How is generator manually synchronized onto a live bus.

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yawadu,

>How is generator manually synchronized onto a live bus.

Nothing like a simple question.

Prior to synchronization, the generator needs to be at or very near rated speed, because speed and frequency of the generator output are directly related.

Prior to synchronization, the generator terminal voltage needs to be at or very near rated voltage (which should be approximately equal to nominal grid voltage).

The generator breaker needs to be in the racked-in position with the primary and secondary disconnects made up (connected) and ready to synchronize.

All lock-out relays must be in the reset position.

There should be a switch or handle on the generator control board/panel to select MANUAL or AUTOMATIC synchronization, and MANUAL synchronization needs to be selected.

The operator then needs to manually adjust the prime mover speed (which adjusts the generator speed and frequency) to make the generator frequency just slightly greater than the frequency of the grid the generator is being synchronized to. Usually, there is a a scope with a moving needle called a synchroscope which is used during synchronization. When the needle is rotating in the clockwise direction, the frequency of the generator is faster than the frequency of the grid the generator is being synchronized to; the faster the needle is rotating the higher the generator frequency is with respect to grid frequency. When the needle is rotating in the anti-clockwise direction, the frequency of the generator is slower than the frequency of the grid the generator is being synchronized to; the faster the needle is rotating in the anti-clockwise direction the slower the generator frequency is with respect to the grid frequency. The general rule is that immediately prior to synchronization the synchroscope needle should be rotating in the clockwise direction at the rate of one rotation every five or six seconds. It could be a little slower, or it could be a little faster, but it should be rotating "slowly" in the clockwise direction during manual (or even automatic synchronization).

Then the operator uses the AVR (Automatic Voltage Regulator) adjust switch to make the generator terminal voltage equal to or just slightly higher than the voltage of the grid the generator is being synchronized to. It could actually be a little lower than grid voltage, but that's not the general rule for synchronizing--it should be equal to or slightly greater than grid voltage.

Then, the operator puts his (or her) hand on the generator breaker close switch handle. Watching the synchroscope needle rotate (slowly in the clockwise direction) the operator waits for the needle to approach the 11 o'clock position (just slightly before 12 o'clock/straight up) and then rotates the generator breaker close switch handle in the CLOSE direction and holds it in the CLOSE position for a couple of seconds and releases the handle (it should return to mid-position by spring action). Once the generator breaker is successfully closed, meaning the generator is synchronized to the grid, the synchronization selector switch should be placed back in the OFF position.

In the "background" there should be a synchronizing check relay which is monitoring the frequency of the generator and the frequency of the grid the generator is being synchronized to--and newer, more modern synch check relays monitor BOTH frequency and voltage of both the generator and the grid. The synchronizing check relay WILL NOT allow the operator to close the generator breaker with the generator breaker close switch handle if the frequency and phase angle of the generator and grid are not within allowable limits. This is to prevent damage to the generator breaker, the generator, the coupling between the generator and the prime mover, and the grid by closing the generator breaker out of phase with the grid voltage sine waves.

Now, why do we do all these things? First, it is CRITICAL that the generator voltage sine waves be properly matched (in phase) with the grid frequency voltage sine waves (most synchronous generators are three-phase generators). If the sine waves of the phases of the generator are NOT "aligned" or very nearly aligned with the sine waves of the phases of the grid, then VERY GREAT mechanical forces--and electrical forces, too--can result which can cause mechanical and electrical damage to BOTH the generator and it's prime mover, and the grid components also. When the synchroscope needle is pointing at 12 o-clock (straight up--vertical) this means the phases are perfectly in alignment. "So," you ask, "you said to close the breaker BEFORE the synch scope needle reached 12 o'clock/straight up--which means the sine waves are NOT exactly in phase (aligned)?!?! WHY??!!?!" Because, the breaker has some mechanical linkages in the operating mechanism which take some time to actually operate and close the generator breaker contacts. So, we send the command to close the breaker slightly ahead of the 12 o'clock/straight up needle position so that when the breaker's main contact do close they will be as close as possible to in phase and aligned.

Why does the operator adjust the generator terminal voltage to be equal to or slightly greater than the grid voltage? Because, if the generator terminal voltage is equal to the grid voltage when the generator breaker closes there will be zero VAr (Volt-Ampere Reactive) current flow across the generator breaker between the generator and the grid. When the generator terminal voltage is slightly greater than the grid voltage when the generator breaker closes there will be a slight amount of VAr current flowing out of the generator breaker and to the grid--which is okay. Most generators are designed to produce reactive current and supply reactive current to the grid. And, a small amount of "positive" reactive current during synchronization and initial loading is desirable. As opposed to "negative" reactive current (VArs) flowing into the generator from the grid if the generator terminal voltage is less than the grid voltage when the generator breaker is closed. There are protective relays monitoring the generator which may open the generator breaker if the magnitude of VAr current flowing into the generator is "excessive" at the time the generator breaker is closed during synchronization. So, it's desirable to have a small amount of VAr (reactive) current flowing out of the generator at the time of synchronization, to prevent a possible breaker trip.

Finally, by having the synchroscope rotate in the clockwise direction, the operator is making the generator frequency be just slightly higher than the grid frequency. This means that the prime mover is producing slightly more torque than is required to keep the generator spinning at the exact speed (frequency) of the grid. When the generator breaker closes during synchronization the generator rotor is "captured" by the grid and slows down <i>immediately</i> to match grid frequency. BUT, the prime mover governor still maintains that slight extra energy flow-rate into the prime mover. This cause the Watts (or kW or MW) being produced by the generator to increase to some positive level flowing out of the generator at the time of synchronization.

If the synchroscope was rotating slowly in the anti-clockwise direction when the generator breaker was closed, that means the generator frequency is less than grid frequency and the prime mover is not producing enough torque to keep the generator spinning at the same frequency as the grid. When the generator breaker is closed with the prime mover not producing the required power to keep the generator spinning at grid frequency the grid will still "capture" the generator rotor and will speed up the generator rotor to make it match grid frequency--and to do that will require that power from the grid (Watts, kW, MW) will be flowing from the grid into the generator to keep the generator rotor (and the prime mover!) spinning at grid frequency/speed. This is called "reverse power", and most generators can tolerate reverse power--but some prime movers (like steam turbines and reciprocating engines) can NOT tolerate reverse power. So, there is at least one reverse power protective relay monitoring the direction of real power (Watts, kW, MW) into and out of the generator to protect the prime mover and generator against the effects of reverse power. By having the generator rotor spinning a little faster than grid frequency when the generator breaker is close during synchronization that ensures that no reverse power will flow into the generator from the grid, possibly opening the generator breaker.

Most, but not all, automatic synchronization relays/schemes do exactly the same as above--adjust generator frequency and phase angle and voltage (sometimes called "speed matching" and "voltage matching") when synchronizing; some only match frequency and phase angle. Prior to the first synchronization of any generator, it is critical to verify the three phases of the generator output are matched to the grid phases, and that all of the metering signals (from PTs (Potential Transformers) and CTs (Current Transformers)) are all providing the proper signals in the proper directions. And, any time those metering circuits are disturbed during any kind of maintenance or upgrade they should be re-checked as they are critical to proper synchronization and unit (and personnel!) protection.

Hope this helps! Synchronization is VERY CRITICAL to the proper operation of a power plant. Done improperly, it can have disastrous and deadly effects. That's why, as was noted above, there is almost always a synchronizing check relay in the manual synchronization generator breaker close circuit to prevent an operator from unintentionally closing the generator breaker when the phases are not aligned--which can cause the most damage to equipment (and personnel if they are too close!).

 

A running Synchronous generator can be manually synchronized to the grid bus by a three-phase circuit breaker just in the condition that the four main and necessary conditions of paralleling the generator with the grid are all certainly obtained. Checking that the condition of having same phase sequence and no un-accepted difference in the voltage and frequency values on both side of this circuit breaker have all been achieved then the moment of closing this circuit breaker would just be when the voltages of same phases on both sides of any one of the three arms of the circuit breaker have zero phase difference angle or very low accepted phase difference angle. This last condition can be checked using the dark lamp method or the synchroscope.

 

Lin Chong,

You mention "... the four main and necessary conditions of paralleling the generator with the grid ..."

Can you please list and describe these four main and necessary conditions? (I believe you have, but you didn't say 'Condition 1' and then 'Condition 2' and ....

The original poster's question was: "How is generator manually synchronized onto a live bus." (Well; it didn't have a question mark, but it was a question.) My interpretation was that he was more or less asking for a procedure, and I offered the procedure and some explanation of the reasons for each step of the procedure.

And, lastly, can you describe how the first condition is satisfied (of your four conditions)?

Thanks!

 

Is it possible to operate a synchronous panel generator (automatic) with manual operation?

 

Can you be more specific about what a "...synchronous panel generator..." is? What is the prime mover of the generator--reciprocating engine, turbine, ??? What is the nameplate rating of the generator set (prime mover and generator)--5 KW, 500 kW, 5 MW, 50 MW, larger?

What are you trying to do by controlling the generator manually? Control speed/frequency? (Because that's possible if you want to maintain a fairly constant generator output frequency.) Are you trying to control the amount of power the generator is producing? Because if the generator is operating independently of any other generator and prime mover (or multiple generators and prime movers) that's not possible while maintaining a fairly constant frequency--the total amount of load(s) connected to and being powered by the generator set determines the amount of power the generator is producing. (If you want the generator to produce more power, you need to connect more load; if you want the generator to produce less power, you need to disconnect some load--but it's not possible to control the amount of power a single generator (synchronous or otherwise) is supplying to one or more loads AND maintain constant generator output frequency.

Is the generator output frequency not stable and not very constant? Is(Are) the load(s) connected to the generator exceeding the generator set's rating? Are the loads constantly starting and stopping? What load(s) are connected to the generator?

Do you know what kind of excitation system the generator has? (If it's NOT possible to change the prime mover speed or the generator voltage, then the easiest answer to your question is: No; it's not possible to operate a "...synchronous panel generator..." manually. You just start it, let it get to rated speed, and connect the load(s) (power tools; lights; fans; etc.) and the generator set (prime mover governor and excitation control) will do it's job as long as the total amount of load doesn't exceed the rating of the generator set.)

Do you have a picture or a data sheet or a manufacturer's name and model number for the "...synchronous panel generator..." you are referring to that you can attach to this thread?

If you can provide more information it's very likely we can provide an answer--but we may ask more questions.... That's why it's important to include as much information as possible in your original post to get the fastest and most concise answer.

 

sorry.. I mean, if we have 2 diesel generators, they operate automatically by Synchronous Panel. Unfortunately, the diesel generator shut down before reaching the nominal speed and before synchronizing with another diesel generator. So, I think I will operate both diesel generators (parallel operation) manually. Am I wrong?

 

It seems you are somewhat new to AC (Alternating Current) power generation and haven’t internalized the basics quite yet. Operating two synchronous generator sets in parallel with each other (synchronized together—synchronized is a very important concept) means the two gen-sets will operate at the same frequency (and at the same speed if the two generators have the same number of electromagnetic poles). If the two synchronized gen-sets will be operated “manually” (I’m presuming that means both diesel governors will be in Droop Speed Control mode) the human operator will need to be very familiar with the loads the system provides power to and respond quickly and accordingly in order to maintain the proper system frequency. And that means training and experience and familiarity are all very important.

However, the REAL problem seems to be why one diesel-generator set shut down before reaching rated speed. The diesel governor (control system) should have annunciated one or more alarms to alert the human operator why the machine was shut down—and THAT is what needs to be investigated and resolved, so the machine can be operated automatically by the synchronous panel.

It is presumed the synchronous panel is some kind of control system that automatically adjust loads on the two machines in order to maintain system frequency with little human attention. But, that’s a presumption because we don’t know enough about the synchronizing panel and the system where you are working to be able to provide any more information.

Best of luck!