Expect the unexpected
Fahd Hashiesh, head of ABB's power consulting business for the UK, Middle East and Africa, explains why network operators must consider the balance between supply and demand - and how system studies can help them.
7th June 2017 by Networks
In the past, grid operators would use frequency as the measure of balance between electricity supply and demand. However, the picture has become significantly more complex as penetration of renewable energy has grown.
Today, many competing factors can affect the balance. On the demand side, these include growth in demand, changing behaviour and introduction of electric vehicles; whereas the environment and mix of generation can affect the supply side. Also, system inertia, losses and power quality can all affect the grid, as can trading behaviour.
The unpredictable nature of renewable energy means grid operators must manage voltage fluctuations and instabilities, balance reactive power and filter harmonics. Also, as renewables have replaced rotating mass generators, there has been a significant loss of system inertia.
Today, operators lack tools that can precisely monitor changes in frequency and, more importantly, its rate of change so they can take timely actions.
As the grid expands to include wind and solar generation, there have been consequences for grid operators. One is the change in the number of short circuits. Another is the potential overloading of equipment to accommodate higher than normal generation across the grid, for example when a wind farm is operating at peak capacity. There have also been problems with fault ride-through, reactive power balance, system inertia and power quality.
Changing load profiles can introduce challenges for grid operators. When industrial consumers connect new loads such as variable frequency drives, furnaces and rolling mills, they also introduce harmonics that might damage the electrical infrastructure.
The grid operator’s own infrastructure can also affect other grid-connected equipment. For example, an operator might install a series compensator to overcome reactive power over a long AC transmission line.
However, an unanticipated result can occur in wind generators when the grid frequency coincides with the resonant frequency of the turbine generator shaft, causing catastrophic failure and literally blowing the generator apart in a phenomenon called sub-synchronous torque interaction.
Even changes to the grid’s protection and control system must be studied carefully to avoid introducing mal-operation as the grid expands. As new generation, loads and relays are installed, protection and control schemes become more sophisticated. Automation engineers should take care to avoid loss of synchronism, which can lead to instability. In turn, this can represent non-operation of primary protection and ultimately equipment failure and blackouts.
When Ukraine’s power grid was infiltrated in late 2015, hackers targeted substation communication devices to open feeder circuit breakers at different substations. While the operator recovered power within hours by manually overriding primary equipment, the hackers had updated firmware in the relays, which had to be replaced.
The experience has not only taught grid operators the value of enhancing cybersecurity but also the importance of considering and analysing scenarios that would once have been unthinkable, such as loss of control centre communications, changes to functionality of key equipment and loss of operational data.
In light of the changing world we live in, system studies and analysis are growing in importance. They have become an essential tool for operators to understand all the potential consequences of changes to the grid, whether initiated by the changing nature of generators and consumers, new technologies or external factors.
The starting point for assessment methodology is properly to model the current system while considering future energy scenarios.
These break down into generation and demand modelling. In terms of generation, auditing grid-connected generation will evaluate the types, installed capacity and load factor of grid-connected generation. Similarly, analysis of loads, real and reactive power demand and daily profile will establish the demand background. Also, the location of generation and loads must be considered.
The other major element of a system study is to take into account the potential impact of network upgrades. This reveals the impact of new overhead lines, cables, transformers and switchgear on the grid.
Operators are using system studies to evaluate the best solution to their challenges when weighing up the advantages of technologies such as FACTS, microgrids, wide area management systems or energy storage.
To support this, our 125-strong team of power consulting experts can combine their know-how to deliver feasibility studies, simulations, grid studies and renewable integration consulting. Their objective is to maximise the value of an operator’s assets and achieve optimum value from investments.
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