Snicker snicker
Do you even know WHY we use AC and not DC?
It's because it's easier to change AC voltage by a large amount (ie 5000V to 120V). That's basically the only reason anyone picks AC.
AC has significant issues with voltage regulation. Connecting a highly inductive load to a synchronous generator causes the voltage to drop incredibly fast as the load increases. Connecting a highly capacitive load causes the voltage to
increase as the load increases, and this can damage other things on the line. This is actually the reason it's illegal in Canada to correct the power factor of a motor to the point that current leads voltage. This effect is called armature reaction. DC does not suffer from this problem because one can add capacitors until the cows come home and it will never have negative voltage regulation.
Protective relaying on an AC system is more complicated because of frequency and phase. If frequency drops below 59.6 Hz, the power company will start rolling blackouts because the frequency is that important. DC doesn't need any of this. It has no frequency; all you look at is voltage. Directional relaying on a DC system is easier because it's simply asking if current is going left or right whereas AC looks at negative sequence, torque angles, and harmonics.
Not only does AC suffer from inductive impedance, but it has higher resistance than DC when using the exact same conductors. This is because alternating current tends to travel along the outside of the conductor. This is called the skin effect.
AC wires require thicker insulation. This is because dielectrics break down based on
peak voltage whereas effective power of AC is measured in RMS. RMS of a sine wave is roughly 0.707 of the peak value. That means if you want to put 70V through an AC wire, you need at least 100V (peak) insulation. DC doesn't have this problem because the peak voltage and RMS voltage are basically the same, so you can put 100V RMS DC on that same 70V RMS AC wire.
DC does not have negative sequence current from either unbalance or harmonics. Unbalancing an AC 3-phase motor by 1% can increase the current by as much as 4%. DC doesn't need balance since it's just 1 phase and it doesn't have harmonics because it has no frequency.
AC hates electrolytic capacitors. Electrolytic capacitors have very high capacitance for their size, but they are not well liked by AC because they are polarity dependant. When starting a cap-start cap-run single phase AC air compressor, the starting capacitor must be removed from the circuit once the motor is started or else it will explode. DC doesn't have this problem because the electrolytic capacitor is similar to your car battery; it just charges and stays charged with that particular polarity. As a result of this, we need to use oil-filled capacitors for AC, which work great but are much larger.
Asynchronous AC power grids cannot be tied together because they are not in phase, but DC systems of the same voltage can always be tied together. The AC power grid in Alberta, Canada cannot be tied to the AC power grid in Saskatchewan, Canada because the two are out of phase. As a result of phase differences, BC and Alberta can share AC but power going anywhere else can only be tied through DC. This is why there are so many DC connections on that wiki grid; the systems would be tied with AC if they were in phase, but they are not in phase.
AC is almost worthless in motors unless you have 3 phases to work with. Without having an expensive cap-start cap-run system, the starting torque is painfullly low. This is why things like electric drills and blenders have rectifiers in them and use DC motors. If you have an old drill like I do, you can actually look inside it and see sparks; that's caused by the DC brushes. Newer and better DC motors, like one in a Toyota Prius, uses brushless DC and will never spark like that.
3-phase AC induction motors suck when they use straight AC. They have almost no speed control. Because of this, industry is moving to Variable Frequency Drives (VFD) which convert 3-phase AC to DC then back to a variable AC via PWM. Since DC doesn't have any inherent frequency, the frequency can be adjusted on the fly simply by switching IGBTs on and off. If you want to control the speed of a a motor, you'll want DC power.
AC systems cannot use batteries. My computer's UPS is a DC system because batteries are DC, so any batteries provided to AC must be converted from DC to AC. At this time, there is no such thing as an AC battery.
tl;dr:
DC is superior to AC is almost every way. It can use less copper, less insulation, has better voltage regulation, lower impedance, lower resistance, higher starting torque motors, PWM speed control, electrolytic capacitors, and almost every device in your house uses DC power. What's the first thing your computer does to the power it gets from the wall? Convert it to DC. AC's only advantage is the ability to use transformers.
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