Have anyone known about the crowbar trip which is issued by ex2100e system
It can cause exciter to trip by initiating " 94EX-1 "
I saw this through ex2100e manuals
It prevents high voltage from generator pole slipping
So i have two questions !

(1) What is " pole slipping "?

(2) how " the crowbar trip" happens?
If the voltage exceeds the certain values of voltage, it happens?

I will really appreciate any reply

Please help me

 

I can only answer the first question: What is "pole slipping"?

In a synchronous generator there is a magnetic field associated with the generator rotor (as a result of the excitation applied by the exciter (ex2100e in this case), and when the generator breaker is closed and current is flowing in the stator windings there is a second magnetic field produced as a result of the current flowing in the stator windings. The generator rotor magnetic field is LOCKED INTO the stator magnetic field, meaning that stator can't spin any faster or slower than the speed dictated by the frequency of the current flowing in the stator windings. (For a 50 Hz generator with a two-pole generator rotor, that speed would be 3000 RPM.) This is called the synchronous speed of the machine, and IT DOES VARY with changes in the frequency of the grid the generator is synchronized to (in parallel with).

The torque being applied to the generator rotor by the prime mover (steam turbine; gas turbine; etc.) is actually trying to make the generator rotor spin faster than the machine's synchronous speed--and this results in a twisting motion of the coupling between the prime mover and the generator rotor. This is typically called the torque angle, and it's a way of measuring how much torque is being applied by the prime mover by the generator rotor (BUT most machines do not have a device for measuring torque angle, so it's really just a theoretical value that is talked about and discussed but is never actually measured, but it can be calculated though again it's not generally a parameter that is calculated for operators to see and monitor).

When the excitation is reduced below the amount required to keep the generator rotor locked into the speed dictated by the frequency of the current flowing in the stator windings it is possible for the torque being applied to the generator rotor by the prime mover to cause the generator rotor to become momentarily unlocked from the speed dictated by the frequency of the current flowing in the stator windings. When this happens the rotor spins VERY FAST for a split second and it can be "caught" or locked back into synchronous speed when the two magnetic fields are properly aligned. This causes VERY GREAT MECHANICAL FORCES during the time when the generator rotor is not locked into synchronous speed with the stator windings which can actually result in serious mechanical damage to the coupling between the generator rotor and the prime mover, the generator rotor, and even the prime mover (because the prime mover also experiences a sharp increase in speed when the generator rotor magnetic field is unlocked from the stator winding magnetic field. It is VERY DESTRUCTIVE, and the result is often described as catastophic, meaning it's very difficult to rebuild the machine after it experiences a pole slippage.

I've been told of machines that had a (short) period of speeding up and slowing down as the generator rotor attempts to resynchronize to the stator winding magnetic field--which causes even worse damage.

So it's important that, one, the excitation on the machine NEVER be allowed to drop below the amount that would allow the prime mover to break the generator rotor's magnetic field out of synchronism with the stator winding magnetic field, and two, to immediately trip the machine to protect both the generator and the prime mover if such a condition even approaches the excitation which will cause the poles to slip.

I have never heard of high voltage being produced/generated when pole slippage occurs--but I can imagine it probably would and it would also damage the exciter as well as the generator windings and possibly even the stator windings.

Usually there is a relay or, these days, some software function, that monitors the level of excitation and if it drops below a value calculated to be very close to causing pole slippage that would alarm and trip the machine. This is usually called an 'under-excitation' relay or function.

It might be better if you can describe what is happening at your site. Tell us a little bit about the machine (steam turbine; gas turbine), rating (MW), and what's happening on the grid when you are experiencing problems (frequency instability; low grid voltage; unusual power factor excursions; etc.). If the site uses tap-changing transformers as part of responding to grid frequency changes or requirements, and the taps can be changed under load (when current is flowing through the transformer), are the tap-changers being used when the machine is experiencing problems? It would also tell us when the problem started (from commissioning; just recently; if any work was done on the exciter/switchgear/transformers/grid connection). All of these things are very important to understand your condition, what's happening, and what might be causing the problem.

As for exactly how the ex2100e monitors and detects a condition resulting in a crowbar trip, you would need to ask GE or the packager/supplier of the equipment. If the ex2100e was installed as part of an upgrade to the machine control systems it's very possible the parameters were not set properly and/or need to be reviewed.

That's all I can add based on the information provided.

 

I can only answer the first question: What is "pole slipping"?

In a synchronous generator there is a magnetic field associated with the generator rotor (as a result of the excitation applied by the exciter (ex2100e in this case), and when the generator breaker is closed and current is flowing in the stator windings there is a second magnetic field produced as a result of the current flowing in the stator windings. The generator rotor magnetic field is LOCKED INTO the stator magnetic field, meaning that stator can't spin any faster or slower than the speed dictated by the frequency of the current flowing in the stator windings. (For a 50 Hz generator with a two-pole generator rotor, that speed would be 3000 RPM.) This is called the synchronous speed of the machine, and IT DOES VARY with changes in the frequency of the grid the generator is synchronized to (in parallel with).

The torque being applied to the generator rotor by the prime mover (steam turbine; gas turbine; etc.) is actually trying to make the generator rotor spin faster than the machine's synchronous speed--and this results in a twisting motion of the coupling between the prime mover and the generator rotor. This is typically called the torque angle, and it's a way of measuring how much torque is being applied by the prime mover by the generator rotor (BUT most machines do not have a device for measuring torque angle, so it's really just a theoretical value that is talked about and discussed but is never actually measured, but it can be calculated though again it's not generally a parameter that is calculated for operators to see and monitor).

When the excitation is reduced below the amount required to keep the generator rotor locked into the speed dictated by the frequency of the current flowing in the stator windings it is possible for the torque being applied to the generator rotor by the prime mover to cause the generator rotor to become momentarily unlocked from the speed dictated by the frequency of the current flowing in the stator windings. When this happens the rotor spins VERY FAST for a split second and it can be "caught" or locked back into synchronous speed when the two magnetic fields are properly aligned. This causes VERY GREAT MECHANICAL FORCES during the time when the generator rotor is not locked into synchronous speed with the stator windings which can actually result in serious mechanical damage to the coupling between the generator rotor and the prime mover, the generator rotor, and even the prime mover (because the prime mover also experiences a sharp increase in speed when the generator rotor magnetic field is unlocked from the stator winding magnetic field. It is VERY DESTRUCTIVE, and the result is often described as catastophic, meaning it's very difficult to rebuild the machine after it experiences a pole slippage.

I've been told of machines that had a (short) period of speeding up and slowing down as the generator rotor attempts to resynchronize to the stator winding magnetic field--which causes even worse damage.

So it's important that, one, the excitation on the machine NEVER be allowed to drop below the amount that would allow the prime mover to break the generator rotor's magnetic field out of synchronism with the stator winding magnetic field, and two, to immediately trip the machine to protect both the generator and the prime mover if such a condition even approaches the excitation which will cause the poles to slip.

I have never heard of high voltage being produced/generated when pole slippage occurs--but I can imagine it probably would and it would also damage the exciter as well as the generator windings and possibly even the stator windings.

Usually there is a relay or, these days, some software function, that monitors the level of excitation and if it drops below a value calculated to be very close to causing pole slippage that would alarm and trip the machine. This is usually called an 'under-excitation' relay or function.

It might be better if you can describe what is happening at your site. Tell us a little bit about the machine (steam turbine; gas turbine), rating (MW), and what's happening on the grid when you are experiencing problems (frequency instability; low grid voltage; unusual power factor excursions; etc.). If the site uses tap-changing transformers as part of responding to grid frequency changes or requirements, and the taps can be changed under load (when current is flowing through the transformer), are the tap-changers being used when the machine is experiencing problems? It would also tell us when the problem started (from commissioning; just recently; if any work was done on the exciter/switchgear/transformers/grid connection). All of these things are very important to understand your condition, what's happening, and what might be causing the problem.

As for exactly how the ex2100e monitors and detects a condition resulting in a crowbar trip, you would need to ask GE or the packager/supplier of the equipment. If the ex2100e was installed as part of an upgrade to the machine control systems it's very possible the parameters were not set properly and/or need to be reviewed.

That's all I can add based on the information provided.

Thank

 

Thanks a lot!!

I learned many things from you

I really appreciate you

 

It is pretty amazing when you think about it--mechanical power generation (not so much photovoltaic or battery power) is all about magnetism. The forces of magnetic attraction, and also preventing the forces of magnetic repulsion. It's the forces of magnetic attraction that keep a synchronous machine synchronized to (operating in parallel with) other synchronous generators and their prime movers--operating at synchronous speed. It's another reason why the act of synchronizing one generator and its prime mover to others is so critical and important. It would be great if a large switch could be simply closed to parallel (synchronize) a synchronous generator and its prime mover to others. But, it's also the magnetic forces of attraction that make all generators and their prime movers synchronized together act as if they were all one, single generator and prime mover, producing voltage and current at a stable frequency. The motors at the other end of the wires from the grid (and generators synchronized to the grid) aren't really doing any work by themselves--they are simply converting power (in the form of electricity) back into work. And it's really the prime movers that are doing all the work. The generators convert work (in the form of torque) into electricity (current and voltage) and that power is transmitted and distributed using wires to places where it is converted back into work using motors--which ALSO operate on magnetic principles. Magnets. Very simple. Very powerful. Very amazing.

 

Have anyone known about the crowbar trip which is issued by ex2100e system
It can cause exciter to trip by initiating " 94EX-1 "
I saw this through ex2100e manuals
It prevents high voltage from generator pole slipping
So i have two questions !

(1) What is " pole slipping "?

(2) how " the crowbar trip" happens?
If the voltage exceeds the certain values of voltage, it happens?

I will really appreciate any reply

Please help me