R
Is it common practice to have a steam turbine generator breaker trip signal initiated in the event of a steam turbine trip (instead of letting reverse power take out the GB)?
The practice of whether or not to trip the steam turbine generator breaker in the event of a steam turbine trip event is probably dependent on the manufacturer's design philosophy, or the plant designers, or even local technical regulations and/or standards.
I've seen it done both ways, by the same steam turbine manufacturer. When asked, it was told that the plant designer had specified a generator breaker trip on steam turbine trip, not relying on reverse power.
And, I've also seen redundant reverse power relays used on some steam turbines, just because it's so critical to make sure the breaker opens on reverse power.
So, it would seem to be a design philosophy issue or a design requirement. But common practice? I don't know about that.
I've seen it done both ways, by the same steam turbine manufacturer. When asked, it was told that the plant designer had specified a generator breaker trip on steam turbine trip, not relying on reverse power.
And, I've also seen redundant reverse power relays used on some steam turbines, just because it's so critical to make sure the breaker opens on reverse power.
So, it would seem to be a design philosophy issue or a design requirement. But common practice? I don't know about that.
RCook... I agree with CSA. Development of the Tripping Logic Scheme is usually a collaborative effort by the facility owner's rep, the facility design engineer, and equipment manufacturers.
However, in those plants I was involved with reverse-power was interlocked wth tripping parameters that could be delayed. Following are examples of trips that could tolerate delay:
o E-stops.
o LoE.
o LO Level & Temp.
o Low Vacuum (Stm plants).
o Transformer Temp.
Regards, Phil Corso
However, in those plants I was involved with reverse-power was interlocked wth tripping parameters that could be delayed. Following are examples of trips that could tolerate delay:
o E-stops.
o LoE.
o LO Level & Temp.
o Low Vacuum (Stm plants).
o Transformer Temp.
Regards, Phil Corso
J
jojo
Apart from the valid comments mentioned above, one needs to check where the emergency steam shut off valve(s) are located with respect to the steam turbine. There are cases where there is enough volume of high pressure steam between the emergency shut off valve(s) and the steam turbine to send the steam turbine in overspeed if the generator circuit breaker is opened at the same time as the trip of the steam turbine. Reason, until that steam is exhausted it still provides motive power, which if not dissipated anywhere will overspeed the steam turbine. In such cases the trip of the generator circuit breaker is delayed. It is up to the designer of the steam turbine to decide this.
R
rcook
Would it be typical (or prudent) to have have a backup trip in the event reverse power did not trip the steam turbine generator breaker?
Again, you're in the realm of design philosophy and/or design requirement. Would it be reasonable to expect the steam turbine manufacturer or packager to include a back-up to the reverse power relay? Sure, it's reasonable, maybe even prudent. But, the designers may have had constraints or considerations that you might never know about. Have you contacted the turbine manufacturer or packager of the turbine-generator about this issue?
Sometimes the instruction manuals provided with a plant have papers that outline the design philosophies and desired operational characteristics used in the design and construction of the plant. Have you looked there?
Many turbines I've worked on have had two (redundant) reverse power tripping schemes, some involving two independent relays set slightly different (time delay settings usually, or even magnitude). Some large steam turbines can't even be run down to reverse power; I know of one 600 MW unit that must be tripped below 200 MW because there isn't enough steam flow to cool the back end of the unit and there is condensation in the middle stages below 200 MW. This unit had triple redundant reverse power relays, plus an emergency back-up relay to them.
Again, I say it's a manufacturer- or packager design philosophy, along with a plant designer philosophy, along with any local technical regulations and standards. Typical, and prudent, being in the eyes of the beholder.
Look, it's been said many times before on control.com: Once you own the machine and it's not covered under any warranty or by any service agreement you are free to monitor, control and operate the unit any way you see fit. If you want to add more protection, I don't think anyone, including the insurance company agreeing to cover the unit, will complain about that. If you want to operate the unit outside it's rated limits, well, if you're self-insured or have informed the appropriate parties of your intention(s) and the basis for your belief that it's necessary and/or won't result in extensive damage or failure (or worse!), you're free to do so.
You just have to have the strength of your convictions to accept responsibility for any consequences, intended or unintended. Including the liability that comes along with making any changes.
So, if you and your management and the turbine's insurer agree it would not be harmful to add this protection, and the risk analysis is favorable (and isn't that what this is ultimately all about, anyway: risk management--isn't that why we all get paid the Big Bucks?!), then have at it!
But, let's step back for a minute and examine what happens if the steam turbine-generator breaker doesn't open on a steam turbine trip (for whatever reason, not just because the reverse power relay(s) didn't operate). The steam turbine is going to be spun by the generator, acting as a motor. Is this bad? Yes. Are there alarms to alert the operator (that human being slumping in the high-backed chair with the processed food in his hand or on the desk within reach that occasionally looks over at the "board") to tell him (or her) the generator breaker has not opened on a steam turbine trip?
Will the turbine be damaged in this case? Likely if the condition persists for too long. How long? Only the steam turbine manufacturer can say for certain.
We don't know how "young" your steam turbine is. It's not likely that many units more than about 10 years old were configured after some kind of statistical or quantitative review of safety considerations. More likely, they were configured "The way we've always done it!"
Newer units may have undergone intensive risk analysis and review (to keep the legal beagles at bay, primarily; or to keep protectionism alive (yes; I said it)), or they may not have.
Again, if you and your management feel this is a serious risk that should be mitigated by the addition of another trip signal in the generator breaker trip circuit, and there's no warranty or other contractual agreement preventing you from modifying the circuit, have at it!
More power to you! (No pun intended.)
(Okay; some pun intended.)
Sometimes the instruction manuals provided with a plant have papers that outline the design philosophies and desired operational characteristics used in the design and construction of the plant. Have you looked there?
Many turbines I've worked on have had two (redundant) reverse power tripping schemes, some involving two independent relays set slightly different (time delay settings usually, or even magnitude). Some large steam turbines can't even be run down to reverse power; I know of one 600 MW unit that must be tripped below 200 MW because there isn't enough steam flow to cool the back end of the unit and there is condensation in the middle stages below 200 MW. This unit had triple redundant reverse power relays, plus an emergency back-up relay to them.
Again, I say it's a manufacturer- or packager design philosophy, along with a plant designer philosophy, along with any local technical regulations and standards. Typical, and prudent, being in the eyes of the beholder.
Look, it's been said many times before on control.com: Once you own the machine and it's not covered under any warranty or by any service agreement you are free to monitor, control and operate the unit any way you see fit. If you want to add more protection, I don't think anyone, including the insurance company agreeing to cover the unit, will complain about that. If you want to operate the unit outside it's rated limits, well, if you're self-insured or have informed the appropriate parties of your intention(s) and the basis for your belief that it's necessary and/or won't result in extensive damage or failure (or worse!), you're free to do so.
You just have to have the strength of your convictions to accept responsibility for any consequences, intended or unintended. Including the liability that comes along with making any changes.
So, if you and your management and the turbine's insurer agree it would not be harmful to add this protection, and the risk analysis is favorable (and isn't that what this is ultimately all about, anyway: risk management--isn't that why we all get paid the Big Bucks?!), then have at it!
But, let's step back for a minute and examine what happens if the steam turbine-generator breaker doesn't open on a steam turbine trip (for whatever reason, not just because the reverse power relay(s) didn't operate). The steam turbine is going to be spun by the generator, acting as a motor. Is this bad? Yes. Are there alarms to alert the operator (that human being slumping in the high-backed chair with the processed food in his hand or on the desk within reach that occasionally looks over at the "board") to tell him (or her) the generator breaker has not opened on a steam turbine trip?
Will the turbine be damaged in this case? Likely if the condition persists for too long. How long? Only the steam turbine manufacturer can say for certain.
We don't know how "young" your steam turbine is. It's not likely that many units more than about 10 years old were configured after some kind of statistical or quantitative review of safety considerations. More likely, they were configured "The way we've always done it!"
Newer units may have undergone intensive risk analysis and review (to keep the legal beagles at bay, primarily; or to keep protectionism alive (yes; I said it)), or they may not have.
Again, if you and your management feel this is a serious risk that should be mitigated by the addition of another trip signal in the generator breaker trip circuit, and there's no warranty or other contractual agreement preventing you from modifying the circuit, have at it!
More power to you! (No pun intended.)
(Okay; some pun intended.)
As a backup, I would put a time delay (maybe 10 seconds - check with the turbine supplier) on feedback that the steam turbine stop valves have closed and there has been a trip command and use that to trip the turbine in the event that the reverse power relay failed to operate. You don't want the generator motoring the steam turbine with the steam valves closed for very long - you can overheat the last stage buckets!
S
santosh singh
It is not required to trip turbine when Generator breaker trip. if generator breaker trip on certain protection like high winding temp, differential, earth fault, Brg temp or other protection of generator lead to mechanical failure then it is required to trip turbine.
M
marvalar
Just a question regarding this last point. If the generator trips and no corrective action takes places, the turbine will overspeed, right?
Thank you
Thank you
If by 'no corrective action' you mean that the control system does not reduce the steam flow or energy input to the prime mover when the generator breaker trips, then, yes; it's very likely the prime mover will trip on overspeed. When connected to a load and producing power the energy input to the prime mover is more than is required to keep the unit (prime mover and generator) spinning at synchronous frequency. If the load is suddenly removed from the prime mover by opening the generator breaker and nothing is done to reduce the energy input to the prime mover, the prime mover will likely overspeed.
Energy input to a prime mover is converted to torque. The generator converts the torque to amps when connected to a load. On an AC system that is properly regulated the speed is fixed so any increase in torque results in an increase in amps, not speed. When the load suddenly "disappears" if nothing is done to reduce the amount of torque being input to the prime mover driving the generator then the energy/torque will result in increased speed, and likely overspeed.
Energy input to a prime mover is converted to torque. The generator converts the torque to amps when connected to a load. On an AC system that is properly regulated the speed is fixed so any increase in torque results in an increase in amps, not speed. When the load suddenly "disappears" if nothing is done to reduce the amount of torque being input to the prime mover driving the generator then the energy/torque will result in increased speed, and likely overspeed.
Marvalar... the decision to trip the CB and not the turbine should be based on severity assigned the generator-fault.
For a trip of relatively minor consequence, i.e., earth-fault, then enable CB tripping via reverse-power. Conversely, if the fault is over-current, then the CB is tripped directly.
Regards, Phil Corso
For a trip of relatively minor consequence, i.e., earth-fault, then enable CB tripping via reverse-power. Conversely, if the fault is over-current, then the CB is tripped directly.
Regards, Phil Corso
M
marvalar
Hey guys, thanks a lot for your help.
My system it's a little bit different. It's an hydraulic turbine on a process unit, recovering some power as electricity. Nevertheless, I think the same principles apply.
My root cause here is the CB trip, and I was interested in the system natural response.
CSA - it is expected to have the control system reacting quickly enough to prevent overspeed in this event?
Thanks a lot, once again
My system it's a little bit different. It's an hydraulic turbine on a process unit, recovering some power as electricity. Nevertheless, I think the same principles apply.
My root cause here is the CB trip, and I was interested in the system natural response.
CSA - it is expected to have the control system reacting quickly enough to prevent overspeed in this event?
Thanks a lot, once again
