Open-circuit test

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The open-circuit test , or "no-load test", is one of the methods used in electro engineering to determine the no-load impedance in the excitation branch of the transformer. No load is represented by an open circuit, which is represented on the right side of the image as "hole" or incomplete part of the circuit.

Video Open-circuit test

Metode

The secondary of the transformer is left open. The wattmeter is connected to the primary. The ammeter is connected in series with the primary winding. Voltmeter is optional because the applied voltage is equal to the voltmeter reading. Measurable voltage applied to the primary.

If the applied voltage is a normal voltage then the normal flux will be adjusted. Since the loss of iron is a function of the applied voltage, a normal iron loss will occur. Therefore it loses the maximum iron at rated voltage. This maximum iron loss is measured using a wattmeter. Since the impedance of the series winding of the transformer is very small compared to the excitation branch, all input voltages are dropped in the excitation branch. So the wattmeter only measures iron loss. This test measures only the combined loss of iron consisting of hysteresis loss and eddy current loss. Although the loss of hysteresis is less than the eddy current loss, it can not be ignored. Two losses can be separated by moving the transformer from a variable frequency source because the hysteresis loss varies linearly with the supply frequency and the eddy current loss varies with the square.

Because the secondary of the transformer is open, the main draws only the no-load current, which will have some copper loss. This no-load current is very small and since the loss of copper in primers is proportional to the square of this current, it is negligible. No copper is lost in the secondary because there is no secondary current.

The secondary side of the transformer is left open, so there is no load on the secondary side. Therefore, the power is no longer transferred from primary to secondary in this approximation, and a negligible current flows through the secondary winding. Since no current passes through the secondary winding, no magnetic field is created, which means zero is currently induced on the primary side. This is very important for the approach because it allows us to ignore the impedance series because it is assumed that no current passes through this impedance.

Shunt parallel components in equivalent circuit diagrams are used to represent core losses. This core loss comes from changes in the direction of the flux and eddy flows. Eddy current losses are caused by currents induced in iron due to alternating flux. Unlike the shunt parallel components, the series components in the circuit diagram show a tortuous loss due to the resistance of the transformer winding coil.

The current, voltage and power are measured on the primary windings to ensure the entrance angle and power factor angle.

Another method to determine the real series transformer impedance is a short circuit test.

Maps Open-circuit test

Calculation

Arus ${\ displaystyle \ mathbf {I_ {0}}}  ÂÂ$ sangat kecil.

Jika ${\ displaystyle \ mathbf {W}}  ÂÂ$ adalah pembacaan wattmeter,

${\ displaystyle \ mathbf {W} = \ mathbf {V_ {1}} \ mathbf {I_ {0}} \ cos \ phi _ {0}}  ÂÂ$

Persamaan itu dapat ditulis ulang sebagai,

${\ displaystyle \ cos \ phi _ {0} = {\ frac {\ mathbf {W}} {\ mathbf {V_ {1}} \ mathbf {I_ {0} }}}}  ÂÂ$

Demikian,

${\ displaystyle \ mathbf {I_ {m}} = \ mathbf {I_ {0}} \ sin \ phi _ {0}}  ÂÂ$

${\ displaystyle \ mathbf {I_ {w}} = \ mathbf {I_ {0}} \ cos \ phi _ {0}}  ÂÂ$

Impedansi

Dengan menggunakan persamaan di atas, ${\ displaystyle \ mathbf {X_ {0}}}  ÂÂ$ dan ${\ displaystyle \ mathbf {R_ {0}}}  ÂÂ$ dapat dihitung sebagai,

${\ displaystyle \ mathbf {X_ {0}} = {\ frac {\ mathbf {V_ {1}}} {\ mathbf {I_ {m}}}}}  ÂÂ$

${\ displaystyle \ mathbf {R_ {0}} = {\ frac {\ mathbf {V_ {1}}} {\ mathbf {I_ {w}}}}}  ÂÂ$

Demikian,

${\ displaystyle \ mathbf {Z_ {0}} = {\ sqrt {\ mathbf {R_ {0}} ^ {2} \ mathbf {X_ {0}} ^ {2}}}}  ÂÂ$

atau

${\ displaystyle \ mathbf {Z_ {0}} = \ mathbf {R_ {0}} \ mathbf {j} \ mathbf {X_ {0}}}  ÂÂ$

Admittance

Masuk adalah kebalikan dari impedansi. Karena itu,

${\ displaystyle \ mathbf {Y_ {0}} = {\ frac {1} {\ mathbf {Z_ {0}}}}}  ÂÂ$

Konduktansi ${\ displaystyle \ mathbf {G_ {0}}}  ÂÂ$ dapat dihitung sebagai,

${\ displaystyle \ mathbf {G_ {0}} = {\ frac {\ mathbf {W}} {\ mathbf {V_ {1}} ^ {2}}}}  ÂÂ$

Oleh karena itu susunannya,

${\ displaystyle \ mathbf {B_ {0}} = {\ sqrt {\ mathbf {Y_ {0}} ^ {2} - \ mathbf {G_ {0}} ^ {2}}}}  ÂÂ$

atau

${\ displaystyle \ mathbf {Y_ {0}} = \ mathbf {G_ {0}} \ mathbf {j} \ mathbf {B_ {0}}}  ÂÂ$

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${\ displaystyle \ mathbf {W}}  ÂÂ$ adalah pembacaan wattmeter

${\ displaystyle \ mathbf {V_ {1}}}  ÂÂ$ adalah tegangan pengenal yang diterapkan

${\ displaystyle \ mathbf {I_ {0}}}  ÂÂ$ adalah Arus tanpa beban

${\ displaystyle \ mathbf {I_ {m}}}  ÂÂ$ adalah komponen magnetisasi dari arus tanpa beban

${\ displaystyle \ mathbf {I_ {w}}}  ÂÂ$ adalah komponen kehilangan inti saat ini tanpa beban

${\ displaystyle \ mathbf {Z_ {0}}}  ÂÂ$ adalah impedansi yang menarik

${\ displaystyle \ mathbf {Y_ {0}}}  ÂÂ$ adalah cara masuk yang menarik

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Referensi

• Kosow (2007). Mesin Listrik dan Transformer . Pearson Education India. Â
• Smarajit Ghosh (2004). Dasar-dasar Teknik Elektro dan Elektronik . PHI Learning Pvt. Ltd
• Wildi, Wildi Theodore (2007). Mesin Listrik, Drive Dan Sistem Daya, edtn ke-6 . Pearson.
• Grainger. Stevenson (1994). Analisis Sistem Daya . McGraw-Hill.

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Source of the article : Wikipedia