Electrical Wiring

No, The windings in single phase and 3 phase are different. A single phase motor may use a capacitor "start" circuit to create a phase shift between windings and determine the direction it will spin. A 3 phase motor has the windings configured to create a directional rotating field which determines the rotation. The capacitor in a single phase motor is not used to convert it to 3 phase or vice-versa.

If you have access to a three-phase supply, then you alsohave access to a single-phase supply by connecting your motor to any two line conductors, or between any one line conductor and the neutral. But you MUST ensure that the motor's rated voltage matches one or other of the single-phase voltages available -that depends on what country you live in, because three-phase voltages vary from country to country. And, obviously, if you don't know what you are doing you must consult a qualified electrician.

In order to transmit electricity efficiently, high voltages are used. This high-voltage electricity is then converted to low-voltage electricity at electricity substations (transformers). I'm not sure whether you want to know the transmission voltage or the voltage that comes out of wall sockets.

Transmission voltage

The national grid in the UK runs on mainly 400kV AC system with an HVDC system, that runs on 400kV too, across the English Channel.

Other voltages in use are 275 kV and 132kV although these are not really classified as transmission voltages.

End-user voltage

If you use electricity in the UK, the nominal voltage at the wall socket is 230V. (This is the RMS voltage, which means if you are running something like a lightbulb, heater or kettle it's equivalent to 230V DC. The peak voltage is this multiplied by the square root of 2.)

Additional Answer

UK transmission voltages are 400 kV and 275 kV; distribution voltages are 132 kV, 66 kV, 33 kV, and 11 kV.

Answer

The rubber or plastic serves as electrical insulation (because they are poor conductors). Without insulation, the electricity running in a bare cable would leap over into any other electrically conducting material it touched. With enough voltage, a human could be electrocuted.

Electrical signals would disappear and get lost, causing equipment to fail.

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So the conductor is insulated against possible metal contact & prevent a short if it's grounded.

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All household electric wires are covered with plastic and rubber. This is called insulation. It keeps the potential of the wire from returning to ground (short circuit) before being used by the load. The higher the potential (voltage) the greater the insulation factor has to be. Bare wires in transmission towers also use insulation in the form of air. To use this method, engineered clearances have to be maintained between the conductors.

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All electrical power wires are covered with an insulating material. This is to prevent the potential on the wire from going anywhere except to the load.

Electrical connecting wires are covered with plastic to prevent the wire under the covering from shorting out against each other or shorting out to ground. The electrical terminology for this covering is the wire's "insulation".

These days most electrical wires are covered with a flexible plastic (rubber starts with the sap from a rubber tree; plastic usually starts with a petroleum base).

Answer

The main purpose of the "cover" (insulation) is to keep the wire from shorting to other objects.

The plastics used generally have a good mix of the following properties:

It is flexible so the wire can be flexed and bent.

It is inexpensive and easy to apply to the wire during manufacturing.

It has resistance to chemicals and UV light.

Sometimes it's also important for it to resist abrasion or temperature extremes, or submersion in water.

You can get wire with different types of insulation depending on what you need it to withstand.

If voltage increases and the resistance stays the same the current must increase. According to Ohm's Law

V~I (Directly Proportional) and V=RI where R is the constant of Proportionality, Resistance.

The Star/Delta starter is probably the most commonly used reduced voltage starter, but in a large number of applications, the performance achieved is less than ideal, and in some cases, the damage and interference is much worse than that caused by a Direct On Line starter.

The Star/Delta starter requires a six terminal motor that is delta connected at the supply voltage. The Star Delta starter employs three contactors to initially start the motor in a star connection, then after a period of time, to reconnect the motor to the supply in a delta connection. While in the star connection, the voltage across each winding is reduced by a factor of (1 /.'/'3) [1 divided by root three]. This results in a start-current reduction to (1 /.'/'3) [1 divided by root three] of the DOL start current and a start torque reduction to one third of the DOL start torque.

If there is insufficient torque available while connected in star, the motor can only accelerate to a partial speed compared to the full speed it would reach if connected in delta. When the timer operates (set normally from 5-10 seconds), the motor is disconnected from the supply and then reconnected in delta, resulting in full line voltage running currents and torque.

The transition from star connection to delta connection requires that the current flow through the motor is interrupted. This is termed "Open Transition Switching" and with an induction motor operating at a partial speed compared to full load speed, there is a large current and torque transient produced at the poi, unless proper protection methods are used, can cause severe damage to the supply service's infrastructire and to other connected equipment.

If there is insufficient torque produced by the motor when running in star, there is no way to accelerate the load to full speed without switching to delta and causing those severe current and torque transients. These must be allowed-for in the design of the motor and its starting system if they are to have an economic useful life.

Update: Electronic motor-control systems, which offer soft-starts in DELTA configuration, are now replacing the use of manual or semi-automatic star-delta starters.

Technical explanation

When the windings of a 3-phase motor are connected in STAR:

• the voltage applied to each winding is reduced to only (1 /.'/'3) [1 divided by root three] of the voltage applied to the winding when it is connected directly across two incoming power service lines in DELTA.
• the current per winding is reduced to only (1 /.'/'3) [1 divided by root three] of the normal running current taken when it is connected in DELTA.
• so, because of the Power Law V [in volts] x I [in amps] = P [in watts],

  the total output power when the motor is connected in STAR is:

  PS = [VL x (1/.'/'3)] x [ID x (1/.'/'3)] = PD x (1/3) [one third of the power in DELTA]

  where:

  VL is the line-to-line voltage of the incoming 3-phase power service

  ID is the line current drawn in DELTA

  PS is the total power the motor can produce when running in STAR

  PD is the total power it can produce when running in DELTA.

• a further disadvantage when the motor is connected in STAR is that its total output torque is only 1/3 of the total torque it can produce when running in DELTA.

For more information please see the answers to the Related Questions shown below.

In what context? Typically people want to know this because someone referred to a residential service as 'two phase', meaning there are two hot wires and a neutral. Technically, there is no such thing as two phase power. Commercial sites are often wired in three phase power, and residences are actually using a special type of single phase power called 'Split single phase'. This has to do with the way the voltage for the hot leads is created. Residential step-down transformers on the ground or on poles use a transformer with a center tapped secondary, making each hot wire about 120 volts. The center tap point becomes the neutral wire. A phase to phase measurement gives you about 240 volts. This is technically created with only one phase from the power generation point, as opposed to commercial services which actually use all three phases. A phase to phase measurement in a commercial service yields 208 volts instead of 240.

A two-phase system should not be confused with the split-phase system used for North American residential supplies.

Answer

A single-phase system has two conductors: a line and a neutral.

A three-phase system has either three or four conductors. For a three-phase, three-wire, system the conductors are called line conductors. For a three-phase, four-wire, system there are three line conductor and a neutral conductor. In Europe, the three line conductors are coloured brown, black, and grey, and the neutral conductor is coloured blue.

The Power Factor is an indicator of the quality of design and management of an electrical installation. It relies on two very basic notions: active and apparent power.

The active power P (kW) is the real power transmitted to loads such as motors, lamps, heaters, and computers. The electrical active power is transformed into mechanical power, heat or light.

In a circuit where the applied r.m.s. voltage is Vrms and the circulating r.m.s. current is Irms, the apparent power S (kVA) is the product: Vrms x Irms.

The apparent power is the basis for electrical equipment rating.

The Power Factor λ is the ratio of the active power P (kW) to the apparent power S (kVA):

The load may be a single power-consuming item, or a number of items (for example an entire installation).

The value of power factor will range from 0 to 1.