Step up current transformer 460 top 575V 2

[Lovison]

Based on available funds we are looking on to ways to increase the existing plant line voltage 460V to 575V for some test we need to make.

From what I've learned is that even though higher voltage means lower amp requirements the existing power supply still will have only the original 200 amp service unless I bring in an additional supply.

We've been quoted a step up current transformer to allow us to connect to our 460V supply and give us 575V outvoltage for those test requiring such voltage. However I'm still limited to my existing 200 amp box. Can anyone tell me how big a motor I can test @ 575V with a 200 amp box?

Wayne E. Lovison
service-parts@naglepumps.com

 

[Lovison]

Secondary question does anyone have any other ideas on how this can be accomplished? Money is tight as we all know but we understand what we have to do to meet testing requirements so any help would be appreciated. Wayne E. Lovison
service-parts@naglepumps.com

 

[busbar]

Except for smaller motors, 575-volt 3ø motors are about ~1 amp/hp. ~1.2 amp/hp for 460V 3ø.

In the US, it’s normal to limit loading on fuses or circuit breakers to 80% of rated. {Flame as desired.} ~150hp approaching continuous with full load (~200hp for shorter runs.) Unloaded—try it out—possibly ~600hp.

N.B.; during testing you may have to disconnect other building loads if 200A is the service-entrance rating.

Another consideration—a 3ø autotransformer in a boost {480>600V} arrangement can also be used to buck. {600>480V} It may be worthwhile to initially size them accordingly. For 200 amp capability—possibly:
Two well-ventilated approximately 25kVA 115°C-rise 480:120V dry-types
VERIFY Before You BUY!!

 

[buzzp]

If you have 460 and want 575 then you need a voltage transformer with a ratio of 1.25. Your 200 amp service on the primary will be able to source 460/575*200=160amps on the secondary. With such a large motor the only way I see to test it is with a transformer. Although, the motor may take off with 460 applied. I guess it depends on what you are trying to test. Are you the one that wanted to test a similar motor in a similar post?
Remember higher voltage does not mean lower current. At least in the context I think you are referring too, motors. That rule can be applied to transformers though, higher voltage out means lower current out.

 

[Lovison]

busbar and buzzp;

Let's see if I got this right. We have a 460V system and a 200 amp service. I want to test 575V motor's through a 460V/575V transformer. Should I get a transformer that is rated 600V and would this be more benefical?

Regardless I think both of you are telling me that regardless of the voltage I only have a 200 amp service regardless is that correct?

Does the rule apply that I can run a motor +/- 5% of its nameplated voltage without getting into trouble?

I think that is what busbar was trying to tell me in his comment. Advise if I should go for a 575V transformer or a 600V transformer. Money can't be too much difference and running at the higher voltage would lower the amp draw requirements (if I read you right above?).
Wayne E. Lovison
service-parts@naglepumps.com

 

[buzzp]

Remember if you use a transformer, you will not be able to get 200 amps from the secondary (600 volt side) because of the nature of a transformer. If you want higher voltage out, you will have lower current out. If you have lower voltage out then you will be able to have more than 200 amps out of secondary. It is an inverse relationship.

You can run the motor at +-10% of rated voltage and not cause problems, if the motor is sized correctly.

As far as selecting the transformer, well thats a loaded question. If you run the motor at 600 volts then it may draw more current than operating at 575 volt. It should draw more current at 5% above nameplate or thereabouts. This is a strong misconception about sq cage motors, reduced or higher voltage does not mean lower current. Lower voltage means higher current for motors and as you get about 5% above nameplate volts then the current will also increase. If your operating between nameplate volts and 5% above nameplate volts then yes the current will generally be slightly lower than operating at nameplate voltage.
If your voltage coming in tends to be on the low side, then go with the 600 volt transformer. If it is on the high side then go with the 575 volt transformer. Just remember the ratios: If you have 460 coming in and have 575 coming out then the ratio is 575/460 (1.25) and the current is reduced to 460/575 (0.8 or 80 % of original value or in your case 80% of 200amps)

 

[buzzp]

Remember if you use a transformer, you will not be able to get 200 amps from the secondary (600 volt side) because of the nature of a transformer. If you want higher voltage out, you will have lower current out. If you have lower voltage out then you will be able to have more than 200 amps out of secondary. It is an inverse relationship.

You can run the motor at +-10% of rated voltage and not cause problems, if the motor is sized correctly.

As far as selecting the transformer, well thats a loaded question. If you run the motor at 600 volts then it may draw more current than operating at 575 volt. It should draw more current at 5% above nameplate or thereabouts. This is a strong misconception about sq cage motors, reduced or higher voltage does not mean lower current. Lower voltage means higher current for motors and as you get about 5% above nameplate volts then the current will also increase. If your operating between nameplate volts and 5% above nameplate volts then yes the current will generally be slightly lower than operating at nameplate voltage.
If your voltage coming in tends to be on the low side, then go with the 600 volt transformer. If it is on the high side then go with the 575 volt transformer. Just remember the ratios: If you have 460 coming in and have 575 coming out then the ratio is 575/460 (1.25) and the current is reduced to 460/575 (0.8 or 80 % of original value or in your case 80% of 200amps).

See my FAQ

 

[buzzp]

Oops, it submitted twice for some reason. The FAQ is in motors and motor controls section.

 

[busbar]

The numbers 460 and 575 are called utilization voltage (for motors and most other load devices/appliances) it’s what’s stamped on the nameplate.

The numbers 480 and 600 are termed service voltage, and components that serve load devices generally have this rating, like transformers, breakers and starters.

A system of 200 amps at 480V 3ø corresponds to a maximum capability of 166kVA, and 200 amps at 600V 3ø corresponds to a maximum of 208kVA. Generally, this is the advantage of higher distribution voltage, but of course there are tradeoffs. For higher voltage, the most obvious concern is that more insulation is needed to isolate ø-ø and ø-ground conductive surfaces. So 480V versus 600V is a ‘regional preference,’ and if you use one it’s likely that your neighbor does too. Generally in the US, 480V is probably more common. In Canada, 600V is used most often.

Voltage limits are in a sort of ‘treaty’ agreed upon by folks like electric utilities and appliance/equipment producers, and published and promoted by ANSI (or CSA to the north.)

The agreed-upon limits for 480V systems are usually 440-504V and for 600V it’s 550-630V. {Note that 460 and 575 fall within this range.} So the percentage limits are close to +5% -8%. Generally equipment won’t necessarily work most efficiently in the extremes, but it’s not supposed to be damaged either.

Transformers can be described as constant-power devices. For a given kVA, [kilovoltamperes] there is a corresponding ratio of voltage and current. 200 amps at 480V 3ø is about 166kVA, which in turn is equal to 160 amps in a 600V 3ø circuit. Roughly 1 hp = 1 kVA.

 

[Lovison]

Hey Guys I really appreciate the learning curve. I will address this with our supplier and see what they recommend as well. Today when you spend money you want to maximize the expenditure. The Boss will be checking out each and every purchase to ensure the we get the most for the buck if you know what I mean.

I won't pretend to tell you I totally understand the logic but I do understand the precautions and can therefore ask better questions.

Thanks Again. Wayne E. Lovison
service-parts@naglepumps.com