Wattmetar na Turbin Electromagnetik
Amsa da muka shafi fayiloci na electrodynamometer type wattmeter, ya kamata a tabbatar da hukuma mai amfani ake da electrodynamometer type wattmeter. Hukuma mai amfani ake da dynamometer type wattmeter yana yi aiki da karamin tsari, kuma wannan hukuma zaka iya bayyana cewa idan karamin abubuwa tana fito a kan magnetic field, tana samun daradara mai kimiyya da kuma saboda hakan tana faru.
Fayiloci da Hukuma Mai Amfani Ake Da Electrodynamometer Type Wattmeter
Tana nan muka nuna cikakken fayiloci na electrodynamometer. Tana da waɗannan muhimman yanayi.
Yana da duɗuwar karamin abubuwan da ke cikin electrodynamometer. Su ne:
Moving Coil
Moving coil tana karɓar da ƙarin ma ake da spring control instrument. Karamin abubuwa masu yawa ta shafi fitowa a kan moving coil don in ba sa gida. Saboda hakan, muna saka high value resistor a kan moving coil. Moving coil tana da air core da kuma tana fito a kan pivoted spindle da kuma tana iya faru da kare. A electrodynamometer type wattmeter, moving coil tana yi aiki a matsayin pressure coil. Saboda hakan, moving coil tana saka a kan voltage, kuma karamin abubuwa tana fito a kan wannan coil tana daidai mutumce a kan voltage.
Fixed Coil
Fixed coil tana da duɗuwar karamin abubuwan da suka zama biyu, kuma suka saka a kan load, saboda hakan karamin abubuwan load tana fito a kan wannan coils. Yadda aka yi hakan ya fi ƙarfin da ita ce a yi biyu fixed coils baki daya, don haka za su iya da yawan karamin abubuwan mai yawa. Wannan coils suna nufin current coils of electrodynamometer type wattmeter. A lokacin da zuwa, fixed coils suna da sarrafa karamin abubuwan da take da 100 amperes, amma a yanzu, modern wattmeters suna da sarrafa karamin abubuwan da take da 20 amperes don in ba da shiga karamin abubuwan.
Control System
Daga biyu controlling systems, i.e.
Gravity control
Spring control, ana amfani da spring controlled systems a kowane wani wannan types of wattmeter. Gravity controlled system ba zan iya amfani ba saboda hakan za a kasance yawan errors.
Damping System
Air friction damping tana amfani, saboda eddy current damping tana juye operating magnetic field da kuma tana iya ba da error.
Scale
Yana da uniform scale da ake amfani a kowane wani wannan types of instrument saboda moving coil tana yi aiki linearly over a range of 40 degrees to 50 degrees on either side.
Tana nan muka nuna expressions for the controlling torque and deflecting torques. Don haka muka nuna circuit diagram given below:
A nan muna sanin cewa instantaneous torque in electrodynamic type instruments tana da damar da product of instantaneous values of currents flowing through both the coils and the rate of change of flux linked with the circuit.
Idan I1 da I2 su ne instantaneous values of currents in pressure and current coils respectively. Saboda hakan, expression for the torque can be written as:
Where, x is the angle.
Idan applied value of voltage across the pressure coil be
Assuming the electrical resistance to the pressure coil be very high hence we can neglect reactance with respect to its resistance. In this the impedance is equal to its electrical resistance therefore it is purely resistive.
The expression for instantaneous current can be written as I2 = v / Rp where Rp is the resistance of pressure coil.
If there is phase difference between voltage and electric current, then expression for instantaneous current through current coil can be written as
As current through the pressure coil is very very small compared to the current through current coil hence current through the current coil can be considered as equal to total load current.
Hence the instantaneous value of torque can be written as
Average value of deflecting torque can be obtained by integrating the instantaneous torque from limit 0 to T, where T is the time period of the cycle.
Controlling torque is given by Tc = Kx where K is spring constant and x is final steady state value of deflection.
Abubuwan Da Electrodynamometer Type Wattmeter Ke Sanya
Wannan ne abubuwan da electrodynamometer type wattmeter ke sanya da suka rubuta a kafin:
Scale is uniform upto a certain limit.
They can be used for both to measure ac as well dc quantities as scale is calibrated for both.
Abubuwan Da Electrodynamometer Type Wattmeter Ke Sanya
Wannan ne abubuwan da ke cikin electrodynamometer type wattmeters:
Errors in the pressure coil inductance.
Errors may be due to pressure coil capacitance.
Errors may be due to mutual inductance effects.
Errors may be due connections.(i.e. pressure coil is connected after current coil)
Error due to Eddy currents.
Errors caused by vibration of moving system.
Temperature error.
Errors due to stray magnetic field.
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