ENTSO-E RG Continental Europe SG System Frequency 30th December 2011
Report about the large frequency deviation on the 13th of December 2011 During the last hour of the 13th December 2011, the frequency of the ENTSO-E Continental Europe synchronous area gradually rises, until it has reached, at 23:53:42, the exceptionally high value of 50,161Hz. Five minutes before the midnight, frequency started to fall, first gradually and then, a minute before and a few minutes immediately after the midnight, swiftly. Finally at 00:04:00 on 14 th December 2011 the frequency was 49,920Hz, of which 10mHz deviation were intentionally due to the new frequency setpoint, 49,99 Hz.
The measurements gathered by Swissgrid are presented on the following figure and the reports received from RG CE TSO-s are added at the end of the Report.
According to the previous data and the reports prepared by TERNA and AMPRION, the source of the large frequency deviation was mainly located in German and Italian control block. A summary of the main data included in the reports prepared by TERNA, AMPRION, RTE and REE is: A big change of generation fleet in the Italian system with an imperfect coordination of simultaneous ramping of the significant number of units, superposed to the large change of load and exchange program. In the German Control Block, there was a large power imbalance around 4.032 MW. The remaining imbalance after the activation of the total negative secondary control reserves in German Block was around 1.988 MW. From the Italian system point of view, between 23:40 and 23:50 power error appeared to take a decreasing tendency so no balancing action was taken. From 23:50 to 0:00 due to some units deviated from their schedules power error in the Italian system started to increase again. In order not only to balance the system but contributing to reduce frequency deviation, TERNA started 1100 MW in pumping units and reduced 600 MW in thermal units. The source of the power imbalance in the German CB has not been yet identified. The increase of the ACE in the most critical period of time follows a ramp rather than a step. This is an indicator that there was no sudden incident on generation or load causing the power imbalance. According to the AMPRION report all control areas inside the German control block were affected by the deviation and activation of negative secondary control reserve, but due to GCC influence on ACE of Control Areas, it is not easy to guess from this data the geographical source of the incident. For the time being it is known that there was no forecast error for generation infeed by renewables, and that the change of total exchange program at midnight was not high (approximately +400 MW). Further investigation is in progress. Additional results and explanations over observability and control capability of generation are necessary for complete analyses of frequency excursion between December 13 and 14, 2011 From RTE side, the first reaction to the large frequency deviation comes approximately 15 minutes before the midnight. The power of ten nuclear units (-330 MW) was reduced by hight frequency deviation automatism, and RTE started some pump units (210 MW) and stopped few hydro units (-340 MW). Due to frequency fluctuation a test on the nuclear unit Golfech 1 was cancelled. No relevant unbalances were detected in the EP CB according to REE report. This incident is just another fact and one of the most severe recorded of the already identified decrease of frequency quality in the synchronous area Continental Europe.
The 13th of December three frequency deviations higher than 100 mHz were recorded: +120 mHz at 6:01:33, -107 mHz at 20:03:21 and +161 mHz at 23:53:42. In addition to the lately “usual” swift deviations of frequency around the beginning of the hour in the morning and around and after midnight, longer periods (15 – 20 minutes) with large frequency deviation are increasingly frequent. The first phenomenon is mainly caused by swift and large changes of generation and/or load and non-coordinated ramping of units as studied by joint Eurelectric and ENTSO-E AhT. The second type of frequency deviations reflects situations where there’s a lack of activation of reserves leading to maintain an unbalanced situation in the synchronous area. This incident was the result of several factors. Some of them are still not clear. However, it shows once again the necessity to change some current practices of generating units ramping , to improve control actions by TSOs concerning generators and to control their response to these actions.