Get grid smart

By turning the classic linear energy grid into an intelligent and interactive network, smart grid is transforming the way we use energy.

There are many definitions, concepts and technologies which claim to encompass the smart grid concept. At Schneider Electric, smart grid is defined as combining electricity & IT infrastructures to integrate and interconnect all users (generators, operators, resellers, consumers etc) to efficiently balance demand and supply over an increasingly complex network.

The four main triggers of smart grid are:

• Renewable energies, allowing consumers to be their own utilities and create the need to connect these distributed sources to the central grid.
• Active energy efficiency and energy management, making energy visible and giving consumers the means to act on their energy consumptions.
• Electric vehicles, reshaping the way everyone thinks about private and public transportation.
• Real-time grid management to anticipate consumption and adapt energy supply accordingly.

We are seeing a change from the traditional one-way, energy-only grid to two-way, energy+data smart grid. This transition is bringing a renewed focus to many aspects of energy management. One area of energy management consideration which this transition has the potential to greatly affect is the topic of power quality.

Power quality

Power quality (PQ) is the quality of the network supply and the customer load determined by the measurement of the following quantities: power frequency, voltage magnitude, voltage dips/swells, voltage interruptions, power factor, voltage and current harmonics, voltage imbalance, load imbalance and flicker.

The IEEE explains power quality from the point of view of the equipment designer, electrical utility and end user:

“A point of view of an equipment designer or manufacturer might be that power quality is a perfect sinusoidal wave, with no variations in the voltage, and no noise present on the grounding system.

A point of view of an electrical utility engineer might be that power quality is simply voltage availability or outage minutes.

Finally, a point of view of an end user is that power quality or ‘quality power’ is simply the power that works for whatever equipment the end user is applying.

An ideal scenario to best avoid power quality problems would be an environment where the equipment designer or manufacturer clearly states the equipment needs, and the electrical utility engineer indicates the system delivery characteristics, and the end user then predicts and understands the equipment operational disturbances that will likely be encountered on a yearly basis. This allows a cost justification to be performed by the end user to either improve equipment operation by installing additional components or improve the electrical supply system through installation of additional, or alteration of existing components.”

Power quality problems can be caused by:

• Loads (electronic equipment that distorts the waveform, unbalanced loads - this can include anything from variable speed drives to arc furnaces or basic modern electrical equipment such as computers)
• Environmental conditions (lightning, storms)
• Operation of substation equipment (switching, transformer tap changing)

With an interactive electrical network what happens in one location has the ability to affect other locations. The extent of the effect is determined by the electrical parameters of the network at each of the locations. For example, a disturbance on the transmission network can potentially affect a low-voltage customer, such as a small to medium business owner with a power outage.

In order to control this effect, each of the connected parties is governed by specific rules. If any of the parties want to continue to be part of the electrical network, then they need to comply with the rules. In Australia, this changes depending on which state you are working in. It is important to be mindful of the power quality compliance standards for the state where the equipment is being installed, rather than manufactured.

Summary of power quality compliance standards:

• NSW - AS/NZS 61000-3-6 to regulate limits of harmonic content.
• Victoria - IEEE519-1992 to regulate limits of harmonic content.
• Queensland - AS2279 Part 2 (replaced by AS/NZS 61000-3-6) to regulate limits of voltage harmonic content. And regulation-based IEEE519-1992 to regulate limits of harmonic current.
• Western Australia - customised tables to limit total voltage harmonic (THD(V)) distortion at the point of common coupling. Requires knowledge of source background harmonics.

The quality of electricity has become a strategic issue for electricity companies, the service sector, industrial sites and equipment manufacturers for the following reasons: the economic necessity for businesses to increase their competitiveness with maximum uptime, the widespread use of equipment which is sensitive to voltage disturbance and/or generates disturbance itself, and the opening up of the electricity market.

The cost of disturbance (interruptions, voltage dips, harmonics, lightning overvoltage, etc) is substantial. These costs must take into account losses in production and raw materials, restarting of production facilities, non-quality of production and delivery delays. The malfunction or shutdown of vital equipment such as computers, lighting and safety systems may put lives at risk (eg, in hospitals, airport lighting systems, public and high-rise buildings, etc). Costs also include high-quality, targeted preventive maintenance measures for anticipating possible problems. There is an increasing transfer of responsibility from the industrial user to the equipment manufacturer for the provision of site maintenance.

Other less obvious consequences of PQ degradation are: overloading of the installation causing premature ageing and increasing the risk of breakdown, leading to the oversizing of distribution equipment.

Taking PQ compliance monitoring a step further, PQ analysis allows utilities to determine the root cause of the power quality problem(s) and suggest solutions. This analysis and solution design might be done strictly for the utility itself, in order to improve its PQ compliance metrics, or for a utility’s key customers.

The benefit of solving end-user problems for a utility is twofold:

1. Improved customer loyalty through assisting to understand PQ issues.
2. Increased level of power quality across the overall transmission and distribution (T&D) network.

Power quality solutions

Most utilities have specific policies for billing reactive energy. Price penalties are applied if the active power/apparent power ratio is not within the guidelines.

Power factor correction solutions modify and control the reactive power to avoid utility penalties and reduce overall kVA demand. These solutions result in lowering utility power bills by up to 10%. Harmonics stress the electrical network and potentially damage equipment - harmonic filtering is required to reduce and eliminate harmonics.

Power factor correction:

Every electrical machine needs active and reactive power to operate. Power factor measurement identifies the level of reactive power and optimises it to minimise cost and avoid penalties. If the power factor drops below the limit set by the utility then the power factor correction bank modifies the level to avoid penalties.

By correcting poor power factor, these solutions also reduce kVA demand. Reduced kVA demand results in lower utility power bills, cooler equipment operation and longer equipment life. In addition, proper power factor correction helps optimise electrical network loading and improves reliability.

Harmonic filtering:

Equipment such as drives, inverters, UPS, arc furnaces, transformers, filters and discharge lamps generate voltage distortion or harmonics. These harmonics stress the network, overload cables and transformers, cause outages and disturb many types of equipment such as computers, telephones and rotating machines. Subsequently, the life of equipment can be greatly reduced.

Harmonic filtering solutions are a means to reduce and eliminate the harmonics. They increase the service life of equipment up to 32% for single-phase machines, up to 18% for three-phase machines and up to 5% for transformers.

The development of smart grid technologies will drive increasing interaction with the electric grid by all parties - utilities, the service sector, industrial sites, equipment manufacturers and consumers. Accurate forecasting of electricity demand by individual players will become increasingly important to ensure continuity of power supply in Australia. Power quality is an integral part of a functional smart grid and this should receive specific consideration from utilities, large electricity consumers and equipment suppliers who will play a major role in the transition to smart grid.

By Samuel Coupel, Product Manager - Energy Management & Power Quality, Schneider Electric Australia