Emergency Management
- Managing Electricity Supply Emergiencies in Tasmania
- The Electricity Supply Industry in Tasmania
- Planning for Electricity Supply Emergencies
- Key Responsibilities During an Electricity Emergency
- What Sort of Emergencies Could Occur
- How are Major Supply Shortfalls Managed
- Load Shedding
- Further Information
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 to affect supply, 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. Aurora Energy (Tamar Valley) operates 4 open-cycle and 1 combined cycle gas turbine at the Bell Bay site. 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 was commissioned in April 2006. This interconnection is now fully operational and allows 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 enables Tasmania to export electricity to help meet the peak demands of the national market, and allows Tasmania to import electricity during off-peak periods to balance its electrical energy needs, and supplement local generation at 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 credible emergencies, and for the processes and procedures that are covered in the plans to be practised on a regular basis.
Electricity supply entities are required, as a function of their operating licence, to develop and maintain emergency management plans, and to coordinate their activities with the other entities at times of emergency. By virtue of these arrangements the entities are able to manage a wide range of incidents and emergency situations without State involvement.
Serious emergencies require the State to become involved and a Tasmanian Electricity Emergency Management Plan has been developed to cover such eventualities. The Tasmanian Electricity Emergency Management Plan was developed to meet the requirements of Part 6 of the Electricity Supply Industry Act 1995, and constitutes a Special Emergency Management Plan under Section 35 of the Emergency Management Act (2006) The plan is also a requirement for Tasmania's participation in the National Electricity Market.
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 and the Department of Treasury and Finance. One of ECAC's key roles is to advise the Minister for Energy, through the Jurisdictional System Security Coordinator, on electricity emergency management arrangements. ECAC reviews and maintains 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. ECAC meets at least quarterly; more frequently when circumstances demand it.
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 usually occurs on a winter morning and reflects the high demand for electric space heating.
The highest ever demand for energy in Tasmania was 1760 MW in 2008. The maximum power output from Tasmanian generators in ideal conditions is currently in excess of 2500 MW.
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, (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 Energy) 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 immediately to 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. This is less likely to occur since 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 with below average water storages.
To date, emergencies associated with the electricity supply system in Tasmania have been confined to the State. With Tasmania connected to the national grid, it is now possible to assist with supply shortages in other States, and in turn Tasmania can be assisted by other States in times of supply shortfall.
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 before advising the Minister for Energy on the need for power restrictions.
In the event of the need for restrictions it is State 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.
Under Frequency (Un-planned) Load Shedding
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.
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, generators' electrical equipment would be at risk and the electricity supply system itself could be damaged. The worst case scenario for the network is a 'system black'. This is where the capacity of the network to transmit electricity collapses altogether. Re-energising the network from a system black is a complex and time consuming process. 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 rise in frequency results in a single block of load being shed, while larger rises 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.
Manual (Planned) Load Shedding
In some circumstances there is 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, for instance, thirty minutes. In such a situation, the system operator can 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.
Managing Power Shortages
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. In these circumstances requests for voluntary restraint on the use of electricity are authorised by the Minister for Energy.
In times of serious prolonged power shortage, the State Government may consider issuing a Mandatory Restriction Order (MRO) requiring consumers to restrict their electricity use. A MRO would specify what appliances or processes may be utilised and any time of use restrictions. MROs have legal force allowing sanctions to apply in the event of non-compliance. Only the Minister of Energy can issue a MRO and that has to be in writing.
