ELECTRICITY AND POWER DEFINITION

Deep Connection
Transmission assets and services provided by the Transmission Network Operator which are:
initially for one participant, but where the assets may eventually become part of the shared network; and
immediately part of the shared network, but are assets which would not need to exist if not for connection to one participant.
Charges and risks associated with Deep Connection services may eventually be shared with other participants, when arrangements change.

DegradationDemand
Deterioration in power output and/or heat rate of an engine or turbine under operating conditions due to, for example, inlet air contaminants, fuel contaminants and thermal stress. Continuous process occurring between overhauls.

Demand
Demand is usually taken to mean the electricity requirements of the end consumer. However, in the NEM, the term "demand" includes consumption and losses in the distribution and transmission networks and in the power stations as well as end user consumption. Extreme care should therefore be taken in the use of published "demand" values.
The demand requirements are usually in two forms:
Instantaneous Demand - the size of the demand at any instance in time and is measured in MW. It is important in determining the generating capacity required to on-line, particularly at peak usage times. It also is important in determining if the transmission and distribution systems can cope with the flow of electricity during peak demand times; and
Period Demand - the amount of electrical energy used by the end use consumers over a period of time (measured in MWh or GWh). This measure is used to estimate how hard the power stations need to operate during that period, the amount of fuel consumed in the generation of that energy and the potential income for electricity retailers and generators.

Demineralised water
Pure water produced by removing mineral salts, usually by an ion exchange process.

Distributed Generation
Is power generation generally located close to where it is consumed, for example, supplying electricity on-site or over-the-fence. Distributed generators can also export electricity into the local grid. Also referred to as decentralised, embedded or localised. Includes cogeneration and other types of generation such as fuel cells and photovoltaic. This can be as small as a 3 kWe micro-cogeneration plant, or as large as a 450 MW industrial on-site system.

Distribution
Electrical cabling system which transfers power, usually over long distances, to the consumers. Distribution systems are usually operated at medium to low voltages (eg 110kV, 66kV, 33kV, 11kV, 6.6kV & 415V).

Dump condenser
Excess steam from the waste heat boiler bypasses the steam turbine and goes directly to the condenser. Used to balance site load with steam generated.

Dump stack & damper
Used to control flow and temperature of exhaust gas to bypass the waste heat boiler. Can also be used to isolate equipment in the exhaust gas stream when the equipment is out of service or requires maintenance. Used to balance steam generated with site load.

DUOS
Distribution use of system charge. In the National Electricity Code, the charge for using the electricity network on or below 66 kV voltage level.

Economiser
A counterflow heat exchanger for recovering energy from the exhaust gas. It increases the temperature of the water entering the boiler drum using otherwise wasted exhaust heat and hence increasing steam-raising ability. Economisers are assumed on WHBs in this analysis.

Efficiency
Thermodynamically, the ratio of useful energy output to energy input into a process. Has many specific definitions and care needs to be taken that the meaning is clear. See also Heat Rate.