hm.... a NEW question.....

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Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
Location
HB, CA (19 Hrs. 22 Min. from Winged Horses)
Occupation
E
i gotta customer who does testing of food processing equipment,
and needs to test 480 volt motors from 50 to 100 HP.

he has been slamming them across the line with a non fused disconnect,
backed up by a breaker.... you know, one of those plastic hubbell
disconnects made for wet locations...

anyway, it blew off the wall, tripping the breaker, finally. some days
are like that, y'know? now, he's a little more gun shy about slamming
in a 100 hp motor with a disconnect.

a couple solutions are:

soft start

or

a fused disconnect, a variety of fuse sizes, with appropriate reducers,
downstream from a 100 hp contactor, with a limit switch on the
disconnect door to disable the contactor when the door is opened
for fuse changing.

or

a VFD, with some programmed setpoints for different motors... just
pick the motor you are going to use with a rotary switch, and hook
it up.

a 100 hp. VFD from allen bradley is about $11,000, so that's not gonna
fly well...

anybody here got ideas for something like this?

thanks...

randy
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
In general only buy a "large" VFD if you need to vary the speed of the motor.

Watch out for the motor horsepower range of electronic soft starts, some of them cannot go from 50-100HP.
 
K

khixxx

Senior Member
Location
BF PA
You serous? I have to say it's funny someone is slamming a motor that size, but it's really not. It most likely broke from using the disconnect for a start and stop device. I think thats what I am reading. When you disconnect a motor like that or anything at the matter an arch occurs and over time it will ware out the blades on the disconnect or just fault. Look at what happens when you turn off a light switch. There is a small arch. Now times that by 100 or more. thats whats happening inside the disconnect.

If nothing more megger the equipment annually or every 6 months that will be cheaper. I guess it really depends more on the application.
 
Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
Location
HB, CA (19 Hrs. 22 Min. from Winged Horses)
Occupation
E
jim dungar said:
In general only buy a "large" VFD if you need to vary the speed of the motor.

Watch out for the motor horsepower range of electronic soft starts, some of them cannot go from 50-100HP.
Click to expand...

agreed.. there doesn't seem to be a soft start on the market with the range
needed.

the vfd would allow running overcurrent protection, and could be set up to
accommodate most any size motor, and ramp up could be set wherever i
wanted it to be, but the cost is prohibitive.

we'll see if anyone else has a genius moment.....:D but right now, the
only viable option seems to be a 100hp mag, with a fused disconnect
downstream.
 
C

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
It sounds like a 100hp motor starter with adj. O/L's for the different size motors is your easiest option.

EDIT: I think your customer needs to buy a megger too...
 
Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
Location
HB, CA (19 Hrs. 22 Min. from Winged Horses)
Occupation
E
iaov said:
They are braver than I am.:D
Click to expand...

they aren't that brave anymore... it grenaded. now, they are
experienced.

it was one of those plastic cased hubbels that are popular in
the food processing industry as a disconnecting means....
the one's with the rotary operator....:smile:

a heavy duty bulldog or something similar would have at
least made an impressive *clunk* when it snapped shut....

instead, they got "tinky, tinky, .... BANG!"
 
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