تێستی ڕەزایی گرینداوەی ترانسپۆرزەر

Testiya Rezistansê Winding-ê

Testi rezistansê winding-ê ya transformerasa ji bo kontrolkirina cihêna winding û peyvên da ku bi pîvandkirina rezistansa xwe hatine çalak kirin.

Rêwaza Pêdivîna Rezistansê Winding-ê ya Transformerasa

Ji bo winding-ê ku bi rêza yêkêtir hêsan e, rezistansa divê di navendê line û neutral terminal de pêdivî bike.

Ji bo autotransformers-ê ku bi rêza yêkêtir hêsan e, rezistansa sêwêya HV divê di navendê terminal HV û IV terminal de, ewedî di navendê IV terminal û neutral de pêdivî bike.

Ji bo winding-ê ku bi rêza delta hêsan e, pêdivîna rezistansê winding-ê divê di jêrberên line terminal de bibe. Wa li ser rêza delta nayê pêdivîna rezistansa her tişt widing beseber, rezistansa her tişt winding divê bi rêzikê wekheviyê têkildar bike:

Rezistansa her tişt winding = 1.5 × Daxwaziyek pêdivî kirin

Rezistansa pêdivî ye di dema hewlê de û vebahandin la 75°C bi bo derbaran bi daxwaziyên dizayn, netayên piştî û têkildar.

Rezistansa Winding la temperatûra standarde 75oC

Rt = Rezistansa winding la temperatûra t

t = Temperatûra winding-ê

Her wiha, winding-ê ya transformerasa di lîqeyê insulation de ne û bi paper insulation veşte, ra nayê pêdivîna temperatûra hake winding-ê di dema transformerasa ku di dema pêdivîkirina rezistansê winding-ê de niha. Yek approximation têkildar bi bo hesabkirina temperatûra winding-ê la vê şertê, wekheviyê:

Temperatûra winding-ê = Temperatûra yekêtir oil-ê ya insulation

Temperatûra yekêtir oil-ê ya insulation divê 3 û 8 saet di dema transformerasa ku bi dema pêdivîkirina rezistansê winding-ê de niha û di dema ku ferqa di temperatûre top û bottom oil de be ma 5oC bigire.

Rezistansa bi rêzikê voltmeter ammeter method, Kelvin Bridge meter an automatic winding resistance measurement kit (ohm meter, preferably 25 Amps kit) pêdivî ye.

Dengê ji bo metoda voltmeter ammeter: Girêja nayê bi tevahî 15% girêja destnîşankirî ya winding-ê be. Girêjên mezin dikarin bi inaccuracy yên bi heating winding û guherandina temperatûra û rezistansê xwe.

Nîşan: Pêdivîna rezistansê winding-ê ya transformerasa divê ji bo her tap pêdivî bike.

Metoda Current Voltage ji bo Pêdivîna Rezistansê Winding-ê

Rezistansê winding-ê ya transformerasa bi metoda current voltage pêdivî ye. Ji bo metoda pêdivîkirina rezistansê winding-ê, test current inject dike û drop voltage di navendê winding-ê de pêdivî bike. Bi apply simple Ohm’s law i.e. Rx = V ⁄ I, yek ê asayî daxwazî rezistansa werin.

Rêwaza Metoda Current Voltage ji bo Pêdivîna Rezistansê Winding-ê

• Pêşî pêdivî, transformera divê off be û pa excitation ji bo 3 û 4 saet. Ev hewce dike ki temperatûra winding-ê bi temperatûra oil-ê were yekêtir.

• Pêdivî dike bi D.C.

• Bi minimizkirina observation errors, polarity of the core magnetization shall be kept constant during all resistance readings.

• Voltmeter leads shall be independent of the current leads to protect it from high voltages which may occur during switching on and off the current circuit

• The readings shall be taken after the current and voltage have reached steady state values. In some cases this may take several minutes depending upon the winding impedance.

• The test current shall not exceed 15% of the rated current of the winding. Large values may cause inaccuracy by heating the winding and thereby changing its resistance.

• For expressing resistance, the corresponding temperature of the winding at the time of measurement must be mentioned along with resistance value. As we said earlier that after remaining in switch off condition for 3 to 4 hours, the winding temperature would become equal to oil temperature. The oil temperature at the time of testing is taken as the average of top oil and bottom oil temperatures of transformer.

• For star connected three-phase winding, the resistance per phase would be half of the measured resistance between two line terminals of the transformer

• For delta connected three-phase winding, the resistance per phase would be 0.67 times of measured resistance between two line terminals of the transformer.

• This current voltage method of measurement of winding resistance of transformer should be repeated for each pair of line terminals of winding at every tap position.

Bridge Method of Measurement of Winding Resistance

The main principle of the bridge method is based on comparing an unknown resistance with a known resistance. When currents flowing through the arms of the bridge circuit become balanced, the reading of galvanometer shows zero deflection that means at balanced condition no current will flow through the galvanometer.

A very small value of resistance (in milli-ohms range) can be accurately measured by the Kelvin bridge method whereas for higher value Wheatstone bridge method of resistance measurement is applied. In bridge method of measurement of winding resistance, the errors are minimized.

The resistance measured by Kelvin bridge

All other steps to be taken during transformer winding resistance measurement in these methods are similar to that of current voltage method of measurement of winding resistance of transformer, except the measuring technique of resistance.

The resistance measured by Wheatstone bridge,