Testi Inda Yawancin Karkashin Kirki ko da PI Test

Muhimmiyar Inda Mafi Ingantacce (Takarda PI) da Takarda Ingantaccen Kirkiya (Takarda IR) suna da shi a cikin karkashin kimiyya mai tsirriyar karkashin kirkiya don tabbatar da kyauwa kan ingantacce. Takarta IP ya kunshi wanda yake da ita don tabbatar da kyauwarsa da gaskiya ta hanyar ingantacce.
A takardan ingantaccen kirkiya, ana kafa sanya mai tsirriya na DC voltage a tafin ingantacce. An yi haɗa wannan voltage aiki zuwa current a tafin ingantacce don samun takarda ingantacce. Saboda, idan ake amfani da Ohm’s law,

Babu karin maida aiki na voltage na musamman, voltmeter da ammeter don ci gaba masu voltage da current, za a iya amfani da potentiometer mai saukarar aiki wanda ake kira megger.

Megger ya ba sanya mai tsirriya na DC a tafin ingantacce, kuma ya bayyana takarda ingantacce a matsayin M – Ω da G – Ω. Ana amfani da 500 V, 2.5 KV da 5 KV megger saboda kyauwar insulasyon. Misali, ana amfani da 500V megger don ci gaba ingantacce da ke da rating ta 1.1 KV. Don transformer mai tsirriya mai yawa, sadima da abubuwa da makaranta masu tsirriya mai yawa, ana amfani da 2.5 ko 5 KV megger saboda kyauwar insulasyon.
Saboda duka ingantacce masu kimiyya suka da alamar capacitive. Saboda haka, a lokacin da ake kafa sanya voltage a tafin ingantacce, a baya ya faru current mai charging. Amma a baya da zaman, inda ingantacce ya zama da charging total, an yi zero current mai charging. Saboda haka, an fi sani da ci gaba takarda ingantacce daga lokacin da ake kafa sanya voltage a tafin ingantacce daɗi 1 minute (kada 15 seconds).

Kawai ci gaba takarda ingantacce da megger ba za su iya ba da natija mai amfani ba. Saboda takarda ingantacce ya iya canza saboda temperature.
Wannan buƙata an yanke da damar muhimmiyar inda mafi ingantacce ko kuma takarda PI. Zan yi rubutu game da takarta PI, a nan.
Idan ake kafa sanya voltage a tafin ingantacce, za a faru current a tafin ita. Idan wannan current yana da kadan, amma yana da kadan da yake da milliampere ko microampere, akwai na kwanaki ne.

1. Capacitive component.

2. Conductive component.

3. Surface leakage component.

4. Polarization component.

Ba ni a rubuta waɗanda waɗanda.

Capacitive Component

Idan ake kafa sanya DC voltage a tafin ingantacce, saboda alamartinsa, za a faru current mai charging a baya. Wannan current ya canza da kasa da kasa da ya zama zero a baya da zaman. Wannan current yana da kadan a baya 10 seconds. Amma ya zama zero a baya da 60 seconds.

Conductive Component

Wannan current yana da alamar conductive, yana zama a tafin ingantacce idan ake kiran ingantacce da kuma alamar resistive. Wannan current yana da alamar flow of electrons. Duka ingantacce na wannan component na electric current. Saboda, a cikin yadda ake amfani da abubuwa a duniya, akwai alamar conductive. Wannan current conductive yana da kadan a cikin test.

Surface Leakage Component

Saboda dust, moisture da abubuwa masu gaskiya a tafin ingantacce, akwai current mai kadan da ya faru a tafin surface na ingantacce.

Polarization Component

Duka ingantacce na alamar hygroscopic. Abubuwa masu gaskiya, misali moisture, na ingantacce suka da alamar polar. Idan ake kafa sanya electric field a tafin ingantacce, abubuwa masu polar suka align themselves along the direction of electric field. Energin da aka fi sifar da ita don alignment of polar molecules, yana zama a tafin voltage source a form of electric current. Wannan current yana kiran polarization current. Yana zama har zuwa inda abubuwa masu polar suka align themselves along the direction of electric field.
Yana zama 10 minutes don align abubuwa masu polar along electric field, saboda haka, idan ake ci gaba takarda megger da 10 minutes, ba zan iya faru effect of polarising a cikin natijar megger.
Saboda haka, idan ake ci gaba takarda megger na ingantacce da 1 minute, natijar irin yana nuna takarda IR wanda bai free ne daga effect of the capacitive component of current. Kuma idan ake ci gaba takarda megger na ingantacce da 10 minutes, natijar megger yana nuna takarda IR, wanda bai free ne daga effects of both capacitive component and polarisation component of the current.

Polarisation index yana da ratio of megger value taken for 10 minutes to the megger value taken for 1 minute.
The significance of polarization index test.
Let I be the total initial current during polarisation index test or PI test.
IC is the capacitive current.
IR is resistive or conductive current.
IS is surface leakage current.
IP is polarization current of the insulator.

Value of insulation resistance test or IR value test, i.e. value megger reading just after 1 minute of the test, is-

Megger value of 10 minute test, is

Therefore, result of polarization index test, is

From the above equation it is clear that, if the value of (IR + IS) >> IP, the PI of insulator approaches to 1. And large IR or IS or both indicate unhealthiness of the insulation.
The value of PI becomes high if (IR + IS) is very small compared to IP. This equation indicates that high polarization index of an insulator implies healthiness of insulator. For good insulator resistive leakage current IR is very tiny.
It is always desired to have polarisation index of an electrical insulator more than 2. It is hazardous to have polarisation index less than 1.5.

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