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A single wattmeter can measure power due to one phase only. But circuit arrangements , popularly called:
1) 2-wattmeter method (requiring two wattmeters)
2)3-wattmeter method (requiring 3 wattmeters)
can be used for measuring power inn 3-phase circuit. The details of these method can be found in any standard book on electrical engineering.
The normal power measurement for a three-phase system has three wattmeters, each one connected in one of the three live wires, with the voltage coils commoned on the neutral. That measures the three separate powers in the phases.
However the total power measurement is still correct wherever the common point is that the three wattmeters have their voltage coils connected to.
If the three wattmeters have their voltage coils connected to one of the live wires, one of the wattmeters will obviously measure zero watts, but the sum of the other two will still give the total power in the three phases.
All that is needed is one watt meter. The meter will monitor all three phases and compile the power usage into one readout. Up to certain voltages and amperage's the wires are brought to the meter. As the amperage and voltages get higher the measuring equipment is left in the main distribution and small signal wires are run to the meter to give the required wattage readout.
Answer for Single-Phase Wattmeters
If you are referring to single-phase wattmeters and unbalanced loads, then the rule is based on Blondell's Theorem, which states that you can use one less wattmeter than there are number of wires connecting the supply to the load.
It is simple to calculate the power of three phase syste using two wattmeter. In this method,current coils of both wattmeter are inserted any of two line and voltage coil of both wattmeter are connected across third line of three phase system.Then total three phase power is sum or difference of the two wattmeter readings.
Blondel's Theorem states that, 'for an unbalanced three-phase load, you can use one less wattmeter than there are wires supplying that load'. So, if you have a balanced three-phase load, supplied with four wires (three line conductors and a neutral), the neutral is redundant (for a balanced load, no current flows through the neutral), so it is equivalent to a three-wire system, so you can use two wattmeters. If, however, the load is unbalanced (with a resulting neutral current), then you would need to use three wattmeters.
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Another AnswerBlondell's Theorem tells us that we can use one less wattmeter than there are wires.Add your answer:
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How would you measure power using three watt meter and one watt meter for balanced and unbalanced loads?
The 'one wattmeter method' can only be used for balanced, wye-connected, loads where the load's neutral point is accessible. The wattmeter's current coil is inserted into any line conductor, and the voltage coil is connected between the same line and the neutral point. The wattmeter reading indicates the power of one phase, so the total power is three times the wattmeter reading.To measure the total power of a balanced or unbalanced wye- or delta-connected load, it is only necessary to use twowattmeters -this is called the 'two wattmeter method'. In this case, the current coils of each wattmeter are inserted into any two line conductors, and the voltage coils are connected between the two line conductors and the third line conductor. The sum of the two wattmeter readings will indicate the total power of the load.
Will the two-wattmeter method work for all three-phase loads eg unbalanced loads inductive loads capacitive loads and delta-connected loads?
Blondel's Theorem tells us that, to measure the total power of a three-phase load (balanced or unbalanced), we can use one less wattmeter than there are conductors supplying that load.So the two-wattmeter method will work for anythree-phase load, provided there are only threeconductors supplying that load, e.g. three-wire delta or three-wire star (wye).Bear in mind that wattmeter's read true power (expressed in watts) and ignores the reactive power of inductors and capacitors.
How would you measure power factor of the balanced three phase load by two wattmeter method?
Yes. The wattmeter's current coil will have to be connected into one of the line conductors, and its voltage coil between that same line conductor and the neutral point of the load. Connected this way, the wattmeter's voltage coil is measuring one of the three phase voltages (line-to-neutral voltage) while its current coil is measuring the corresponding phase current (for a 4-wire system, the phase current = line current). The power factor (cosine of the phase angle) is accounted for automatically within the wattmeter. So the wattmeter will measure the true power (in watts) of one phase. The total power, therefore, will be 3x the wattmeter reading -providing, of course, that the load is balanced (i.e. each phase is identical). WebRep currentVote noRating noWeight
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Blondel's Theorem states that you can have one less wattmeter than there are conductors supplying a balanced or unbalanced load. In either case, the sum of the wattmeter readings will give you the total power of the load.
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Is it possible to measure power factor of the balanced three-phase load by two-wattmeter method?
yes.
How would you measure power using three watt meter and one watt meter for balanced and unbalanced loads?
The 'one wattmeter method' can only be used for balanced, wye-connected, loads where the load's neutral point is accessible. The wattmeter's current coil is inserted into any line conductor, and the voltage coil is connected between the same line and the neutral point. The wattmeter reading indicates the power of one phase, so the total power is three times the wattmeter reading.To measure the total power of a balanced or unbalanced wye- or delta-connected load, it is only necessary to use twowattmeters -this is called the 'two wattmeter method'. In this case, the current coils of each wattmeter are inserted into any two line conductors, and the voltage coils are connected between the two line conductors and the third line conductor. The sum of the two wattmeter readings will indicate the total power of the load.
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A method of making a rough measurement is: Estimation Answered by :PopTy13
Will the two-wattmeter method work for all three-phase loads eg unbalanced loads inductive loads capacitive loads and delta-connected loads?
Blondel's Theorem tells us that, to measure the total power of a three-phase load (balanced or unbalanced), we can use one less wattmeter than there are conductors supplying that load.So the two-wattmeter method will work for anythree-phase load, provided there are only threeconductors supplying that load, e.g. three-wire delta or three-wire star (wye).Bear in mind that wattmeter's read true power (expressed in watts) and ignores the reactive power of inductors and capacitors.
