transformer question? please help.

Status
Not open for further replies.

rick711

Member
Location
Michigan
I am a industrial mechanic, have been for going on two years now, I am learning about three phase voltage systems, my question is this, I have at work 3 phase 240 VAC and I have to use leg 1 and leg 3 to go to the high side of a transformer (the side that is marked H1, H2, H3, H4), Is this considered single phase or two phase or three phase? And I looked up the formula for KVA and it doesn't tell when to use 1, 2 or 3 phase.

I am trying to put a 120 volt AC plug on a 240 volt 3 phase piece of equipment by installing a transformer and using leg 1 and 3 on the primary and have it step down the voltage on the secondary to single phase 120V for a outlet to run a 7 amp hand grinder and I am trying to figure out the KVA needed.

Any help would be appreciated.


Thanks Rick
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Assuming your 240 system is a delta system so you don't have 120v to ground (neutral) already, you can use a single phase 240/120 transformer and connect the primary side H1-H2 to any two phases of your 240v system.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
There is a lot to this issue. First, what is the voltage rating of the transformer? It appears that it has a dual voltage primary. Second, what are you going to use for the required grounding electrode on the secondary side? Third what is the rating of the supply side OCPD (overcurrent protective device). And last, what are you going to use for the secondary OCPD. (with a properly sized primary OCPD, you would not need one on the secondary side of this transformer)
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
... Is this considered single phase or two phase or three phase? ...
The others answered the rest, I'll just address this question.

Here in North America, we call this "single phase", because if power flows from A to C only, that's just one "phase" of a 3 phase system, which is comprised of A-C, A-B and C-B phases. Also, because there is a DIFFERENT form of poly-phase power called "two phase" in some isolated older areas like Niagara Falls and Philadelphia.

In other countries, where they have never heard of that separate form of two phase power, they would call this "two phase". It can be confusing when you read equipment catalogs from European suppliers sometimes, so just keep that in mind.
 

templdl

Senior Member
Location
Wisconsin
I am a industrial mechanic, have been for going on two years now, I am learning about three phase voltage systems, my question is this, I have at work 3 phase 240 VAC and I have to use leg 1 and leg 3 to go to the high side of a transformer (the side that is marked H1, H2, H3, H4), Is this considered single phase or two phase or three phase? And I looked up the formula for KVA and it doesn't tell when to use 1, 2 or 3 phase.

I am trying to put a 120 volt AC plug on a 240 volt 3 phase piece of equipment by installing a transformer and using leg 1 and 3 on the primary and have it step down the voltage on the secondary to single phase 120V for a outlet to run a 7 amp hand grinder and I am trying to figure out the KVA needed.


Any help would be appreciated.


ThanksRick

Can you attached a picture of the name place of the transformer?
The only way that I can see you getting 120v is if your transformer ihas a 240/120 3ph4w secondary which you have not clearly stated as knowhere do I see that in your post.What I would be looking for is a Delta secondary that is centertapped between the A and C phase which would be appearent if you to attach an actual picture of the nameplate of the transformer in question.
 
Status
Not open for further replies.
Top