Urgent, need advice please. What's the difference between 1, 2 and 3 phase power?

[robmac]

Rob, you say short runs seldum cause problems. Well, one the the guys here is your age and well experianced, he put a scenario out for the boys one day to see who could get it. I'm not sure this is up your alley, but give it a go. I was the only one who got it but I'm a bit older than the others and knew straight out and didn't have to think.

Problem- Sub-station supplies a main board at a large complex. It has three sets of 240mm2 SDI's per phase run in parallel. The run is only 11m long and the cables are run flat on cable tray. The cables were running very hot so thermal imaging was taken. There was no hot spot at fixing point as thought but the entire cables were red hot. Why?

What is the MDI indicator saying?

What is ambient temperature of the environment.

Were the SDIs run as four groups. Ie red (3xsdi) white (3xsdi) blue (3xsdi) red neutral (3xsdi)

If they are laid out in some side by side layout or worse still random layout then there could be electric field heating effects.

Then of course it could just be heat concentrating if they are jammed against each.

If I did the job I'd layout them on the tray

R
R
R

S
S
S

T
T
T

N
N
N

In horizontal layout.

Was the tray earthed?

I'll read some books about electric fields and get back.

 

[63-1092]

What is the MDI indicator saying? no

What is ambient temperature of the environment. no

Were the SDIs run as four groups. Ie red (3xsdi) white (3xsdi) blue (3xsdi) red neutral (3xsdi) a factor

If they are laid out in some side by side layout or worse still random layout then there could be electric field heating effects. a factor

Then of course it could just be heat concentrating if they are jammed against each. no

If I did the job I'd layout them on the tray no

R
R
R

S
S
S

T
T
T

N
N
N

In horizontal layout. no

I'll read some books about electric fields and get back.

Close in theory but wrong answer. Read those books.

 

[robmac]

Close in theory but wrong answer. Read those books.

Just realised what should happen. Tie to the tray it three (R,S,T,N) groups of four, the fields cancel.

Of course electric field is circumferential. Whilst magnet field is parallel.

Better still would be run each group in a steel duct. - but that won't happen.

Remember - my qualification is communication engineering (39 years ago) not electrical engineering.

EDIT: The industry definition is to install the cables in "trefoil" pattern. IE the same layout as circular orange cable.

Thanks for the lesson as I've said many times we live to learn.

 

[68 404]

thanks, chaps.
these are just two irrelevant asides...

the corner substation next to my house was refitted about 4 years ago. the guys were here every day for 3 weeks or so, and told me the hardware had not been changed for something like 50 years. i did see the cables which fed the substation under the street, and boy were they huge! i was amazed by how much manpower, time and hardware can be absorbed by a substation measuring about 10m x 8m (with 2 levels in side). their final push was a 36 hour marathon non stop. i was away at the time, but they told me when i got back at the tail end of it, that someone had made a noise complaint to the police in the middle of the night! you have to wonder if some people have a brain at all...

last year, a truck hooked the power cables at the family home of my former partner. pulled the barge board off the house etc. she went outside to find the cables on the ground, and the truck driver, who decamped quite quickly told her that it wasnt a problem, as they couldnt be live if they were on the ground!! she called me and of course i said dont go anywhere near them, and to call the police immediately.

apparently, live power cables on the ground wasnt a good enough reason for the police to attend! so they sat there for an hour till the power guys arrived. unbelievable on all counts.

Perhaps suggesting the fire brigade or the electricity people may have been better advice? A typical whinge about lack of police response for a patently non police issue.

 

[alexander]

Perhaps suggesting the fire brigade or the electricity people may have been better advice? A typical whinge about lack of police response for a patently non police issue.

the electricity supplier was also called.
why is a life-threatening hazard in a public place, "a patently non police issue"??

-it is a public place
-it was on a road related area
-it posed an extremely high risk of death
-police are supposedly equipped to attend things quickly
-police have a rescue section which is equipped to deal with accidents, just as much as the fire brigade is.
-when i had a look at the classic car display in Australia Day in the city again this year, i reckon there must have been 100 police hanging around doing FN. similarly the food festival in hyde park. if these are police issues, why is downed live power lines in the street not?

 

[robmac]

the electricity supplier was also called.
why is a life-threatening hazard in a public place, "a patently non police issue"??

-it is a public place
-it was on a road related area
-it posed an extremely high risk of death
-police are supposedly equipped to attend things quickly
-police have a rescue section which is equipped to deal with accidents, just as much as the fire brigade is.
-when i had a look at the classic car display in Australia Day in the city again this year, i reckon there must have been 100 police hanging around doing FN. similarly the food festival in hyde park. if these are police issues, why is downed live power lines in the street not?

There are two sides to this I see.

1) Public Safety is involved - Police are always involved with maintaining Public Safety

2)It's a supply authority asset that is damaged- the onus is for the supply authority to contact the Police.

To be fair Dave, Police aren't interested in attending these day (Vic anyway). I can tell you after the minor riot we had a nearby Party last week.

Three calls to 000. Any knives? Any guns ? well f-off and let them sort it out themselves. I'll let D24 know - never got an attendance.

 

[alexander]

it would certainly have very quickly become a patently police issue if a pedestrian had stepped on the live wire and died.

 

[Mort_Q]

Very old thread, but I found it helpful when looking at a 480V 2 phase supply on our farm, so this post is to reinforce that the info is still current and may be useful to some.
We are just now installing a replacement pump for an old 480V unit that isn't economical to repair. Wasn't sure I could still get one, but the company rep said they are actually still quite common (relatively speaking) for people "out west" where there are long SWER lines, so they can get enough power for deep bores or higher pumping capacities, big air compressors, etc. They don't keep them in stock, but order motors in as needed to build the pump set.
We don't have a SWER, but couldn't afford 3 phase when connecting the pump shed, so it has a two wire 11kV line to its own transformer substation nearby. The shed is supplied with 2 actives and a neutral. Active (L1 or L2) to neutral is 240V and L1 to L2 is 480V. The lights and power point are L1 - N, a single phase smaller pump the same, and the larger 480V/2 phase pump is L1 - L2.
From my physics major (a long time ago), the two actives are actually in phase (not 180 degrees out of phase, as mentioned above) - they sum to 480V. If they were out of phase, I think you would see 0 volts as the phasor sum would always be zero. That fits with them being the two ends of a winding with the neutral as the centre tap.

 

[driven]

Three calls to 000. Any knives? Any guns ? well f-off and let them sort it out themselves. I'll let D24 know - never got an attendance.

The thread on your extension pole for the paint roller is the same as the thread on the main 60A house fuse holder.
Any wild party, just go and remove the fuse, party over, so easy

 

[Roger Wilkinson]

Very old thread, but I found it helpful when looking at a 480V 2 phase supply on our farm, so this post is to reinforce that the info is still current and may be useful to some.

Yes. My setup is still the same. I have since purchased (for $1 at a clearing sale) a single phase to three phase converter that has a 415 volt single phase input, that is achieved by a single phase transformer that converts 480 volt input to 415 volt output. The transformer was included in the $1 lot, along with a couple of 3 phase power points. I suspect no one but me knew what it was!

And Ken has indeed visited me.

From my physics major (a long time ago), the two actives are actually in phase (not 180 degrees out of phase, as mentioned above) - they sum to 480V. If they were out of phase, I think you would see 0 volts as the phasor sum would always be zero. That fits with them being the two ends of a winding with the neutral as the centre tap.

I don't think any of us actually said the two actives were 180 degrees out of phase. We just said they were 180 degrees apart, to distinguish them from the 120 degree separation in three phase systems. As you say, if they were 180 degrees out of phase they would sum to zero.

Roger

 

[pugwash]

Was amased whilst traveling through country south australia to see poles with a single wire attached disapearing over the horison to no dought a farm house ,i had heard of but never seen SWER before, the conductivity of the soil no dought makes a difference to its efficiancy .i recently installed ug sub mains at my sons property near coffs 3 phases but only single phase load ,in the house ,its a 200 metre run from the road ,so its all down to voltage drop over the distance ,cheaper to run 4 35mm cables than 2massive cables, 3 phase was available at the road ,and in fact run UG to a pit on the property 80 meters in by the previouse owner live unmetered for the last 2 years a bit of a surprise to say the least !