Figs. 2,379 and 2,380.—Diagram showing connections of horn type lightning arresters on series circuits.
The necessity of service requires that series lightning systems be fully equipped against damage by lightning and similar trouble. The most common disturbances occurring on series circuits are the surges set up by the sudden opening of the loaded circuit. These disturbances are especially severe where circuits are accidentally grounded, due to contact of the wires where they pass through other circuits.
Ques. How are the spark gaps adjusted?
Ans. They are set to give a low spark pressure relative to the voltage of the line.
Fig. 2,381.—General Electric horn type arrester, mounted for 15 light series arc circuit. The horn type arrester consists of a horn gap with series resistance between each line and ground. The resistances and horn gaps are mounted on porcelain bases and the latter on insulating wooden supports. The supports have asbestos barriers (except for lowest voltages), and backs to eliminate liability of damage from the arc which forms in the horn gap at the time of the discharge. The spark gaps are adjusted to give a low spark pressure relative to the voltage of the circuit. The number and ohmic value of the resistance rods used in the various arresters depend upon the voltage and current of the circuit.
Ques. Why are horn arresters well suited to protect series lighting circuits against surges?