Network integration of wind power - Wind Power Integration: Connection and System Operational Aspects - page 113

to how to plan the network and the low probability that even 90% of wind capacity
will ever run concurrently.
As the penetration of electric vehicles and energy storage systems increase,
network utilisation at times of high wind will be improved, because additional load
allows a higher level of both wind farms and plant with inertia to be operated
during periods of otherwise naturally low demand. It will be important to factor this
higher use opportunity into backbone network development for wind.

4.4.4 Equipment issues
When conductors carry large currents they are heated by the conductor's resis-
tance. Eventually they reach a knee-point temperature, where the tensile strength
(TS) of the conductor is much reduced; it sags and may undergo plastic defor-
mation. 'Gap' conductor allows the aluminium to lose its tensile strength and to
move relative to an inner steel core because a gap is maintained between the two
throughout the length of the conductor. The tensile strength of the steel core is
sufficient to avoid excessive sag up to high temperatures and the conductor
recovers. The layer of aluminium around the steel core is segmented so that its
inner surface forms a smooth tube. The steel core within is packed in high
temperature resisting grease. Forming conductor joints is exacting work. The
carbon cored conductor ACCC has a similar mode of operation. Other high
temperature conductors are based on tightly packed hexagonal segmental cross
sections of alloys which have both low resistance and higher knee-point char-
acteristics. TS and coefficients of expansion (CoE) differ markedly: galvanised
steel has a TS of about 140 N/mm 2 and a CoE of 11.5 10 -6 / 0 C, whereas gal-
vanised Invar has a TS of 110 N/mm 2 and a CoE of 2.8 10 -6 / 0 C and glass/
carbon fibre in a resin mix has a TS of 246 N/mm 2 and a CoE of 1.5 10 -6 / 0 C.
Clearly the latter has a great advantage, but needs to be proven in climatic
conditions for a significant period.
Load flow analysis is undertaken to show whether the circuits, mainly over-
head lines, can cope thermally with the transfers. Summer conditions may be more
arduous than winter because of ambient temperature de-rating. In temperate cli-
mates this is combined with lower loads at B and C in Figure 4.10. If, for simpli-
city, we assume that lines 1-6 are rated equally, the outage of 1 or 2 represents a

3

1 5

2 6

4

A B C

Figure 4.10 Assessment of line thermal ratings