Transmission, distribution, and domestic power supply
– Electrical energy is distributed as alternating current (AC) to allow for efficient transmission through power lines at high voltage.
– Higher voltage leads to more efficient transmission and reduces power loss due to resistance in the wire.
– Power loss in the wire is determined by the square of the current and the resistance of the wire.
– Power transmitted is equal to the product of the current and the voltage.
– Power is transmitted at high voltage on pylons and then transformed to lower voltages for domestic use.
– High-voltage transmission requires increased insulation and poses safety challenges.
– Energy is generated at a convenient voltage and then stepped up to a high voltage for transmission.
– Near the loads, the transmission voltage is stepped down to the voltages used by equipment.
– Consumer voltages vary depending on the country and size of the load.
– High-voltage direct current (HVDC) transmission systems have become more viable with advancements in technology.
Three-phase electrical generation and distribution systems
– Three-phase electrical generation involves three separate coils in the generator stator.
– Three current waveforms are produced that are equal in magnitude and 120° out of phase.
– Higher pole orders are commonly used for lower rotational speeds and the same frequency.
– In a balanced load, no current flows through the neutral point.
– Non-linear loads may require oversized neutral conductors to handle harmonics.
– A four-wire system is often used for three-phase distribution at utilization voltages.
– Transformers with Delta primary and Star secondary configurations are commonly used.
– Smaller customers may only receive a single phase and neutral, while larger installations receive all three phases and neutral.
– Three-wire single-phase systems are common in residential and small commercial buildings in North America.
– Bond wires are connected between non-current-carrying metal enclosures and earth ground for safety.
AC power supply frequencies
– The frequency of the electrical system varies by country, with most power generated at either 50 or 60 Hertz.
– Some countries have a mixture of 50Hz and 60Hz supplies.
– Lower frequencies ease the design of electric motors and traction motors, but cause flicker in arc lamps and incandescent light bulbs.
– Lower frequencies also result in lower transmission losses.
– The original Niagara Falls generators produced 25Hz power for a compromise between low frequency for traction and incandescent lighting operation.
Techniques for reducing AC resistance and radiation loss
– Litz wire is constructed by dividing conductors into stranded wires, reducing skin effect.
– It is used for high-Q inductors, flexible conductors carrying high currents at lower frequencies, and windings of devices with higher radio frequency currents.
– Stranded conductors with specially arranged strands help distribute current more evenly.
– Litz wire reduces losses caused by skin effect.
– It is commonly used in switch-mode power supplies and radio frequency transformers.
– Twisted pairs of wires are used up to 1GHz to reduce electromagnetic radiation and inductive coupling.
– Each wire in a twisted pair radiates a signal, but the radiation is cancelled out by the other wire, minimizing loss.
– Coaxial cables are used at audio frequencies and above, with a conductive wire inside a conductive tube separated by a dielectric layer.
– The electromagnetic field is contained within the tube, minimizing energy loss to radiation or coupling outside.
– Waveguides, without an inner conductor, transmit energy through guided electromagnetic fields, preventing leakage.
Mathematics of AC voltages and fiber optics
– AC voltage can be described mathematically as a function of time using the equation v(t) = V_peak*sin(ωt).
– V_peak represents the peak voltage and ω is the angular frequency.
– The angular frequency is related to the physical frequency (f) by ω = 2πf.
– AC voltage is often expressed as a root mean square (RMS) value, denoted as V_rms.
– Time-averaged power is calculated using V_rms, where P_time_averaged = (V_rms)^2 / R.
– At frequencies greater than 200GHz, waveguide dimensions become impractically small.
– Ohmic losses in waveguide walls also become large.
– Fiber optics, a form of dielectric waveguides, are used instead.
– Fiber optics do not rely on voltages and currents at such high frequencies.
– Fiber optics are used when waveguides are not feasible due to size and losses. Source: https://en.wikipedia.org/wiki/Alternating_current
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Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time, in contrast to direct current (DC), which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans and electric lamps into a wall socket. The abbreviations AC and DC are often used to mean simply alternating and direct, respectively, as when they modify current or voltage.
The usual waveform of alternating current in most electric power circuits is a sine wave, whose positive half-period corresponds with positive direction of the current and vice versa (the full period is called a cycle). In certain applications, like guitar amplifiers, different waveforms are used, such as triangular waves or square waves. Audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current carry information such as sound (audio) or images (video) sometimes carried by modulation of an AC carrier signal. These currents typically alternate at higher frequencies than those used in power transmission.
