Publication: Electrical Review
New York, NY, United States
A New Italian Insulator.
A new Italian insulator designed by Signor Guido Semenza is being shown at the Milan (Italy) exhibition. One of the troubles encountered in high-tension plants in Italy has been the breaking down of the insulators during heavy rains. To guard against this trouble it has been unusual to make the upper petticoat with very large diameter to enable it to protect the lower part of the insulator. The conductor is carried on this head. This necessitated making the whole of this petticoat of the same insulating material which forms the chief part of the insulator, and it had to be made with just as much care as the lower petticoats. This type of insulator is shown in Fig. 1. The recent tendency to increase the working pressures has made it necessary to increase correspondingly the diameter of the upper petticoats, which resulted in a great increase in cost. It was to get over this difficulty that Signor Semenza designed the insulator shown in Fig. 2, which is taken from the Electrical Review (London), August 31.
In this insulator the wire is fastened below the upper petticoat. It is therefore unnecessary for this petticoat to be strong enough to resist perforation; it need only be watertight and sufficiently hard to resist mechanical shocks and rough usage in transportation. It is therefore made of a form of terra-cotta, which is neither so costly nor so breakable as porcelain or glass. Since the point of attachment of the wire in the Semenza type is somewhat lower than that in the old type, the strain moment of the wire is greatly reduced, which makes allowable a reduction in the thickness of the insulator and in the diameter and cost of the iron bolt; and since this upper petticoat or umbrella is not connected in any way with the pin, complications due to increased capacity are avoided. It is found possible to use a much lighter insulator of the Semenza type in order to secure the same breakdown voltage.
It is claimed that there is a savings of from thirty to forty per cent for an equally safe installation by using the Semenza insulator, with pressures from 35,000 to 50,000 volts. For higher voltages up to 80,000 or 90,000 it is thought that a saving of fifty per cent will be effected. One of the reasons for the excellent performance of this insulator is said to be the fact that the wire is at no time in touch with the stream of water running over the surface of the effective petticoats of the insulator.