72 kw chidlow electraire blowing fuses

[jumpin jax]

I currently have a problem with a 72 kw storage heater which is blowing 100 amp BS88 about one every 4 days, it is now on its third. The fuse is always on the same phase. I have measured the line currents as L1 33A L2 99A L3 105A Neutral 69A, line/line voltage under load measured approx 405V between the 3. Some of the elements had failed before I got involved with the heater hence the 33A on L1 and 69 on neutral. The elements appear to be wired in delta. This heater has ran for approx 25 years and was installed with a MEM 100A exel switch fuse with 100A BS88( a bit close would have been better with 125A). The Heater works on economy 7 with boost overide but this is never used except when testing. The manager tried to get a manual with a wiring diagram but with no luck as only one firm deals with these now and is very closed shop in the help department unless you want to pay them to travel 200 miles which is no good on a call out. The fuses that have blown look overheated and not just ruptured instantly.
At this building we had a fuse blow on one phase on the pole transformer in December and was wondering wether there is a voltage surge at night time causing overload of the fuse. The Coke machine went wrong this weekend and the engineer told the manager it was probably due to a surge. How easy is it to get UKPN to data log the incoming supply? Or do you guys have any other ideas? Thanks

 

[telectrix]

something seriously wrong here. should be balanced at approx. 100A/phase. think you need further investigation of the red ( L1 ) phase.

 

[jumpin jax]

Cheers Tel, I would put the imbalance down to the failed elements. It is always L3 yellow phase at 105A that always blows.

 

[Top Cat]

Wow, that's a big storage heater! Is it an electricaie type with fan? Agree with Tel about red phase but that could be just elements. You don't say which fuse (phase) is blowing. Could the overheating of the fuse carrier be the cause of the blowing fuse because once the carrier "goes" it can get very hot under normal conditions?
You could try:-http://www.storageheater.co.uk/ they are quite helpful.
Keep us posted.

Just seen about yellow phase.

 

[jumpin jax]

Hi TC , yes it is rather large, the fan is mounted on top and thermostatically controlled during the day, there is in fact 2 heaters side by side. To say the power bill each month is high is an understatement

 

[Knobhead]

72KW with a balanced 3Ph load @400V the FLC should be 104A. What is the rated and supply voltage? It would help to give more accurate figure.

With you readings of 33, 99, 105A the OP is in reality 55KW. Neutral would be 69A

A fuse isn’t designed to run at full load continuously even at 125A your pushing it! I’m surprised you haven’t had problems with the other heater.

 

[silva.foxx]

I have measured the line currents as L1 33A L2 99A L3 105A Neutral 69A, line/line voltage under load measured approx 405V between the 3. Some of the elements had failed before I got involved with the heater hence the 33A on L1 and 69 on neutral. The elements appear to be wired in delta.

Delta and neutral???

Balance out elements if possible.

 

[jumpin jax]

Hi Tony, heater is rated at 415V and supply voltage with heater elements on is 405v approx,cheers

 

[Knobhead]

It’s not going to help much but at 405V the output is reduced to 68.6KW, which equates to 97.7A.

To be honest despite the imbalance in load, the heater supplies are being pushed to the limit. I wouldn’t be surprised if the 2[SUP]nd[/SUP] unit has failed elements if the fuses haven’t been blowing.

 

[jumpin jax]

It also surprises me that it has ran this long but it all looks original. Usual story though, if i say the equipment requires upgrading i know they will say that it has been ok up to now. Thanks for all your replies so far, i will do a bit more investigation. When this was new it must have been drawing 100amps per phase, being a resistive load it is no different from 3 different single phase consumers running at different loadings or is it?

 

[Top Cat]

It also surprises me that it has ran this long but it all looks original. Usual story though, if i say the equipment requires upgrading i know they will say that it has been ok up to now. Thanks for all your replies so far, i will do a bit more investigation. When this was new it must have been drawing 100amps per phase, being a resistive load it is no different from 3 different single phase consumers running at different loadings or is it?

Not many consumers running 100Amps or they would have to upgrade the grid!

 

[Knobhead]

Not many consumers running 100Amps or they would have to upgrade the grid!

If the increasing trend to electric heating is correct* I don’t think that will be to far away.

*I’m just going on things I’ve read about new builds being discouraged to use gas heating. I’ll be glad if you lads can say I’m wrong on this point.

 

[Top Cat]

If the increasing trend to electric heating is correct* I don’t think that will be to far away.

*I’m just going on things I’ve read about new builds being discouraged to use gas heating. I’ll be glad if you lads can say I’m wrong on this point.

Maybe my NSH's are coming back into fashion! Hey I'M TRENDY!

 

[Knobhead]

TC, can you say I’ve misread something or are you just Yowling like most cats?
I’ll kill the two that wake me every morning ! ! ! !

I would like to be proved wrong, as it’s a retrograde step for energy conservation. More profits for the energy companies though due to inefficient power transfer.

 

[cooper]

Can anyone please help with the following question
what are the implications of of carrying out safe isolation procedure to
a) yourself
b)public
c)customer/clients
d) building systems
Thank you in advance

 

[Knobhead]

What has this got to do with a storage heater fault?

 

[Engineer54]

After 25 years of service, this unit is rapidly coming to the end of it's life. Your going to be chasing round like a blue arsed fly, trying to keep this unit in service from now on!!

The only way to bring this unit back to full service for any length of time, is by replacing ALL the heating elements. Probably the cost of the elements and your time to replace them, is going to be a very big chunk of a replacement unit!! The time has come for this unit to be replaced for an up to date unit that in all likelihood will have lower running costs. If your clients can't see this, then it's time to walk away... lol!!!

 

[jumpin jax]

Hi, I understand what you are saying and agreed it is reaching the end of its life but where in this heater, with resistive loading, is the extra draw of current coming from to cause this sudden problem?

 

[Top Cat]

Hi jumpin jax, just wondered if you put your location maybe one of us could give a second opinion. Sometime two heads are better than one!

The only other thought i had was could either an element lead or some other feed to the elements be breaking down on that phase so when it gets hot it shorts to earth or neutral

 

[jumpin jax]

Hi TC, i like your chain of thought but i would have thought that on the initial short circuit the element would have failed completely, i will try and post a picture, the 3 contactors on the left control the elements and the contactor with overload supplies the fan.