# Thyristor Controlled Heater

D

#### Diaa

what is the recommended solution to prevent the sudden load changes on the generators due to thyristor controlled heater?

J

#### JRaef2

Ramp the power into the heater. Some SCR power controllers don't provide that function, use one that does.

>what is the recommended solution to prevent the sudden load changes on the
> generators due to thyristor controlled heater?

D

#### Diaa

Could you please explain more what do u mean by ramp the power into the heater?

R

#### Roy Matson

> Could you please explain more what do u mean by ramp the power into the heater?

He means don't suddenly turn it on at 100%, start at a low power setting and ramp it up so the generator can keep up.

Heater controls are usually Pulse Duration i.e. the SCRs fire for a portion of a fixed Cycle Time.
For example if the cycle time is 10 seconds
Turning the heater on for 1 second each Cycle time would be 10%
Turning the heater on for 3 second each Cycle time would be 30%

For a generator you might need to go with a shorter cycle time to prevent wide speed fluctuations.

D

#### Diaa

> For a generator you might need to go with a shorter cycle

This is the problem exactly, but it is so hard to implement the solution at zero crossing SCR's

I set the Duty cycle to 0.25 sec and it prevented the voltage flickers but still have speed fluctuations!

S

#### Steve Myres

Maybe divide up the heater into several separate loads firing synchronously but out of phase, to even out the load over time.

Or add some other loads to the generator so it won't see the heater variations as such a big percentage change in load.

Maybe adjust the controller on the generator not to respond so quickly, so it in effect responds to the time-averaged power rather than instantaneous. (assuming the speed variations are due to controller action, rather than the generator simply slowing down under load).

#### PhilCorso

1) Is the generator's prime-mover a combustion engine?

2) What is the combustion-engine's Hp or kW capacity?

3) What is the Generator's capacity, kW?

4) What is the maximum load requirement, kW?

6) Are load-changes ramped over several cycles, seconds, or minutes?

7) Is Thyristor control done manually by a measured variable?

Regards,
Phil Corso

D

#### Diaa

> 1) Is the generator's prime-mover a combustion engine?
the prime mover is gas combustion engine (does it differ if the prime mover is gas turbine? )

> 2) What is the combustion-engine's Hp or kW capacity?
the combustion engine capacity is 1300 kw

> 3) What is the Generator's capacity, kW?
two running generators with capacities of per each 1250 kva

> 4) What is the maximum load requirement, kW?
the maximum load onsite is 900 kw and p.f. 0.93 and the heater full load is 250 kw

> 5) Are load-changes in steps?
the heater load changes instantaneously as follow (0-25-55-79-92-120-155-160-185-220-250-220-185.......0)kw and this cycle takes about 2 seconds at max. Which makes the machine speed to fluctuate.

The SCR is in zero crossing mode and it is derived via PID controller with pband 12 ,int 8 kd 10 and derv 0.015

> 7) Is Thyristor control done manually by a measured variable?
the PID input signal comes from temp transmitter on the heater

#### PhilCorso

Diaa...

Hmmm... CSA hasn't asked yet... but is problem new, or has it existed since commissioning?

If the latter then it's my "guess" that engine/generator has too little inertia.

You said both generators are in parallel at the time! They lose sync when load changes! How much, 20kW, 100kW, 250kW?

What are the changes of electrical parameters of each machine, i.e., V, A, PF, kW, kVA, kVAr and speed, upon load excursion?

Can you obtain the inertia data.

Phil

Ps: If you want to know why I asked the above, search Control.Com archive for "Detroit Engine Problem". You will see a totally different approach.

Diaa...

Phil

#### Frank Fernandez

1) Is the generator's prime-mover a combustion engine?

2) What is the combustion-engine's Hp or kW capacity?

3) What is the Generator's capacity, kW?

4) What is the maximum load requirement, kW?

6) Are load-changes ramped over several cycles, seconds, or minutes?

7) Is Thyristor control done manually by a measured variable?

Regards,
Phil Corso
I have the same issue on a 125KW generator running a 70KW heater controlled by SCR using phase angle control, not zero crossing. At 35KW load (50% load) the generator reaction id OK, but when heater load is increased the generator cannot maintain 480V consistently. The other loads are chiller and it's auxiliary loads of about 40KW

#### PhilCorso

Frank...
So, machine is handling about 35 kW heater load, plus 40 kW chiller and other load and all's OK. Problem starts when heater load increased !
1) How old is unit?
2) What do you mean by "cannot maintain 480 V"?
3) Is voltage fluctuating?
3) Does Engine speed change?
4) Any noises in Engine or Generator?
5) When was genset's last maintenance carried out?
Regards, Phil Corso