#17 - Increasing the electrical load carried on a

[Administrator]

Please post your questions below!

[Andro10]

I'm having a hard time making a distinction between answers C and E. Could you please help?

[kithly]

We don't know that the "maximum operating temperature" of a transmission line can ever be changed or influenced. Say the "maximum operating temperature" is 100. Two things that affect the temperature of the transmission line are: amount of electrical load, and wind speed/direction. When there's too much electrical load on the line, the temperature will exceed 100 degrees. When there's an average electrical load on the line, maybe the resting temperature is 85 degrees. While operating at this "average load", the temperature of 85 degrees can still be affected by strong & perpendicular winds. If it's a particularly windy day, maybe the line temperature is 75 degrees as opposed to a completely still & neutral day.

C) Says that the electrical load the line can carry WITHOUT reaching maximum increases when wind speed increases. Maybe the average electrical load is actually 50% of maximum capacity (because if we turn it up to 100% then the line temperature will pass 100 degrees temperature). Since wind speed decreases the "resting temperature" from 85 degrees to 75 degrees, we can lightly assume that the average load can be turned up - from 50% to at least 51%.

E) This says that the MAXIMUM OPERATING TEMPERATURE - the one we established to be 100 degrees - is changed by windy degrees. This is unsupported. Maximum operating temperature is just that - the maximum. It's like the limit that comes with the design of the product. You can't change the maximum temperature you can set your oven to, but you can change the temperature of your oven WITHIN that range.

[Andro10]

Hey Kithly, thank you so much for your explanation. It makes sense now.

[Jon Denning]

Kithly is spot on here! Electrical loads and wind speed/direction aren't said to affect the maximum operating temperature, which could be a fixed number at all times. Electrical loads and wind only affect the actual temperature, so (E) is a classic shell game trap: the maximum electrical load a given line can carry without exceeding the max temp is higher on windy days than on calm days (since the wind helps offset the temperature increase), but the maximum temp the line can stand may not change at all.

Answer choice (C) on the other hand fits with what we're told, in that you can run a greater load through a line when there's more wind to cool it off.

As for the other three wrong answers:

(A) we don't know the behavior of electrical companies based on this stimulus.

(B) we don't know the wind speeds in this answer choice, so even though right angle winds are more effective than parallel winds, without knowing the other key factor—prevailing wind speed in each case—we can't say that (B) is true.

(D) air temperature is never mentioned in the stimulus (only air movement), so (D) includes new information the effect of which cannot be known.

[cpihl13]

Just for my clarity, is this considered a Must be True/Most Supported question or a Strengthen/Support?

I feel that it is a MBT/Most Supported because it reads as "most strongly supported" but I wanted to make sure!

Thanks,

[Adam Tyson]

You're correct, Cole! The stimulus here is supporting the correct answer, not the other way around, so it's a "Most Strongly Supported question, which we treat as a subset of Must Be True. If it were a Strengthen question the stem would have to say something about the answers being accepted as true, like "which of the following, if true, would..."

[jyjyk24]

I'm confused with the difference between (B) and (C).

(B) is wrong because we can't know whether or not that line can carry more without knowing the wind speed.

But, isn't that the same for (C)? We can't know whether it can carry more without knowing whether or not wind is blowing across it or parallel to it?

[Jeff Wren]

Hi jyjyk,

For Answer B, there's really two problems with it. The first, as you mentioned, is that without knowing the wind speeds (which is the other relevant factor along with wind direction), we cannot compare transmission lines that run parallel to the winds with other transmission lines that run at a right angle to the winds.

Second, which is perhaps the bigger problem, even if we were to assume that the wind speeds were identical in this comparison, this answer would still be wrong because it's actually saying the opposite of what the stimulus states.

In the stimulus, wind blowing across a line (meaning perpendicular, or at a right angle) would cool the line more than wind blowing parallel to the line. The cooler the line temperature is, the more electrical load the line can carry before it reaches its maximum operating temperature. Therefore, transmission lines that run parallel to the prevailing winds would actually carry a smaller electrical load than transmission lines that run at a right angle to the prevailing winds rather than a greater load, all else being equal.

In other words, if you were deciding which way to run the transmission lines and your goal was to maximize the electrical load that the lines can carry, you would prefer to run the lines perpendicular to the prevailing winds rather than parallel to them.

As for Answer C, the key difference is that this answer is talking about the same transmission line (and the wind going in the same direction). This answer is basically saying that, if you have a transmission line, and the wind speed increases (but the wind is still going in the same direction that it was already going, only faster), then the line will be able to carry a higher load. Obviously, in the real world, wind directions can change, but this answer (unlike Answer B) is assuming that the wind direction has not changed. The only change that is mentioned is an increase in wind speed, so here everything else (like wind direction) is assumed to remain the same.