Lightning tends to strike elevated objects that acquire large charges that are opposite to those of the clouds. Since transformers are often elevated and they are connected to wires that allow them to become highly polarized when a charged cloud passes overhead, transformers are good targets for lightning.
In most situations of AC electric power generation or AC electric power consumption, the current flowing through the circuit is in phase with (or, more simply, directly proportional to) the voltage across the circuit. But that isn’t always the case. In situations involving reactive components (e.g., capacitors and inductors), it’s possible for the current and voltage to be out of phase with one another. If the current and voltage are a full 90° out of phase, there is no average power flowing through the circuit. I believe that VAR is a reference to this portion electricity in the circuit—the portion for which the voltage and current are 90° out of phase. While this portion of the electricity doesn’t transfer any power, it does place demands on the power transmission system. I think that the distinctions between “importing” and “exporting” and between “consuming” and “producing” are related to the phase ordering of the current and voltage (whether a device is acting as a capacitor or an inductor). In one case, the voltage leads the current by 90° and in the other the current leads the voltage by 90°.
A metal’s conductivity is related to how far an electron can coast through the metal before suffering a collision that reduces its kinetic energy. Since an electron can collide with an impurity in the metal or a region of local disorder, the first task in obtaining a good conductor is to make a pure and uniform metal. Increased temperature also enhances these inelastic collisions, so keeping a metal cool improves its conductivity. Finally, different metals exhibit different couplings between the electrons and the metal ions from which those electrons came. Copper and aluminum have relatively weak electron-ion couplings while steel and lead have stronger couplings. The stronger the coupling, the more likely is a collision between an electron and an ion. Because of their weaker couplings, the electrons in copper and aluminum suffer far fewer collisions per centimeter than the electrons in steel and lead. That’s why copper and aluminum are better conductors of electricity than steel and lead. The coupling in copper is only slightly weaker than that in aluminum, so they have similar conductivities. However, aluminum’s tendency to form a very hard, insulating oxide coating (aluminum oxide or “alumina” is the mineral sapphire) makes it a bit tricky to use in wiring.
Most homes receive power through three wires: two power wires and one neutral wire. Each power wire is at 120 volts AC with respect to the neutral wire, meaning that its electric potential fluctuates up and down with respect to the neutral wire and behaves as though, on average, it were 120 volts away from the potential of the neutral wire. But the fluctuations of the two power wires are opposite one another—when one power wire is at a positive voltage relative to the neutral wire, the other power wire is at a negative voltage relative to the neutral wire. If you compare the two power wires to one another, you’ll find that they behave as though, on average, they are 240 volts away from one another. Thus home appliances that need 240 volts are powered by the two power wires, rather than one power wire and one neutral wire.
kVA is the product of kilovolts (kV) times amperes (A) and is a measure of power. In fact, if you multiply the voltage in volts delivered to an electric heater by the current in amperes sent through that heater, you will obtain the electric power in watts consumed by the heater. Thus the heater’s power consumption in watts is the same as the product of its voltage times its current, or its kVA. However, there are many devices that don’t behave like an electric heater. The heater is purely resistive, while many other devices such as motors are both resistive and reactive. Reactive devices don’t obey Ohm’s law and may not draw their peak currents at times of peak voltage. Therefore, the power in watts consumed by a reactive device isn’t the same as the product of its current times its voltage, or its kVA.
Electronic dimmers do clip the AC cycle. They use transistor-like devices called triacs to switch on the current to a lamp part way into each half-cycle. By shortening the time that power is delivered to the lamp, the dimmer reduces the total energy delivered to the lamp during each half-cycle and the lamp dims. But while a triac turns on easily, the only way to turn it off is to get rid of any voltage drop across it. The dimmer uses the alternating current itself to turn off the triac—the voltage of the power line naturally goes to zero at the end of each half-cycle and the triac turns off. The triac then waits until the dimmer restarts it, sometime into the next half-cycle.
Since the dimmer messes up the waveform of the electric current flowing through the lamp circuit, what you measure with a voltage meter depends on how that meter works. Since many AC voltmeters just measure peak voltage and assume that they are looking at a pure sinusoidal current, they don’t give you an accurate sense for what is really happening to the voltage of this clipped waveform as a function of time. Unless an electronic dimmer is turned way down, the peak voltage it delivers will be close to the normal power line peak, a fact which tricks the voltage meter into reading a high value and which allows a properly designed fluorescent lamp to continue operating normally but at a dimmer level.
The generating station uses a large generator to transfer energy from a giant turbine to an electric current flowing through a coil of wire. Current from this generating coil then flows through the primary coil of a huge transformer, where it transfers its energy to the magnetic core of the transformer. The current then returns to the generator to obtain more energy.
The magnetic core of the transformer transfers its energy to a second current—one that is passing through the secondary coil of the transformer. Because this current consists of far fewer electric charges per second, each charge receives a very large amount of energy. This large energy per charge gives the current a high voltage and it flows very easily through a high voltage transmission line. Because the amount of power that a wire loses is proportional to the square of the current passing through it, this high-voltage, low-current electricity wastes very little power in the transmission line on its way across country to your city. When the current reaches your city, it passes through another transformer and its energy is transferred to a third current. The cross country current then returns through the transmission line to the original power station to obtain more energy from the first transformer.
This third current involves more charges per second, so each charge carries less energy and the voltage is lower. This medium voltage electricity travels to your neighborhood before passing through a final transformer. This final transformer is probably either a gray metal can on a utility pole or a green box on a nearby lawn. In passing through the final transformer, the current transfers its energy to a current which then enters your home. This last current delivers energy to your appliances and lights and then returns to the final transformer to obtain more energy.
Electricity typically costs about 7 cents per kilowatt-hour. Over the course of an hour, a 100-watt light bulb will use 100 watt-hours or 0.1 kilowatt-hours, at a cost of about 0.7 cents. That’s about 0.012 cents per minute.
The electromagnetic fields (EMF) produced by the currents in an electric blanket are very weak and it takes a pretty sensitive electronic device to detect them. You body is not nearly so sensitive and I still haven’t seen any credible explanation for how these fields could cause any injury to biological tissue. I strongly suspect that all the concern about EMF is just hysteria brought about by a few epidemiological flukes or mistakes.
Probably not very dangerous. The radiation itself is so weak that it can’t cause significant heating in your body (as the microwaves used in diathermy treatment do) and so low frequency that it can’t do chemical damage (as the X-rays from a CT scan do). The only possible source of trouble is the small electric and magnetic fields from the power lines and there is still no credible evidence that these affect biological tissue. Moreover, there are sound physical arguments why those fields should not be able to affect biological tissue. Only in rare cases of an organ that is devoted to sensing magnetic fields (e.g., in migratory birds) is there any reasonable interaction between tissue and small magnetic fields.