Dear all
As far as I know there are 2 types of HIPOT test : DC and AC. Theoretically, the two methods would give same results. A couple of days ago, we were performing HIPOT test for 20kV installation and found the leakage current could reach 500mA which, in our discussion with the sub con, is too high. The subcon said that if we performed the test using DC HIPOT tester, then the leakage current must be much smaller than above value.
I guess the 'too high' leakage current was caused by the capacitance of the system. The 500mA was the sum of "real" leakage and "pseudo" leakage. Pseudo leakage (i use my own terminology) is the current that flow from live conductor to ground through system capacitance (capacitive coupling).
Let say V=testing voltage, It = current measured by tester, I = real leakage current, Ic = pseudo leakage current, and Xc = system reactance.
It = I + Ic, where Ic = V/Xc
thus
It = I + V/Xc
we know that Xc = 1/(2*phi*f*C)
thus
It = I + V*2*phi*f*C (f=operating frequency, C = system capacitance).
thus
I = It - 2*phi*V*f*C.
If I can find the value of C (using capacitance meter), then the real leakage current can be determined, and this result should be EQUAL if I perform DC HIPOT test.
I need you guys to confirm this calculation. Maybe I missed something that should be considered.
Regards
Hendra
As far as I know there are 2 types of HIPOT test : DC and AC. Theoretically, the two methods would give same results. A couple of days ago, we were performing HIPOT test for 20kV installation and found the leakage current could reach 500mA which, in our discussion with the sub con, is too high. The subcon said that if we performed the test using DC HIPOT tester, then the leakage current must be much smaller than above value.
I guess the 'too high' leakage current was caused by the capacitance of the system. The 500mA was the sum of "real" leakage and "pseudo" leakage. Pseudo leakage (i use my own terminology) is the current that flow from live conductor to ground through system capacitance (capacitive coupling).
Let say V=testing voltage, It = current measured by tester, I = real leakage current, Ic = pseudo leakage current, and Xc = system reactance.
It = I + Ic, where Ic = V/Xc
thus
It = I + V/Xc
we know that Xc = 1/(2*phi*f*C)
thus
It = I + V*2*phi*f*C (f=operating frequency, C = system capacitance).
thus
I = It - 2*phi*V*f*C.
If I can find the value of C (using capacitance meter), then the real leakage current can be determined, and this result should be EQUAL if I perform DC HIPOT test.
I need you guys to confirm this calculation. Maybe I missed something that should be considered.
Regards
Hendra