Saturday, September 8, 2012

Ferrorresonance a Bizarre Electrical Condition I hope you never come across it.

Many years ago while helping  some other electricians to change out a 208 volt  400 amp 3 phase 4 wire  partial underground electrical service  we hit a bizarre situation.

The power company Troubleshooter  had come out and turned off  the transformers to the electrical service with a special fiberglass  rod  which opened internal switches in the transformers .We measured with testers and had no voltage . But when we undid the first neutral wire all of a sudden there was a sustainable voltage of 400 volts on the wires which shocked us.

Puzzled we called the power company back up who sent a trouble shooter out and who also measured the voltage and then put a set of grounding jumpers on the transformers to get rid of the stray voltage as he called it from the 28 ,000 volt down to 208  volt transformers which  he called Ferrorresonance .






The problem is when you run electrical wires thru metal piping and then run high amounts of current thru them the piping becomes  energized just like a transformer works. 
This is one of the reasons metal piping and surfaces must be grounded to reduce these effects and drain it off  as well as insure the operating of overcurent devices as well.
Now that I know to look for this and be careful of it and put on grounding jumpers it has not been a problem but this again is one of those things they do not teach you at electrical  school  and you may never run into it your entire life as an electrician but I did and it has taught a valuable lesson to always be on your guard when working on electrical services, which have not been completely detached from power company's service lines and just switched off at the transformer.
In our case it was determined the jumpers should have been in place before we started the job and the first trouble shooter was written up.
 With many new regulations in NEC 70E Electrical safety practices for workers  which came on line a few years back  it is mandatory to now use them on many jobs.
to prevent exactly what happened to me and electricians  I was working with.
While the use of jumpers has always been taught as a practice to prevent an accidental electrocution should a service line be turned on by mistake while it is being worked on  and the jumpers will cause the over-current protection to trip out .As more and more complex power systems come on line jumpers  there ability to eliminate stray and transformed voltages  has become much more recognized. But as with any safety equipment jumpers must be properly and carefully placed to operate properly  or you can cause serious injury's or death.

Example of jumpers set being installed on overhead lines to protect workers down stream in case the overhead lines would become energized




No comments:

Post a Comment