Power Factor verses Efficiency

Status
Not open for further replies.
mivey said:
The power we speak of in AC circuits is not instantaneous. Active power is the result of a time integral and is not an instantaneous value. Instantaneous power includes active power and intrinsic power. Instantaneous power = P - Pcos(2ωt) where the first term is the active power and the second term is the instantaneous intrinsic power.

The energy transferred over time t is: energy = Pt − P/2ω*sin(2ωt). Pt is the net energy flow.
Click to expand...
mivey -
I've never heard the terms "active power" or "intrinsic power" used in this context. Do you have any references showing definitations - as used in this context?

I'm pretty sure I understand your concepts. If so, you're correct. However, there are already definitations for rms (V and I), average power, instantaneous power. They don't include the terms "active" or "intrinsic".

ice
 
Sahib said:
So you do not want to recognize or use either average speed as speed or average power as power?!
Click to expand...

I recognise average speed as just that - average speed.
I had a round trip of just over 49.5 miles today. My average speed was 35 mph. Both according to the trip computer.
Had the police clocked me doing 90 mph on the motorway, do you think I could have used my displayed average speed as evidence that I had driven within the speed limit?
 
iceworm said:
mivey -
I've never heard the terms "active power" or "intrinsic power" used in this context. Do you have any references showing definitations - as used in this context?

I'm pretty sure I understand your concepts. If so, you're correct. However, there are already definitations for rms (V and I), average power, instantaneous power. They don't include the terms "active" or "intrinsic".

ice
Click to expand...
see:

IEEE Std 1459

"Power Definitions and the Physical Mechanism of Power Flow" by Alexander Eigeles Emanuel
 
Besoeker said:
Average power. But see my analogy with average speed and speed.
Click to expand...

Besoeker said:
I recognise average speed as just that - average speed.
Click to expand...
Which is the power we are talking about. I'm not understanding your continued referral back to the peak instantaneous value when we do not use that.

Besoeker said:
I had a round trip of just over 49.5 miles today. My average speed was 35 mph. Both according to the trip computer.
Had the police clocked me doing 90 mph on the motorway, do you think I could have used my displayed average speed as evidence that I had driven within the speed limit?
Click to expand...
If that was the law: yes. In fact, that is the law when we seek the active power: P = 1/T * Integral{[0,T] P(t)dt} = 1/T * Integral{[0,T] v(t)i(t)dt}
 
Besoeker said:
I recognise average speed as just that - average speed.
I had a round trip of just over 49.5 miles today. My average speed was 35 mph. Both according to the trip computer.
Had the police clocked me doing 90 mph on the motorway, do you think I could have used my displayed average speed as evidence that I had driven within the speed limit?
Click to expand...

Kind of the opposite of what you are saying but my understanding from a truck driver I know, is he can get a speeding ticket if he is recorded as being present at say a weigh station at a specific time and if he would happen to be recorded at another place - say another weigh station, and there were no way he could have gotten there in the the time elapsed if following speed limits.

He says it doesn't happen much but is possible, even if his log book shows something like this he says he could get a citation of some sort. Guess they can not really say just how fast one was traveling without actually recording them at any certain instant. I guess power factor has some similarity, so maybe this is not as far off topic as I first thought.
 
kwired said:
Kind of the opposite of what you are saying but my understanding from a truck driver I know, is he can get a speeding ticket if he is recorded as being present at say a weigh station at a specific time and if he would happen to be recorded at another place - say another weigh station, and there were no way he could have gotten there in the the time elapsed if following speed limits.
Click to expand...
Besides the GATSO radar speed which pick you up at at a point, we do also have average speed cameras (SPECS)which are located at intervals, usually on sections of the highway which have roadworks.
The analogy with power and average power applies. The GATSO gets excessive speed at one location. The SPECS could allow you exceed the speed limit for some of the distance between the two consecutive locations.
[/QUOTE]
 
iceworm said:
I won't have access to Emanuel.
Click to expand...
That is unfortunate as he covers the topic in more detail. It is an excellent reference and I highly recommend it.

iceworm said:
I can get IEEE 1459 Monday. I'm really curious why two new terms are defined that appear to be already well understood and well defined.
Click to expand...
There's the rub. The terms we have used for so long are only well defined and understood in certain circumstances. Active power is not a new term. From IEEE 1459:
IEEE 1459 said:
The definitions for active, reactive, and apparent powers that are currently used are based on the knowledge developed and agreed on during the 1940s. Such definitions served the industry well, as long as the current and voltage waveforms remained nearly sinusoidal.

Important changes have occurred in the last 50 years...
Click to expand...

The changes they list include harmonics, non-sinusoidal and/or unbalanced and/or asymmetrical conditions, traditional instrumentation based on sinusoidal modeling, modern metering capabilites including advanced mathematical models.

There is also the age-old problem of apparent power and power factor in poly-phase circuits so be prepared for dealing with the terms "system effective voltage", "system effective current", and "effective apparent power" as well (not new terms either but just not commonly used and/or recognized).

As for the intrinsic term, it separately identifies the part of instantaneous power that is always present with oscillating systems. This presence is often forgotten when we speak of powers over integer cycles and when we speak of active power. Intrinsic power does not contribute to losses during steady-state conditions. In a DC system there is no intrinsic power and our use of RMS values with AC systems can make one forget that different transient conditions can result in the same average power.

This intrinsic power oscillation is similar to the reactive power oscillation but does not cause power loss in the supply lines like we get with the reactive power. In his book, Emanuel has a problem for the student where a prime mover supplies power through a lossless alternator. The prime mover delivers a constant torque and can't supply the intrinsic power, leaving that to be supported by kinetic energy in the moving mass (i.e. the rotor velocity oscillates).

Intrinsic power is similar to non-active power and is present in fundamental and harmonic power equations. One should be able to identify it and not confuse it with the nonactive power terms which do lead to steady-state losses. It is also important to recognize it as a physical power oscillation that also appears when studying the mechanisms of power flow and the fields surrounding the conductors, as detailed in Emanuel's book.
 
Besoeker said:
I'm not referring to that. Maybe that's what you are not understanding.
Click to expand...
OK. Then somewhere we went down the path of instantaneous power, average power, and time integrals. I guess I lost track of what point you were driving at. Back to the original topic.

So while power factor and efficiency are not the same thing, power factor is a measure of utilization. For example, power factor indicates how well a conductor is utilized. Also supply losses are a factor of S^2. In fact, Actual_feeder_loss = Unity_feeder_loss / pf^2. So pf is not the same as efficiency but, in the light of feeder losses, is an indicator that one is not being as efficient as they could be if they fully compensated the load.
 
mivey said:
OK. Then somewhere we went down the path of instantaneous power, average power, and time integrals. I guess I lost track of what point you were driving at. Back to the original topic.

So while power factor and efficiency are not the same thing, power factor is a measure of utilization. For example, power factor indicates how well a conductor is utilized. Also supply losses are a factor of S^2. In fact, Actual_feeder_loss = Unity_feeder_loss / pf^2. So pf is not the same as efficiency but, in the light of feeder losses, is an indicator that one is not being as efficient as they could be if they fully compensated the load.
Click to expand...

What is is "S'?
 
Status
Not open for further replies.
Top