Transient voltage fault for NVQ

[Callum Jackson]

Hi guys

Doing my NVQ and have to locate and fix a transient voltage, after speaking to my assessor we agreed i was unlikely to come across one before my time was up and very very unlikely to come across two on different occasions.

So not sure what we will do yet, maybe a simulation in the work shop or a detailed write up to prove my understanding and knowledge. However there lies a problem i have a rough idea of what is going on but would be grateful of anyone with first hand experience to just give me a rough idea of how the fault came to be and how you found it and fixed it.

Many thanks.

 

[Lucien Nunes]

Do you mean fix a fault caused by a transient, such as a flashover that has damaged insulation, or correct a situation that is causing transients such as a highly inductive load being switched without suppression?

 

[Callum Jackson]

yeah a big load, im meant to identify the fault and take action to prevent it i think.

 

[firemanowl]

I thought with the NVQ you had had to sort 3 different faults from a list of 6? That's what I had to do, was struggling to finish fault section so got my mentor to put a fault on a circuit and got the tester out.

 

[Marvo]

Do you even have the test equipment to identify a transient voltage from a switched inductive load? This could be a tricky one, if there's alternatives available as Firemanowl thinks there are you may be better looking at one of them instead.

 

[Besoeker]

Do you even have the test equipment to identify a transient voltage from a switched inductive load? This could be a tricky one, if there's alternatives available as Firemanowl thinks there are you may be better looking at one of them instead.

Or an oscilloscope which is what I would use.

 

[Marvo]

We have a PQA but they're not cheap, even hiring one costs a considerable amount and there's a fair learning curve for using one as well. You could possibly get away with using the wave capture facility on this kinda tester but it would be pushing the boundaries of what it's designed for.

 

[Callum Jackson]

Hahaha feels like I may be up against it with this one, and yeah I thought I only needed a few faults my assessor is very strict on some things he says I have to get them all including incorrect phase rotation not being funny that dosnt happen anytime any one from my company do mains or DBS we just get someone else to check it over quick, check the phases and connections it's just common practice for us. I will literally have to purposely install a 3 phase supply wrong and take a photo... -_- it's like consumer units! I've never put up a cu not in five years I've put up loads of DBS but he is saying now I can't pass without doing two consumer units. I may need to speak to him I mean it's always better to do more then less but itdon't getting to a point now if he is asking me to do things I don't need to do I'll have to say something... 95% done Am2 in two weeks I don't want to be stuck trying to get stupid faults for a few months.

 

[Lucien Nunes]

incorrect phase rotation not being funny that dosnt happen anytime

Really?

If I can offer you one tip from 25 years experience fault-finding, it's never to take anything for granted. I've been to a site where a pump motor had been running the wrong way for 18 months before anyone noticed. How about a TP+N DB that had the same phase twice (L!, L2, L1) that had been in use for years supplying only single-phase loads. Would you be certain of the phase rotation at these boards?

 

[UKMeterman]

Ok,
To measure the transients you need sutiable test equipment, I would suggest if you want to get a handle on transients go shares with a few of your mates and hire Fluke VR1710 Voltage Quality Recorder | hire | inlec and plug it in on a big plant / or comercial site. I have even known offices where the mains has spikes when all the lights come on via a contactor.

As for the physics look up inductors and V=L dI/dT ...

Oh,
And don't just connect up any old oscilloscope to the mains. The 0V connection of most scopes is connected to mains PE. If you connect that 0V clip to the supply neutral with most oscilloscopes you will have caused a neutral earth fault and possibly cause a dangerous fault in the scope. If you do want a scope that will do that Inlec will help or suggest models that your college could purchased. Never under any circumstances disconnect the earth in the plug from the scope or try to use an isolation transformer to float a scope.

 

[Besoeker]

Oh,
And don't just connect up any old oscilloscope to the mains. The 0V connection of most scopes is connected to mains PE. If you connect that 0V clip to the supply neutral with most oscilloscopes you will have caused a neutral earth fault and possibly cause a dangerous fault in the scope. If you do want a scope that will do that Inlec will help or suggest models that your college could purchased. Never under any circumstances disconnect the earth in the plug from the scope or try to use an isolation transformer to float a scope.

I use two channels in differential mode. Actually, the scope I normally use, and the one I cart around in the boot of my car, has facilities to add, subtract, or multiply the two channels.