Seismic code and design standard
for transmission line and substation
in Japan
September 3, 2003
Hajime Imura
The Kansai Electric Power Co.,Inc.
Contents
1. Basic concepts on seismic design of electric facilities
2. Seismic design of electric facilities
- Overhead transmission line
- Underground transmission line
- Substation
3. Evaluation of the present seismic design
4. Summary
Basic concepts on seismic design of electric facilities
There are two categories(Category 1 & 2) according to the kinds of facilities.
Electric facilities performance that can be expected is decided by intensity of
earthquake(Level A & Level B).
Level A : An earthquake which occurs once or twice in the lifetime of facilities.
Level B : An earthquake with a vertical shock or a trench-type earthquake which
seldom occurs (ex. Hanshin-Awaji earthquake).
Category 1
Dams
LNG tanks
Oil tanks
Category 2
Power generation facilities
Transmission lines
Substations
Distribution lines
Load dispatching center
Telecommunications
a) No serious trouble occurs for
a) No serious trouble occurs for
a Level A earthquake.
a Level A earthquake.
b) No serious damage on human lives
occurs for Level B earthquake.
Seismic design of electric facilities
1. Overhead Transmission Line
No criteria in the aspect of seismic design
[Overhead transmission tower is designed so as not to be fallen down
by 40m/s-wind (typhoons are assumed). The wind force is severer
than earthquake motions.]
40m/s
wind
earthquake
Seismic design of electric facilities
2. Underground transmission line
(1) Cables
No criteria in the aspect of seismic design
[Reason]
Cables have flexibility and strength against earthquake motions,
and it is laid with off-set considering thermal elasticity and good
working conditions.
(2) Cable heads and oil supplying systems(for OF cables)
It is designed based on seismic design of substation equipment.
(3) Conduit and human maintenance hole
No criteria in the aspect of seismic design
[Reason]
Polycon FRP Pipes (PFP) have been usually adopted. They have
flexibility on their joints and can withstand earthquake motions.
Seismic design of electric facilities
3. Substation (Outdoor)
Transformer
(CB, DS, PCT, Cable head)
Bushing
Body
Dynamic
3 m/s2
5 m/s2
－
Design
Resonant sine wave, 3 cycles
force
Static
5 m/s2
－
－
(horizontal)
The force is assumed to be applied to the lower end of the equipment
Porcelain type equipment
Design
Technique
Bushing
Pocket
Position of the
force being
applied
Transformer
body
foundation
foundation
* 1F and underground of indoor substation : Same as outdoor
Others :designed one by one considering the motion of the building
Evaluation of the present seismic design
The present seismic design was established in 1980 based
on the experience of “Off-Miyagi earthquake”, which occurred
in 1978.
Hanshin-Awaji earthquake
occurred in 1995
We reviewed the present design
after Hanshin-Awaji earthquake.
[The viewpoints of evaluation]
- Theoretical evaluation
- Demonstrative evaluation
1970
earthquake
Seismic Design of
Substation
1980
1995
▼Off-Miyagi
■
1980
Dynamic Seismic Design
2000
▼Hanshin-Awaji
□
(1998)
review
Theoretical evaluation on Hanshin-Awaji earthquake
1) Frequency
Expectation in return period is around 1000 years.
2) Actual earthquake motions and response acceleration
Maximum
acceleration
(1)
Response
coefficient
(2)
Response
acceleration
(1) * (2)
Dominant
frequency
Shin-Kobe S/S
5.84m/s2
4.4
26 m/s2
KEPCO R&D Center
6.48m/s2
8.18m/s2
3.0 m/s2
3.9
3.3
4.7
23 m/s2
27 m/s2
14 m/s2
3.05 Hz
1.49 Hz
1.49 Hz
0.5 -10 Hz
KOBE meteorological
observatory
Present seismic criteria
Theoretical evaluation on Hanshin-Awaji earthquake
3) Response acceleration spectrum at Shin-Kobe S/S
30
1.5
Design:14m/s2 1.0
10
0
0.05 1
2
3
4
5
6
7
8
9
Safety Factor
Acceleration(m/s2)
2.0
Maximum Acceleration
26m/s2 at 3.05Hz
20
(Cont’d)
10
Natural frequency (Hz)
In specific frequency range(1.15 - 4.85Hz), response acceleration
exceeds the present seismic criteria(14m/s2).
4) Seismic strength of substation equipment
- Porcelain insulators and bushings have some margin(about 2 times)
of its strength considering the strength variation on the process.
- Even if considered the variation of it strength, only 1% of the insulator
would be damaged.
Demonstrative evaluation on Hanshin-Awaji earthquake
1) Strong earthquake motions, but little serious damage
- Strong earthquake
a) Shin-Kobe S/S
: 5.84 m/s2
b) KEPCO R&D center : 6.48 m/s2
c) Kobe meteorological
observatory : 8.8 m/s2
- Some equipment were damaged in Itami & Shin-Kobe S/S, but not so
much serious damage which leads to loss of function.
2) Damaged equipment was designed based on older design.
- Many of damaged equipment were designed based on older seismic
design before 1978 and almost all of the equipment designed on the
present design do not suffer significant damage.
3) Experiences of other big earthquakes
- There were strong earthquakes other than the Hanshin-Awaji, but
we did not suffer severe damage.
Evaluation of the present seismic design (Cont’d)
[Overhead transmission]
According to the analysis of seismic response by using the waveform
observed at Kobe meteorological observatory (8.1m/s2; maximum
acceleration in the Hanshin-Awaji), typical transmission towers of 500, 275,
77 kV have enough strength against maximum possible acceleration.
[Underground transmission]
Only some of the transmission line based on former design (laid without
off-set) suffered damage.
The present seismic design has good performances.
Summary
(1) The present seismic criteria is:
a) Substation
Resonant 3 cycles sine wave
- Porcelain type equipment : 3m/s2 (Horizontal acceleration)
- Transformer : 5m/s2 (Horizontal acceleration)
b) Overhead transmission line
No criteria in the aspect of seismic design
(If the structure withstand 40m/s-wind, enough strength for earthquake)
c) Underground transmission line
No criteria in the aspect of seismic design
(The components have various flexibility and have enough strength.)
(2) Experiences of strong earthquake such as the
Hanshin-Awaji, proved good performance of the
present seismic design.
End