DOC. MIE11110 Rev. 5
Page 92 of 110
The voltage drop caused by the soil resistance of the system
under test is measured between the connection to the system
grounding (point A) and a voltage spike (point B), that shall be
placed on the line between this point and the auxiliary earth. The
second problem is that the current drops on the system area
resistance as well as on the auxiliary earth resistance. For this
reason, the voltage drop Vd, measured between A and B, as it
moves towards the auxiliary earth goes from zero to the applied
voltage Vout; the voltage to distance curve has the following
shape.
The test is performed moving the voltage probe along the line,
until the voltage drop Vd does not change significantly; as a rule
of thumb, the good point is located from 30% to 50% of the
distance d.
The third problem is that for small systems D is small, and the
cable provided (100 m long) is far enough to reach the auxiliary
earth connection.
With larger systems, such as substations, the dimension becomes
much larger, in the order of hundreds of meters; also the short-
circuit current is much larger than 500 A, and the test current
should be proportionally larger. In this situation it is possible to use
a power cable or an overhead line, out of service, to reach
another substation, whose grounding net can be used as the
auxiliary earth connection. Another mean can be the grounding
Summary of Contents for T2000
Page 1: ...DATE 18 11 2009 DOC MIE11110 REV 5 T 2000 APPLICATION GUIDE ...
Page 45: ...DOC MIE11110 Rev 5 Page 45 of 110 ...
Page 81: ...DOC MIE11110 Rev 5 Page 81 of 110 2 Selection time about 30 ms LTC fails ...
Page 83: ...DOC MIE11110 Rev 5 Page 83 of 110 4 Same LTC as above fault on this selection ...
Page 91: ...DOC MIE11110 Rev 5 Page 91 of 110 The connection diagram is the following ...
