Wattamita da Karshe Faktori na Nau'i: Me ke Wani? (Da Kyake Yana Amfani Da Ita)
Mai Daƙa Ƙarfin Ƙarin Ƙarfin Wattimeter?
Wattimeter da ƙarfin ƙarin ƙarfin shi ne wani alama da ake amfani da ita don ƙirƙira ƙarfin ƙarin ƙarfin da duka. Idan ba na yi la'akari game da wattimeter da ƙarfin ƙarin ƙarfin, zan iya tabbatar da mu iya fahimta cewa yana da kyau a yi amfani da wattimeter da ƙarfin ƙarin ƙarfin (wanda ba ce electrodynamometer wattimeter na gaba)
Amsa ta daidai: wattimeter na gaba tana bayar da abubuwa mai asali.
Yanzu akwai biyu waɗannan yanayin da muna da shawarar da ba a yi amfani da wattimeter na gaba a ƙirƙiri ƙarfin ƙarin ƙarfin:
Zamantakewa da yaɗuwar kofin mutumma ya kasance daɗe saboda hakan da muna ƙoƙarin jin current da pressure coils.
Abubuwan da suka faruwa saboda inductance da ke pressure coil.
Waɗannan biyu waɗannan sun bayar da abubuwa mai asali, saboda haka ba zan iya amfani da wattimeters na gaba a ƙirƙiri ƙarfin ƙarin ƙarfin.
Amma idan muna yi some modifications ko kuma add some new features, muna iya amfani da electrodynamic wattimeter da ƙarfin ƙarin ƙarfin don ƙirƙiri ƙarfin ƙarin ƙarfin daidai.
Idan ba ni da shawarar da a yi amfani da power factor correction don ƙara ƙarfin ƙarfin. Amma yana da lokaci da ba za a iya ƙara ƙarfin ƙarfin da ɗaya (saboda dalilai masu ilimi ko budget).
A nan za a tattaunawa inda muna bukatar da zuwa a yi amfani da modification. Wadannan suna nufin da za a tattaunawa a nan:
(1) Resistance da ke pressure coil na wattimeter na gaba an ƙara ta zuwa ma'aici mai ƙarin saboda hakan da current a cikin circuit na pressure coil ya ƙara, saboda hakan an samu. A nan an samu biyu waɗannan diagrams, wadannan suna nuna a nan:
A nan an fi sanya biyu waɗannan ends da ke pressure, an kofa supply-side (i.e. current coil ana ci gaba da load). Supply voltage ce da ke voltage across pressure coil. Saboda hakan a nan an samu power da ke first wattmeter ce da ke power loss a cikin load plus power loss a cikin current coil.
A nan an samu biyu waɗannan category, current coil bai ci gaba da load, voltage across pressure coil bai ci gaba da applied voltage.
Voltage across pressure coil ce da ke voltage across load. Power da ke second-watt meter ce da ke power loss a cikin load plus power loss a cikin pressure coil.
Daga cikin tattaunawa a nan, muna ƙarfafa cewa a biyu waɗannan cases muna da abubuwan da suka faruwa, saboda hakan muna bukatar da zuwa a yi modification a cikin circuits don ƙara error da ɗaya.
Circuit da ya ƙara ta shi ne a nan:
An amfani da special coil wanda ake kiran compensating coil, ita ce da ya ƙara current da ke sum of two currents i.e. load current plus pressure coil current.
Pressure coil an kofa ta shi saboda field produced by compensating coil an kafin field produced by pressure coil kamar yadda ake nuna a diagram na circuit.
Saboda hakan net field ce da ke current I only. Don haka, errors caused by pressure coil an ƙara ta shi.
(2) Muna bukatar compensating coil a cikin circuit don ƙara wattimeter da ƙarfin ƙarin ƙarfin. Wannan shi ne modification na biyu wanda ake nuna cikakken bayan a nan.
(3) Idan an samu point na uku, muna ƙara compensation of inductance na pressure coil, wanda ake iya ƙara ta shi don yi modification a cikin circuit.
Yanzu muna ƙara expression for correction factor for pressure coil inductance. Kuma daga wannan correction factor, muna ƙara expression for error due to inductance of pressure coil.
Idan muna ƙara inductance na pressure coil, ba muna da voltage across pressure in phase with applied voltage.
Saboda hakan, ita ce da ke lagging by an angle
Where, R is electrical resistance in series with pressure coil, rp is pressure coil resistance, here we also conclude that the current in the current coil is also lagging by some angle with the current in pressure coil. And this angle is given by C = A – b. At this time reading of the voltmeter is given by
Where, Rp is (rp+R) and x is angle. If we ignore the effect of the inductance of pressure i.e putting b = 0 we have expression for true power as
On taking the ratio of equations (2) and (1) we have an expression for correction factor as written below:
And from this correction factor error can be calculated as
On substituting the value of correction factor and taking suitable approximation we have an expression for error as VIsin(A)*tan(b).
Now we know that the error caused by pressure coil inductance is given by the expression e = VIsin(A) tan(b), if the power factor is low (i.e in our case the value of φ is large hence we have a large error).
Thus in order to avoid this situation, we have connected the variable series resistance with a capacitor as shown in the above figure.
This final modified circuit so obtained is called the low power factor meter.
A modern low power factor meter is designed such that it gives high accuracy while measuring power factors even lower than 0.1.
Bayanin: Jin ƙungiyar, rubutu na gaskiya za a shara, idandansa babu ƙungiyar za a ɗauki.
