Generator parallel with mains

[lyledunn]

Just as a matter of interest what effects might there be when a 1000Kva 400v 3phase generator is paralleled with the main supply without being synchronised?

 

[jstickley]

Let's just say that it's not a very good idea....

Assuming that by paralleled, you mean that the generator is supplying the same loads as the main supply, the instant the generator is closed to supply load, you're going to see some nasty transient currents and voltages throughout your system, not to mention some pretty good stresses on your generator. In all likelihood, if you have any kind of protective relaying on the generator, the generator won't be online long after its closed to supply your loads. Protective devices on your main supply may trip as well.

All of this depends on how out-of-synch your generator happens to be with the main supply -- if the frequency, phase, and voltage of the generator and main supply just happen to be close enough (and they have the same phase sequence), the generator will synchronize with the main supply. As for your chances of this actually happening through blind luck.... not good.

 

[dpc]

In addition to the high transient currents mentioned, your machine will be subject to excessive mechanical forces and can suffer damage due to these stresses.

 

[MqPower]

I recall a 500kw generator "walking itself" engine stand and all right off the loading dock when it went unstable after being tied in with an unparalleled load. Like the previous messages - not a good idea. If this and the other responses make you unhappy just consider the owner of the classic MG that was parked "under" the generator when the unit went over the edge.

 

[lkgupta]

It all depend upon the instant of synchronising the generator with the mains. Your set may be subjected to severe mechanical stresses if it is out of phase synchronised with mains. I personaly have seen a 1000 KVA generator breaking into two parts in one of the plant.

 

a german company called dsl (amongst others)provide a controler that will monitor mains and plant phase and give a signal when the waveforms are within 5 degrees or so of one another. the signal can be used to close a contactor and your done. it is still not a very good idea to 'tinker around' with such a system as it is easy to shear the crank/alternator coupling on the genset. ATTEMPTING SYNCH TO THE MAINS IS ALWAYS DANGEROUS..

 

[quark]

To All!

Asking such a type (?) of question in any of the mechanical engineering forums would have been a blind error for, you get answers like go back and read the fundamentals or why can't you consult a professional nearer to you sort. I liked you guys patience and explanation without any pun. As I always think to be a succesful electrical engineer one has to be very patient.

Keep it up.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[lyledunn]

Quark,

Come on Quark!! I have no objection to your implication that my question was fundamental. Of course it was. But why do you think all the good buddies out there use handles? The malaise within engineering in general is a distinct inability to admit that you are not as expert as you would like others to think you are. These forums provide a wonderful opportunity to bare your soul without being scoffed at! Although, I am bound to say that LyleDunn is my real name. As a law graduate, I was late to electrical engineering, but it did teach me to ask fundamental questions without getting a red face! Sometimes even the most knowlegable lecturers found great difficulty in answering my "fundamental" type questions.
I also thank the electrical guys out there who take the time and trouble to respond.

Regards,

Lyledunn

 

[quark]

LyleDunn!

As far as the handles are concerned I totally disagree with you. For example my handle 'Quark' is my obsession with quantum physics. (It will also allow me entering eng-tips.com without anybody's knowledge during working hours) I always like the kind of spirit you have.

Note: I am sorry if I offended you unknowingly.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.