Open and Closed Transition

As if I didn't have enough to do, I get hit with two more big projects.

First - Rebuild a transfer switch and install it with generator, shipped in from closed plant. So far, no problem. Thursday morning, supply purchasing with a list of parts, and give us a status report. And tell us if you will be using open or closed transition.

Second - Rebuild high pressure low volume pump and controls (2 speed motor?), also from closed plant. So far, no problem. Thursday morning, supply purchasing with a list of parts, and give us a status report. And tell us if you will be using open or closed transition.

I don't know where they came up with the open or closed transition. I don't have a clue. I did several searches, but didn't come up with anything I can use.

Can one of you out there help me?

Would the motor control and the transfer switch transitions be similar?

Doing the controls and transfer switch in the normal fashion should be fine, my guess is that this is open transition.

Help!

Del

Transitions ????

What an interesting term.

THEY are the ones who cooked it up ask THEM for a definition.

I wold be curious to hear it.

Dan Bentler

Transition means change...ie from on to off, off to on, open to closed or closed to open.

I believe they need to know what type contacts are needed...ie Normally Open or Normally closed....ie if a pump pressure switch is used will it "close" or "open" a contact when pressure or a pressure range is obtained.

Open transition means the device is totally disconnected from the power source as it changes from one state to another. Closed transition meant the device is still connected somehow to the power source. Closed transition can reduce power grid "glitches" associated with opening and closing large motor loads.

For transfer switches a more common term is "make before break" or overlapping contacts where power power sources are momentarily paralleled. The way this is accomplished depends on the type transfer switch involved.

For two speed motors special control circuitry is required as well as additional components such as resistors and more contactors. Simple two winding and consequent pole two speed motors do not typically have closed transition designs. However this option is normal with wye-delta starters.

As a side note, If you were talking about Hydraulic or Pneumatic Directional Control Valves:

Open Transition (also called "Open Cross Over") would mean all flow paths are connected as the valve shifts from one condition to another.

Closed Transition (also called "Closed Cross Over") would mean all flow paths, or at least Pump flow, are blocked as the valve shifts from one condition to another.

Ron, you can see the many variations available in the Symbols Book I sent you on page 12.

In hydraulics the wrong Crossover condition can cause pressure spikes and undesired movement, plus other screwy things, when the wrong transition condition is applied.

Just my two cents worth from a Fluid Power standpoint. Note the oposite meaning of "OPEN" and "CLOSED." I usually use "PASSING" or "NON-PASSING" when conversing with electrical types.

I think leitmotif is on the right track...

Just from the context, I doubt this is a technical issue. If I had to guess, I would say it's an internal project management type buzzword. If I had to really go out on a limb, I would guess that it indicates if the project is going to require plant downtime, or if it can be done while the plant is running.

I'm interested to hear what it really is...

I agree with Jim. Closed transition uses resistors to maintain the motor current during switching, though I have also only seen it with star-delta. I have got a formula somewhere for sizing the resistors. I'll post it if I can find it.

Management may or may not know the difference, but they have been prompted to ask by someone who does know. They probably have an answer in mind.

So, after reading the replys, and playing around with a pad of paper, we have decided the following.

Motor control will be an open transistion. It will be a typical star-delta starting sequence. This will eliminate the need for a bypass contactor and timer, when the unit was originally installed elsewhere, would trip out the overloads, and was held in for three minutes until someone could reset them. Starting slow, will reduce the inrush current problem.

Transfer Switch will be planned as an Open Transition, since we do not want to parallel the mains, and possible fry a lineman accidentally. We will consider the poassibility od converting to closed transistion, at a later date, should the local utiklity request it. That will never happen, and keeps me covered.

Thanks for the input guys, now back to something important, working on my in-plant traffic lights!

Del

With respect to controlling flow from pumps...

Transitioning means moving a valve from Full Closed to Full Open, or vice-versa.

A Closed Transition means that when the valve, after the pump, goes through the middle of the transition, the pump "sees" a dead-spot. That is, in the middle of the transition, there is no flow... the pump "sees" a dead-head!

An Open Transition means that when the valve, after the pump, goes through the middle of the transition, flow is liable to move through both of the output ports in the valve. (Flow will go to the port with the lesser pressure head.)

If you use a Closed Transition then the transition MUST occur very quickly to prevent the pressure relief valve in the pump from popping off. This also leads to "Slam-Bang" pressure control... not so good on the pump, valves or pipes. The slower the transition, the greater the stress caused on the system.

Depending on your particular situation, you should consider carefully which one you choose.

I had a valve that was designed to present a Closed Transition. I had the valve spindle re-machined to present an Open Transition. Now I'm a happy camper.

The following comment is Bogus!

Now that you've narrowed down the topic. Closed transition motor starters are used to prevent a current spike caused when the motor starts to decelerate when it is disconnected from the power source and then slammed back on line at full voltage. This is not always a problem but you should be aware of it.

Hard to Start??

Del Monte you may want to check into another way of starting your motor if it`s starting a heavy load

Motor control will be an open transistion. It will be a typical star-delta starting sequence. This will eliminate the need for a bypass contactor and timer, when the unit was originally installed elsewhere, would trip out the overloads, and was held in for three minutes until someone could reset them. Starting slow, will reduce the inrush current problem.

Click to expand...

with a star/delta starter you only have 57% starting torque. Before you spend much $ on an old starter you may be able to replace it with a new soft start starter for about the same money. We have used these new starters on chippers up to 600 HP and they work fine (cost less than auto transfomer starters too). Good luck with your traffic signals!

:site:

So far...

It appears that Del Monte doesn't know if the question posed to him refers to a power situation or a valve situation.

As I read his post and as he related the question posed to him, the question is in regards to a valve.

Let's hope that he comes back and says one way or the other.

As for me, and what he said, I'm going for the valve question.

As a philosophical rule...

"The Question is MUCH MORE important than the answer!"

Also... and more importantly...

Be careful what you ask for... you just might get it!"

REF Post #8

Strictly Electrical. The high pressure pump is for a plant wide pressure wash system.

Soft Starters are not permitted. I don't know if it is corporate policy, somebody long gone's personal preference, or has something to do with customs and import tariffs.

There is a timer preventing restart before the pump has completely stopped. In event of a momentary power outage, the control relay drops out killing everything, and someone has to physically walk to the panel, and push the start button.

Del

If I may, I am quite sure Mr Dungar is correct. I am not sure what hp of motor you will be starting, but usually on large wye/delta ( star/delta ) circuits there is a resistor or a bank of resistors that are brought in during the "transition" from wye to delta. This prolongs contact life and is a fairly common practice. We have two 1000 hp chillers that are started with NEMA size 7 Allis Chalmer starters in this fashion. If you are concidering modifying the design variable speed drives have advanced in technology and now have decreased in price enough to easily out perform antiquated mechanical starters. I understand the installation of " previously owned " equipment has it's challenges, but please research the original design carefully, and understand why it was a part winding start, and redesign with safety a #1 priority.
I wish the best of results!

1000hp? WOW!

The high pressure pump will be our largest motor. We had to pull (hired it out, thank goodness) 2x4/0 through the plant for the power, to keep the voltage drop down. Doesn't use a lot when running, it just takes a lot to get it going, as the pump is coupled direct 1:1. Motor is currntly configured for 3600 rpm, was at 7200. I don't know how it can go that fast, or how it could stay together. Motor and pump are in a mesh cage. No one is allowed in there whenit is running. It makes a racket like you wouldn't belive. I had to go inspect it before it was tore down and shipped to us so I knew what some of its charactoristics were. I think a couple of portable sprayers on fork trucks would have been more useful and a lot cheaper. But then, maybe that is why I am not in management.

Everything we had here is well under 100hp. Most equipment is 5hp or smaller. The largest starter in stores is Size 2. I have 3's and 5's in my maintenance crib, but never have used them. A lot of the old plant is still 230, 2 and a half phase (open delta). When I started 30 years ago, the pump house was the only 460. Some parts were 230, others 208, and a lot 120/240. We had a lot of SO cord strung all over. As the plant started converting to 460, I loved it. Pulling smaller wires = more fun.

Del