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It has been always observed that while synchronization of GAS TURBINE with Gas Engine, Turbine goes to negative power (kvar)& pf. what are the action to overcome this?
M
M M Ahsan
When generator terminal voltages are equal to the grid or to the other generator(s) it is being synchronized to, then the VAr reading will be zero, and the power factor will be 1.0.
If your generator's terminal voltage is lower than the other generator(s), the VAr reading will increase in the Leading direction and the pf & VAr value will be negative.
If your generator's terminal voltage is greater than the other generator(s), the VAr reading will increase in the Lagging direction and the pf & VAr value will be positive.
Check your generator's terminal voltage before synchronizing and keep it slightly above the grid's or other generator's voltage while synchronizing and your problem should be gone. Further you can increase var/pf ( bring them in to positive / in to lagging direction) using the AVR (Automatic Voltage Regulator) to Raise Volts AFTER synchronization.
Pls provide more information while posting for answers. And don't forget to provide feedback if the comments made by the posters were useful or not. Good luck.
-M M Ahsan
If your generator's terminal voltage is lower than the other generator(s), the VAr reading will increase in the Leading direction and the pf & VAr value will be negative.
If your generator's terminal voltage is greater than the other generator(s), the VAr reading will increase in the Lagging direction and the pf & VAr value will be positive.
Check your generator's terminal voltage before synchronizing and keep it slightly above the grid's or other generator's voltage while synchronizing and your problem should be gone. Further you can increase var/pf ( bring them in to positive / in to lagging direction) using the AVR (Automatic Voltage Regulator) to Raise Volts AFTER synchronization.
Pls provide more information while posting for answers. And don't forget to provide feedback if the comments made by the posters were useful or not. Good luck.
-M M Ahsan
Great response, M M Ahsan.
Just to clarify, "back power" is usually called reverse power. And reverse power is usually referring to watts ("real" power). Reverse power (watts) can be very damaging to a prime mover.
The originator seems to be referring to reactive power (VArs) not real power (watts).
Synchronization to a grid with other generators and their prime movers generally involves three things. The first is verification of phasing (Phase A is being connected to Phase A, Phase B to Phase B, Phase C to Phase C), and that is usually done the first time a unit is being synchronized prior to actual synchronization. Because these are typically high-voltage connections and many times the connections are made using solid bars or connectors which are rarely, if ever, disassembled it's not usually necessary to re-check phasing on every successive synchronization.
The second is to make sure that the voltage sine waves of the phases are "in phase" or very close to being in phase with each other prior to closing the breaker. In other words, that both sine waves are at about the same magnitude, which will mean that the contacts of the generator breaker can be closed as easily (with as little mechanical force) as possible. When both magnitudes are the same, the difference in potential is the least, and the lower the difference in potential the lower the force required to close the breaker contacts and keep them closed.
The third is to make the generator terminal voltage equal to or slightly higher than the system voltage which is being synchronized to. This is done to ensure that the VARs will be close to zero (when the two voltages are equal) and the power factor will be close to unity (1.0), or to ensure that any VArs will be Lagging (considered to be "positive"), making the power factor also lagging when the generator terminal voltage is higher than the system voltage being synchronized to.
When a prime mover and generator are being synchronized to a grid with other prime movers and generators, it is incumbent on the operator to ensure these three things are done prior to initiating a breaker closure. Now, again, the first is usually only done on the initial synchronization attempt or after any outage where the high-voltage connections were disturbed or the sensing instruments (potential transformers) were disturbed (primary or secondary circuits). The second is done either by the operator or by some automatic synchronization relay or control scheme and is very, very important. It's sometimes referred to as "speed matching".
The third is generally referred to as "voltage matching" and is done by the operator if synchronizing manually. Some, but not all, auto-synchronizing schemes will automatically adjust generator terminal voltage prior to breaker closure to some preset difference.
Many auto-synchronizing schemes <b>do not</b> make any automatic adjustments to the generator terminal voltage, instead relying on an adjustment of the excitation system and the stability of the system voltage (which is sometimes not very stable!) to hopefully have zero VArs or a slight Lagging Var indication at breaker closure. Of course these control schemes are generally more expensive, and so are not always purchased as options when the power generating equipment is provided.
It would be very helpful to understand if this leading VAr/pf situation just started happening, and if so, was it after some kind of maintenance outage, after an adjustment of some transformer tap-changer, after a "tune-up" or upgrade of the generator exciter controls (the "AVR"), or after some new generation plant came on line relatively close this generation plant, or what. Or, if this has been ongoing since the original commissioning of the plant and for how long. We also don't know how many VArs or what the pf was after synchronization, and if anything was done after synchronization to correct the situation. Also, we don't know if the unit was being synchronized manually, or if it was being auto-synchronized if the auto-synchronizing scheme is configured to adjust generator terminal voltage (if it has voltage-matching capability).
There's just a lot we don't know about the site and the conditions.
But, the short answer to the problem for most sites (not all!) is exactly as M M Ahsan says: It is desirable to have the VAr indication at zero or slightly Lagging immediately upon breaker closure, and the way to do that is to ensure that the generator terminal voltage is equal to or slightly higher than the system voltage which is being synchronized to.
And, "Feedback is the most important contribution!"(c)
Just to clarify, "back power" is usually called reverse power. And reverse power is usually referring to watts ("real" power). Reverse power (watts) can be very damaging to a prime mover.
The originator seems to be referring to reactive power (VArs) not real power (watts).
Synchronization to a grid with other generators and their prime movers generally involves three things. The first is verification of phasing (Phase A is being connected to Phase A, Phase B to Phase B, Phase C to Phase C), and that is usually done the first time a unit is being synchronized prior to actual synchronization. Because these are typically high-voltage connections and many times the connections are made using solid bars or connectors which are rarely, if ever, disassembled it's not usually necessary to re-check phasing on every successive synchronization.
The second is to make sure that the voltage sine waves of the phases are "in phase" or very close to being in phase with each other prior to closing the breaker. In other words, that both sine waves are at about the same magnitude, which will mean that the contacts of the generator breaker can be closed as easily (with as little mechanical force) as possible. When both magnitudes are the same, the difference in potential is the least, and the lower the difference in potential the lower the force required to close the breaker contacts and keep them closed.
The third is to make the generator terminal voltage equal to or slightly higher than the system voltage which is being synchronized to. This is done to ensure that the VARs will be close to zero (when the two voltages are equal) and the power factor will be close to unity (1.0), or to ensure that any VArs will be Lagging (considered to be "positive"), making the power factor also lagging when the generator terminal voltage is higher than the system voltage being synchronized to.
When a prime mover and generator are being synchronized to a grid with other prime movers and generators, it is incumbent on the operator to ensure these three things are done prior to initiating a breaker closure. Now, again, the first is usually only done on the initial synchronization attempt or after any outage where the high-voltage connections were disturbed or the sensing instruments (potential transformers) were disturbed (primary or secondary circuits). The second is done either by the operator or by some automatic synchronization relay or control scheme and is very, very important. It's sometimes referred to as "speed matching".
The third is generally referred to as "voltage matching" and is done by the operator if synchronizing manually. Some, but not all, auto-synchronizing schemes will automatically adjust generator terminal voltage prior to breaker closure to some preset difference.
Many auto-synchronizing schemes <b>do not</b> make any automatic adjustments to the generator terminal voltage, instead relying on an adjustment of the excitation system and the stability of the system voltage (which is sometimes not very stable!) to hopefully have zero VArs or a slight Lagging Var indication at breaker closure. Of course these control schemes are generally more expensive, and so are not always purchased as options when the power generating equipment is provided.
It would be very helpful to understand if this leading VAr/pf situation just started happening, and if so, was it after some kind of maintenance outage, after an adjustment of some transformer tap-changer, after a "tune-up" or upgrade of the generator exciter controls (the "AVR"), or after some new generation plant came on line relatively close this generation plant, or what. Or, if this has been ongoing since the original commissioning of the plant and for how long. We also don't know how many VArs or what the pf was after synchronization, and if anything was done after synchronization to correct the situation. Also, we don't know if the unit was being synchronized manually, or if it was being auto-synchronized if the auto-synchronizing scheme is configured to adjust generator terminal voltage (if it has voltage-matching capability).
There's just a lot we don't know about the site and the conditions.
But, the short answer to the problem for most sites (not all!) is exactly as M M Ahsan says: It is desirable to have the VAr indication at zero or slightly Lagging immediately upon breaker closure, and the way to do that is to ensure that the generator terminal voltage is equal to or slightly higher than the system voltage which is being synchronized to.
And, "Feedback is the most important contribution!"(c)
S
sd
Does the situation occur before synchronization, while synchronization or after synchronization? Things would be really different who all the three cases 
