How to convert generator to synchronous condenser 6

[DrDrreeeaaa]

Hi All

Interested in knowing what work is required, in principle, to convert a generator to a synchronous condenser.

I could write alot of possibilities out here that I have been thinking about but it is probably going to muddle the discussion - I will let you much more knowledgeable engineers paint the picture

thankyou

 

[RRaghunath]

Generator is connected to a prime mover to provide active power input, that the generator converts to electrical power.
If prime mover is disconnected and generator is supplied from the grid, the same generator works to provide VARs to the grid, taking small watts from grid) to compensate its friction and windage losses no-load power). This is now Synchronous condenser.

 

[waross]

There are two issues with a conversion.
Supporting the shaft and starting.
Almost all diesel generators are single bearing machines.
If these generators are removed from the engine, there is no bearing on the drive end.
You must fabricate a bearing and an end plate to support the drive end of the rotor.
Many generators may be started as a synchronous motor, the damper winding acting as a squirrel cage winding.
If the generator will not start on the damper winding, it may be started with a VFD.
A much cheaper option is to use a pony motor to spin the machine up to speed and then sync to the grid.
All that remains is to replace a simple AVR with a VAR controller or set a more advanced AVR to VAR control.
That being said, I do know of one very large exception.
Running a diesel engine at light or no load is not generally considered good practice.
The engines have a tendancy to slobber or pump oil out the exhaust, but it can be done.
Case in point:
A city was originally supplied with power from a diesel generator plant.
Hydro power became available and the generator plant was mothballed.
As time passed and the city grew and electric usage per household grew, the capacity of the transmission line was reached.
Transmission line capacity is often limited by the ability of the transformer on-load-tap-changers to compensate for voltage drop in the transmission line.
This voltage drop is usually more reactive than resistive.
Solution:
The diesel plant was taken out of mothballs and put into service as a synchronous capacitor station.
With the VARs being supplied locally the reactive voltage drop was reduced and the capacity of the transmission line was greatly increased.

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

 

[bacon4life]

The main component in allowing units to run in both modes is installing a method to prevent damage and losses in the prime mover:
1) In hydro units, this is accomplished by pressurizing the turbine scroll case with compressed air to lower the tailrace level so that the turbine spins in air. If the unit was not initially designed to allow pressurization, significant work may be required to reduce leakage. Running as a sync condenser with the scroll case filled with water is possible for short durations, but is has very high losses and would lead to cavitation damage.
2) In gas turbines, steam turbines, or diesel motors, a clutch can be added between the electric generator and the prime mover.

Some additional control work is needed to change the startup/shutdown procedure and to enable the unit to automatically switch from sync condense mode to generate mode based on a frequency excursion. Units converted to synchronous condensers may experience a dramatic increase in the number of hours of operation, which in turn drives an increased frequency of maintenance activities.

 

[waross]

In hydro units it may be much easier, safer and cheaper to run the generator at about 5% or 10% kW output and use the balance of the capacity for VAR production.
As to adding clutches to diesel generation units.
That would be expensive and challenging. Remember that the majority of diesel units are single bearing generators.

As to wet stacking or slobbering:
Wet stacking is worse with some brand new sets and with very worn sets.
Many sets will run clean at light load.
I would run at light or no load, just burning enough fuel to keep the engine up to temperature for the sake of proper lubrication.
The OP has not indicated whether he is considering a duel purpose set that may be changed between kW production and VAR production or a permanent conversion to a synchronous condenser.
Some sets may not be suitable for duel use.

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

 

[davidbeach]

As for the hydro units you have to stay out of the rough zone. The output range associated with the rough zone varies based on unit specific conditions including the penstock and tailrace geometries.

 

[waross]

I toured an old hydro plant before it was modernized.
Completely manual control.
One operator on duty.
While I was there one generator was running at 10% load.
The phone rang.
The load dispatch center with an order to go to 90% load.
The gate was controlled by a shaft exiting the turbine housing.
On the end of the shaft there was a large bell-crank.
A hydraulic cylinder was connected to the bell crank.
There was a small enclosed water turbine driving a hydraulic pump.
The operator directed water to the water turbine and then went to a control switch.
Three positions; Extend cylinder, off, retract cylinder.
He started to extend the cylinder while watching the Power Factor Meter.
As the power factor started lagging he went to the field control rheostat and increased the excitation.
No AVR, just a maually controlled rheostat.
Then he went back and continued to open the flow gate.
Back to the field control.
It was a long time ago but as I remember it took 4 or 5 iterations to bring the set up to 90% output.
A few years later the plant was completely automated and was remotely controlled with no local operator on duty.
The powerhouse was once British Columbia's largest hydroelectric power source and is a National Historic Site of Canada.
They don't make 'em like that anymore.
It is now a visitor center with more staff on duty than when it was a working powerhouse
Wiki

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

 

[crshears]

Ontario Hydro constructed numerous hydraulic generators using Francis turbines whose runners, nose cones included, were well above tailrace elevation. The turbines were provided with check-valve-supervised scroll case vent valves; going from generating operation to synchronous condenser operation was a simple matter of unloading the unit most of the way [ partially closing the wicket gates ] via governor speeder gear so as to scoot through THE ROUGH ZONE [ thanks for the memories, davidbeach! ] as quickly as possible, then slowly closing the wicket gates to "pinch" at which point is was no longer passing any water. The draft tube vacuum would be broken by the scroll case vent valves, and the water level in the turbine runner cavity and draft tube would drop down to the prevailing tailrace level, leaving the turbine runner spinning in air and the generator now functioning as a synchronous condenser.

Simple, huh?

The above had the added benefit that if the governor speeder setting was lowered only as much as needed to obtain "pinch" and no more, in the event of the generator becoming part of an undergenerated island due to system disturbance, that generator would, due to frequency decline and without operator intervention, "come out of the hole" to support the island and arrest further frequency decline.

Other units functioned differently and had to be taken out of condense operation manually / by operator intervention.

There were some units that used compressed-air tailrace suppression as bacon4life alluded to; this is an expensive proposition that requires considerable system or economic justification.

 

[waross]

More pics
Here you can see the hand brake to hold the rotor stationary in the event of water leakage when a unit is shut down.
Governors, we don't need no stinkin' governors!
I don't think that these had governors.
Then they would have needed AVRs as well.
The school bus crossed the dam above the power house on the way to school each day.

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

 

[crshears]

Numerous smaller hydro plants owned by Ontario Hydro had been built with governors, but as the system grew to Brobdingnagian scale these little puppies no longer held the frequency-anchoring status they had in times past, and when the governors were worn out they were often replaced with DC motor driven actuators powered with truck batteries; inexpensive, provided secure shutdown capabilities, and didn't take the governor maintenance and adjustment experience that was lost when all the old guys retired.

 

[waross]

We have drifted off topic here a little. If anyone is interested in this aspect of hydro generators there is some more information here.
Hydro Power

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

 

[crshears]

Maybe there's been some topic drift, but the OP hasn't chimed in with further info, either, so who knows if it's off topic or not?

Had experience some years ago running up and operating the uncoupled high and low pressure generators of a pair of tandem cross-compound steam turbines, good for 160 MX once on line...

Talk to us, 123MB!

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[DrDrreeeaaa]

Hello all

I am so sorry I have been offline for AGES - thankyou all sincerely for the time taken to respond to my post - I will digest and respond ASAP.

Sincerely, Michael!