crane regenerative power protection

[BobB]

regenerative motor power?

My pet hate!!! Lifts in buidings do terrible things to generators. I have seen power factor down to 0.22 lag - overheats the alternator to blazes!!
Harmonics are the other pain in the "A"!!! Unless there are appropriate harmonic filters on the AVR, the AVR goes nuts!!!
Take note of Paul Lucas as he is very experienced here. The values need to be calculated by someone who really knows what they are doing or it will never work. If the system has been changed by someone else, as appears to be the case, it is probable that the whole protection system will have to be re-calculated by an engineer that really knows what he/she is doing. If not, a disaster is waiting to happen!!!

 

[PLucas]

Plucas : Do you know the conditions to couple the resistors?

Yes I do, but the value of -KW that we use will not help you in this case.

if you read currents and power how can you know when you reached the maximum amount of reverse power ?

I am not sure I fully understand what you mean when you state 'reverse power', we are only looking for the value of regenerative power to reach the maximum that our generators can handle (or there abouts), then we switch the resistors online. we are not interested in the total regenerative power being put back into the line by the drives.

I would do as Bob says and get a consultant in to look at the whole protection system, especially as drives have been changed for a different type. In the short term that might cost you a few quid, but in the long run it will save money, after all you could be running the risk of dives and generators letting their smoke out.

Take note of Paul Lucas as he is very experienced here.

Thanks for the praise Bob, but I beg to differ on that, I know enough to get by in my present job.

Paul

 

[catalin78]

Ok , but how can you read the regenerative power? the drives here supply the total amount of power used on the motor .

 

[BobB]

Thanks for the praise Bob, but I beg to differ on that, I know enough to get by in my present job.

Paul, you know a heck of a lot more about this subject than most of us. You have been working with cranes for a long time and I am a great believer in "gut feel" from seeing things happen over a period of time.

Ok , but how can you read the regenerative power?

Our company installed a system some years ago that was designed by an engineer (no offence meant here Peter Nachtway) who, quite frankly, did not have a clue. The system was to prevent problems to generators when the lifts in the buildings were regenerative braking. The theory was that we put in a power factor correction controller that was set on a very "short fuse". The controller was to quickly switch in capacitors to "up" the power factor and make the generators happy (not overheat the alternators). The system actually worked very well when the engineer re-calculated all the values and increased the capacitor bank to a working level. The controller actually "measured" the power factor in th same way as utilised by power factor correction controllers. The BIG difference was that normally power factor shifts slowly - with lifts coming on and off regenerative braking, the power factor shifts extremely quickly and standard controllers are not built for very fast shifts in power factor.

When the engineer got his act together and we were able to find a controller that would work very quickly, the system worked very well and we had "happy" generators.