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Author Topic: Auto or Manual transfer switches  (Read 30673 times)

pigseye

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Re: Auto or Manual transfer switches
« Reply #30 on: May 05, 2006, 04:33:34 PM »
I don't blame utilities for looking for worst case scenarios.  That's exactly what they are trying to prevent.

I'll keep plugging away, but even i'm starting to think i'd feel better with more controls on the generator.

schoust

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Re: Auto or Manual transfer switches
« Reply #31 on: May 05, 2006, 05:23:07 PM »
   I will be sending in my application soon and we will see how big an issue it is in the Nuttmeg State.Somthiing tells me this won't be easy....

Doug

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Re: Auto or Manual transfer switches
« Reply #32 on: May 05, 2006, 07:15:10 PM »
Worst case scenarios.....

Who many times do you hear people discribe an accident as a one in a million kind of thing?
The truth is your not very lucky when your the one who says this more than once in a life time.

I've got a limp, and a scars on my arm from an industrial accident and I don't feel to lucky anymore. I may not agree with many of the rules, but its arogant to think I know better.

Doug

trigzy

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Re: Auto or Manual transfer switches
« Reply #33 on: May 06, 2006, 01:18:00 AM »
List,
      Not disagreeing with any points made, but there are some points I'll add about utility capactior installations just for FYI:

1) Often near the end of lines where there might not be much load
2) Often 50-150kvar per-phase in size

Typical installation:

[Transformer station] --[Recloser A]---------------[Long lines, Loads A, more reclosers]------[Recloser Z]-----{CAP BANK 1}--------[Loads B]

(For those unaware, a recloser is a self resetting circuit breaker that usually tries 2-3 times to re-energize the load before locking off)
Pictures of utility capactiors here: http://www.nepsi.com/capacitor.htm
Pictures of reclosers here: http://www.setransformer.com/gallery/equip8_lg.jpg

Here is where my concern lies:

1) "Recloser Z" is opened
2) "Cap Bank 1" often provides many more kvars than "Loads B" is often able to accept.  This is because the system was designed to supply power in one direction only, and a capactior bank normally affects the line a great deal on both sides of it for some distance.
3) This MAY keep an induction generator downstream of Recloser Z engergized, even if at a low level.

Again, not likely, but possible.  Fast acting voltage cutout relays (cut out ouside of 226-254V) aren't terribly expensive and would be easy to add.  I'll have to put some more time looking through the catalogs for that Freq. relay I thought I saw.

The concern (probably even more remote) with the UPS is that thier input has a leading pf when the UPS is trying to charge it batteries, it wouldn't feed any power back in to the system.  Probably not enough kvars to excite any generator, but it's there.


Steve

Power Anand 24/2, Brushless 20kW, some other antique iron.
Vendor of AVR's, Small Clones of Yanmar Diesel and Honda Gasoline Engines

Doug

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Re: Auto or Manual transfer switches
« Reply #34 on: May 06, 2006, 02:42:41 AM »
See....

There you go, Steve has explained a condition where a compensated line can have a leading power factor.
And I'll bet everyone who reads ths post will look for the 3 flashes before the automation gives up because a line is actualy down.
There is a Shawm's outline available at most college book stores that goes into power line calculations ( high brow math involved ) that will actualy show you equiv circuts of short and long power lines, and how capacitors(or in some cases unloaded syncronous machines called syncronous condensors to adjust PF of a dynamic load ) or inductors are used to make these lines efficient at transmitting power.


Doug


schoust

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Re: Auto or Manual transfer switches
« Reply #35 on: May 07, 2006, 02:57:40 PM »
   Wow this stuff gets deeper and deeper!I guess my question should be would the installation of a fast acting voltage cut out relay take care of this concern??If so where would one get such a relay?

GuyFawkes

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Re: Auto or Manual transfer switches
« Reply #36 on: May 07, 2006, 03:18:09 PM »
   Wow this stuff gets deeper and deeper!I guess my question should be would the installation of a fast acting voltage cut out relay take care of this concern??If so where would one get such a relay?

you've just cleared up something I remember seeing years ago, it was a home made device, an electromagnet held a ball in suspension, the ball was on an arm, and the other end of the arm over the pivot was a contactor which was wired to the field coils, you had to push the ball up to the energised electromegnet, as it was only powerful enough to hold the ball there at full voltage.

the whole thing was a bit heath robinson, and it was used for an overshot six foot water wheel powering a genny of some sort, which linked into a big windmill which also generated power.

at the time I didn't understand what purpose it could have, but looking back I can see it was a failsafe to ensure the thing only put power into a live system, clever.
--
Original Lister CS 6/1 Start-o-matic 2.5 Kw (radiator conversion)
3Kw 130 VDC Dynamo to be added. (compressor + hyd pump)
Original Lister D, megasquirt multifuel project, compressor and truck alternator.
Current status - project / standby, Fuel, good old pump diesel.

schoust

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Re: Auto or Manual transfer switches
« Reply #37 on: May 07, 2006, 11:47:37 PM »
   Hey Guy,
Don't you just love those old electro mechanical devices :)I only wish that things would have stayed that simple instead of the solid state black box.Now I need to find out if somone makes a device like that??

GuyFawkes

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Re: Auto or Manual transfer switches
« Reply #38 on: May 08, 2006, 12:04:43 AM »
you might like to read this site
http://www.ytmag.com/articles/artint29.htm

and these (PDF) will do what you want
http://energy.tycoelectronics.com/getDocument.aspx?PRD_ID=412
--
Original Lister CS 6/1 Start-o-matic 2.5 Kw (radiator conversion)
3Kw 130 VDC Dynamo to be added. (compressor + hyd pump)
Original Lister D, megasquirt multifuel project, compressor and truck alternator.
Current status - project / standby, Fuel, good old pump diesel.

GuyFawkes

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Re: Auto or Manual transfer switches
« Reply #39 on: May 08, 2006, 12:11:45 AM »
--
Original Lister CS 6/1 Start-o-matic 2.5 Kw (radiator conversion)
3Kw 130 VDC Dynamo to be added. (compressor + hyd pump)
Original Lister D, megasquirt multifuel project, compressor and truck alternator.
Current status - project / standby, Fuel, good old pump diesel.

mobile_bob

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Re: Auto or Manual transfer switches
« Reply #40 on: May 08, 2006, 12:48:04 AM »
is it possible that their concerns about controls stems from the possibility that your induction generator will not uncouple or stop generating if the mains go down?

capacitance in the mains, from all sorts of places might keep your generator spitting power back up the grid.

just wondering

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

Doug

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Re: Auto or Manual transfer switches
« Reply #41 on: May 08, 2006, 02:44:14 AM »
Yes thats the concern Bob.
A power transmission line looks like a capacitor because of coupling to ground.
Steve will correct me if I'm wrong, but I believe most lines are still compensated with grounded line reactors and further corrected with series capacitors for the inductance of the lines. This is also why the utility would prefer that industrial consumers remain slightly lagging in their PF and don't push the point to reach unity and make the line unstable.

Doug

trigzy

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Re: Auto or Manual transfer switches
« Reply #42 on: May 08, 2006, 03:34:01 AM »
Doug & List,
       Any scenarios that I have seen have always required the utility to add (parallel) capacitors to offset the lagging power factor of loads, and inductance in the transformers.  Although I'm aware that they exist, I dont think that there are many series capactors or line reactors in use in this part of the land, but I've only really gone over distribution stuff, not transmission.  (Definition here: Transmission 50+kV, Distribution 1kV-49kV)  "Old-timers" have talked about special cirumstances where you might need this stuff in response to my inquiry of "What the hell would you need this for?" while looking through some catalogs.  I think I recall something about smelting plants or a plating plant of some description having a 0.55 LEADING power factor...... just a vauge memory about what actually had that pf though.

There is an entire science to modelling distribution and transmission circuits, and "guessing" various loads/voltages/PFs so you know how to adjust, compensate and protect a certain section of line or a station.  There is some nice software for it, and it's one of those things you wonder how it ever gone done before computers.  Not that it would be impossible, but you cant be as "creative" when it takes you several hours to re-test each scenario.  Doing things manually (transparent sheets laid over each other ect) didn't allow you to push equipment closer to tolerances, so I think you actually ended up with a better designed system however.  (Ie. If the computer says within specs, even if it's within 0.5%, you probably do it, but if the dot is right on the line, most engineeers would say NO and rethink their setup)

The utilies rely on most customers averaging a 0.90 lag pf.

Just another point: Yes, a "fast acting voltage cut out relay" is fine, but that means it has a KNOWN or ADJUSTABLE cut out point. DO NOT rely on a standard relays/contactors, I have known many to hold at 50 volts or lower.  Preferably a relay with a high and low cut out setting, and a trip time of 30 cycles (0.5 seconds) or less.  A generic motor starter is not what you are looking for here.


Steve
Power Anand 24/2, Brushless 20kW, some other antique iron.
Vendor of AVR's, Small Clones of Yanmar Diesel and Honda Gasoline Engines

pigseye

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Re: Auto or Manual transfer switches
« Reply #43 on: May 08, 2006, 04:58:47 AM »
After a lot of internal debate, I'm going to incorporate some type of over/under voltage control and a shut off that is more sophisticated than a magnetic motor relay.

I'm looking for ideas.  Initially I'm considering a M3410A ($1200) from Beckwith but am looking for more cost effective options.  Your suggestions are appreciated.

Thanks,
Steve 

GuyFawkes

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Re: Auto or Manual transfer switches
« Reply #44 on: May 08, 2006, 10:59:31 AM »

There is an entire science to modelling distribution and transmission circuits, and "guessing" various loads/voltages/PFs so you know how to adjust, compensate and protect a certain section of line or a station.  There is some nice software for it, and it's one of those things you wonder how it ever gone done before computers.  Not that it would be impossible, but you cant be as "creative" when it takes you several hours to re-test each scenario.  Doing things manually (transparent sheets laid over each other ect) didn't allow you to push equipment closer to tolerances, so I think you actually ended up with a better designed system however.  (Ie. If the computer says within specs, even if it's within 0.5%, you probably do it, but if the dot is right on the line, most engineeers would say NO and rethink their setup)

You will probably take this as a flame / personal attack, it isn't.

I want to pull my hair out when I read stuff like you just wrote, you are making the classic mistake, assuming the computer software is "modelling" something with accuracy.

If it was Open Source software and anyone could see the code then I would have some sympathy with anyone claiming they knew what was going on.

If it is closed source / proprietary code then it doesn't matter how accurate it appears to me, you are using the Magic 8 ball to get answers, because you cannot manually check the calculations that the computer is doing.

This software by the way will be written by coders, not qualified and experienced electrical engineers.

So you run some numbers manually, it is slower, and you get DIFFERENT ANSWERS.

So you turn around and ignore this discrepancy as being hugely significant, declare the computer to be accurate and the manual system to be less precise, and away you go.

The truth is hidden in what you said, computers are fast, you can run ten or twenty scenarios in the time it takes to do one manually.

The calculation process thus loses it's importance, and your respect, and as soon as that happens you stop adhering to all the traditional rules, based on experience, that were there simply because calculation took a long time to do right, so you didn't mess with it.

But the real problem is unless you have a set of "workings" for each calculation, you're using a Magic 8 ball, but nobody is admitting that, everyone is claiming the computer calculations are god.

I knew someone who used to work on finite element modelling at a university with close links to the auto industry, which uses it to design and predict things like crumple zones, so he decides to compare real wrecked cars with the models, and found HUGE differences, and started to investigate... he doesn't work in finite element any more...

I use computers all day, but when I started using them everyone constantly drummed a phrase in to you, Garbage In, Garbage Out, so unless your transmission line modelling software can include calculations for the effects of humidity, rain, ice on the cables (capacitance etc) precise grades of cable metal, wooden vs steel tube vs steel frame towers, etc etc etc etc, you have no way of assessing how much garbage is going in.
--
Original Lister CS 6/1 Start-o-matic 2.5 Kw (radiator conversion)
3Kw 130 VDC Dynamo to be added. (compressor + hyd pump)
Original Lister D, megasquirt multifuel project, compressor and truck alternator.
Current status - project / standby, Fuel, good old pump diesel.