Environmental Engineering Reference
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cally charged with investigating these future scenarios and coming up with technological
solutions to the operational challenges that can in the end deliver reliable power supplies at
reduced cost.
Changes to be expected will include active and automatic network reconfi guration schemes
aimed at facilitating a high penetration of distributed generation while reducing customer
minutes lost due to faults.
8.6.2 Active Networks
The network above the 11 kV system is actively controlled with activity increasing as the
voltage is increased. For example, the 30/10 kV tap-change transformer in Figure 5.11 is fi tted
with an automatic voltage controller that monitors the low voltage level and adjusts the taps
to keep it within specifi ed limits. Higher up in the chain, at the transmission level, not only
active but also reactive power fl ows are appropriately regulated down transmission lines to
ensure that the voltage profi le is acceptable, the system is secure under contingencies and
that it operates as economically as possible. Additionally under fault conditions, reclose
circuit breakers are controlled to improve reliability of supply.
Active control involves some or all of the following functions performed on a continuous
basis:
￿ the measurement of system parameters, for example V,I,P,Q, f and network topology;
￿ comparing these measurements with set values or with desirable values obtained from
analytical computations of the network model, for example load fl ow analysis, contingency
analysis, optimum economic dispatch etc;
￿ activating a control element to implement the desirable changes, for example increasing
the excitation of or the steam input to a synchronous generator, opening or closing a trans-
mission line;
￿ checking that the changes have been implemented and warning control engineers if the
control actions fail.
Distribution networks are extremely extensive. For example, the UK has over 290 000 km
of overhead and 470 000 km of underground cable. The conversion of this mostly 'passive'
network into an 'active' network would be a major task and will take place gradually
as distributed generation is adopted. A key fact is that distribution networks in developed
counties have been in place for several decades and will require updating soon due to
ageing. This is a unique opportunity to enforce a culture change and design in the new
networks the capability of embracing embedded generation rather than repeat yesterday's
technology.
In the UK, Ofgem, the Offi ce of Gas and Electricity Markets in a recent consultation docu-
ment has established an incentive mechanism to encourage Distribution Network Operators
(DNOs) to establish what are known as Registered Power Zones (RPZs). These are 'nursery
sites' in which DNOs can develop and demonstrate cost-effective ways to connect distributed
generation to networks. Typical projects within the RPZs focus on active voltage control,
fault level management and power fl ow control.
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