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Electrical Services

TITLE OF PRESENTATION (ON MASTER SLIDE)

History of Electrical Services

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Wye Line-to-Neutral Voltage 120 120 220 230 277 374

Wye or Delta Line-to-Line Voltage 208 240 400 415 480 600

Electrical Service Voltages

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Single Phase

Single-Phase electrical service wires usually have a three wire configuration, also known as the edison system or the center-tapped neutral. This type of single phase wiring is most commonly found in the United States. It provides 120 Volts for lighting and conventional plug loads and 240 volts for single phase appliances.

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Common Electrical Services

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Single Phase Three Wire


Three-Phase

Three-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by grids worldwide to transfer power. It is also used to power large motors and other heavy loads. A three-phase system is generally more economical than others because it uses less conductor material to transmit electric power than equivalent single-phase or two-phase systems at the same voltage. The three-phase system was introduced and patented by Nikola Tesla in 1887 and 1888. There are two commonly used types. The four-wire wye and the three-wire delta.

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Three Phase Four Wire Wye



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Three Phase Three Wire Delta


Benefits of Three Phase Systems

The phase currents tend to cancel out one another, summing to zero in the case of a linear balanced load. This makes it possible to eliminate or reduce the size of the neutral conductor; all the phase conductors carry the same current and so can be the same size, for a balanced load.Power transfer into a linear balanced load is constant, which helps to reduce generator and motor vibrations.Three-phase systems can produce a magnetic field that rotates in a specified direction, which simplifies the design of electric motors.3 phase power is typically 150% more efficient than single phase in the same power range.

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Benefits of Three Phase Systems

• Constant power delivery. Single-phase delivers zero power each time the voltage crosses zero (120 times per second in the US), while with 3 phase each time a phase crosses zero there is still power being delivered. This leads to 2 phase motors in machinery running more smoothly.

• Easier motor wiring. 3 phase induction motors don’t require brushes, start capacitors, or any of the complexities of single-phase motors, and are easy to reverse as needed.

• Smaller wires required for connecting 3 phase equipment. Because the current is divided among the 3 phases instead of between just two, the wires can be smaller and therefore often easier to handle.

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Three-wire versus Four-wire

• Three-phase circuits occur in two varieties. In one case, there are only three energized ("hot") wires; in the other case, there are three hot wires plus a neutral wire. Four-wire circuits offer flexibility, since a load may be connected "line-to-line" or "line-to-neutral"; three-wire circuits offer economy, since the neutral conductor is eliminated. Commonly, distribution voltage circuits are four-wire, while higher voltage transmission circuits are three-wire. Transmission lines often feature a ground wire, but this is solely for fault and lightning protection and is not connected to deliver electrical power.

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Benefits of Single Phase Systems

• Single-phase power distribution is widely used especially in rural areas, where the cost of a three-phase distribution network is high and motor loads are small and uncommon. (so in other words its cheaper!)

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Business

111118 electrical services