, because 3ø was desirable for ‘transmission,’ but at that time 2ø was preferred for generators, motors and local ‘distribution.’ IEEE-article excerpt

http://6L6.net/localuser/busbar/imag/etip.iam.cfscott.jpg

Aside to ScottyUK —

http://www.iee.org/OnComms/pn/History/HistoryWk_Single_&_2_phase.pdf

 

[jbartos]

Comment on PECO "nominally 120/240 volts, 2 phase, 5 wires; only available in areas supplied by 2-phase distribution facilities located along public highways or private rights-of-way and limited to service capacities of 100 kVa or less;" in the Busbar posted link pertaining to Philadelphia Electric Co.
Visit

http://www.exeloncorp.com/peco/library/pdfs/2_Definitions.pdf

for:
2.45 TWO PHASE, 5-WIRE SYSTEM
A system of alternating current supplies comprising five conductors, consisting of
four phase conductors and one common grounded neutral conductor.

Also:
Two overhead (pole) transformers, each with a centertap, connected in open delta will provide three phases, 2 neutrals, 5 wire power distribution system. Two overhead transformers in open delta use two phases. The advantage of this system is in its utilization of the overhead transformers and 5-wire transmission.

 

[jbartos]

Comment on aolalde (Electrical) Feb 28, 2004 marked ///\\jbartos:

Please explain how to get “two phases” 220 V from a 220 V three wire three phase system.
///I interpreted the 240/2 phases in the original posting as one phase supply two "hot" wires often called two phase. It is actually a single phase. The single phase machine using 240/2 phases, i.e. two hot conductors can be connected to the three phase system, "three hot wires" by connecting it to any combination of 2 hot wires in the available three hot wire power supply.\\ To me it looks like 220 V singlephase.
///Yes, agreed. A machine with true two-phase motors would be very rare since the two phases would be taken from the three phase power supply system. Then, the three phase power supply system would not be properly utilized. The two-phase motor is somewhat less efficient than the three phase motor.\\

 

[unitedmachineworks]

cbarn, it is 2 phase, not single phase

 

[jbartos]

Question to unitedmachineworks (Industrial) Feb 28, 2004 marked ///\\cbarn, it is 2 phase, not single phase
///Please, would you clarify two phase displacement. Is it true two phase with 90° displacement or two phase of the three phase system with 60° or 120° displacement?\\///Also, it would be helpful to post the motor nameplate data, which was requested by busbar in posting Feb 27, 2004.\\\

 

[ScottyUK]

unitedmachineworks,

I think you will find it is cheaper to replace the motor with a modern IEC or NEMA 3-phase type, which will almost certainly be much smaller than the existing one.

If you are stuck with the existing motor, you will need a Scott-connected transformer (Not sure if he was a relative ) to convert 3-phase supply in to a 2-phase output. In the UK these transformers are 'specials' and are therefore expensive as there are no economies of scale from mass production.

Busbar,

That was a really good link. Thanks. I enjoy reading about the early days of our industry - sometimes I'm not sure how much progress we have actually made, having gone from a national organisation that was the envy of the world (CEGB) to a fragmented and directionless mess created by the politicians.



-----------------------------------

Start each new day with a smile.

Get it over with.

 

[G1ZFS]

cbarn

A definition of "expert" from the UK. (exspurt!!)

An "ex" is a has been, a "spurt" is a drip under pressure.

I dont see any point in your expert post, everyone is trying to help, and over here at least it is very common to find older machines retro fitted with all types of equipment.

Sorry for the rant gentlemen.

Best wishes

Nigel

Arvor engineer

 

[cbarn24050]

Hi guys, I'm willing to bet that what we have here is a brigport with a DC motor fed with a single phase thyristor drive connected to line to line rather that line to nuetral on a 3 phase supply.

 

[G1ZFS]

Hello cbarns

Please refer to my earlier posting, its the second reply.

Maybe were not as dim as you first thought eh ?

Best wishes

Nigel

Arvor engineer