Energy Recovery Turbines (ERT)

[buddy91082]

Anyone have experience with the electrical operation of operating these in parallel to serve pumps. The turbines are about 2000kw each and the pumps they will operate are at 1500HP each.

I assume the turbines will operate similar to disel engine generators in parallel.

Thanks.

 

[buddy91082]

Would I also need external excitation for the generator part of the turbine? I assume i do not. The turbines will operate via water pressure.

 

[davidbeach]

What kind of electrical machine? Synchronous or induction?

 

[buddy91082]

synchronous. I guess my real question is, does anyone have experience with hydroelecric turbines operating pumps and is there a problem with starting the pumps across the line versus using vfds with the turbines?

 

[rasevskii]

Your questions need more information.

1. Is this an existing or planned (non-existing) installation?

2. What are the ratings of the hydro units /voltage/excitation type/ turbine type/ governors or not/head/ flow...

3. Parallel with a utility or islanded?

4. Pumps: Horizontal, started DOL with pump dewatered, or what..

It would seem unlikely that you could start such large pumps DOL with such small hydro units unless paralled with a utility source. You said VFD. Maybe you meant soft start.

It would seem that this is something in the planning stage.

Others invited to comment here.

regards, rasevskii

 

[Kiribanda]

buddy91082,

Basically it is a type of energy conservation method similar to wind turbines.
High Pressure Recovery Turbines (HPRT) are very common in petrochemical industry where a large induction motor is in between a pump and a turbine.At the start,the ind motor is driving the pump.After sometime, when the plant is settled there is a liquid head freely available through the turbine and by using a clutch arrangement now the motor is coupled to the turbine at a certain speed which is above the syn speed.As a result,now the induction motor is running as a simple induction generator thereby transferring active power (MW) to the network.

Unfortunately I donot have actual numbers with me at this momement.

 

[rcw retired EE]

The energy recovery turbines I've seen are all induction machines. They have to be connected to the grid to function. A synchronous machine could be applied, but more exotic governors, exciters and control valves are needed.

Is this really a stand alone, islanded system? Or is it connected to the utility grid?

As others stated, there will be problems running a 1500 HP motor on a VFD with a 2 MW turbine. The harmonic currents alone will create issues with the generator unless the unit is a special design to handle the extra heating.

 

[buddy91082]

The ERT we are using is a synchrounous type with a PMG for self excitation on the generator side.

I am not understanding why the ERTs need to be connected to the grid to operate.

Good point about harmonics from VFDs

 

[davidbeach]

Induction machines have to be tied to the grid; synchronous don't.

 

[rasevskii]

OK so your ERT is not on the grid, that is, it is an island system? How about a one line diagram. You likely cannot start or run these large motors as said by others, unless there is a grid tie-in. But not absolutely impossible. Is there more than one ERT, or will be?

To help we need more information about the existing setup, and what you intend to do or add onto the existing. Is there a tie with the utility or not... What kind of plant is this..for example a paper mill..in an isolated location with a weak tie to a grid?

There are many VFD and soft start experts on this forum available, I am not one of them, but they are waiting as ever for more adventures...

regards, rasevskii

 

[waross]

If these are one on one with the pumps, you may get lucky.
An undersized diesel generator may often start a motor that rules of thumb and sizing programs say that it can't.
If the turbines are 2000 kW that would be 2500 KVA.
The 1500 HP pumps will be about 1250 KVA with allowances for efficiency.
That meets some rules of thumb for starting a motor with no other load on the system.
When the pump motor is connected to the turbine generator, the load will most likely pull the frequency down. (If it doesn't pull the frequency down you have no worries.)
Assuming 60 Hz, when the frequency drops below 58 Hz the Under Frequency Roll Off feature of the Automatic Voltage Regulator will drop the voltage in proportion. This drops the load on the turbine and assists it it recovering speed. The voltage drop with frequency gives the motor a friendly Volts per Hertz ratio and avoids saturating the motor.
It sounds as if your turbines are well matched to your pump motors.
I expect that the system will work well. In any event please let us know how it works out when it goes into service.

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