Fluctuation in active power cause turbine set shutdown

[Emadshaaban1987]

hello
can you please help diagnostic the issue :
our platform running by 3 generators each sized 6.6kv 11kva ,2 running and one in standby controlled by load sharing system .
the normal power demand is about 6400kw , the load in 0.4kv level contains high power heaters that consume 1000kw per each (two heater units)and driven by VFC, the power consumption of each heating unit is in-stable it fluctuated by 300kw per less than second ,current harmonic 11 THD.
time to time a fluctuation in power between the two turbines cause nuisance shutdown .
for instance last shutdown :
1-Before shutdown unbalance occurred in power load suddenly increase in Turbine A from 3,478MW up to 5,116MW, and after decrease back to 3.478MW then increased again to 4.876MW see below photos with trends(the power load is the red line on trend):
2-After one second the power suddenly decreases in Turbine B from 3,272MW up to 2,316MW, to compensate load sharing see below photos with trends:
please see the trend of both :
TG-A:

https://files.engineering.com/getfile.aspx?folder=5b818d85-c0d2-43b8-998c-5b3ce48531ee&file=tg_a.jpg

TG-B

https://files.engineering.com/getfile.aspx?folder=13412fae-2cff-4b56-ab81-82299563b671&file=tg_b.jpg

[/indent
note the reactive power for each turbin was totally shared the same : TG-A 1550 KVAR ,TG-B 1250KVAR

 

[waross]

I think that you should be looking at the controls of the heaters rather than the turbines.
That sudden load fluctuation is not good for a generator or a prime mover.
Anecdote warning:
In a remote construction camp, building a world class mine mill, the construction power was supplied by diesel generators until the 140 kV power line was constructed.
Things went well for months and them a diesel generator lost its engine bearings. (I'm not sure if it was mains, rods or both.)
A replacement generator lost its bearings a short time later.
I am not sure how many engines they went through but at least two.
The problem? Electric heating.
The office complex had been completed, complete with proportional control electric heating.
Zero point switching, so many cycles on, so many cycles off.
A substantial load was hitting the engines every few cycles.
It was hammering out the bearings.
The sophisticated controls were replaced with ON/OFF thermostats and there was no more problems.

I suspect that you should be looking at the load and the associated load controls.
Fix the cause, not the symptoms.

Bill
--------------------
"Why not the best?"
Jimmy Carter