180 
The N.Z. Journal of Science and Technology. 
[Aug. 
ELECTRIC-POWER LOAD-CURVES. 
By L. Birks, B.Sc., M.Inst.C.E., M.I.E.E. 
In dealing with the problem of electric-power supply the first question is 
to obtain the actual or estimated load-curve of the daily output of the 
power plant, as on this depend all questions of cost of production and 
revenue required. Owing to the different conditions of supply, various 
stations differ in their load-curve characteristics. A station supplying 
mainly industrial demands or tramways will have a heavy all-day load 
with a high average over the twenty-four hours. Stations supplying 
mainly lighting will have an evening peak with a low average over the day. 
The ideal of the national electric-power-supply scheme is to connect up al] 
consumers of each Island into a single network fed from a few of the most 
economical sources, and in order to determine the probable shape of the 
load-curve on such a system under New Zealand conditions a composite 
load-curve has been prepared. The actual load-curves for an equinoctial 
day (30th September, 1920) were selected as giving an average between 
summer and winter conditions. The load-curves of the following stations 
for this particular day have been obtained and included in the composite 
load-curve (see accompanying figure) :— 
Installed 
Capacity. 
Maximum Load recorded 
on 30th September, 1920. 
Water-power plants— 
Kilowatts. 
Kilowatts. 
1. Coleridge 
6,000 
6,550 at 9.30 a.m. 
2. Waipori 
6,000 
6,175 at 2.42 p.m. 
3. Horahora .. 
6,300 
2,600 at 11.0 a.m. 
4. New Plymouth 
850 
672 at 11.50 a.m. 
5. Tauranga . . 
160 
160 at 6.0 p.m. 
Steam-power plants— 
6. Auckland City Lighting Station 
7,000 
4,050 at 11.0 a.m. 
7. Auckland Tramway Station* .. 
6,000 
5,400 at 5.20 p.m. 
8. Wellington City Lighting Station 
3,500 
2,160 at 7.30 p.m. 
9. Wellington Tramway Station . . 
3,000 
3,100 at 5.45 p.m. 
10. Invercargill.. 
975 
500 at 7.0 p.m. 
11. Gisborne 
650 
275 at 7.30 p.m. 
Gas-engine station— 
12. Napier 
950 
330 at 8.0 p.m. 
Oil-engine stations— 
13. Hastings .. 
360 
300 at 9.0 p.m. 
14. Feilding 
310 
95 at 4.30 p.m. 
Totals 
42,055 
32,367 
* See footnote to table of data, p. 181. 
Ratio of peak-load to installed capacity, 0'75. 
