Author/Authors :
Rakov، نويسنده , , V.A.، نويسنده , , Uman، نويسنده , , M.A.، نويسنده , , Fernandez، نويسنده , , M.I.، نويسنده , , Mata، نويسنده , , C.T.، نويسنده , , Rambo، نويسنده , , K.J.، نويسنده , , Stapleton، نويسنده , , M.V.، نويسنده , , Sutil، نويسنده , , R.R.، نويسنده ,
Abstract :
Lightning triggered from natural thunderclouds
using the rocket-and-wire technique was employed in order to
subject to direct lightning strikes the lightning protective system
of a test house at the International Center for Lightning Research
and Testing (ICLRT) at Camp Blanding, FL. The electrical circuit
of the test house was connected to the secondary of a padmount
distribution transformer located a distance of about 50 m from the
house. The transformer primary was connected to a 650-m long
unenergized underground power cable. The test house had two
ground rods, one for the lightning protective system grounding
and the other for the power supply system grounding. The two
rods were about 3 m apart and were connected by a metallic cable.
Lightning current was injected into the lightning protective system
ground rod, and the currents and voltages at different points in
the test system were measured. The waveshapes of currents in the
ground rods of the test house differed markedly from the current
waveshapes in other parts of the overall system. The ground
rods at the test house appeared to filter out the higher frequency
components of the lightning current, allowing the lower frequency
components of the current to enter the house’s electrical circuit,
that is, the ground rods appeared to exhibit a capacitive behavior
rather than the often expected resistive behavior. This effect was
observed for dc grounding resistances of the rods (driven in sandy
soil with conductivity of about 2 5 10 4 S/m) ranging from
more than a thousand ohms to some tens of ohms. The peak values
of 1) the current entering the test house’s electrical circuit, 2) the
current flowing to the distribution transformer secondary neutral,
and 3) the current flowing through the surge protective devices
at the test house’s service entrance were observed to be greater
than in either of the two scenarios suggested by the International
Electrotechnical Commission.
Keywords :
Ground rods , Lightning , lightning protectivesystem , surge protective devices.
