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We have installed at our facility a 13.8 kV, 16.8 MW synchronous turbine-driven generator. We are currently experiencing an issue when placing the generator in service which I will attempt to summarize as best as possible.
Initially, the total power consumption by the facility is approximately 10 MW, which is supplied by the utility, at 13.8 kV with a power factor of 0.83 (or thereabout). When placing the generator in service, the excitation is turned on, after which the generator's supply is automatically synchronized to the utility's supply. Once the three breakers (generator, utility and tie) are closed, the generator is then loaded in Droop.
A power factor switch is turned on in order to toggle the excitation's control system (DECS 200) mode from AVR to PF control. Once this is completed, despite the power factor setpoint of the DECS being set at 0.8, the actual power factor drops immediately to approximately 0.2 - 0.3. The amperage drawn by the generator increases instantaneously from 250A to 800A. As the generator is loaded to match the demand from the users on its own loads, the power factor indicated for the utility drops from 0.83 to 0.4 or thereabout, with an additional current draw as well.
Once the generator is loaded to the required 5.5 MW, the tie breaker is opened and the power factor switch immediately turned off to return the mode of the DECS to AVR (with a pre-position setpoint of 13.8 kV). At this instant, there is a voltage spike from the generator, sometimes reaching between 14.8 - 15 kV (max range of the measurement device), which oftentimes causes upsets to lower-voltage equipment. The system then normalizes to the required 13.8 kV and 0.8 power factor while being operated in isochronous control. Based on this response, it seems that there is significant additional excitation which is immediately dissipated when the control is switched from power factor to AVR control.
Thus far, we have listed the DECS as the most likely cause of the issue, specifically when it is operated in power factor/droop control mode. The generator appears to be performing as required based on the output from the DECS as it functions without any issues in AVR/isochronous mode. Checks on the DECS were made to verify that the contacts were switching correctly based on the input signals received.
Although I do not believe that the generator's performance is to be questioned, it must be noted that this action was only observed after conducting some repairs to the unit approximately 1 year ago.
We do understand that operating the generator under these conditions means that we will be generating power inefficiently, as well as placing strain on the generator's windings based on the increased current draw/heating of the windings.
Based on the scenario provided, I would like to request the assistance of anyone who can provide some further insight/guidance into this issue, as it pertains to the reason for the behaviour of the generator in this condition, as well as any possible corrective measures that can be implemented (beside replacing the DECS) in order to resolve the issue or other checks that can be done on the system to gain more insight into the issue.
I do look forward to any feedback and questions.
Thanks and Best Regards.
Initially, the total power consumption by the facility is approximately 10 MW, which is supplied by the utility, at 13.8 kV with a power factor of 0.83 (or thereabout). When placing the generator in service, the excitation is turned on, after which the generator's supply is automatically synchronized to the utility's supply. Once the three breakers (generator, utility and tie) are closed, the generator is then loaded in Droop.
A power factor switch is turned on in order to toggle the excitation's control system (DECS 200) mode from AVR to PF control. Once this is completed, despite the power factor setpoint of the DECS being set at 0.8, the actual power factor drops immediately to approximately 0.2 - 0.3. The amperage drawn by the generator increases instantaneously from 250A to 800A. As the generator is loaded to match the demand from the users on its own loads, the power factor indicated for the utility drops from 0.83 to 0.4 or thereabout, with an additional current draw as well.
Once the generator is loaded to the required 5.5 MW, the tie breaker is opened and the power factor switch immediately turned off to return the mode of the DECS to AVR (with a pre-position setpoint of 13.8 kV). At this instant, there is a voltage spike from the generator, sometimes reaching between 14.8 - 15 kV (max range of the measurement device), which oftentimes causes upsets to lower-voltage equipment. The system then normalizes to the required 13.8 kV and 0.8 power factor while being operated in isochronous control. Based on this response, it seems that there is significant additional excitation which is immediately dissipated when the control is switched from power factor to AVR control.
Thus far, we have listed the DECS as the most likely cause of the issue, specifically when it is operated in power factor/droop control mode. The generator appears to be performing as required based on the output from the DECS as it functions without any issues in AVR/isochronous mode. Checks on the DECS were made to verify that the contacts were switching correctly based on the input signals received.
Although I do not believe that the generator's performance is to be questioned, it must be noted that this action was only observed after conducting some repairs to the unit approximately 1 year ago.
We do understand that operating the generator under these conditions means that we will be generating power inefficiently, as well as placing strain on the generator's windings based on the increased current draw/heating of the windings.
Based on the scenario provided, I would like to request the assistance of anyone who can provide some further insight/guidance into this issue, as it pertains to the reason for the behaviour of the generator in this condition, as well as any possible corrective measures that can be implemented (beside replacing the DECS) in order to resolve the issue or other checks that can be done on the system to gain more insight into the issue.
I do look forward to any feedback and questions.
Thanks and Best Regards.