Film-Tech Forum ARCHIVE: 3 phase protection

This is topic 3 phase protection in forum Ground Level at Film-Tech Forum ARCHIVE.

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Posted by Adam Fraser (Member # 1074) on 07-03-2005, 12:36 PM:

We have a 3 phase 3 hp 380/460v water well pump that has been killed twice in the past 5 years by I believe losing one of the phases (during storms or when power lines go down) and overheating. I am sure that is what happened the first time a few years ago, and pretty sure that is what happened on Wednesday, making us lose our opening day of War Of The Worlds.

The pump sits at the bottom of an 80ft well if that makes a difference.

The electrical in our theatre is 60+ years old and im sure protection devices have gotten much better in that time. Can anyone make a suggestion to keep this from being a regular occurrence?

[ 07-03-2005, 04:32 PM: Message edited by: Adam Fraser ]

Posted by Paul J. Neuhaus (Member # 3205) on 07-03-2005, 04:00 PM:

electrician

Posted by David Buckley (Member # 2600) on 07-04-2005, 07:17 AM:

Bad installation sixty years ago, I'm afraid.

Although motor controls have "improved" over the years (the semiconductor and microprocessor revolution), the basic motor protection for small motors still works the same way today as they did back then. There are two things you have to have for motor protection, which is undervolt (on any phase if a polyphase motor, like yours) and overcurrent.

An electrician will be able to install a suitable motor protection device. And for a lot less than the cost of a new pump. A simple Direct Online (DOL) Starter will do all that you need. Only downside is that if you do brownout or lose a phase then the starter will click off, requiring a press of the green button when the power returns. If that is unacceptable then other solutions are possible, but will cost a bit more.

Posted by Frank Angel (Member # 248) on 07-08-2005, 11:53 PM:

Climbing down an 80ft well shaft in order to push a green button every time the pump stops working sounds like what most theatre managers would expect to be a routine part of any projectionist's job. After all, what else do those good-for-nothing-getting-paid-more-than-what-I'm-getting-paid-lazy projectionists have to do anyway? Push the play button on the DVD player? [evil]

Posted by Gordon McLeod (Member # 33) on 07-09-2005, 08:44 AM:

There are many good phase protection devices but in many older locations they had a set of contactors with a contact in serries so that if one phase was missing none could be energized

Posted by David Buckley (Member # 2600) on 07-09-2005, 03:34 PM:

quote: Frank Angel
Climbing down an 80ft well shaft in order to push a green button every time the pump stops working sounds like what most theatre managers would expect to be a routine part of any projectionist's job.

As I'm the only mentioner of green buttons, I guess this is aimed at me?

I did omit to mention that you could put the starter switch anywhere, didnt I...? Silly me. It doesnt need to be next to the motor, it could be somewhere really convenient.

Posted by Frank Angel (Member # 248) on 07-11-2005, 10:24 AM:

quote: David Buckley
As I'm the only mentioner of green buttons, I guess this is aimed at me?

No David, I was just poking fun at some theatre managers who don't like projectionists because they think 1)projectionists are overpaid, 2)they just sit around waiting to push a start button on something akin to a DVD player, 3)since they have so little to do, projectionist should do anything they are asked without objecting, even if it's climbing down an 80ft well or septic tank for that matter, 4)they make more money than managers do, which brings us back to #1, managers think projectionists are overpaid. That is, of course, unless the manager has been made the projectionist by upper management. Then the manager thinks the projectionist is underpaid! [Big Grin]

Posted by Helmut E. Dorausch (Member # 1356) on 07-11-2005, 11:54 AM:

"Pump sits at the bottom of an 85 foot well."

You would be well served putting the pump at the TOP of the well, and drop a suction line to the bottom. For one thing, the pump is more readily servicable. With a check valve properly installed on the inlet side, the pump will maintain its prime. I feel you might be overtaxing a 3hp pump, by "pushing" a column of water 85 feet up! Head pressure on the outlet of a pump generally cannot exceed 30 or 40 feet, unless of course it was a rather expensive mag drive unit! A decent pump these days can suck a tennis ball through a garden hose. [Eek!]

Posted by Dick Vaughan (Member # 540) on 07-12-2005, 03:22 AM:

quote: Helmut E. Dorausch
A decent pump these days can suck a tennis ball through a garden hose.

You mean Mr Hill?

Oh! Sorry thats a " u" in Pump not an "i" [Big Grin]