Iyakaranta na Iskaɗaƙi Masu Gaba-gaba
A nan tsari insulation resistance da ita ce mafi yawan karamin birnin kasa daga insulation zuwa amfani da shi.
Maida insulation resistance yana da muhimmanci. A gaba na lura ne suka yi karatu a wasu lokaci bayan a yi amfani da test voltage. Tsari na amfani da voltage suna cikin 1 minute ko 10 minutes. Saboda haka, za a iya kiran insulation resistance a matsayin 1 minute insulation resistance ko 10 minute insulation resistance idan an yi wata wannan lokacin.
NB: – Amfani da voltage na maida insulation resistance yana cikin birnin kasa.
Idan a yi amfani da birnin kasa across the insulation, zai faru current kan insulation. Wannan current yana da biyu masu muhimmiyar banga.
Current da ke faru across leakage path over the surface of the solid insulator. Wannan leakage path yana form mainly saboda moisture, dust etc. wadanda suka jiha natural ce a tsakiyar solid insulator.
Current da ke faru through the volume of the insulator body.
Na biyu a cikin current yana cikin uku masu muhimmiyar banga kamar yadda ake bayyana a cikin:
Saboda insulation materials suna cikin dielectric nature, zai faru capacitive charging current, ba tare da application of test voltage. Wannan current yana instantaneous in nature. Zai zama da wuya a fadada lokaci. Saboda haka, wannan current ba sa iya samun wani takarda a cikin karatu idan an yi shi bayan 1 minute ko daidai.
Akwai wata banga a cikin current da ake kira absorption current. Yana decay from high value to zero. The insulation resistance value taken within first few minutes of test is largely dominated by absorption current.
Wata kuma da muhimmiyar banga a cikin current shine conduction current. Yana basta da wuri throughout the insulation resistance test. Saboda haka, ba tare da charging current then absorption current becomes insignificant, the test result is mainly predominated by this conduction current.
Sannan kafin a yi karatu insulation resistance, leakage current and conduction current ne suka faru.
Saboda haka, karatu insulation resistance yana da yawa a yi bayan 15 seconds ko 1 minute ko sometimes after 10 minutes during the test.
Hanyar Maida Insulation Resistance
Akawo kimiyya da ake amfani da su don maida insulation resistance wa electrical equipment.
Direct-indicating ohmmeter with hand driven dc generator. Wannan ya fi sani a wurin da ake kiran hand driven megger saboda Megger shine wanda ya fi shahara a matsayin mai ban sha wannan instrument.
Direct-indicating ohmmeter with motor driven dc generator. Wannan ya fi sani a wurin da ake kiran motorized megger.
Direct-indicating ohmmeter with self-contained battery.
Direct-indicating ohmmeter with self-contained rectifier. Wannan instrument takes power from an external AC supply.
Resistance bridge circuit with self-contained galvanometer and battery.
Za a iya yi measurement of insulation resistance with an external dc supply. In that case, we take voltage and current reading with the help of a dc voltmeter and a micro ranged dc ammeter, respectively.
In that case, we can calcula the insulation resistance with the help of ohm’s law
Where, V is the voltmeter reading and I is the ammeter reading.
The ammeter is micro ranged because, a very tiny current passes through the insulation during test and he current is in that range only. But at the moment of voltage application, the micrometer has to take initial capacitive charging current as well as absorption current. So the ammeter should be capable of withstanding both of these currents for at least initial duration. The voltmeter, ammeter and source should also be capable of withstanding short circuit current in the case of insulation failure if occurs during measurement.
When we use direct indicating ohmmeter of simply megger, the leads of the instrument are connected across the insulator to be tested. After driving the instrument the value of insulation resistance is indicated on the analog or digital dial of the instrument directly.
In both of the above-mentioned methods of insulation resistance measurement, the reading is taken after a standard time delay to get more accurate and error-free reading.
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