Assessing adequate spacing between directly buried automatic electrical and polyethylene gas distribution networks

This paper reports experimental work conducted in 3/spl times/150 mm 2 pT 240 VAC directly buried cables energized at 120 V under laboratory conditions with the goal of assessing an adequate spacing between automatic electric networks and gas lines. Evaluated cables were intentionally faulted using a metallic element and then they were located in the vicinity of a simulated gas line inside a wooden box. This test arrangement represents a typical Mexican underground automatic electric distribution network with the addition of a buried gas line. Applied fault currents were 5, 20 and 50 kA until the fault self-cleared or reached 3 seconds. Fault characteristics like voltage and current waveforms as well as cable temperatures were recorded while condition of both simulated gas line and cables after each fault were assessed. Experimental results obtained show random damage to adjacent gas line reaching 90 cm. This damage is related to fault duration and fault current magnitude that in combination, produce diverse behaviours in cable fault responses, including conductor evaporation, metallic particles detachment, insulation tire and fuse action. The effects of explosions were analysed for direct exposed gas line and for barrier protected gas lines. Results demonstrate that 30 cm spacing between gas and electric lines is not safe for the arrangements evaluated.