ELECTRICTY SERVICES

4

THE 1968 INANGAHUA EARTHQUAKE A N D

ELECTRICTY SERVICES

^{H. C.} Hitchcock, B.E. (Hons.) M.N.Z.I.E. M.LE.E Including Information supplied by -

W. H. Brown. Chief Engineer ^ Buller Electric Power Board N.R. Langbeln^ Chief Engineer, Grey Electric Power Board J•E. Cogian^f Chief Engineer, Waimea Electric Power Board D. S. Cannon, Electrical Inspector of Mines and Quarries

Electric power is carried into the area by the N.Z .Electricity Department over 66kV transmission lines as shown in Pig* 1 , and supplied to the Electric Power Boards at Substations as indicated.

Figure 1 also shows the estimated location of the epicentre of the main shock and its distance from the principle installations *

The main shock at 5*24- a.m. on 2^ May 1 9 6 8 interrupted supply over most of the northern end of the South Island and ii/some places in the North Island. Where this was due to false operation of Buchholz relays, supply was restored in a matter of minutes. It was three hours before temporary repairs and bypassing arrangements

at I n a n g a h u a made power available at Waimangaroa and Westport and

it was still later before supply could be provided in Inangahua itselfo

N.ZoE.D. radio and telephone facilities Initially provided the only links with the worst affected area.. Inangahua. and were the means of conveying the evacuation order v t i ^ n the flood threatened.

N. Z.E.D. staff and vehicles. car lied out the evacuation of nearly 50 of the women and children.

The high voltage equipment involved was designed for 66 kV or in some cases 1 1 0 kV so that the detailed reports of damage are similar to those made after the Napier earthquake of 1 9 5 1 (Ref. 1 ) .

The effects of the earthquake can be summarised thus;

Transmission lines

The design of transmission line towers and terminal gantries is dominated by wind loading.

Earthquake loads on such structures axe insignificant and the only real risk of failure Is from disturcance to foundations. Pig. 2 shows how nearly this occurred in the Upper Buller Gorge near Lye11 - at a point only 7*5 miles from the epicentre* The worse damage to towers themselves was on top of a ridge of poorly consolidated

alluvial material near Dee Creek 2 miles rorth of Inangahua. The upper levels of the ridge were c isiiitegrated with the violence of the shaking and the disturbance of the grillage footings was so great that an angle leg was fractured > J'criy towers were

distorted to a lesser degree but ncne fazi-d In service.

WESTPOTT

5/5TN

^ 10,000 KVA

,1

LE G E N D

BU L L E D E.P.B.

ftiV£rs and Coast CrC» ^fcV J^anirriiS5/o/-i L i n e

Fatulf L i n e s D o w n / U p . FOLJI t r a c e s 24- ^{- 5 -} <i»8 (Re£ ^{l )}

Power Q>oard B o u n d a r i e s

Supply from Souih f s f o m d network via Arthurs PAS

5ca/*. / : 2 5 0 0 0 0 (ApproA <€miks ^ I/nc*»)

2/N.Z. S « # f e g i W 5urv«y M#p. 5*>e«f 15 Buffer

Substations

Inang;aqua, J3ubstation (Fig* y"- ^rvas 9 ~ but ?/as TrTthe zrone^oT^rSximum ground Is ::

In she small control building tie s~'~

control, relay and communications l s ; inadequate fastening,

In tne outdoor s^itohi.ng sts^i.'v- Kr >

structure was nnlamaged and its IDurd- • ^fc . bulk oil type circuit breakers and t^eir of the 66 ktT insulabor stacks in bhe ~?nrl off because jumpers did n^t have enough s movement between thp steel structure 2cd broken Insulator stacks swung down c : t h e damaged the transformer neutral b u sh i 1 5 1 for the power line carrier coupling capac

The small permanent staff ao the su:

able to carry out sufficient repair wr/ik circuit breakers and allow through tr^nsi.

resumed about t h r e e hours after the mbI^

The six departmental houses and - Lie severely shaken. In contrast, ^oe

same genera] construction b\rj with a ~^r-ia: ~ strength ratio" showed no sign 01 d i ^ r s E were of weatherboard construction . 0 :

foundations and aad .just had the:. ^.^; ^ ~ I_

corrugated iron (in accordance vvi^r t*~^c ^ not using concrete tiles in hard i'rost a relief of roof weight they were bo st~-vor and refrigerators were i brown -^bcoj e t c - cylinders broken frem their c : m^c: t i r . ^ . pi lignting f itring torn from the eel] [ -^Ac ,

At Beef ton Sub station 25 miles f r . i- f 1 ang eT^TheelTT r a ns f or me r s had each ~v -5 gripping the head of the rail *^ri t h the <;^: bolts) j by about 1-J inches©

In contrast nearby wooden nrusr - wl foundations,, were undamaged ;^J~hougr - - c thrown to the floor) and in "he .c^:. :i:::- e building not a single item v/as displaced j

At Murchison Substation 21 miles 13* _r no trace of earthquake disturbance woattr . from the Murchison Post Office where tg was recorded* This substation stands c — river where foundations are very firm a;

the severity of ground .surface shakings

8

tor d^lorr^id ^{^acrol} ti-sris"formers or"

bending td~„ holdinr scraps a~nd in oro Dolt ,

?be 5^{, r} ^ 3^fl ?/^d*' angle frames s v u r-r r^f,

a. "3 :re ilanra cf oo- -Led were di~dr' c ~

ton transdoraers

place aoc-;> ia:aiaerc-^G 6r6 ^{i P} 2 I' M \ '

Di3 ul j D D O O

Retail distxdb^ti:n rf e] ^cdro^ *~otv^

by the ^ar ^q^ake 5 o undertaken id • indicated L:±

Dama;³e exper rere ?c ^^r thes : ar -¹ Napier ear ':L crake ^{f' i}^ f / , ) sjsoiy oso'rd • damag e ro hor o e *dr:i ng ^$ some c I a t* bi rr 11 k^ lines * poi?s ieailing ovet, i-r allowed s.nd deeper. ^fl v ae

embaniiir^jitfc or ry siir-

~ad

the r . r **" 11dele

< ^r Bca^ae i N i t h . a maid: bad:: . : Waimea; r e p ^^J ?c - ^ne damage to or /rl Boards aupji;;:r»r rhe coal lairing a r r heavy iiicr^aee rox electricity den-arrl to eleo-nrie ^{^s-tkw} beceuee or > red. en -

r

d

_{'*r;-S j/T'O ~\?rned} ^{a: very}

Coal Mires

No danago do ^Leetrrcei eq workings a d~ a•: S r as Iron ore previously d - d; i/nao ground ijinderground ( dio^ga ne. less "oei electrical ir^rails ;ions rrabarg extensive*

S u m m a r y

( 1 I rra 1 - 2 az i quake de

l a - ,

of selecting tower sites leasr- lonely quake s• Toe adoic e

routes for deviations made Builer (Jorge.

or a ^treologxE

r- - c - r "

;2)

The damage to battery and ccid3*0J p quakes design mast attend ro roror major provisions eo ^ oict r^ do ordl

1 > r--r r .0 a - i i y

* j ', K . r a 0 1 r a r 11^

art

The damage caused by -~ighb jumper^c isinuats experience at

Wapier in ' 9 3 1. The 'earthquake release clamps¹' demised at that time were found unsata^fsc scrv cnoaose they gate trouble in storm conditions aid c ^cate la:r c ^ -~ingj 2; lif f 10 a] to design i or H I G H E R current z e " : :.g:

I

r is ⁰ i~un^h inning challenge to engineering ingsluity :o devise connections

which are tidy and will cot clash In "he wind cut which allow e arth quake movement *

Buchhoiz relays almost mir'-u a" V incorporate o>c'~c\ar' switches which falsely trip •vi^ci^t 1 ~ - akc r 3 5*ilri - ax ~^q~ tk^ s~ A type using reed relay? in: c ^v~a 1 - 1 aw .^a; i t J e out for existing Installations a a 1:1 1 t ^oi::i⁵ p-irulur tea been

developed ^btcli will energise a ^Jfxnz aeiaye^ re ¹ a;y to interrupt the tripping circuit for the Uti. it ion 'if an aa:~ h quake and about a second thereafter,, Tais is being fitte; to a trans- former bank on a trictl basis

Permanent repairs tc Electrical equipment «^Ttre hampered by the need to rehabilitate & c c n; ^ o d 3 t : : first- This suggests that houses and buildings s or pit 1:: .vilt~ies vat¹i better serve their purpose if by closer p_at er^ti 1 ^0 data? 1 they were

designed to survive an earthque i- j f this size ro ~" necessarily without damage but "in working cctdition¹¹ * In mils connection

it should be noted ^{Ghat the} ^ no aid of eartbqucJte resistance provided by the N.Z, Model BuiloJng Bylams FZrS 1?0O. Chapter 8 is a minimum ana as India atec ^{1 0} sec slon 3-9 "f the ^Commentary on Ohaptei ^8''

07?"*?

^'955> the writ n° a i tilt 11 g should

decide whether for economic ci operatecnal reason: ce snculd specify ana pay for a tigher i^a¹ card ai •:ors^raa^ icn*

The violent snaking :f voce- . ta.teo houses or lo*- sirengbi foundations ann of the x :oriy traf-d depot buiIcing ic spite of Its solid foundations can lie em-lamed, l'^T inspee gj :n if an earthquake response spec n u n a a an example of th- ^f!fa^l

unsafe" potential of rigia constrictions /itich loose rlisxr rigidity by yielding at acce] eiation less ~har a a out *4g or

• 5g - sl point which must be h^mie m mind when da signing earthquake fastenings for ^v«ea-y pi arJ~ like transf rrmers®

Distribution Authorities have less choice In locating poles and substations and some damage must be enpe^ied© I" Is pleasing to note that no pole mounted transformers exe reported thrown to the ground as they were In previous a arth^uakes.

The more modern higher voltage equipment i„i use ir other parts of IT*Z. has yet to be earthquake res "-a-i but It is now known to bi more susceptible and measures are in hand to improve its

resistance•

A study on this subject will be published shortly (Refo 3) which shows the need for dynamic analysis of the earthquake

response of electrical equipment and where this Is not available suggests a seismic design factor of *75g for general use but with special consideration as follows:

large transformers - reduce to ⁰4-g if installed so that natural period of vibration on its final foundations is less than 0*1 second;

equipment which fails in porcelain or other brittle components - increase to 1.5 g if nothing is known of its dynamic

properties but if Equivalent Viscous Damping (Fraction of Critical) can be shown to be not less than . 0 2 , . 0 5 , . 1 , . 2 or «4 then the Seismic Design factor must be at leasb 1 «3g*

• 9 5 g f •75g> .55g> or ^#4g respectively. Equipment with more than one mode of vibration requires an appropriate dynamic analysis©

References

(1) Effect of Earthquakes on Electric Supply Systems.

I .R. Robinson and H.L. Benjamin; Proc. N.Z. Soc• G.E.

V.XIX 1932 - 33.

( 2 ) Earthquake Risk in New Zealand: Jo Henderson.

N.Z. Journal of Science and Technology, V.XXIV N0.5B, W 3 ® (3) Electrical Equipment and Earthquakes.

H.Oo Hitchcock N . Z . ENGINEERING 1 9 6 9 V.2U ^{N o .} 1