In the 1995 Southern Hyogo prefecture earthquake (Great Hanshin-Awaji earthquake) a large number of power stations and substations were damaged within the service area of Kansai Electric Power Co. [52].
Kansai Electric Power Company recorded acceleration time-histories at 18 sites; those are power plants, substations and their technical institutes. In this report, eight of them are selected as typical observed earthquake motions for the calculation of DIPs at power facilities, as shown below:
Amagasaki No.3 power station (Fossil, 156 MWe, 3 units, epicentral distance: 34.2 km)
Takasago power station (Fossil, 450 MWe, 2 units, epicentral distance: 34.2 km)
Nanko generating station (Fossil, 600 MWe, 3 units, epicentral distance: 29.1 km)
Gobo power station (Fossil, 600 MWe, 3 units, epicentral distance: 34.1 km)
Akoh power station (Fossil, 600 MWe, 2 units, epicentral distance: 62.3 km)
Shin-Kobe substation (275 kV, epicentral distance: 24.7 km)
Kainanko substation (275 kV, epicentral distance: 51.4 km)
Nishi-Kyoto substation (500 kV, epicentral distance: 67.6 km)
Typical recorded acceleration time-histories are shown in Fig. 32 and Fig. 33. The data in Fig.
33 shows that the nature of the waveform changed during the earthquake. This is thought to be due to the liquefaction of the ground on which the seismometer was installed.
FIG. 32. Acceleration time-history observed at Shin-Kobe substation.
-600 -400 -200 0 200 400 600
0 2 4 6 8 10 12 14 16 18 20
Time (sec)
Acceleration (Gal)
TABLE 20. SUMMARY OF ITEMS LOCATED AT THE TWO SELECTED EPRI SQUG DATABASE SITES (COURTESY OF EPRI) Selected EPRI/SQUG Database Earthquakes Equipment Meeting SQUG Caveats Equipment Not Meeting SQUG Caveats No.EPRI/SQUG Equipment ClassImperial Valley Earthquake Items
Coalinga Earthquake Items Total Items SuccessDamageMalfunction Success DamageMalfunction 1 Motor control centers6 18 24 200 0 0 4 0 2 Low voltage switchgear 6 1 7 7 0 0 0 0 0 3 Medium voltage switchgear 7 1219160 0 0 3 0 4 Transformers12 7 1916 0 0 1 2 0 5 Horizontal pumps 13435652 0 0 0 4 0 6 Vertical pumps3 24 27 270 0 0 0 0 7 Air operated valves255075740 0 0 0 1 8 Motor operated valves 15728787 0 0 0 0 0 9 Fans 4 4 8 8 0 0 0 0 0 10Air handlers0 8 8 8 0 0 0 0 0 11Chillers 0 2 2 2 0 0 0 0 0 12Air compressors 4 22 26 260 0 0 0 0 13Motor generators1 0 1 1 0 0 0 0 0 14Distribution panels2 4 6 5 0 0 0 1 0 15Battery racks 3 9 127 0 0 4 0 1 16Battery chargers and inverters3 8 118 0 0 3 0 0 17Engine generators 0 1 1 1 0 0 0 0 0 18Instruments on racks 9 2736330 0 0 3 0 19Temperature sensors 1 5 6 6 0 0 0 0 0 20Controland instrumentation panels and cabinets 6 131915 0 0 0 2 2 Totals120 330 450 419 0 0 8 194 Note: SQUG Caveat:An equipment installation condition which needs to be satisfied, for instance, (1) item needs to have engineered anchorage or installation; (2) item does not have potential for seismic interaction with adjacent structures, systems, or components; (3) item needs to have line connections (conduit, piping, tubing) which have adequate flexibility, etc.).
FIG. 33. Acceleration time-history observed at Amagasaki No.3 power station.
TABLE 21. ANALYSIS IN JAPAN FOR INDUSTRIAL FACILITIES - COMPUTED DIP VALUES AT THE SITES
Observation Point
PGA
(ZPA) Standardized
CAV AJMA
JMA Instrumental
Seismic Intensity
Average Elastic Spectrum1 (2-10 Hz)
Average Elastic Spectrum1 (10-20 Hz)
Average Elastic Spectrum1 (20-30 Hz)
Gal g-sec Gal - Gal Gal Gal
Amagasaki 3 Power Station
NS 227 0.99
174 5.4
335 422 336
EW 354 0.96 387 859 792
UD 373 0.91 581 1000 6633
Takasago Power Station
NS 191 1.48
178 5.4
376 206 193
EW 198 1.70 342 205 200
UD 182 0.94 321 415 207
Nanko Generating Station
NS 107 0.55
94 4.8
206 229 135
EW 126 0.72 220 314 149
UD 199 0.61 347 475 283
Gobo Power Station
NS 60 0.11
27 3.8
148 86 63
EW 74 0.16 180 101 77
UD 26 0.01 38 84 44
Akoh Power Station
NS 104 0.46
35 4.0
180 215 150
EW 84 0.37 156 145 122
UD 122 0.32 142 232 182
Shin-Kobe Substation
NS 511 1.34
416 6.1
1110 675 555
EW 584 1.76 1433 872 693
UD 495 1.11 1055 1058 994
Kainanko Substation
NS 98 0.36
69 4.6
277 139 103
EW 128 0.39 267 163 132
UD 92 0.17 128 160 116
Nishi-Kyoto Substation
NS 114 0.24
79 4.7
317 155 118
EW 129 0.24 349 242 140
UD 83 0.17 163 192 105
Notes: (1) 5% damping; 80 evenly spaced points in the logarithmic frequency domain
-300 -200 -100 0 100 200 300 400
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (sec)
Acceleration (Gal)
DIPs computed from the earthquake motion data recorded at these sites are shown in Table 21.
Due to these earthquake motions, turbine trips occurred at a large number of thermal power plants as a result of excessive turbine shaft vibrations. Those at which no damage was found were restarted, while many power plants had to be shut down for extended periods of time.
At the power stations and substations for which DIPs were computed, damage listed in Table 22 was reported.
TABLE 22. MAJOR DAMAGE OBSERVED AT CONVENTIONAL POWER STATIONS AND SUBSTATIONS
No. Station Major Damages
1 Amagasaki No.3 power
station ・ Damaged boiler anti-vibration devices (16 sections)
・ Damaged anti-vibration devices for downcomer tube of main steam line (4 sections)
・ Deformed boiler frames (braces) (13 sections)
2 Takasago power station ・ Cracked on-site roads and others
3 Nanko power station ・ Deformed boiler cooling spacer tubes (5 tubes)
・ Deformed anti-vibration devices for low-temperature reheated steam tube of main steam line (2 sections)
4 Gobo power station No damage
5 Akoh power station No damage
6 Shin-Kobe substation ・ Fractured and moved 275 kV transformer foundation anchor bolts
・ Dislocated 275 kV breaker bushing
・ Fractured pressure relief panel of 275 kV transformer
・ Fractured 77 kV breaker bushing
・ Fractured frame supporting insulator for 77 kV power capacitor
・ Fractured radiator piping of 77 kV bypass reactor
7 Kainanko substation No damage
8 Nishi- Kyoto substation No damage
In Fig. 34 through Fig. 36 solid markers identify the cases in which some sort of damage was observed. In Fig. 34 the data from the EPRI SQUG database analysis mentioned in the previous section are also plotted (solid markers are used because damage is observed in these examples).
The standardized CAV observed at Takasago power station is relatively large, but no significant damage of plant facilities was reported, even though the steam turbine was tripped due to the
excessive turbine vibration. It also needs to be noted that cracks on station roads were observed.
The Takasago power station restarted successfully around two hours after the earthquake.
FIG. 34. Analysis in Japan for conventional facilities - Standardized CAV vs. AJMA.
FIG. 35. Analysis in Japan for conventional facilities- Mean response acceleration (2-10 Hz, h=0.05, SRSS) vs. AJMA.
FIG. 36. Analysis in Japan for conventional facilities- Mean response acceleration (10-20 Hz, h=0.05, SRSS) vs. AJMA.
As seen in Fig. 34, the JMA seismic intensity level that serves as a threshold at which some sort of seismic damage will occur to plant equipment is 5U, approximately. This value is close to the value discussed in Section 3.2.3, where the original JMA seismic intensity scale 5 was seen as a threshold of damage to industrial conventional equipment. The good correspondence between calculated and observed JMA value encourages application of IJMA not only to buildings but also to mechanical equipment, and AJMA to be studied further as a promising DIP for nuclear power plant SSCs.
4.4. DAMAGE TO NUCLEAR POWER PLANT FACILITIES AND DAMAGE