Generator voltage fluctuation

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ArchieMedes

Member
I have a question about our diesel generator (400kW), the installation's total load normally is about 50kW and we have another load also 50kW which has a switching controller (thyristor cycle controller) which switches the 50kW load at high speed the fastest is 1 cycle for 50 Hz, on and off. We noticed that if this 50kW load is being controlled (switched on and off) by the thyristor, the generator's voltage fluctuates as well. If that load is not used and the load is only lighting or motors, , the generator's is not fluctuating.
My question are:
The generator is obviously over sized but still being affected, why?
Is there any kind of voltage stabilizer / regulator to eliminate the voltage fluctuation of the generator?

Thanks in advance
 

robbietan

Senior Member
Location
Antipolo City
assuming that the thyristor controlled load is a motor, the fluctuations may be the result of inrush current.that being said, thyristors also act like a "short circuit" when conducting electricity, which could also explain the fluctuations.

I would not recommend anything unless the other equipment connected to the generator is affected by the fluctuations. this happens to the power grid everyday and is a normal phenomena due to the varying types of loads being connected/disconnected to the grid
 

ArchieMedes

Member
Thanks Rob. Will it cause a problem to the generator itself? Assuming the generator have to compensate for the voltage fluctuation caused by the very fast switching of the thyristor?
 

Electric-Light

Senior Member
Reality is that on a grid, a load is like a car being towed behind a titanic while on a generator, it's like behind a semi.

It's within capacity, but still large enough to create more than negligible effect.
 

Electric-Light

Senior Member
If it's causing problems, though quite inefficient, one thing you could use is a 1:1 ratio motor generator set. It will completely isolate harmonics from generator power and provides substantial dampening of sudden change in load. Sometimes, they're used in amusement park rides that require very high peak load to prevent sags and flicker problems to other utility customers. Albeit those use over sized flywheels.

If it's a DC load, capacitors can be used, but for AC, as far as I know, there isn't much you can use other than mechanical inertia to serve the purpose of a capacitor.

Sometimes the power source can't accommodate sudden demand placed upon by elevator starting up and prevents the use of static converter which will immediately transfer the demand onto the power source. The mechanical inertia of MG-set cushions it and are still used in such situations.

Take a look at this article:
http://www.mceinc.com/DMS/Article\Tom\static_drives.pdf
 
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