Electronic – Why do power grids tend to operate at low frequencies like 60 Hz and 50 Hz

Guy Allee at Intel Research wrote about this topic last year -- DC - An idea whose time has come and gone? -- in support of a 380VDC grid, with the following bullet points:

• 7% Energy Savings vs. High-Efficiency 415VAC; 28% vs Current Typical 208VAC
• 15% Less Capital Cost
• 15% fewer PSU components
• 33% Datacenter Space Savings
• 200% Reliability Improvement, which goes to 1000% if you directly connect the battery bus
• Elimination of harmonics and inherently immune to other AC power quality issues
• Natural affinity to alternate energy generation (Photovoltaic, and wind are ~400Vdc internally, and you actually lose energy & efficiency when you are forced to convert to AC)

He added in the comments:

We very deliberately picked 380Vdc because you want to get to as high a voltage as you can afford for efficiency. At the same time this standard is targeting Low Voltage applications only (<600V). We would have gone higher, but there are structural cost barriers at 400Vdc and 420Vdc. At 380Vdc we stay with the same volume parts ratings that AC is using and get the volume cost benefits of piggybacking on the bulk of current AC power supply component volumes. I’m sure you can also appreciate the significant cost adders that +/-340Vdc has on the personal safety equipment, which is why the standard allows for a cost-effective +/-190Vdc distribution. Thus we have the highest efficiency yet cost effective standard. And with the affinity among other industries, PV, wind, electric vehicles, and lighting, the volume economics seem compelling.

He also mentions the idea of a mixed distribution of both AC and DC within a building (e.g. data centers). For more on that initiative, see the EMerge Alliance website: http://www.emergealliance.org.

Am I correct that the faster processor draws more power (and thus dissipates more heat) under a computational load?

Not necessarily. There are two major components of power dissipation - static power (the power you burn when the chip is on) and dynamic/switching power (the power burned when the clock is running). While running the same chip at a higher frequency will result in more power dissipation, a chip may have a static power dissipation that is too high when combined with the faster clock rate to meet the bin requirements for the faster rating.

If so, is the power under computational load approximately proportional to the rated/clocked frequency? In other words, inasmuch as the one processor is clocked 8 percent faster than the other, does it run about 8 percent hotter under load? Another way to ask the same question is to ask: does each processor process about the same quantity of data per unit of energy? or, if battery powered, can each accomplish about as much before its battery dies?

For a given chip running identical calculations, the dynamic portion of the power consumption will be proportional to the clock frequency. The total power dissipation of the processor will increase a bit less than 8% for an 8% increase in clock frequency due to the static power dissipation.

When not under load, do the two processors idle equally cool, or are there practical or theoretical factors that make the one idle cooler than the other?

If you had two identical chips idling, the one with the lower clock frequency would dissipate less power. When the chips are idling, the static power becomes a much larger portion of the active power dissipation, so any differences there would be more noticeable.

Even if the processor's price were not determinate, might one prefer the slower processor merely for the sake of cooler operation and extended battery life?

Possibly, but again, you have a lot less of a guarantee that this would be the case. If you bought chips with different rated TDPs, then you could safely make this argument. Otherwise, you're at the mercy of the binning algorithm and the consistency of the manufacturer's process. Also, note that we're talking about power dissipation, not energy consumption. A faster processor may be able to complete a computationally heavy task faster, and switch to a low power idle mode sooner than a slower processor.

Would the answers differ for embedded processors?

Yes. The static power dissipation is most significant on the bleeding edge processes that Intel, TSMC, IBM, and Global Foundries use. Embedded processors are often optimized for low static power dissipation and use larger processes where static power dissipation is a much smaller portion of power dissipation. The variation at those larger process nodes is much less, so microcontrollers are much less susceptible to variation in power and frequency performance.