Reverse Power

I worked in power stations for many years but I do not recognise the term "Reverse Power".

Are you talking about the anti-motoring protection for the generator?

If your main generator trips then it should also trip the outgoing transmission Circuit Breaker which will disconnect the generator from the surge load. Do you have a separate incoming line from the distribution network to provide station auxiliaries supplies or is this facility provided by your export line and CB.

Are you saying that you have two station auxiliary standby generators of which one of these also tripped. If it tripped on anti-monitoring then appears that this generator could not reach the required speed for synchronisation or that after synchronisation it could not maintain the shaft speed and was being motored by the other generator. If both the generators are obtaining the require physical conditions, then this points to calibration problem of the synchronisation and anti motoring relays.

We use the same term here (reverse power) or, at least, in the factory where I work. In simple terms, the generator turns into a huge motor instead of a generator so I guess your interpretation is correct.

I don't work in power stations but I occasionally talk to the guys working in there.

What we use Reverse power is anti motoring protection. We use both kw sharing and KVAR sharing also. I have seen generators tripping due to improper sharing and pf going to lead. In some case i heard people disconnection UPS filter to bring back the pf as nearest to .8pf.

Regards,

Hareesha

Hola Ziazia: first of all, you loose your generating station and since the 5 generators where supplying power to the electrical grid they suddlendy went into overspeed and triped. Is not clear if all the units triped or only 3 of them, but from the time you have 2 units supplying power to the station, and since this power is only 1/25 of the power then you have two large generators for a very small load. This is not the problem because you could generate from 0 up to 100%. The real problem is in your governor settings. The speed droop may have a different value from one generator to the other. When you are in an isolated station and you have 2 or more generators running, they will start loading and loosing power from one generator to the other and viceversa, you should hear the units exchanging power at this time and in any moment one of them is going to trip because the reverse power or because can not hold all the load from the other generator. If this is your case you should check your governor settings, if your governors are digital you may solve this problem by changing the speed droop. you may program a speed droop value for isolated station operation. The biggest unit in the station will have a speed droop value of 0.0% and the rest of the smaller units should have any value above cero but it should be identical for all the generators. Remember that the speed droop off line value in the governor may refer to the the speed no load condition (wich is not the same as the isolated station condition).The reason for this is that you have to be ¨on line¨ to generate ( generator brake close) even for station service and at the same time you are not connected to the electrical grid but only to your own station. If your governor is not digital then you will have to change the speed droop manually or consider using the same exact value of speed droop for all the units with the same power output. Usually the old timer governors behave better than the digital governors because they react more sluggish. Hope you find ussefull this information. Our system has two hydroelectric stations, Madden Hydro has three 12 MW units two of them with Woodward digital governors and one with a Woodward mechanical governor ( every time we have a load rejection the digital units trip on overspeed and the unit with the Woodward mechanical governor always stay running on speed no load ). The other station is Gatun Hydro and there we have 3 units of 3 MW and 3 of 5 MW. all with plc governors (most of the time they will trip after a load rejection and subsecuently we lost the station). Regards. Luis

I have worked in powerplants for over 25 years and have seen the results from reverse power.It is simply power coming into a generator rather than going out.If unit is already spinning and matched to the grid and in sync mode then all is fine.If unit is not spinning (and I have seen this happen) and you have reverse power then 200 firefighters show up and put out the fire. Lots of paper work and lawsuits happen.If not in sync mode and the generator reverses power then a relay should trip unit.These relays are required to be tested by an independent company every year.If unit does not trip and generator reverses power but is matched to grid it becomes a motor.A lot of folks think this means unit reverses direction which is not true it just keeps on spinning the same way.

well, explained it very well, but can you please be specific about which type of power flows back to generator, active or reactive ??

reverse power happens when active power flows back into the generator. Reactive can flow into or out of the generator and it wouldn't be considered reverse power.