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Emergency Management

Managing Electricity Supply Emergencies in Tasmania

Tasmanian electricity consumers enjoy an electricity supply, which by international standards is extremely reliable. However, even the most reliable electricity supply systems may have to cope with emergency situations from time to time.

Tasmania has long-established and proven mechanisms and procedures to monitor and manage electricity supply.

This article looks at the sort of emergency situations that could occur and describes the way in which the participants in the Tasmanian electricity supply industry have planned to manage these situations.

The Electricity Supply Industry in Tasmania

Until the mid 1990s the Hydro-Electric Corporation was the organisation that generated electricity, and delivered it to homes and businesses via transmission and distribution networks.

The Tasmanian electricity supply industry was restructured in 1998 and the responsibility for electricity supply is now shared by several entities. Hydro Tasmania retains the task of generating electricity which it does at hydro-electric power stations throughout the State, and at wind farms in the North West. Bell Bay Power Pty Ltd now owns the gas-fired thermal power station at Bell Bay. Transend Networks has the responsibility for transmitting electricity from power stations to substations strategically located around the State. At these substations high voltages are reduced through transformers to allow the electricity to be safely supplied to consumers. From these substations Aurora Energy (Distribution) distributes and meters the electricity to industrial, commercial and residential consumers. Retailers such as Aurora Energy (Retail) are responsible for commercial arrangements including customer liaison, and collecting payment for the electricity consumed.

While Tasmania has always been self sufficient in terms of electricity supply, the opportunity for constructing more hydro-electric generators is limited. To meet future electricity growth requirements, safeguard against water shortages, and enable Tasmania to capitalise on its status as Australia's largest renewable energy supplier, a transmission interconnection with the mainland called Basslink will be commissioned in April 2006. Basslink will allow Tasmania to participate in the National Electricity Market (NEM), which has been developed in the mainland States (excluding WA and NT). The NEM utilises a transmission grid, which interconnects all of the participating States, and allows electricity to be traded across State boundaries.

Basslink will enable Tasmania to export electricity to help meet the peak demands of the national market, and allow Tasmania to import electricity during off-peak periods to balance its electrical energy needs, and supplement local generation in times of low water availability.

Tasmania officially joined the NEM on the 29 May 2005 to allow market arrangements to be established ahead of Basslink commissioning. The National Electricity Market Management Company (NEMMCO) is responsible for managing the NEM and controls the interconnected electricity supply system. One of NEMMCO's key roles is to manage the process of dispatching generation in order to meet customers' demands for electricity on a day-to-day basis. Transend assists NEMMCO by performing a number of system operator activities and is able to take control of the Tasmanian power system in an emergency.

Planning for Electricity Supply Emergencies

Emergencies associated with electricity supply are rare, but in today's society they have the potential to cause considerable inconvenience, loss of production, and may even impact on personal safety. It is therefore essential that appropriate plans be in place to cover all conceivable emergencies, and for the processes and procedures that are covered in the plans to be practiced on a regular basis.

All of the electricity supply entities are required, as a function of their operating license, to develop and maintain emergency management plans to manage their own assets and consumer responsibilities, and to coordinate their activities with the other entities. By virtue of these arrangements the entities are able to manage a wide range of incidents and emergency situations without State (or jurisdictional) involvement.

Serious emergencies require the jurisdiction to become involved and a Tasmanian Electricity Emergency Management Plan has been developed to cover such eventualities. The Tasmanian Electricity Emergency Management Plan is provided for under Section 6 of the Electricity Supply Industry Act 1995 and is also a requirement for Tasmania's participation in the National Electricity Market.

To ensure that responses to emergencies are consistent and appropriate, important decisions are made at a senior level and only after appropriate consultation. The processes provide for the Minister for Energy to be aware of all serious emergencies.

Key Responsibilities During an Electricity Emergency

In Tasmania there are long-standing electricity emergency management arrangements in place that are updated regularly. Key players are:

  • the 'Responsible Officer' (currently the Chief Executive Officer of Transend) who has operational responsibility for managing power system emergencies as provided for under the Power System Emergency Management Plan (see below);
  • the 'Jurisdictional System Security Coordinator' (Deputy Secretary of the Department of Infrastructure, Energy and Resources and Director, Energy Planning), who is responsible for advising the Minister for Energy on the need for jurisdictional interventions, such as voluntary or mandatory power restrictions
  • the Electricity Coordination and Advisory Committee (ECAC), which is chaired by the Jurisdictional System Security Coordinator and which comprises the Responsible Officer, and representatives from Aurora Distribution, the State Emergency Service, the Tasmanian Energy Regulator, the Minister for Energy and key Government agencies, including the Department of Premier and Cabinet and the Department of Treasury and Finance, and NEMMCO (see below).
    One of ECAC's key roles is to advise the Minister for Energy, through the Jurisdictional System Security Coordinator, on electricity emergency management arrangements, both in preparation for and during emergency events. ECAC oversees the operation of the Tasmanian Electricity Emergency Management Plan, which sets out the roles of key parties and the procedures to be followed in an emergency situation.

The Tasmanian Electricity Emergency Management Plan is updated regularly and exercises (simulated emergencies) are also conducted on a regular basis (three in the 2004-05 year). ECAC meets at least quarterly, but more frequently when circumstances demand it. For example, an ECAC working group has been meeting more regularly to monitor and provide advice on low water storages due to the prolonged below average rainfall.

NEMMCO is responsible for power system security in Tasmania and co-ordinates responses to power system emergencies. NEMMCO exercises this responsibility under a common, agreed framework in all NEM States (Tasmania, Victoria, South Australia, New South Wales and Queensland) known as the Power System Emergency Management Plan (PSEMP). In an emergency situation NEMMCO co-ordinates its activities with the State by direct contact with the Responsible Officer, Jurisdictional System Security Coordinator and local energy entities.

What Sort of Emergencies Could Occur?

To understand the nature of electricity supply emergencies, some understanding of the normal variation in electricity demand and supply is necessary.

Unlike the supply of water and gas, electricity needs to be produced at the same time it is used. This means that generating companies need to increase or reduce output to meet the variation in electricity demand throughout the day. Electricity demand varies according to the time of day as well as time of year. Periods of peak electricity demand tend to occur early in the day as a result of businesses starting up and a high level of household use, or in the evening when household use is again high. Peak load is often accentuated by extremes of weather (either hot or cold). In Tasmania the maximum peak load of the year usually occurs on a winter morning and reflects the high demand for electric space heating.

The frequency at which electricity is supplied is also important. The frequency determines the speed at which electric motors turn and a reduction in frequency would cause most electric motors to slow down. This is not a situation that can be tolerated by many modern appliances and its implications will be discussed later.

Electricity supply emergencies usually fall into one of the following four categories:

- Failure of local distribution system.

- Loss of generating capacity.

- Loss of transmission facility.

- Shortage of fuel supply, or in Tasmania's case, water.

Failures in the distribution system can be due to a range of causes including traffic accidents, fires, lightning, animal and vegetation interference, wind storms and minor equipment failure. These failures affect only those consumers on that particular circuit. While such an incident is of concern to the consumers disrupted, and the local distribution company (in Tasmania's case Aurora) the emergency is usually confined to a limited area. Reconnection is usually possible as soon as the fault has cleared itself or Aurora has made repairs. Occasionally a particular occurrence such as a severe storm may cause damage to a number of elements of a distribution system causing problems over a wider area and delaying the return of electricity supply.

In the event that generating capacity is lost due to the failure of a power station or individual generator the impact may be widespread. If other generators in service are unable to immediately increase output to make up for the lost supply the total electricity demand will not be able to be met. Some of the techniques for managing such an emergency are discussed in the next section.

The failure of an element of the transmission system, either a transmission line or transformer, could also result in a disruption to supply if an alternative circuit or device is not available for use. Under some circumstances an inability to meet demand may be confined to a particular geographical area. However, if the failure occurs in a key transmission line or substation, a significant part of the State could be affected. The techniques for managing such an emergency are similar to those used in the event of major generator failure.

Emergencies resulting from a shortage of stored water for hydro generation have affected the supply of electricity in Tasmania in the past but are less likely to occur following the interconnection to the national grid via Basslink in April 2006. Nevertheless, provision is made in the planning process for such eventualities, as in the current situation (2005) with below average water storages.

To date, emergencies associated with the electricity supply system in Tasmania have been confined to the State. When Tasmania is connected to the national grid, it will be able to assist with supply shortages in other States, and in turn can be assisted by other States if the supply shortfall occurs in Tasmania.

How Are Major Supply Shortfalls Managed?

This section deals with the techniques used to minimise the effect of a disruption.

In an emergency situation, the first priority of NEMMCO and the electricity businesses is to restore normal electricity supply as quickly as possible and to protect public health and safety.

Most minor or local level power system incidents are managed by the relevant electricity businesses and/or by NEMMCO without any intervention from Government, although they must comply with any Government policy direction provided to them in advance.

Only in extreme circumstances, when there is insufficient power available to maintain normal energy supplies (for example, if water storages fell to a critical level) or where the overall safety or integrity of the power system is threatened, will the jurisdiction consider intervening in normal market processes. In these circumstances, the Jurisdictional System Security Co-ordinator will consult with the Responsible Officer and ECAC before advising the Minister for Energy on the need for power restrictions.

In the event of the need for restrictions it is Government policy to give priority to the protection of public health and safety and the delivery of essential services.

Disruption and inconvenience to the community and industry users should be minimised to the extent possible, with any burdens shared as equitably as possible.

Load Shedding

To a large extent the management of emergencies depends on whether the emergency can be foreseen, or if it happens unexpectedly. The management of emergencies also depends how long the emergency is expected to continue.

When an unexpected major supply shortfall occurs, as a result of a major generator or transmission line "tripping out" of service, the first thing that happens is that the frequency at which the electricity is supplied starts to fall. If the frequency were allowed to fall unchecked, consumers' electrical equipment would be at risk and the electricity supply system itself could be damaged. To prevent this happening, automatically operated devices disconnect a predetermined number of consumers from the system to allow the frequency to return to normal. This process is called Under Frequency Load Shedding.

The objectives of under frequency load shedding are to restore the balance of supply and demand, minimise the harm and disruption to consumers, and restore the normal supply as soon as possible.

In order that the under frequency load shedding process can handle a range of supply shortfall situations, electrical loads are shed (disconnected) in large blocks. A block of load will include particular consumers. A modest fall in frequency results in a single block of load being shed, while larger falls in frequency result in more blocks of load being shed. The blocks are designed to reduce the electricity demand in a way that is most effective for safeguarding the system.

In some circumstances there is some warning of a need to shed load. For example, a problem may have been discovered with a major power station that requires it to be removed from service in, say, half an hour. In such a situation, the system operator may progressively shed load as the power station is being removed from service. This process can be carried out in a controlled and deliberate manner and there may be an opportunity to advise consumers whose supply is going to be disrupted. This process is called Manual Load Shedding.

The principle guiding all load shedding is that essential services have the highest priority for electricity supply. The next highest relate to loads where loss of supply causes particular harm or economic loss.

For the guidance of NEMMCO and electricity entities in Tasmania the Jurisdictional System Security Coordinator has issued a document setting out load shedding priorities for the Tasmanian Jurisdiction. A link to a copy of this document is provided at the conclusion of this paper.

While residential and general commercial consumers are only involved in load shedding in rare emergencies, the planning procedures provide for such an eventuality. Residential and commercial consumers may lose their supply as a result of an under frequency load shedding event or as a result of manual load shedding.

Most emergencies requiring load shedding are relatively short lived and normal electricity supplies can be restored to consumers within a few hours. If however, there is an ongoing severe supply shortfall provisions are in place to prevent just a few consumers bearing all the inconvenience. Again, the aim is to share the burden as equitably as possible. Consumers who have had to be disconnected may be reconnected again and others disconnected instead. This happens about every two hours and the process is termed Rotational Load Shedding.

Under some emergency circumstances the electricity supply situation may be in balance but insufficient generation reserves exist to cover any increase in demand. In such cases some prudent management of electricity use may be all that is necessary to avoid having to shed load. Under such circumstances consumers may be requested to restrict their use of electricity on a continuous basis, or simply during the period when peak loads usually occur. Consumers would be advised of the details via local media outlets.

If the circumstances are considered to be even more threatening the Government may consider issuing a Mandatory Restriction Order requiring consumers to restrict their electricity use. Such an order has the force of law and failure to comply can result in penalties. A mandatory restriction order would specify what appliances or processes may be utilised and any time of use restrictions.

A request for voluntary restraint on the use of electricity can only be authorised by the Jurisdictional System Security Coordinator or the Minister for Energy. Only the Minister can issue a Mandatory Restriction Order and that has to be in writing.

Futher Information

PDF Icon Jurisdictional System Security Coordinator Load Shedding Priorities document

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