reverse power in powerplants

Reverse power CR4 threads.

Regards JD.

Yes it will turn all the steam back into water, and all the smoke and fire back into coal. It's very bad.

That's a possibility!!!

Don't you think it will be very bad good ?

This solves the Green House Gas problems?

(May be as a bonus it collects more SOx and NOx than it originally were there?)

But the OP means (probably) that when power is fed from the grid to the motor (I don't think it is the reverse phasor, rather the reverse power flow)

On this, there are a few threads, with one even a day or two old.

As far as steam inputs and other steam lines do not obstruct, it is OK, since this acts now in a motor mode.

But if you want a reverse rotatiion, nothing is OK, The turbine blades aerofoils are not designed for bidirectional movement and unfortunately it will not work as a compressor, rather like a self disintegrator (or a potentioal suicidee)

Assuming we are talking about AC, possibly 3 phase (you missed vital information for a proper answer), there should be a small bit of electronics that simply drops the generator off line.

If that is missing, broken or slow acting, you may see one of the generators "take a walk"......its not a pretty sight....and you don't want to be anywhere nearby when it happens.....its DEADLY boring!!

In Reverse Power action, Generator will draw power from Grid or other Generators running in parallel. There will be motoring action on turbine. It may go up to the rating of Generator MW. This will increase load on other sources & they may trip on over load.

With motoring action, Steam will be trapped inside the turbine & heavy hammering may occur, which can damage trubine blades.

This is very dangerouse setuation. that is why, Low Forward Power Relay is being used as first action & reverse Power relay is also used as back up protection for turbine & complete system.

From the strictly point of view of a generator, the sequence of the phases will be reversed ( A,C,B instead of A,B,C) . This does not allow the generator to be run in parallel with the grid. To be able to connect it, you have to swap 2 terminals to change to the right phase sequence (A,B,C). So from its point of view it is not a reverse power situation (Power flows from generator to load, but its parameters are different)

From the point of view of the driving machine (Diesel, turbine, etc) it is not possible.

??????

Andy,

The initial term "rotates with reverse power" is more than ambiguous. I interpreted it as with a different rotation direction (CCW vs CW).

If it was used in the sense of power flow - generating power vs consuming power (generator vs motor), the generator part is OK since each electrical machine is reversible. The other parts ( turbine, etc) are not.

The statement about the generator is based on how a generator works and not on different protection/safety devices normally attached to a generator, installed to prevent it from going into a motor run, overload, etc

When two alternators are running in parallel, say each takes 50% of the load (the complete load is far less than either alternator can supply) for starters, and you reduce the power to one alternator slowly. The load it takes is reduced, the load is shifted onto the other alternator, assuming it has an AVR....

If you shift MORE that 50%, then the online generator will attempt to drive the unloaded generator "IN THE SAME DIRECTION BUT FASTER THAN IT IS AT THIS TIME". This needs power, reverse power. Whz reverse, because normallz the power comes OUT of an alternator, now its just a big motor TAKING power IN.....

The Reverse power does NOT reverse the direction that the alternator is turning.....

Are you OK with that now?

Nobody said that when you switch from generator to motor mode the machine changes its rotation direction.

Why the 50% load shift ? If a machine runs as a generator or as a motor depends in the end of the losses to be covered. You put in the machine more power than covering the losses, it runs as a generator, you put less, it runs as a motor.

With regard to the turning speed, the speed is the same if we are talking about synchronous machines.

If you turn the speed governor down on on an alternator that is running in parallel with another, the speed does not change, but the load shifts to the other alternator, provided the other alternator has AVR installed and is in operation.

Actually it happens even if AVR is not switched on, but then some speed loss and voltage loss is to be expected.....

All a speed governor does is to control the amount of energy, steam or diesel fuel depending upon the type of prime mover, less energy = less load.

If you have not been trained or had first hand personal experioence of this, it may not appear to make complete sense......but for those with such experience and knowledge, its just "business as usual!"

Reverse power operation implies a turbine/generator connected to a grid. If the turbine trips for whatever reason, usually the generator should also trip. If for some reason this doesn't happen, and the generator stays connected to the grid, then it will continue to rotate at the same speed, but will take power from the grid, and will operate as a motor.

The effect on the turbine can be more severe than the effect on the gen, as the blades will be rotating at operating speed but without the 'cooling' effect of the steam. This can result in severe overheating of the turbine blades, and possible rub against the casing.

The generator will probably be ok, but may suffer surface heating/arcing damage as a result of the negative phase sequence currents flowing in the surface.

There is usually a reverse power relay which operates to protect the generator/turbine from an event of this nature.

Your worst case scenario we call switch-onto-standstill - when the gen breaker is closed with the unit at standstill. It tries to run up like an induction motor, but generally the surface currents will cause catastrophic failure before it reaches synchronous speed. Not recommended operating practice!