Single Phase v 3 Phase

[CathalX]

Diversity can only be applied to the power and light in this situation.

The heating is designed with 5 zones each having 3 elements. There is an under floor probe for each zone feeding back to a controller. The whole system will run during the night on low tariff .

Since I haven't run the system yet, I can't say what power will be drawn each night. However, in the heart of Winter if the temperature of the house drops sufficiently low, ALL of the elements will be energised as Andrew has said.

I have calculated the expected power and light load using the standard formulae and need to allow for a load of 80A.

Sockets - 50 (there are also for radial circuits)
Spots - 120
Electric Shower 10KW - 1
etc

 

[plugwash]

yeah you need to talk to your rec and ask what options there are and at what price. i'd imagine split phase would be the cheapest way to go for the damand you have in a situation with a dedicated but thats only a guess.

 

[Agile]

What fun!

Since its an 11 kV line there will be relatively little extra cost in replacing the transformer!

FWL, I agree with the others that you cannot apply diversity to u/f heating. However there is a cyclic load factor which I understand can be used with pole mounted transformers of about 180% for up to two hours. Explained simply if its a heating load its required during cold weather and the transformers rating is limited by heat buildup so it can be overloaded by 80% (?) for up to an expected two hours when the weathers cold and heat disipation is highest.

Plugwash, surely a two phase ( or two cable) split load is only available for u/g cable fed supplies. A two wire o/h supply has no neutral???

Tony Glazier

 

[andy]

Plugwash, surely a two phase ( or two cable) split load is only available for u/g cable fed supplies. A two wire o/h supply has no neutral???

Tony Glazier

neither does an underground 11KV. its only 3 phases. the neutral comes from the transformer which is on the pole, on in ground situations, a substation.

 

[CathalX]

Will keep you posted. Will talk to Suply Authority tomorrow or Tuesday - should have a solution by then.

 

[plugwash]

Plugwash, surely a two phase ( or two cable) split load is only available for u/g cable fed supplies. A two wire o/h supply has no neutral???

Tony Glazier

split phase starts at the step down transformer. The output winding is centre tapped the input winding is not.

[code:1]
_________ __L
)|(
)|(
)|(
)|(__N/E
11KV two wire input )|(
)|( 240v/480V split phase output
)|(
)|(__L
_________)|

[/code:1]

 

[andy]

[code:1]
_________ __L
)|(
)|(
)|(
)|(__N/E
11KV two wire input )|(
)|( 240v/480V split phase output
)|(
)|(__L
_________)|

[/code:1]

dont you remember we use 230V/460V?!

 

[kendor]

You say there are 5 heating zones then one solution could be to utilise a PLC and occupancy switches to control the heating through contactors/relays so that only necessary heating is on at any time, also energy efficient. Reason for the PLC would be that you program it so that it becomes impossible for all 5 zones to be on at any one time so limiting the current demand. with a bit of intelligent programming you could have adjacent zones working so walking between rooms will keep a constant temperature, if you move more than two zones away those zones >2 away then switch off. At night you might program so only the upstairs heating will be allowed to energise and daytime the upstairs probably doesn't need heating as the heat from downstairs will rise and keep upstairs warm.

 

[CathalX]

No upstairs heating by the way.

Spoke to the Electricity supply engineer. With a standard three phase supply, I can only be given 80A per phase. This would leave me short. The solution will probably involve a current transformer with up to 300A output. I am not sure if the transformer is supplied with 220 or 380v.

I believe the prices being mentioned are £10, 000 +

 

[kendor]

Far cheaper route would be as i suggested, using the plc, the zones could be sequenced to heat the whole building initially say 20 mins per three zones, the zones first or mainly used, could overlap with next heating sequence, all zones would eventually be heated up and hopefully the building meets current insulation requirements so loss of heat will be kept to a minimum with only three zones on at any one time during normal use also. The total flexibility of using a plc and programming it to your requirements should solve any potential use of the zones, coupled with thermostats and a bit of forethought there would never be a need for all 5 zones switched on at the same time.

 

[kendor]

MOD error double post please delete