Jirgin Dabbobi: Takaitaccen, Mafi Girman da Ma'aikataccen Daidai na Iya Koyarwa
Amsa da Earth sunan da ake cewa wani amsa da take aikin aiki kan aikin current zuwa tsakiyar kasa. Ana kiran shi da sunan amsar da Earth ko amsar da ground. Amsa da Earth yana da muhimmanci a fice da kuma gudanar wasu aikinsu, saboda haka yana taimakawa da ingantaccen aikin da kuma ziyartar aikin.
Muhihimmiya Earth Electrode?
Earth electrode yana nufin wani batu ko plate mai sarrafa da ake sauka a tsakiyar kasa da ake kofara kan terminal da Earth na aikin. Yana bayar da hanyar aiki da amsa da dama ga fault currents da lightning surges zuwa tsakiyar kasa. Yana taimakawa da kula da voltage na aikin da kuma kula da electromagnetic interference.
Earth electrode zai iya zama ne mai sarrafa da copper, steel, galvanized iron, ko wasu manyan abubuwan da suka da aikin da kuma amsa da korosyon. Girman, shape, length, da depth na Earth electrode suna da lafiya ga soil conditions, current rating, da application na earthing system.
Me Da Duk Muhimmin Da Sun Taimakawa Wajen Earth Resistance?
Amsa da Earth yana da muhimmanci ga resistivity na soil bayan electrode da point of zero potential (infinite earth). Resistivity na soil yana da muhimmanci ga wasu abubuwa, kamar:
Electrical conductivity na soil, wanda yake da electrolysis. Concentration na water, salt, da wasu chemical components na soil ke taimakawa da conductivity. Soil mai ruwa da masu salt da ake fiye ya fi amsa da dama ba wajen dry soil da low salt content.
Chemical composition na soil, wanda yake taimakawa da pH value da corrosion properties. Soil mai acid ko alkaline zai iya korode Earth’s electrodes da kuma karshen amsa.
Grain size, uniformity, da packing na soil particles yana taimakawa da porosity da moisture retention capacity. Fine-grained soil da uniform distribution da compact packing ya fi amsa da dama ba wajen coarse-grained soil da irregular distribution da loose packing.
Temperature na soil, wanda yake taimakawa da thermal expansion da freezing point. High temperature zai iya karshen conductivity na soil ta haka da ion mobility. Low temperatures zai iya kula da conductivity na soil ta haka da freezing water content.
Amsa da Earth yana da muhimmanci ga resistance na electrode da kuma contact resistance bayan surface na electrode da soil. Amma, waɗannan abubuwa suna da muhimmanci ba a matsayin soil resistivity.
Yadda Ake Bincike Earth Resistance?
Ana da wasu hanyoyi na bincike Earth resistance a wasu aikinsu. Wasu na hanyoyin da ake amfani da su:
Fall of Potential Method
Wannan an kiran da 3-point method ko potential drop method. Yana bukata da two test electrodes (current electrode da potential electrode) da kuma Earth resistance tester. Current electrode yana sauka a distance daga existing Earth electrode zuwa depth equal to its depth. Potential electrode yana sauka bayan them at a suitable distance such that it is outside their spheres of influence (resistance areas). Tester yana inject a known current through the current electrode and measures the voltage between the potential electrode and the existing Earth electrode. Earth resistance is calculated using Ohm’s law:
Idan R yana nufin Earth resistance, V yana nufin measured voltage, da I yana nufin injected current.
Wannan hanyar yana da kyau da accurate amma yana bukata da disconnecting all connections to the Earth electrode before testing.
Clamp-On Method
Wannan an kiran da induced frequency testing ko stakeless method. Ba a bukata test electrodes ko disconnecting any connections to the Earth electrode. Yana amfani da two clamps wadanda ake sauka a existing Earth electrode. One clamp induces a voltage to the electrode and another clamp measures the current flowing through it. Earth resistance is calculated using Ohm’s law:
Idan R yana nufin Earth resistance, V yana nufin induced voltage, da I yana nufin measured current.
Wannan hanyar yana da kyau da fast amma yana bukata da parallel Earth network with multiple electrodes.
Attached Rod Method
Wannan hanyar yana amfani da one test electrode (current electrode) da kuma Earth resistance tester. Current electrode yana kofara kan existing Earth electrode with a wire. Tester yana inject a known current through the wire and measures the voltage between the wire and the existing Earth electrode. Earth resistance is calculated using Ohm’s law:
Idan R yana nufin Earth resistance, V yana nufin measured voltage, da I yana nufin injected current.
Wannan hanyar ba a bukata disconnecting any connections to the Earth electrode but requires good contact between the wire and the current electrode.
Star-Delta Method
Wannan hanyar yana amfani da three test electrodes (current electrodes) arranged in an equilateral triangle around the existing Earth electrode. An Earth resistance tester injects a known current through each pair of test electrodes in turn and measures the voltage between each pair of test electrodes in turn. Earth resistance is calculated using Kirchhoff’s laws:
Idan R yana nufin Earth resistance, VAB, VBC, VCA yana nufin measured voltages between each pair of test electrodes, da I yana nufin injected current.
Wannan hanyar ba a bukata disconnecting any connections to the Earth electrode but requires more test electrodes than other methods.
Dead Earth Method
Wannan hanyar yana amfani da two test electrodes (current electrodes) connected in series with an Earth resistance tester. One test electrode yana sauka near the existing Earth electrode, and another test electrode yana sauka far away from it. Tester yana inject a known current through both test electrodes into the ground and measures the voltage between them. Earth resistance is calculated using Ohm’s law:
Idan R yana nufin Earth resistance, V yana nufin measured voltage, da I yana nufin injected current.
Wannan hanyar ba a bukata disconnecting any connections to the existing Earth electrode but requires a very long wire between both test electrodes.
Slope Method
Wannan hanyar yana amfani da one test electrode (potential electrode) da kuma Earth resistance tester. Potential electrode yana kawo along a straight line away from the existing Earth electrode at regular intervals. Tester yana inject a known current through the existing Earth electrode into the ground and measures the voltage between it and the potential electrode at each interval. A graph of voltage versus distance is plotted and extrapolated to find the intercept on the voltage axis. Earth resistance is calculated using Ohm’s law:
Idan R yana nufin Earth resistance, V0 yana nufin intercept on the voltage axis and I yana nufin injected current.
