Lower power factor on a line means that higher current is flowing through it. The following are a few disadvantages to that:
Higher current results in a greater voltage drop on the line, especially if the line is marginally sized or very long. Its like trying to push too much water flow through a pipe; the pressure drops as you move down the pipe. In the cable, this results in an energy loss due to heat dissipation. The higher current can push equipment closer to their rated capacities. Cables are rated based on their current carrying capacity. Transformers and generators are rated by VA (Volt-Amps) which is current carrying capacity at a certain voltage.
Another disadvantage to higher current flow, and it can be a big one, is the Reactive Demand Charge. The Utility that delivers the power to you will likely charge you if your Power Factor is too low. There are many different ways to determine this charge but the rational is this. If the transmission line that delivers your power (remember all lines have a current carrying capacity) is carrying your magnetizing current (current that could be supplied locally by you), then you are eating into the capacity of that line and taking away the ability for them to sell power to other customers with that line.
Which power factor ? Displacement or True ?Taking about true power factor. For non linear loads, power factor remains the ratio of kw and kva but kva has harmonic components also so true power factor becomes combination of distortion and displacemnt pf. Displacement pf remains near unity for typical non linear load and true pf will be nealy very low because of distortion component.
So why do utiliities still (in the main) measure only displacement power factor ? Utilities typically charge additional costs to customers who have a power factor below some limit. Yes, many utilities do not measure total power factor but are looking for metering devices to begin tracking total power factor information and including it in the billing mechanism.
A simple way to determine the extent of harmonic distortion caused by a single-phase non-linear load would be to make two separate current measurements. Make the first measurement using an average responding current clamp or meter with clamp on probe. Make a second measurement of the same circuit using a true RMS current clamp meter. Divide the results of the first measurement by the second measurement. This will give you the A/R ratio. A ratio of 1.0 would indicate little or no harmonic distortion. A ratio of 0.5 would indicate substantial harmonic distortion. This test method works because an averaging meter will read a true sine wave correctly, as will the true RMS meter. If the waveform is distorted, the true RMS meter will read correctly, while the averaging meter will read up to 50% low, depending on the amount of distortion.
The above measurement method is not a substitute for a harmonic analyzer, but it is a simple way to determine if there is a need for more sophisticated equipment.
Ever heard of a remote power quality monitoring system call PQGuard ? That does all PQ parameters including event recording and trending. It can gather kWhr, maximum demand, DPF/TPF et al which the customers/utility can access over the internet. Their is also a marine/offshore and standard version.
The Smart Grid and metering is broad in its scope, so the potential standards landscape is also very large and complex. It is a technical challenge that goes way beyond the simple addition of an Information Technology infrastructure on top of an electrotechnical infrastructure. I wonder how many utilities in different countries are applying these for biling consumers. The costs associated with a poor power factor are "built in" to domestic power rates. So we all pay those costs collectively regardless of our actual household power factor. As far as measuring only displacement power factor is concerned,for large industrial customers they do measure it. Most of us view low power factor as direct cost to our electricity billing but it is a direct cost to utility company. kva demand, pf penalty,monthly kvar hrs are direct cost while Indirect costs can include loss in efficiency of equipments at distribution point,loss in distribution capacity and larger investment in case of expansion because of oversized transformer switchgears.. so with low pf of an installment, surcharge to electric bill is only part of problem.
Higher current results in a greater voltage drop on the line, especially if the line is marginally sized or very long. Its like trying to push too much water flow through a pipe; the pressure drops as you move down the pipe. In the cable, this results in an energy loss due to heat dissipation. The higher current can push equipment closer to their rated capacities. Cables are rated based on their current carrying capacity. Transformers and generators are rated by VA (Volt-Amps) which is current carrying capacity at a certain voltage.
Another disadvantage to higher current flow, and it can be a big one, is the Reactive Demand Charge. The Utility that delivers the power to you will likely charge you if your Power Factor is too low. There are many different ways to determine this charge but the rational is this. If the transmission line that delivers your power (remember all lines have a current carrying capacity) is carrying your magnetizing current (current that could be supplied locally by you), then you are eating into the capacity of that line and taking away the ability for them to sell power to other customers with that line.
Which power factor ? Displacement or True ?Taking about true power factor. For non linear loads, power factor remains the ratio of kw and kva but kva has harmonic components also so true power factor becomes combination of distortion and displacemnt pf. Displacement pf remains near unity for typical non linear load and true pf will be nealy very low because of distortion component.
So why do utiliities still (in the main) measure only displacement power factor ? Utilities typically charge additional costs to customers who have a power factor below some limit. Yes, many utilities do not measure total power factor but are looking for metering devices to begin tracking total power factor information and including it in the billing mechanism.
A simple way to determine the extent of harmonic distortion caused by a single-phase non-linear load would be to make two separate current measurements. Make the first measurement using an average responding current clamp or meter with clamp on probe. Make a second measurement of the same circuit using a true RMS current clamp meter. Divide the results of the first measurement by the second measurement. This will give you the A/R ratio. A ratio of 1.0 would indicate little or no harmonic distortion. A ratio of 0.5 would indicate substantial harmonic distortion. This test method works because an averaging meter will read a true sine wave correctly, as will the true RMS meter. If the waveform is distorted, the true RMS meter will read correctly, while the averaging meter will read up to 50% low, depending on the amount of distortion.
The above measurement method is not a substitute for a harmonic analyzer, but it is a simple way to determine if there is a need for more sophisticated equipment.
Ever heard of a remote power quality monitoring system call PQGuard ? That does all PQ parameters including event recording and trending. It can gather kWhr, maximum demand, DPF/TPF et al which the customers/utility can access over the internet. Their is also a marine/offshore and standard version.
The Smart Grid and metering is broad in its scope, so the potential standards landscape is also very large and complex. It is a technical challenge that goes way beyond the simple addition of an Information Technology infrastructure on top of an electrotechnical infrastructure. I wonder how many utilities in different countries are applying these for biling consumers. The costs associated with a poor power factor are "built in" to domestic power rates. So we all pay those costs collectively regardless of our actual household power factor. As far as measuring only displacement power factor is concerned,for large industrial customers they do measure it. Most of us view low power factor as direct cost to our electricity billing but it is a direct cost to utility company. kva demand, pf penalty,monthly kvar hrs are direct cost while Indirect costs can include loss in efficiency of equipments at distribution point,loss in distribution capacity and larger investment in case of expansion because of oversized transformer switchgears.. so with low pf of an installment, surcharge to electric bill is only part of problem.
No comments:
Post a Comment