*7.2. Test Results of Synchronization Interval and Breakaway Interval*

7.2.1. Test Results for ESS Synchronization and Breakaway

Figure 16 shows the voltage fluctuation trend of the ESS before and after the synchronization in the MCFC system. It can be found that the system voltage before the ESS synchronization encountered a slight deviation, but the follow-up control was effectively confirmed after the ESS synchronization.

**Figure 16.** Voltage change during ESS synchronization.

In Figure 17, the synchronous signal from IMES followed the system voltage and frequency. The reference frequency for both MCFC and ESS was 60 HZ, and that was exactly matched each other after synchronization.

**Figure 17.** Frequency change during ESS synchronization.

When a system breakaway signal was generated from the IMES, the ESS was disconnected from the system. As shown in Figure 18, the separation time of the ESS from the system was estimated less than 0.5 seconds, which was the same as the synchronization time. The voltage fluctuation trend of the ESS, before and after synchronization in the MCFC system, was also clearly presented in the figure.

**Figure 18.** Voltage change when the ESS system was disconnected.

Figure 19 shows that the parallel operation of the MCFC and the ESS and the breakaway proceedings when the system breakaway signal was sent from the IMES to the ESS. In this case, the frequency was observed to be slightly hunt, but it did not affect the existing system.

**Figure 19.** Frequency change in ESS system deviation.

Figure 20 shows the voltage fluctuation trend before and after the synchronization of the diesel generator with the MCFC and ESS systems. When the EMS sent the synchronization signal, it followed the system voltage so that the voltage could be synchronized—thereby, the system voltage was exactly matched.

**Figure 20.** Voltage change when synchronizing diesel generators.

Figure 21 shows the frequency fluctuation trend before and after synchronizing the diesel generator with the MCFC and ESS systems. It revealed that once the EMS sent the diesel generator synchronization signal, it started to follow the system voltage and achieved the voltage synchronization. Thereafter, it followed the system frequency and attained frequency synchronization.

**Figure 21.** Frequency change when synchronizing diesel generators.

When the system separation signal was generated from the EMS, the diesel generator was disconnected from the system by the synchronization switch fitted in the synchronization controller. In Figure 22, a waveform similar to the synchronous voltage waveform was plotted in the same manner as in the system state before synchronizing the diesel generator.

**Figure 22.** Voltage change when diesel generators are broken away.

Figure 23 shows the synchronous operation of all power systems in parallel. When the system breakaway signal went off to the IG-NT from the IMES, the frequency was observed to be a hunt, which occurred after the breakaway, thereby such an outage had no effect on the existing system.

**Figure 23.** Frequency change when leaving diesel generator system.

*7.3. Analysis of Frequency Variation Rate and Frequency Stabilization Time Data Based on Load Scenarios*

7.3.1. Power Data before and after Synchronization for Normal Seagoing Case 1

Table 10 shows the analysis results pertinent to the voltage and frequency fluctuation measured in the load pattern of the normal seagoing case 1.


**Table 10.** Power data analysis before and after ESS synchronization.

When the ESS was synchronized with the system, the voltage fluctuation rate was within ±1.01%, and the voltage fluctuation rate ranged from +6 to −10 %. Therefore, it could be confirmed that the voltage fluctuation hardly occurred during system synchronization, and the voltage characteristic was kept stable.

Likewise, the stability of frequency was also confirmed since the frequency variation rate was within ±1.01%, much lower than the standard of ±5%.

7.3.2. Power Data before and after Synchronization for Normal Seagoing Case 2

Tables 11–14 describe the analysis results from power data measured during synchronization and breakaway of the diesel generator under the normal seagoing case 2.


**Table 11.** Power data analysis before and after ESS synchronization.

**Table 12.** Power data analysis before and after diesel generator synchronization.






The voltage fluctuation rate was observed within ±1.01% when the ESS and the diesel generator were synchronized to the system. Since the voltage fluctuation was placed in the standard range of +6 to −10 %, the system stability was verified for this case as well.

The frequency deviation was within ±1.01%. In the same way, given the standard range of ±5%, frequency stability has been confirmed.

7.3.3. Power Data before and after Synchronization for Normal Seagoing Case 3

The analysis results for the voltage and frequency variation measured in the load pattern of normal seagoing case 3 are shown across Tables 15–18 which deal with power data for ESS synchronization and breakaway, as well as that for the diesel generator.


**Table 15.** Power data analysis before and after ESS synchronization.


**Table 16.** Power data analysis before and after ESS system outage.




**Table 18.** Power data analysis before and after diesel generators outage.

Since when synchronized to ESS and diesel generators, voltage stability was confirmed with the voltage fluctuation rate measured between ± 1.01 % (standard range of +6 to −10%).The frequency variation was measured within ± 1.01 %—therefore, it can be seen that frequency fluctuation hardly occurs during system synchronization.

During the breakaways of ESS and diesel generator, it was confirmed that the voltage and frequency were not subjected to the deviation from the acceptable ranges.
