While inductive losses of a transmission line are the dominant compared to the resistance, they can be compensated for. And BTW, a purely inductive circuit is not lossless. (OK at DC it is, but not with an AC current.) It can be made lossless with the use of capacitors. Read on...
Loss can be due to resistance or it can be due to reactance, capacitive and inductive. Inductive reactance is directly proportional to frequency and capacitive reactance is inversely proportional to frequency. Thus, one can dircetly offset the other. At zero frequency (DC) a pure inductor has no reactance and a perfect capacitor has infinite reactance.
The reason capacitive and inductive reactances can cancel one another is that they are vector quantities. Capacitive reactance causes current to lead voltage in phase by 90 deg. and inductive reactance causes current to lag (follow) voltage in phase by 90 deg. By using vector addition, capacitive reactance and inductive reactance can cancel each other out. i.e. 10 ohms of pure capacitive reactance added to 10 ohms of pure inductive reactance will result in a net reactance of 0 ohms. This is because both quantities are vectors which have a magnitude and angle component which must be accounted for when adding them together.
In the real world, power factor correcting capacitors are used to "cancel out" the effects of inductive loads on the power grid. (These inductive reactances can be due line inductances or inductive loads like air conditioners and motors.) This means the capacitors effectively supply VARs to inductive loads while generators provide the Watts. (See the aside on power below) Power factor is the angle between apparent power and real power. The capacitor ends up making the circuit look closer to completely resistive, "correcting" the power factor back to 1.0.
Interestingly enough, some types of line construction, like that used for 765 kV, can be very capacitive. (Think of large surface area over a ground plane.) This can really help on hot days when everyone is running their a/c, but this can actually cause system voltage to rise when the inductive load is low. Because of this, shunt reactors may need to be switched in on long 765 kV lines to keep the system voltage from getting too high.
Superconducting lines are interesting because they produce no heat. Heat is one of the limiting factors of power transmission lines. Too much current causes the lines to stretch (expand) and break. (The capacity can be further constrained by power system dynamics and stability which I don't understand enough to even begin to explain.) Even though a line may have little resistance, driving 1000 MW or real power through it will generate a lot of heat, even if it's only 10 ohms. Take that down to 0 ohms, then you don't need to worry about heat.
As an aside, many folks don't realize is that power (more correctly apparent power) is made up of two components. There is the "real" power measured in watts and the reactive power measured in VARs. Some folks call reactive power "imaginary" power since it falls on the imaginary axis of the complex number plane, but make no doubt about it, there is nothing imaginary about reactive power; it must be produced, transported, and delivered by the power company. The apparent power of an AC circuit is measured in VA (volt-amps) and is the magnitude of the phasor representation of the real and reactive components.
Another way to look at it is that apparent power is that drawn by the total impedence of the load. Just like apparent power is made up of real and reactive components, impedence is made up of (DC) resistance and (inductive) reactance. Resistance is responsible for the real power drawn by the load, reactance is responsible for reactive power drawn by the load. So you can look at the losses and associated powers individually (resistance/real power & reactance/reactive power) or as a vector sum (impedence/apparent power).
Since reactive power is a somewhat difficult concept to grasp, some folks like to think of it as the energy required to magnitize the coils of a transformer or motor as opposed to the energy required to do real work like turning a shaft or lighting a light bulb. You don't get anything done by simply magnetizing the coils, but the energy can't get transfered without that process.
I have this sort of thing rigged up in my entertainment system minus the DVD player. I've been using a P3-500 with an ATI All-in-Wonder card hooked up to my stereo and 32" TV. I also added an infra-red keyboard so I can use it from my couch. It's great for ripping and playing back mp3s, listening to radio stations over the Internet, and general web surfing. And BTW, it's all mounted in a desktop case so it fits in with the rest of my A/V components.
Recently I've been trying to decide whether to add a DVD drive to the PC or add a stand-alone DVD player. I'm probably going to get the stand-alone player, here's why:
The hard drive noise is noticable when the volume on the TV or stereo is low... It's not bad when I've got the stereo cranked up, but I'm sure it would annoy me during dialog of a movie. I currenlty don't have the machine up and running unless I'm using it for one of the forementioned purposes.
Sometimes it's a real pain-in-the-ass to operate. I don't want to boot up to watch a movie. I don't want to have to mouse around the screen to run the dvd player software and hit play. (Is mouse a verb?)
I want to drop the disk in the player and hit the play button. Also, My wife (who's not a nerd but pretty technically adept) wants something easy to operate as well.
I'm worried about the video quality. When I watch video through the all-in-wonder card, it's not bad but I still seem to notice that video is not going direct to the video input of the TV. I can't quite put my finger on what it is, but I notice a hit in resolution. If I buy a DVD player, I want it to look perfect. I'd be interested to hear from folks who have a hardware DVD decoder board with an S-video output to know whether or not this would really be a problem.
Who knows, I may eventually have both (stand-alone and one in the PC) as I can see the value in both types.
Ah yes, I remember when email addresses could be written so that the sender could pick the best route to send the email. It was considered helpful to make your bang path long enough to contain at least one major UUCP site like UCBVAX or Indian Hill so the sender didn't have to get out the maps to figure out how to get the message to you.
I was lucky; mine was short: {ucbvax | rutgers}!pur-ee!zawada
Try the Container Store, they may have something you're looking for. They have a lot of the usual CD storage devices, but also a couple high-volume options. They are pricy but the nice thing is some of their stuff doesn't look like CD storage.
I put together a Skandia shelving system for my entertainment center. I put four drawers (with CD inserts) along the bottom that hold probably around 400 CDs. It wasn't cheap (well over $1000) but then again it also holds a 32" TV, all my stereo components, multi-media PC, and a bunch of picture frames and the like. It's really sturdy stuff.
Hey, I've still got my "fat" 4032 packed up in the
basement along with a 8050 floppy drive. When
is the Linux/FreeBSD crowd going to get their
act together and do a port to some serious 1 MHz
hardware ?
Slashdot Mirror
Loss can be due to resistance or it can be due to reactance, capacitive and inductive. Inductive reactance is directly proportional to frequency and capacitive reactance is inversely proportional to frequency. Thus, one can dircetly offset the other. At zero frequency (DC) a pure inductor has no reactance and a perfect capacitor has infinite reactance.
The reason capacitive and inductive reactances can cancel one another is that they are vector quantities. Capacitive reactance causes current to lead voltage in phase by 90 deg. and inductive reactance causes current to lag (follow) voltage in phase by 90 deg. By using vector addition, capacitive reactance and inductive reactance can cancel each other out. i.e. 10 ohms of pure capacitive reactance added to 10 ohms of pure inductive reactance will result in a net reactance of 0 ohms. This is because both quantities are vectors which have a magnitude and angle component which must be accounted for when adding them together.
In the real world, power factor correcting capacitors are used to "cancel out" the effects of inductive loads on the power grid. (These inductive reactances can be due line inductances or inductive loads like air conditioners and motors.) This means the capacitors effectively supply VARs to inductive loads while generators provide the Watts. (See the aside on power below) Power factor is the angle between apparent power and real power. The capacitor ends up making the circuit look closer to completely resistive, "correcting" the power factor back to 1.0.
Interestingly enough, some types of line construction, like that used for 765 kV, can be very capacitive. (Think of large surface area over a ground plane.) This can really help on hot days when everyone is running their a/c, but this can actually cause system voltage to rise when the inductive load is low. Because of this, shunt reactors may need to be switched in on long 765 kV lines to keep the system voltage from getting too high.
Superconducting lines are interesting because they produce no heat. Heat is one of the limiting factors of power transmission lines. Too much current causes the lines to stretch (expand) and break. (The capacity can be further constrained by power system dynamics and stability which I don't understand enough to even begin to explain.) Even though a line may have little resistance, driving 1000 MW or real power through it will generate a lot of heat, even if it's only 10 ohms. Take that down to 0 ohms, then you don't need to worry about heat.
As an aside, many folks don't realize is that power (more correctly apparent power) is made up of two components. There is the "real" power measured in watts and the reactive power measured in VARs. Some folks call reactive power "imaginary" power since it falls on the imaginary axis of the complex number plane, but make no doubt about it, there is nothing imaginary about reactive power; it must be produced, transported, and delivered by the power company. The apparent power of an AC circuit is measured in VA (volt-amps) and is the magnitude of the phasor representation of the real and reactive components.
Another way to look at it is that apparent power is that drawn by the total impedence of the load. Just like apparent power is made up of real and reactive components, impedence is made up of (DC) resistance and (inductive) reactance. Resistance is responsible for the real power drawn by the load, reactance is responsible for reactive power drawn by the load. So you can look at the losses and associated powers individually (resistance/real power & reactance/reactive power) or as a vector sum (impedence/apparent power).
Since reactive power is a somewhat difficult concept to grasp, some folks like to think of it as the energy required to magnitize the coils of a transformer or motor as opposed to the energy required to do real work like turning a shaft or lighting a light bulb. You don't get anything done by simply magnetizing the coils, but the energy can't get transfered without that process.
--zawada
Recently I've been trying to decide whether to add a DVD drive to the PC or add a stand-alone DVD player. I'm probably going to get the stand-alone player, here's why:
The hard drive noise is noticable when the volume on the TV or stereo is low... It's not bad when I've got the stereo cranked up, but I'm sure it would annoy me during dialog of a movie. I currenlty don't have the machine up and running unless I'm using it for one of the forementioned purposes.
Sometimes it's a real pain-in-the-ass to operate. I don't want to boot up to watch a movie. I don't want to have to mouse around the screen to run the dvd player software and hit play. (Is mouse a verb?) I want to drop the disk in the player and hit the play button. Also, My wife (who's not a nerd but pretty technically adept) wants something easy to operate as well.
I'm worried about the video quality. When I watch video through the all-in-wonder card, it's not bad but I still seem to notice that video is not going direct to the video input of the TV. I can't quite put my finger on what it is, but I notice a hit in resolution. If I buy a DVD player, I want it to look perfect. I'd be interested to hear from folks who have a hardware DVD decoder board with an S-video output to know whether or not this would really be a problem.
Who knows, I may eventually have both (stand-alone and one in the PC) as I can see the value in both types.
-z
I was lucky; mine was short: {ucbvax | rutgers}!pur-ee!zawada
-z
I put together a Skandia shelving system for my entertainment center. I put four drawers (with CD inserts) along the bottom that hold probably around 400 CDs. It wasn't cheap (well over $1000) but then again it also holds a 32" TV, all my stereo components, multi-media PC, and a bunch of picture frames and the like. It's really sturdy stuff.
They also sell a media storage cabinet that is rather compact for holding 210 CDs.
--z
The pound force (lbf) is the measurement of force. Keep in mind that lb != lbf.
-z
...for another Internet Cleanup Day.
--z
Hey, I've still got my "fat" 4032 packed up in the basement along with a 8050 floppy drive. When is the Linux/FreeBSD crowd going to get their act together and do a port to some serious 1 MHz hardware ?