LPF

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P.A.C.RAMASAMY RAJA POLYTECHNIC COLLEGE RAJAPALAYAM-626 108

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Voltage (V) ? Current (I) ? Relationship b/w V , I & R ? Resistance (R) ?

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Relation b/w V , I & R ?

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Power (P) ? Wattmeter-use ?

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To measure power accurately at low values of PF.

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“when current carrying conductor is placed inside a magnetic field , it experiences a mechanical force and due this mechanical force deflection of conductor takes place”.

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Why we ca n’t measured accurate reading in ordinary wattmeter at low PF? Deflecting Torque. Errors.

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DEFLECTING TORQUE Reason T d α VI Cos ɸ Cos ɸ is small so T d is low T d is low

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ERRORS Reason Due to Pressure Coil Inductance a t low PF. Error introduced.

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LPF WATTMETER SUPPLY VOLTAGE LOAD P.C Compensating Coil C .C C R

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ORDINARY WATTMETER TO LPF WATTMETER Modifications

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Modifications To reduce Pressure Circuit resistance. To connect Compensating Coil. Compensation for Pressure Coil Inductance. Small Control Torque .

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1.To reduce Pressure Circuit resistance PC - designed at low resistance – more current flow - to develop more torque . In PC L PF wattmeter = 10 ×UPF wattmeter

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2.To connect Compensating Coil. Low PF – high ct ( vge drop also increase in CC). So we connect the PC after the CC (it also have some error due to PC ct ).

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1 2

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If you want to increase ct in PC means , you’ll connect the Compensating Coil with CC in LPF wattmeter. Compensating Coil to reduce the flux in CC.

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3.Compensation for Pressure Coil Inductance PC inductance α Sin ɸ Cos ɸ = 0 (low) Sin ɸ = 1 (high) Sin ɸ - high - connect one Capacitor across Rse in PC.

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4.Small Control Torque LPF wattmeters are designed to have a very small control torque so they can provide Full Scale Deflection .

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Application Used in Open-Circuit test ( LPF ) Used in Short-Circuit test ( UPF )

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THANK YOU

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Created by Chandru.G

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