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Michal Kabrhel

Electric current

• An electric current is a flow of electric charge. Electric charge flows when there is voltage present across a conductor.

• In electric circuits charge is often carried by moving electrons in a wire.

• The SI unit for measuring an electric current is the ampere (A)• The conventional symbol for current is I• Ohm's law

• V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms =

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Power grid

Power station• A power station is industrial facility for the generation of electric power• At the center of nearly all power stations is a generator, a rotating machine

that converts mechanical power into electrical power• Most power stations in the world burn fossil fuels such as coal, oil, and natural

gas to generate electricity, and some use nuclear power• increasing use of cleaner renewable sources such as solar, wind and water

• The system of three-phase alternating current electrical generation, transmission, and distribution was developed in the 19th century by Nikola Tesla, George Westinghouse and others

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Power grid• Transmission lines become transmission networks (power grid, grid)

• Most transmission lines use high-voltage three-phase alternating current (AC)• Electricity is transmitted at high voltages (110 kV or above) to reduce the energy

lost in long-distance transmission.• Electric power - distribution local wiring between high-voltage substations and

customers

Transformer (substation)

• A transformer is a static electrical device that transfers energy by inductive coupling between its winding circuits

• Example 32/04• 32kV is transfered to 0,4kV=400V

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Current• Alternating current (AC,ac) the flow of electric charge periodically

reverses direction• AC is the form in which electric power is delivered to businesses and

residences.• usual waveform of an AC power circuit is a sine wave

• In direct current (DC, dc), the flow of electric charge is only in one direction.

• Direct current is produced by sources such as batteries, solar cells, and commutator-type electric machines of the dynamo type

• Direct current may be made into alternating current with an inverter or a motor-generator set.

Current

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Electrical wiring• Electrical code

• is a set of regulations for electrical wiring• provide standards to ensure electrical wiring systems that are safe and unlikely

to produce either electric shock or fires• devised by national or international technical organizations

• IEC 60364 is used as a basis for electrical codes in many European countries• DIN VDE (German Institute for Standardization) published by DIN-Norms is used in

Germany• British Standard BS 7671 is the set of regulations for electrical wiring in the United

Kingdom.• NF C 15-100 is used for low voltage installations in France• National Electrical Code has been adopted for electrical wiring in the United States and

for Mexico, Costa Rica, Venezuela and Colombia

Building wiring• The live wire (also known as phase, hot or active contact),

carries alternating current between the power grid and the household. Live (L).

• The neutral wire completes the electrical circuit by also carrying alternating current between the power grid and the household. The neutral is connected to the ground, and therefore has nearly the same electrical potential as the earth. This prevents the power circuits from rising beyond earth, such as when they are struck by lightning or become otherwise charged. Neutral (N).

• The earth wire or ground connects cases of equipment to earth ground as a protection against faults (Electric Shock). Protective earth (PE)-conductor connects the exposed metallic parts of the consumer's electrical installation.

• Mixed 230V/400V Three-phase electric power (common in northern and central Europe) or 230V single-phase based household wiring

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Networks• International standard IEC 60364 distinguishes three families of earthing

arrangements (TN, TT, IT)• TN−S PE and N are separate conductors that are connected together only

near the power source. This arrangement is the current standard for most residential and industrial electric systems partially in Europe.

Networks• TN−C-S Part of the system uses a combined PEN conductor, which is

at some point split up into separate PE and N lines. The combined PEN conductor typically occurs between the substation and the entry point into the building, and separated in the service head.

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Socket

Color code

• Flexible cable

u Fixed cable

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Conductors

• Copper conductors wire are common because of their multiple beneficial properties, including their high electrical conductivity, tensile strength, ductility, creep resistance, corrosion resistance, thermal conductivity, coefficient of thermal expansion, solderability, resistance to electrical overloads, compatibility with electrical insulators, and ease of installation.

• Aluminium wire was common in North American. Because of its greater resistivity, aluminium wiring requires larger conductors than copper.

Electrical wiring• Small portable electrical equipment is connected to the power

supply through flexible cables terminated in a plug, which is then inserted into a fixed receptacle (socket).

• Larger household electrical equipment and industrial equipment may be permanently wired to the fixed wiring of the building.

• Circuit breakers and fuses are used to detect short circuits between the live and neutral wires, or the drawing of more current than the wires are rated to handle to prevent overheating and fire.

• Protective devices are usually mounted in a central panel in a building

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Protection• A circuit breaker is an automatically

operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit.

• Its basic function is to detect a fault condition and interrupt current flow.

• A circuit breaker can be reset• Fuse operates once and then must be replaced

Distribution board

• A distribution board (or panelboard) is a component of an electricity supply system which divides an electrical power feed into subsidiary circuits, while providing a protective fuse or circuit breaker for each circuit, in a common enclosure.

• Distribution boards may be surface-mounted on a wall or may be sunk into the wall.

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Residential electrical installation - Circuits

• National standards commonly recommend the subdivision of circuits according to the number of utilization categories in the installation concerned

• At least 1 circuit for lighting. Each circuit supplying a maximum of 8 lighting points

• At least 1 circuit for socket-outlets rated 10/16 A, each circuit supplying a maximum of 8 sockets. These sockets may be single or double

• 1 circuit for each appliance such as water heater, washing machine, dish-washing machine, cooker, refrigerator, etc. Recommended numbers of 10/16 A (or similar) socket-outlets and fixed lighting points

Bathroom electrical installation• Bathrooms and showers rooms are areas of high risk, because of the very

low resistance of the human body when wet or immersed in water.• The definition of zones, numbered 0,1, 2, 3 in which the placement (or

exclusion) of any electrical device is strictly limited or forbidden and, where permitted, the electrical and mechanical protection is prescribed

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Electrical bonding• Electrical bonding is the practice of intentionally

electrically connecting all exposed metallic items not designed to carry electricity in a room or building as protection from electric shock.

• If a failure of electrical insulation occurs, all bonded metal objects in the room will have substantially the same electrical potential, so that an occupant of the room cannot touch two objects with significantly different potentials.

• In a building with electricity it is normal for safety reasons to connect all metal objects such as pipes together to the mains earth to form an equipotential zone.

Electromagnetism• Electric current produces a magnetic field. The magnetic

field can be visualized as a pattern of circular field lines surrounding the wire that persists as long as the current flows.

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Stray voltage• Stray voltage is the occurrence of electrical potential between two

objects that ideally should not have any voltage difference between them.

• Stray voltage is not related to power system faults, and is generally not considered hazardous.