Network integration of wind power - Wind Power Integration: Connection and System Operational Aspects - page 103

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33 kV 11 kV Load

Figure 4.5 Wind farm connected directly to a substation low voltage busbar

believing that the network is experiencing light load conditions. Thus the LDC
element mal-responds, believing there to be little demand-related voltage drop on
the load circuits. Some systems can be thoroughly confused by a reversal of power
through the transformers resulting from high wind farm output at low load periods.
To correct this issue properly would require a substation overall voltage control
system which would, at the least, establish the load as the sum of the transformer
flows and the wind farm flows. The LDC could then act properly and, provided the
wind farm objective was unity power factor, the tap change control would operate in
a normal manner to control network voltage. The above discussion on direct con-
nection to the sub-transmission system is then relevant in assessing the voltage
variation seen by connected customers.
It is important to assess the ability of tap-changers to deal with reverse power
and/or reactive power flow conditions.
Finally, it needs to be remembered that not only the voltage on the wind farm
feeder but the voltage at all points of the local distribution system needs to be
controlled to within the license standards, otherwise there are potential legal con-
sequences for the utility. SMART Grid systems which measure voltage at many
points and adjust load and generation output are likely to be the way forward, but
the required telecommunications infrastructure and the various levels of control
involved have slowed the deployment of such advanced technology in many places.
The following paragraphs expand on the complexity of managing voltage in this
environment.

4.3.1.6 Generation embedded in distribution circuits
The key distinguishing feature of distribution circuits is that demand is connected
directly, or connected through fixed-tap transformers. These circuits are designed
on the basis of voltage standards, so that customers at the sending end can receive
up to the maximum allowable voltage while customers at the receiving end can be
supplied at the lowest allowable voltage. The voltage drop between the ends varies