Across the line and y-delta connections

[jojhanv]

hi,

i just want to ask at what Hp rating should i start to use the y-delta connection instead of the across the line connection. the main would be a 3Ph, 50Hz.

thanks in advance.

 

[pmac10]

above 7KW should be about right

 

[pmac10]

or about 9.5 HP

 

[jojhanv]

that means if i have an electric motor of 10Hp, then i should use the y-delta connection?

 

[silva.foxx]

I've worked on refrig. compressors with star-delta starting on motors as small as 4kw... but I'm sure it depends on load type (high inertia such as fans and flywheels) and the supply available.

It's a good question... not sure if there is a textbook answer but I'll dredge the 'net!

(Howdy Pmac)

 

[silva.foxx]

Dol < 5HP here http://in.answers.yahoo.com/question/index?qid=20080602204054AAHNo5R and http://www.allinterview.com/showanswers/84988.html

Dol < 5kw > YD

http://books.google.co.uk/books?id=...esnum=4&ved=0CDAQ6AEwAzge#v=onepage&q&f=false

 

[pmac10]

i agree with you there Mr Foxx that it depends on loading, those figures i posted are from a intro to electrical engineering maintenance textbook, i remember them cause we have gucci servo motors operating alongside prehistoric electrical machines (kW/HP)

 

[Engineer54]

Totally agree, it will always depend on the type of load the motor is supplying...

 

[jojhanv]

ok...so it depends on the type of load it will drive right?
the electric motors are going to be used to drive FIRE PUMPS, and the smallest fire pump power i have in my series is a 10HP pump all the way to a 350Hp pump.
by the way, do we have a standard de-rate factor for ambient temperature changes?

 

[Marvo]

Are the pumps centrif or positive displacement? Can you give a link to some specs on the pump range?

 

[silva.foxx]

Fire pumps... hmmm... best get the starter right on that subject!

In my ignorance I didn't think the primary fire pumps could be electro-motive, thought they had to be non-power supply dependant ie. engine driven, but a quick squint at the web shows differently.

So is 10HP just the jockey pump?

Tell us more!

 

[Chr!s]

A lot of it comes down to the supply, and the frequency of switching, dnos normally have a percentage of volt drop to which must not be exceeded.This percentage varies upon application.

 

[jojhanv]

actually, there are 10hp ratings for smaller apps like a [email protected] bigger (as big as 300Hp) for bigger apps like a 4000gpm. the jockey pumps are only used for system balancing...like pressure losses due to leaks etc...the frequency of switching...well i hope to god it doesn't activate remotely which means a fire in the building but for maintenance purposes at least every 6 months. Here in kuwait, they are using 2 electric driven pumps if the location is near the city area and a 1-electric, 1-diesel configuration in remote areas...i.e. oil fields.