Transmission of Electricity

[gorilla]

Just thought I would post here and see if anyone could help me out regarding the transmission of electricity from power stations to the home/industry.

I have done this at college and I'm just doing a diagram of the system but unfortunately my lecturer missed out a stage and I would like to include it in my diagram.

This is what I have so far:

Electricity produced at power station using 3 phase generator that outputs 11kV to 25kV

This is then increased to the distribution voltage of 400kV using a transformer that outputs it as 3 Phase Delta

Once at 400kV the electricity is distributed to a Substation where it is reduced to 132kV remaining as 3 Phase Delta.

The electricity then moves onto another substation and reduced to 33kV and then to another where it is reduced to 11kV before it arrives at a local substation where it is reduced to 415V and distributed to our homes in 3 Phase Star where using one of the phases connected to the central neutral return gives a final output of 230V

Now that is the bit I know. Here is the bit where the lecturer stopped and told us we don't need to know it (it wouldn't hurt if we did though)

Electricity produced at power station using 3 phase generator that outputs 11 Kilo-Volts (kV) to 25kV

This is then increased to the distribution voltage of 400kV using a transformer that outputs it as 3 Phase Delta Once at 400kV the electricity is distributed to a Substation where it is reduced to 275kV remaining as 3 Phase Delta.

I know it needs to get brought down to 33kV, 11kV and then 415V but from my research it doesn't really do this directly. All though I have found a few places that say it goes from 275kV down to 33kV but I'm unsure of this.

can anyone help me out thanks, I would have asked another lecturer today but unfortunately didn't have time and I'm not back at college until Monday now.

 

[ian.settle1]

just thought i would post here and see if anyone could help me out regarding the transmission of electricity from power stations to the home/industry.

I have done this at college and i'm just doing a diagram of the system but unfortunately my lecturer missed out a stage and i would like to include it in my diagram.

This is what i have so far:

Electricity produced at power station using 3 phase generator that outputs 11kv to 25kv

this is then increased to the distribution voltage of 400kv using a transformer that outputs it as 3 phase delta

once at 400kv the electricity is distributed to a substation where it is reduced to 132kv remaining as 3 phase delta.

The electricity then moves onto another substation and reduced to 33kv and then to another where it is reduced to 11kv before it arrives at a local substation where it is reduced to 415v and distributed to our homes in 3 phase star where using one of the phases connected to the central neutral return gives a final output of 230v

now that is the bit i know. Here is the bit where the lecturer stopped and told us we don't need to know it (it wouldn't hurt if we did though)

electricity produced at power station using 3 phase generator that outputs 11 kilo-volts (kv) to 25kv

this is then increased to the distribution voltage of 400kv using a transformer that outputs it as 3 phase delta once at 400kv the electricity is distributed to a substation where it is reduced to 275kv remaining as 3 phase delta.

I know it needs to get brought down to 33kv, 11kv and then 415v but from my research it doesn't really do this directly. All though i have found a few places that say it goes from 275kv down to 33kv but i'm unsure of this.

Can anyone help me out thanks, i would have asked another lecturer today but unfortunately didn't have time and i'm not back at college until monday now.

transformers

 

[gorilla]

transformers

I know that. I am wanting to know what the next step down will be from 275kV.

 

[raylewis]

The reason for generating between 11Kv - 25Kv is for altenator insulation properties,can you imagine the insulation req'd for 400kv in the altenator
Delta-Delta HV transformers are use because you dont need a neutral phase in transmission.
Standard is to transmit as high as you can(400KV) - main grid
Then as you get closer to the demand like Areas you step down to 275KV or 132KV for that area.Then depending on the area - city,industrial site,housing is the factor that determines the next step down according to the load demand.
Industrial main subs go down to 33KV and then 11kV as close as you can to the demand and then to 415/230v for light industry.buisness and domestic.
Pylons too big in built up areas and 275KV not good in built up area
Rule is get as close as you can with HV safely
As you can understand the closer you can get the HV to the load the better(lower losses).
Please dont make the common electricians mistake - the higher the voltage the lower the current,this rule only applies to transmission.
In standard circuits the higher the voltage the higher the current(Ohms Law)

Hope this helps you out

 

[gorilla]

The reason for generating between 11Kv - 25Kv is for altenator insulation properties,can you imagine the insulation req'd for 400kv in the altenator
Delta-Delta HV transformers are use because you dont need a neutral phase in transmission.
Standard is to transmit as high as you can(400KV) - main grid
Then as you get closer to the demand like Areas you step down to 275KV or 132KV for that area.Then depending on the area - city,industrial site,housing is the factor that determines the next step down according to the load demand.
Industrial main subs go down to 33KV and then 11kV as close as you can to the demand and then to 415/230v for light industry.buisness and domestic.
Pylons too big in built up areas and 275KV not good in built up area
Rule is get as close as you can with HV safely
As you can understand the closer you can get the HV to the load the better(lower losses).
Please dont make the common electricians mistake - the higher the voltage the lower the current,this rule only applies to transmission.
In standard circuits the higher the voltage the higher the current(Ohms Law)

Hope this helps you out

Thanks so the drop is from 275kV down to 33kV. That's all I needed to know. The rest of it my lecture told us but decided that 275kV wasn't important as it is being phased out but it would have been good to know for reference purposes at least.

 

[shep]

this is what we were given when i was at college

 

[gorilla]

this is what we were given when i was at collegeView attachment 159

If only my college gave out handouts that had information like that on them. I found a similar one on the web but it didn't show 275kV like your one.

 

[Des 56]

Just having a quick nose through and couldnt let this go without comment

Please dont make the common electricians mistake - the higher the voltage the lower the current,this rule only applies to transmission.
In standard circuits the higher the voltage the higher the current(Ohms Law)

Please elaborate because the reply should be very interesting

 

[raylewis]

Reply to Des 56
Hope this is interesting enough for you
Ohms law V=IR
I=V/R
or R=V/I

or Z replaces R in AC circuits

Remember the load stays constant in normal circumstances for example a kettle
3kw measured as 18 ohms approx.This ohmic value does not change.
Use 230v
therefore I=V/R I=230/18 I=12.78A
Now use 250v
I=250/18 I=13.88A

Basic electrical formula(learnt this 1st year ONC)

In transmission over distances when transforming voltages using transformers on two sides of a circuits different rules (formulas) apply(winding turns of transformers,voltage drop over distance,conductor sizes types of transformer etc)

This is done to overcome losses over distances and lower current capacity for lower cable sizes
Learnt this the first month of my HND Electrical Engineering 25 yrs ago
Different set of rules and Elect formula come in to use
Guys ohms law isn't the only formula

Common mistake I have come accross in my Engineering career

Hope this reply was interesting enough for you
Have a think and give us a reply

Regards

 

[DPG]

Mmm. Yep, fairly interesting. Are you saying ohms law applies only up to a certain distance of cable??

Also, transformer turns ratio is exactly that - a ratio of primary/secondary turns. This would apply for a large distribution transformer or a small mains transformer.

Just out of interest if you wound the grid supply (400kV) up a few thousand volts, what would happen to the current?

Look forward to replies

Darren