Economy & Energy
Year III - No 13 March/April 1999

ollaoro.gif (978 bytes) Main Page
ollaoro.gif (978 bytes)The Structure of the Crisis
ollaoro.gif (978 bytes)Privatization in the Energy Area
ollaoro.gif (978 bytes)Energy Equivalence Coefficients
ollaoro.gif (978 bytes)Glossary of Energy
ollaoro.gif (978 bytes)e&e links
Following the Brazilian Economy:
ollaoro.gif (978 bytes)Brazilian Public Debt
ollaoro.gif (978 bytes)Internationl Reserves
Graphical Edition:
Editoração Eletrônic
Saturday, 14 April 2001.

Glossary of Energy Terms

  Production: Coordenação Geral de Informações Energéticas
Secretaria de Energia 
Ministério de Minas e Energia (*)
Contacts: João Antônio Moreira Patusco
English Version: Frida Eidelman

(*) General Coordination of Energy Information
Department of Energy
Brazilian Ministry of Mines and Energy


The Ministry of Mines and Energy is editing a Glossary where the terms currently used are defined for each specific energy area. In the present issue of e&e the following items are available:

- Measurement Units
- Common Unit
- Conversion Factors
- Calorie (cal)
- Calorific Power
- Watt (W)
- Watt-hour (Wh)
- Joule (J)
- Newton (N)
- British thermal unit (Btu)

Hydroelectric Energy

- General Terms
- Terms Relative to Location and Heads
- Storage
- Terms Relative to Time
- Volume (flow)
- Terms Relative to the Brazilian Hydraulic Potentiality


- Generation
- Transport and Distribution
- Power and Energy
- Consumption


 The measures are given in terms of unit, namely, a magnitude is expressed by means of a numerical value multiplied by a unit.
1. Concepts

1.1 - Measurement Units (Commercial) - units that usually express the commercialized quantities from energy sources, for example: for solids, ton (t) or pound (lb.), for liquids, the cubic meter (m3) or cubic feet (ft3) and for electricity, watt (W) for power and watt-hour (Wh) for energy.
1.2 - Common Unit - unit to which the measurement units are converted for the different energy forms. This unit allows for adding different energy quantities in the Energy Balance. According to the International Unit System - IUS, joule or kilowatt-hour are the regulatory units used as Common Unit, nevertheless, other units are correctly used by different countries and international organizations such as ton oil equivalent (toe), ton coal equivalent (tce), the calorie and its multiples, British thermal unit (Btu), etc.
1.3 - Conversion Factors (equivalence coefficients) - coefficients that permit to convert the quantities expressed in a measurement unit to a common unit. For example, in the case of Brazil, in order to convert ton of firewood to toe it is used the coefficient of 0.306 which is the ration between the calorific power of firewood and that of petroleum (3300 Kcal/Kg / 10800 Kcal/Kg), that is, 1 t of firewood = 0.306 toe.
1.4 - Calorie (cal) - quantity of heat necessary to raise the temperature of one gram of water from 15.5 0C to 15.5 0C at normal atmospheric pressure (760 mm Hg).
1 cal = 4,1855 J and 1 J = 0,239 cal
1.5 - Calorific Power - quantity of heat, in kcal, liberated by 1 kg or 1 m3 N of fuel after complete combustion.
Note : The fuels that give rise to H2O in the combustion products (originating in the combustion or from impregnation water) have a higher calorific power and a lower calorific power, Since H2O, in most cases, escapes by the chimney as vapor, the lower calorific power is the one that has practical significance.

1.6 - Watt (W) - Power unit -Watt is the power of an energy system in which 1 Joule of energy is uniformly transferred during one second.
1 W = 1 J/s
1.7 - Watt-hour (Wh) - energy uniformly transferred during one hour.
1 Wh = 1 x 3600 s x J/s = 3600 x (0,239 cal) = 860 cal
Therefore, theoretically, 1 kWh = 860 kcal
Note: watt and watt-hour and their multiples are measurement units used for hydraulics and electricity, for power generation and distribution.
1.8 - Joule (J) - Unit of work, energy and quantity of heat. Joule is the work produced by one force of one Newton whose application point moves one meter in the direction of the force.
1 J = 1 N . m
1.9 - Newton (N) - Force unit, Newton is the force that, when applied to a body with a mass of one kilogram, transmits a gravity acceleration of 9,806 m/s2. Then 1 N = 0,102 kg

1.10- British thermal unit (Btu) - Corresponds to the quantity of heat necessary to raise the temperature of one pound* of water by 39,2 0 F. 1 Btu = 1055, 6 J.
* British weight unit

Hydraulic Energy

The use of kinetic energy and the water power by humanity dates to times immemorial for different devices have always been installed at riverbeds and riverbanks.
But only in the XIX century the use of this form of energy became attractive from the economical point of view when the invention of electric energy turbo-generator machines and the possibility of transporting electricity to large distances made possible to obtain a high economical yield of its use.

1 - General Terms

1.1 - Hydroelectric Energy -Water potential and kinetic energy.
1.2 - Reservoir - Large deposit artificially formed closing off the mouth of a valley by means of dikes or barrages in which the waters of a river is stored aiming at using them for regulating the flow of water, for irrigation, for electric energy production, etc.
1.3 - Hydroelectric Power Plant - Installation in which the potential and kinetic energy of water is transformed into electric energy.
1.4 - Power station with reservoir - A hydroelectric power station associated with storage capacity to regulate the water supply to the turbines.
1.5 - Run-of-river power station - A hydroelectric power station which has no significant regulating reservoir.
- Pumped storage power station (pumped storage plant) - A hydroelectric power station with two reservoir, one upstream the other downstream with the respective pumping and turbine installations, that allows for returning to the upstream reservoir the water stored in the downstream after its use for generating energy.
1.7 - Tidal power station - A hydro-electric power plant that exploits the head occurring between the level of the water in the sea at low tide and that of seawater impounded in a basin separated from the sea at high tide.

2 - Terms relative to Location and Head

2.1 - Hydrographic Basin - Surface of land measured in horizontal projection from which effectively comes the water from a watercourse to the considered point.
2.2 - Full Reservoir Level - the highest level normally allowable in the working of a reservoir with no margin for flood.
Note: the maximum level of the reservoir corresponds to the largest allowable level in the case of floods.
2.3 - Lowest operating level - the lowest level normally allowable in the working of a reservoir or other impounding works, measured at a specific point.

Note: below the lowest operating level, emptying of the reservoir can be made down to the bottom outlet
2.4 - Freeboard - Vertical distance between the top of the dam and the maximum elevation attained by the water in the reservoir.

2.5 - Head loss - Reduction of useful energy caused by water runoff in a hydraulic system.

3. - Storage

3.1 - Daily storage - Storage in which the reservoir has a daily filling and emptying cycle.
3.2 - Weekly storage - Storage in which the reservoir has a weekly filling and emptying cycle
3.3 - Seasonal storage - Storage in which the reservoir has a seasonal filling and emptying cycle
3.4 - Annual storage - Storage in which the reservoir has a annual filling and emptying cycle
3.5 - Storage of more than one year - Storage in which the reservoir is able to even out fluctuations in water availability over a period in excess of one year.
3.6 - Useful water capacity - The volume of water available in a reservoir between the lowest and highest levels normally allowable in use.
3.7 - Flood water retention area - The storage volume of a reservoir that exists between the highest level normally available in its working and the maximum possible water level.
3.8 - Passive storage (dead volume) - Volume retained in the dam below the minimum exploration

4. - Terms Relative to Time

4.1 - Hydrologic Year - Period of one year (twelve months) based on hydroelectric criteria.
4.2 - Average Year - Year (fictitious) whose hydraulic characteristics correspond to the average of a coherent series of the largest possible number of years. The series on which the average or normal year is based must be specified in each case.

- Wet year - Year based on statistical criteria in which a water stream has higher influx than the average.
- Dry year - Year based on statistical criteria in which a water stream has lower influx than the average.
- Exploration time - Number of days in an average year during which the flow is higher than the exploration flow.

 5. - Volume (flow) Terms

5.1 - Discharge flow - The volume of water flowing through a cross section in unit time.
5.2 - Useful inflow - The part of the available flow which after subtracting compensation water and unavoidable losses, is available for generating electricity.
5.3 - Nominal discharge (turbines) - The rate of flow for which the turbine is designed.
5.4 - Nominal delivery (pumps) - The rate of flow for which the pump is designed
5.5 - Cumulative flow - the volume of water corresponding to the flow which passes a given cross section in a given period of time
5.6 - Hydraulicity - the ratio of total flow in an observed period to the total mean flow for the corresponding period over a long series of years (mean year).

6.- Terms Relative to the Brazilian Hydraulic Potential

 6.1 - Gross Hydraulic Theoretical Potential - Maximum quantity of electric energy that can be obtained from a specific region or a hydrographic basin during an average year taking into account the corresponding heads referred to a given point of this region or basin.
6.2 - Definition of the Developing Stages of the Hydraulic Potential

6.2.1 - Remnant - Result of the estimation made in office from existing data without any complementary survey considering the reaches of the river, usually at the head without considering the location where the exploitation will be implanted;
6.2.2 - Individualized - Result of estimation made in office for a specific location from existing data or rough survey without any detailed survey;
6.2.3 - Inventory - Result of hydrographic basin study in order to determine its hydroelectric potential through the choice of the best alternative to head division, characterized by the set of exploitation that are compatible among themselves and with projects aiming at obtaining the best evaluation of available energy, environmental impacts and implementation costs of the undertaking;
6.2.4 - Viability - Result of the global conception of the exploitation, considering its technical and economical optimization, comprising the dimensioning of the main structures and the local infrastructure works, the definition of the respective area of influence, the multiple use of the water and the effects on the environment;
6.2.5 - Basic Project - Detailed exploitation with defined budget that allow for the elaboration of documents for civil work procurement and supply of electromechanical equipment;

6.2.6 - Construction - exploitation that had its works started, without any generation unit in operation;
6.2.7 - Operation - Exploitation that has at least one generation unit in operation;
Composition of the Brazilian Hydroelectric Potential - the value of the Brazilian hydroelectric potential is composed of the sum of the estimated part (remnant +individualized) and that part that was inventoried. The inventoried part includes plants in different levels of study - inventory, viability and basic project - besides the exploitations in construction and operation.

Stage Power Record Number Remnant Individualized Total



Powera (MW)

Record Numbers










Estimated Inventory 






Basic Project












Total Inventaried








Electricity is a derived energy that can be produced from most forms of energy. The most important process of its production is to use a generator or alternator that converts mechanical energy supplied by a thermal process or by a hydraulic turbine. In most of its applications electricity is a network energy that must be produced in the moment of its consumption. Actually, its storage is only indirectly possible and in very restricted applications.

1 - Production

1.1 - Hydraulic or Hydroelectric Power Plant - Installation in which the mechanical energy of water is converted into electric energy.
1.2 - Classical Thermal Power Plant - Installation in which chemical energy contained in solid, liquid or gaseous fossil fuels is converted into electrical energy.
1.3 - Nuclear Power Plant - Installation in which the energy released from nuclear fuel is converted into electrical energy.
1.4 - Base load plant - Power station used mainly to cover the base of the load curves.
1.5 - Peak load plant- Power station used mainly to cover the peaks of the load curve.
1.6 - Power station internal load - The electrical capacity of a power station that is required for its auxiliary plant, including when it is not in operation, together with the capacity represented by the losses in its generator transformers.
1.7- Heat rate- The ratio of the heat content of the fuel burned and the quantity of electric energy produced in the designated period of time
1.8 - Operating time - The period of time during which a plant or part of a plant supplies energy.
1.9 - Stand-by availability - The period of time during which a plant or part of a plant could supply usable energy after the normal period of start-up.
1.10 - Planned unavailability time (planned down time) - The period of time during which a plant or part of a plant is not in running order due to planned maintenance
1.11 - Unplanned unavailability time (unplanned down time) - the period of time during which a plant or part of a plant is not in running order due to unforeseen breakdown.
1.12 - Availability time - the sum of the operating time and the stand-by availability.
1.13 - Nominal power - the maximum continuous power for which the plant has been designed. Usually it is indicated on the maker’s nameplate or in the manufacturers’ specifications.
1.14 - Internal load of energy - Average demand required from one or a group of installations during the reference period (rate between the energy generated in MWh and the operating period of the installation).
1.15 - Internal load of demand - Largest average of demand measured in 60-second intervals and verified over a reference period.
1.16 - System load factor (annual) - The ratio of the average load throughout the year of an energy system to the maximum load on the system during that year , expressed as a percentage and employed as a measure of the fluctuating pattern of consumer demand. In order to allow for weather variation when comparing one year to another, the true system load factor may be adjusted to average climatic conditions.
1.17 - Load factor - the ratio of consumption within a specific period (year, month, day, etc.) to consumption that would result from continuous use reflecting maximum or other specified demand occurring within the same period.
1.18 - Instantaneous demand - The load required at any designated instant.
1.19 -Peak demand - Maximum instantaneous demand required at any designated period of time (day, month, year, etc.)
1.20 - Base load - The constant part of the network load during a designated period (for example, day, month, year, etc.)
1.21 - Peak load - Maximum power that a network must supply during a designated period (for example, day, month, year, etc.).
1.22. Capacity factor - The ratio of the energy load and the installed capacity of the installation or group of installations.

2. - Transport and Distribution

2.1 - Electrical Installation - Civil engineering works, buildings, machines, apparatus, lines and associated equipment together forming an integrated unit for the generation, conversion, transformation, transmission, distribution, storage or utilization of electrical energy.
2.2 - Electric Line - A set of conductors, with insulation and accessories, used for the transmission or distribution of electrical energy.
2.3 - Transforming station - A substation which includes transformers for transferring electricity between systems operating at different voltage levels.
2.4 - Converter station- An installation for converting current of one form into another or for converting one frequency into another.
2.5 - Rectifier station - An installation for converting single or multi-phase alternating current into direct current.
2.6 - Inverter station - An installation for converting direct current into single or multi-phase alternating current.
2.7 - Network system - A grouping of lines or other electrical equipment connected for the purpose of conveying electricity from generating station to the ultimate consumer.
2.8 - Transmission network - A system of electricity lines above X voltage level serving for the inter-regional transport of electricity and feeding to subsidiary systems.
2.9 - Distribution network - A system of distribution lines serving for the intra-regional and local transportation of electric energy.
2.10 - High voltage - A voltage equal to or higher than a specified voltage that may vary legally from one country to another.
2.11 - Low voltage - A voltage equal to or lower than a specified voltage that may vary legally from one country to another.
2.12 - Rated voltage - The voltage used in the specification of a machine, plant, network or apparatus and from which the test conditions and the voltage limits for the use of the machine etc. is calculated.
2.13 - Operating voltage - The voltage at any moment across two line wires of machines or apparatus in operation.
2.14 - Network consumption - Such consumption of electrical energy by ancillary equipment as is required for the operation of the network.
2.15 - Network losses - The energy losses occurring in transmission and distribution in a specific network
2.16 - Quality of an electric network service - grade of conformity with contract clauses between distributor and consumers of electrical energy delivery in a designated period of time or, more generally, perturbation grade of electricity supply.

Note : The elements to be taken into account to determine the quality of the service refer to: the time of programmed or occasional non-supply; Allowable supply conditions relative to voltage drop, no voltage and the harmonics of an alternated current network.
The contract clauses for electricity supply and, consequently, the quality of the service may vary according to the nature of the apparatus to be fed.

3. - Power and Energy

3.1- Direct Current - Current whose polarity and intensity are constant
3.2 - Alternating Current - Current whose polarity and intensity vary periodically with time.

Note 1 : There are single-phase and three-phase currents
Note 2: The usual frequencies are: 16 2/3, 50 and 60 Hz

3.3 - Gross power - electric power at the generator terminals
3.4 - Useful power - electric capacity at the outlet of the power station
3.5 - Maximum electric power - the maximum electric power that could be produced in a power station during a defined period of operation with the entire plant running and with optimum feeding conditions (fuel or water)
3.6 - Available electric power - at any given moment, the maximum electric power at which a station or unit can be operated, for a given period under the prevailing conditions assuming unlimited transmission facilities.
3.7 - Technical minimum power - the lowest power in which the station can operate with correct technical conditions.
3.8 - Useful energy produced - electric energy at the outlet of the power station

4 - Operation

4.1 - Control room - a room in which control boards are installed
4.2 - System control center - the appropriate center for switching or directing the switching of the lines of a network/system.
4.3 - Load dispatching center - the appropriate center for switching or directing the switching of power stations on-line and for loading changing. In general the load-dispatching center and the system control center are one and the same in the case of centrally controlled systems/networks.
4.4 - Ripple control - a method of load management control which involves connecting and disconnecting consumer groups, the necessary remote control being affected via the distribution network /system.
4.5 - Primary regulation - Modification of the turbine power by its regulator as a function of the rotation velocity (frequency).