Managing the System
Decisions
System Control
Electricity cannot be stored, except in small quantities in batteries. It is therefore necessary to produce it as it is required. Hydro Tasmania's power system is designed to supply electricity day and night according to demand. Each power station is connected to a State-wide network of conducting wires. Electricity can be sent from any power station to different parts of the State for use by any of nearly 240,000 customers.
The complex task of deciding which power station should operate at any given time is preformed by a command centre in Hobart known as System Control. These decisions depend on two main factors:
- The amount of water available for use in the various storages.
- The amount of electricity being used around the State
The Availability of Water
When making decisions about which water storages and power stations to use it is necessary to have an understanding of likely rainfall over catchment areas. Large inflows of water into a small storage could lead to spillage over the top of the dam. Water is used with a view to keeping losses due to spillage to a minimum. Long-term planning is also geared to ensure enough water is available during extended periods of drought.
Priorities for water release are set on a daily basis. Small run-of-the-river storages such as Trevallyn, Paloona or Meadowbank, rely on daily flows of water and are used more frequently during periods of wetter weather. Big storages like Lake Gordon and Great Lake fill up and draw down over a number of years. They are used more frequently when drier weather reduces water availability in the run-of-the-river storages. Extra complexities are introduced into the decision-making process when you consider that as the level of water in a storage drops so does the head (or water pressure). More water is then needed to produce the same amount of power.
Demand for Electricity
Electricity is an unusual product - it is created as it is used. The average demand for electricity at any one time is about 1010 MW but this can vary from a low of about 750 MW to a high of about 1500 MW.
About two thirds of the electrical energy used in Tasmania goes to 19 major industrial customers. These large industries generally operate 24 hours a day and use electricity at relatively constant rates. The variability in total demand on the power system is due to patterns of use by households and small businesses. Between 2.00 am and 4.00 am electricity use is low because people are asleep and businesses are closed. A maximum demand is reached between 7.00 am and 10.00 am when people are showering and cooking breakfast and when businesses and schools begin operating.
Another peak is reached in the evening as meals are cooked and televisions, heaters and lights are switched on. The demand for electricity is considerably higher during winter months due to heating requirements. It is generally lower during weekends and holidays when people are not at work and factories are closed.
When planning which power stations to operate, System Control makes a prediction of the following day's likely power demand. They look at the weather forecast and even such things as the types of programs on television. This information is coordinated with decisions about which water storages to use and an operation schedule is drawn up. This schedule identifies when generators are to be started and stopped to ensure that the fuel (water) is used in the most efficient manner.
An added complication in organising the operation of power stations is the need to cope with planned and unplanned outages of equipment. Power stations are off-line at different times for maintenance purposes. A more difficult problem arises when equipment fails suddenly. The loss of a large transmission line during a storm or the unforeseen failure of generating equipment require rapid changes to operating schedules.
In addition to the complications associated with meeting the generation and transmission requirements, other community activities that rely on particular water discharges from lakes into rivers or the maintenance of particular levels in lakes for recreational activities such as rowing, canoeing, water skiing and fishing need to be included in the schedule.
System Control utilises a state of the art Energy Management System (EMS) to directly control generators and transmission equipment. The EMS communicates with power stations and substations over Hydro Tasmania's Digital Microwave System. This is an example of where Hydro Tasmania has used the latest technology to better utilise the capabilities of the integrated generation and transmissions systems to provide our customers with a highly reliable, high quality electricity supply.
A typical winter's day
Domestic and Commercial
Major Industial
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