Abstract: This study describes analysis of tower grounding
resistance effected the back flashover voltage across insulator string
in a transmission system. This paper studies the 500 kV transmission
lines from Mae Moh, Lampang to Nong Chok, Bangkok, Thailand,
which is double circuit in the same steel tower with two overhead
ground wires. The factor of this study includes magnitude of
lightning stroke, and front time of lightning stroke. Steel tower uses
multistory tower model. The assumption of studies based on the
return stroke current ranged 1-200 kA, front time of lightning stroke
between 1 μs to 3 μs. The simulations study the effect of varying
tower grounding resistance that affect the lightning current.
Simulation results are analyzed lightning over voltage that causes
back flashover at insulator strings. This study helps to know causes
of problems of back flashover the transmission line system, and also
be as a guideline solving the problem for 500 kV transmission line
systems, as well.
Abstract: This paper presents the experimental results on
artificial ageing test of 22 kV XLPE cable for distribution system
application in Thailand. XLPE insulating material of 22 kV cable
was sliced to 60-70 μm in thick and was subjected to ac high voltage
at 23
Ôùª
C, 60
Ôùª
C and 75
Ôùª
C. Testing voltage was constantly applied to
the specimen until breakdown. Breakdown voltage and time to
breakdown were used to evaluate life time of insulating material.
Furthermore, the physical model by J. P. Crine for predicts life time
of XLPE insulating material was adopted as life time model and was
calculated in order to compare the experimental results. Acceptable
life time results were obtained from Crine-s model comparing with
the experimental result. In addition, fourier transform infrared
spectroscopy (FTIR) for chemical analysis and scanning electron
microscope (SEM) for physical analysis were conducted on tested
specimens.