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Transformers #129485
03/31/05 11:41 AM
03/31/05 11:41 AM
R
rad74ss  Offline OP
Member
Joined: Apr 2004
Posts: 156
Pryor, OK USA
I have a job with .65A 460V 3Ph motors. The customer has 575 3Ph. I was told to use two 575 1Ph to 460 1Ph transformers to change over from 575/3 to 460/3.

That just seems really odd to me. How would you connect four leads to make 3 phases and how would that affect the leads that are doubled up.

I am brain dead right now, I have finished 30 production drawings in four days and every time I try to concentrate on this problem all I hear is static from my synapses mis-firing.

I would appreciate anyones expertise on this setup.

Thanks,

Tools for Electricians:
Re: Transformers #129486
03/31/05 01:13 PM
03/31/05 01:13 PM
B
Bob  Offline
Member
Joined: Feb 2002
Posts: 182
Mobile, AL, USA
You only need one transformer that is rated
600 volt/480/277 volt three phase.
Check ACME Transformer Company. They have one listed.

Bob

Re: Transformers #129487
03/31/05 04:01 PM
03/31/05 04:01 PM
J
JBD  Offline
Member
Joined: Jul 2001
Posts: 599
WI, USA
At that small of KVA requirements it is less expensive to use two standard single phase 480->120 transformers connected in an open-delta autotransformer arrangement.

See page 11 of Square D handout 7400HO9501 .

Re: Transformers #129488
03/31/05 04:12 PM
03/31/05 04:12 PM
B
Bob  Offline
Member
Joined: Feb 2002
Posts: 182
Mobile, AL, USA
JBD
Would that be an approved and listed
configeration?

Re: Transformers #129489
03/31/05 06:44 PM
03/31/05 06:44 PM
R
rad74ss  Offline OP
Member
Joined: Apr 2004
Posts: 156
Pryor, OK USA
Square D techs found a buck-boost setup that will work. Now I just have to figure out if I need to fuse it to protect a: the motor, b: the transformer, or c: the wire. And I have to try to calculate what sizes fuses once I get that sorted out.

It would have been easier if they would have sold it with 230/1 motors which we offer with this line of coolers.

Re: Transformers #129490
04/01/05 02:50 AM
04/01/05 02:50 AM
B
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
PROVIDED that NONE other than 460V 3ø—3-wire and 1ø—2-wire loads are served, a pair of properly sized and correctly wired in the right open-delta connection, pair of 1ø units applied similar to that shown on pg 14 of “Three-Phase Ventilated Transformers.”  Contact Jefferson Electric www.jeffersonelectric.com  Fuse hiside with dual-element fuses sized per NEC 450-4 and that may adquately protect the secondary and tap conductors also.  (If CEC applies, it may apply different rules.)

Duck Soup with extra crackers and butter...




[This message has been edited by Bjarney (edited 04-01-2005).]

Re: Transformers #129491
04/01/05 05:13 PM
04/01/05 05:13 PM
B
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
BTW, the Jeffers pdf is www.jeffersonelectric.com/pdf/3-PhaseVent.pdf

rad74 — You probably have access to some UL-508x[/x]–type enclosed-panel assemblers, so consider using some decent epoxy-potted 240x480—120V 55°C-rise machine-tool transformers like Micron Impervitran www.microntransformers.com/products/impervitran.php
or Hammond PH www.hammondpowersolutions.com/i_controltrantext.html#ph
and LPJ fuses in a Boltswitch PJ-series pullout block www.boltswitch.com/O-1374.pdf [Suggest avoiding CCs at 600V.] About 300VA of capacity per transformer {when wired 480:120 in an [i]open-delta autotransformer pair
] is needed for each 0.65-ampere of 460V-3ø balanced load. (Motor count and auxiliary load not specified in thread.)

Use common sense, sensible troubleshooting methods and check ø·ø hiside voltages before heatup, and after heatup check ø·ø hi- and loside voltages, and noload hiside currents. Then check for balanced hi- and loside ø currents and ø·ø voltages with all running load applied. Check for even, non-excessive transformer heating and sniff everything carefully after running for ½-hour, too.

[Linked Image]


Understand that [for the last 40 years in particular] 1ø TENV and TEAO appliance motors are value{!¡!}-engineered to run very close to the edge even brand new—with auxiliary windings in PSC motors and start windings in other 1ø motors of smaller-gauge conductor, making them physically harder to protect (ergo, quicker to fry) through thermal damage than “main” windings. 3ø squirrel-cage-motors don’t have that crippling limitation leading to a virtually universal M·R·O habit of nothing other than ready disposal.

[ Also, there is a wonderful but {in some circles} slightly lewd term for these components—they may be referred to as ”((insert national-brand-name absorbent wimens-health’n’freshness item that men really, really hate to buy at 1AM in a QwaKKy·Mart where your sniffling nephew works graveyards, while having to use a pers'nl check—forgetting all three *mandatory* IDs no less)) type of moter.” ]

 

[This message has been edited by Bjarney (edited 04-01-2005).]

Re: Transformers #129492
04/02/05 10:12 PM
04/02/05 10:12 PM
J
JBD  Offline
Member
Joined: Jul 2001
Posts: 599
WI, USA
Bob,
There is no need for the actual connection to be Listed it only needs to be approved by the AHJ. Each individual transformer winding is being connected to voltage sources per it's Listed wiring diagram.

If you look the Square D connection says it can be used for 480->384V transformation also. Note however, the NEC does not recognize autotransformers for this step down voltage.


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