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Electrical Quizzes - QUIZ 8 POSTED

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LAN_403

HV Enthusiast

Mon Feb 20 2006, 05:10PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Yes, you can post a quiz, but remember that only one quiz is allowed at a time, otherwise it will be deleted.

Thanks

Marko

Mon Feb 20 2006, 05:22PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Easy one.
You have three phases, R,S and T and 0. You must provide a constant supply to heater (resistor) using two 3-contact relays if one or two phases fail.
Phases must not short in any case or there must not be a possibility of shorting...

IamSmooth

Mon Feb 20 2006, 08:48PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

I can calculate the 1.6... with some number crunching. Is there a link to how this power series reduces to the simple solution?

Marko

Mon Feb 20 2006, 09:06PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Maybe I wasnt clear: you should draw a schematic, using two 3-pin relays, that will make constant supply to single phase load even if one or two (any) phases of 3-phase supply fail.

Each relay has one SPDT contact, like shown here:

This is all relevant and so simple quiz can really be done in few minutes :)

IamSmooth

Mon Feb 20 2006, 09:27PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Never mind, I found it. I have to find some problems to post, too.

...

Mon Feb 20 2006, 09:49PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

sorry about the poor quality, using the touch pad on my laptop with ms paint...

Simon

Mon Feb 20 2006, 10:03PM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

IamSmooth wrote ...

I can calculate the 1.6... with some number crunching. Is there a link to how this power series reduces to the simple solution?

If anyone's interested I can give a neat solution to this problem using high-school algebra. PM me and maybe I'll start a new thread on it.

Let's keep this thread tidy, though. No more about the golden ratio here; stick to one question at a time.

[Edit: could we also number and flag every new question, like
### Question 5 ###
I'm already getting confused. I've just been through counting the questions to update the thread title.]

dan

Mon Feb 20 2006, 11:56PM

Registered Member #223 Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125

here is my solution:

1. If R fials the first relay from the left will realase connecting S to the load. Current will from from S to ground.
2. If T fails nothing happens.
3.If S fails nothing happens.
4. If R & S fail the second relay from the left will relase connecting the load to T and since S is now 0 current will flow through the load. (however this is assuming a power failure and S is not an open circuit. If S is open circuit this will not work.)
5. If R & T fail, see 1
6. If S & T fail, nothin happens.

Marko

Tue Feb 21 2006, 01:59PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

There is one major problem here: as said, any phases must not short in any way never...

In reality if R and T are present and S not load is not connected to one but to two phases, without ground...

You may be somewhere in the middle of the way.. ?

For hint, if all phases are present in schematic and someone manually moves relay contacts they will never short... (one asked me for schematic on one bosnian forum, so I drew it)
Tought it may be interesting for quiz...

PS. ... - this is a nick?

I dont understand your schematic but you may be on a right way, can you explain it a bit

...

Wed Feb 22 2006, 01:19AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Ok, you have a relay with the coil connected to T, and it no contact also connected from T to 0, and it common going to the load (so as long as T is hot it goes to the load). Then you have another relay with it's no contact on R, its nc contact on 2, and it's coil from R to 0. The common from this relay goes to the nc contact of the first one, so...
If they are all on, the first relay is activated, to the load is connected from T to 0
If T fails, the relay opens, and is now connected to P
If P fails, the second relay opens and the load is connected to S
I don't see why I didn't win...

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