GB2093279A - Sealing Means for a Cable - Google Patents

Abstract

A sealing arrangement is disclosed for a cable lead-through between a pressurized chamber and atmosphere. In this lead-through, a conductor connection pin 2, embedded in hard rubber insulation 4 is provided for electrical connection with the cable 5. The pin 2 with insulation 4 is sealingly disposed in a passage through the wall 1 of said chamber and a central portion of the conductor connection pin 2 is formed as a valve member engageable, upon melting of the insulator 4, with a valve seat provided by a ring 6 located in said passage. Thus leakage of fluid from the pressurized chamber is avoided in the event of the insulation in which the pin is embedded being destroyed. The valve seat may have different cross-sections (Figs. 4 and 5 not shown) and the valve member may be a ring (Fig. 3 not shown). A ceramic insulator 3 is secured by nut 10. <IMAGE>

Description

SPECIFICATION Sealing Means for a Cable This invention relates to a sealing arrangement for a cable lead-through between a pressurized chamber and atmosphere, more particularly, but not exclusively, for electric motors of glandless circulators.

Sealing means for cable lead-throughs for electric motors are known, e.g. in the form of glands (German Patent Documents 715,496; 2,730,675 and 7,705,153). The insulation or sealing between two chambers is embodied in these constructions to some extent by insulant and to some extent by O-ring seals.

In the case of glandless circulators, e.g. such as used in nuclear power stations, it is essential to seal off the pressurized chamber from atmosphere (c.f. Brennstoff-Warme-Kraft (1979) Nr. 4, April, Kapitel 4, p.1 76.) The pressure differences involved are approximately 110 bar. The quality of insulation depends upon the voltages and currents required. This in turn is a main factor determining the dimensioning of the lead-through and of the conductors. As a rule, the conductors are soldered to the corresponding cable, the insulation taking the form of shrink hoses and insulating strips or tapes. Insulation between the lead-through wall and the conductor usually takes the form of solid insulating bushes, e.g. of hard rubber or ceramic. Also, elastomers such as 0rings are used as sealing means.These materials are designed as regards temperature for normal operating conditions.

Unfortunately, the known constructions fail to ensure that anything like adequate sealing will survive after the damage to the insulators.

It is an object of the invention so to devise a cable lead-through system that the insulation walls can be of the requisite thickness and in the event of over-heating -- i.e., of destruction of the insulators -- adequate sealing tightness still remains between the pressurized chamber and atmosphere even though the insulation has been destroyed, so that, when applied, for example to a nuclear reactor, primary medium cannot issue from the reactor pressure vessel and the cable does not rupture.

The problem is solved by providing a sealing arrangement for cable lead-throughs of the kind specified with a conductor connection pin which is embedded in the insulant between the pressurized chamber and atmosphere is adapted to be pressed on to a kind of valve seat either in the event of destruction of the insulation or permanently and is in the form of a valve member and which, by virtue of its geometric shape, closes the aperture opened by the melting away of the insulation.

A check valve effect is therefore provided and issuance of the pressurized liquid is substantially prevented, as is excess pressure in the cable box.

Embodiments of the invention are described below with reference to the accompanying drawings, in which: Figure 1 is a schematic sectional view showing part of a reactor vessel, a glandless circular and electric motor unit fitted therein and, (enclosed in a circle) a cable lead-through between the interior of the motor casing, subjected to the pressure of the fluid in the reactor vessel, and the atmosphere, Figure 2 is a sectional view, to a larger scale, of a cable lead-through arrangement embodying the invention, and which may be utilised in the installation represented in Figure 1, Figure 3 is a sectional view showing part of a variant of the arrangement of Figure 2, and Figures 4 and 5 illustrate different sectional shapes of valve seat members which may be used in the arrangement of Figure 2 or Figure 3.

Referring to Figure 2, there is indicated at 1 a pressure-receiving wall 1, e.g. the wall of the motor casing of Figure 1, between a pressurized chamber (above wall 1) and atmosphere (below wall 1). A cable 5, e.g. from a motor winding within the pressurised chamber is connected with a source of electricity outside said chamber by means of a conductor connection pin 2 which extends through a bore through the wall 1. The pin 2, at least over the portion thereof which passes through said bore is embedded in a hard rubber insulator 4 which fits closely within said bore, is sealed with respect thereto by an 'O'-ring 11 and supports the pin 2 coaxially within said bore. The end of pin 2 nearer the pressurised chamber receives the conductor of cable 5 in a socket provided in the end of pin 2, and in which socket said conductor is soldered.This end of the pin is covered by the insulation 2, through which the end part of cable 5 extends and the junction of cable 5 with the insulation 4 is covered by two layers of insulating tapes 7, 8 and a covering of shrink hose 9.

At the end of said bore remotefrom,the pressurised chamber, the bore is of reduced diameter to afford an annular shoulder, and an annular stop ring 6, fitting closely within the bore, is held between this shoulder and an opposing annular shoulder afforded by the insulation 4 around a reduced-diameter portion of said insulation 4 which, together with the lower part of pin 2 extends through the ring into the space below wall 1.

On the underside of wall 1, the pin 2 projects beyond the insulation 4, and an annular, cap-like ceramic insulator 3, fitted over the pin 2 and the projecting portion of the insulation bears against the undersurface of the wall 1 around said bore and is held in place by a nut 10 screwed onto a screw-threaded part of pin 2. The nut 10 is tightened to hold the pin 2 firmly in place.

Whilst the pin 2 is generally cylindrical, a portion thereof within the insulation 4 above the ring 6 is formed as an enlarged head, which, as explained below, can act as a valve member, and which, in the embodiment of Figure 2 is bevelled to provide a downwardly facing, downwardly tapering frusto-conical surface, which at its upper end is of greater diameter than the aperture through ring 6 and at its lower end is lesser diameter.

In the event of the insulator 4 melting, the pin 2 will be thrust axially downwardly by the pressure of the fluid in the pressurised chamber, to engage the conical surface of the valve member sealingly in the aperture through ring 6 and thus prevent the escape of the pressurised fluid.

The distance between the cone and the metal support is such that the resilience of the connecting cable prevents tearing away and the projection surface of the cable cross-section is so determined by the dimensions of the insulant that there is no risk of the insulant being overstressed in the cone region.

Pin 2 has a bevel such that maximum diameter can be combined with minimum spacing for the insulation in relation to the wall 1 and ring 6. As shown in Figure 3, the part of pin 2 which forms the valve member can have a planar, axially facing lower surface instead of the bevel. The ring 6 provided as an abutment or valve seat for the valve member, as shown in Figures 4 and 5, can have, at choice, an appropriate bevel or radius at the edge of its central aperture. The corresponding bearing edge may vary between being sharp-edged and angled in dependence upon the pairing of materials and the internal pressure involved. In the event of the insulator 4 failing, the internal pressure presses pin 2 against the ring or corner and thus ensures automatic sealing.The loosely fitted ring 6 can be replaced in the event of destruction after dismantling the assembly. If desired, the ring 6 can be omitted, and the lower portion of the bdre through wall 1 dimensioned appropriately to afford an annular valve seat for the valve member.

The main advantages of the embodiments of the invention described are the provision of a self sealing lead-through system in normal operation and emergencies -- i.e., no liquid issues to atmosphere -- a replaceable seat by a separate ring, the use of resilient and efficient insulators which, should they overheat in emergencies, do not impair sealing tightness, and the possibility of replacing conductor connections and support rings after damage.

Thus, after such damage, the cable 5 may be disconnected from the pin 2 by unsoldering and moving the conductor end slightly away from the pin 2 to allow the latter to be removed after undoing the nut 10. The ring 6 may then be replaced, a new pin 2 with undamaged insulation reinserted, the cable 5 soldered to the new pin 2, and the insulator 3 and nut 10 re-fitted. The movement required of the end of the cable 5 in this procedure is sufficiently small to be accommodated by the resilience of the cable, even when this comprises a single, solid conductor, to avoid any risk of tearing the cable away from the motor winding.

Claims (7)

Claims

1. A sealing arrangement for a cable leadthrough between a pressurized chamber and atmosphere, and wherein a conductor connection pin, embedded in electrically insulating material is provided for electrical connection with the cable and is sealingly disposed in a passage through the wall of said chamber, said conductor connection pin being formed as a valve member either permanently engaged with a valve seat provided in said passage or adapted to be pressed into engagement with said valve seat by the pressure in said chamber in the event of the insulation in which the pin is embedded being destroyed.

2. A sealing arrangement according to claim 1 wherein said valve seat is provided by an annular insert disposed in said bore.

3. An installation incorporating a sealing arrangement according to claim 1 or claim 2.

4. An installation comprising a glandless circulator with an electric motor the casing of which defines a chamber pressurised with respect to atmosphere, the electric motor being connected with a source of electricity via a leadthrough traversing the wall of said casing and having a sealing arrangement according to claim 1 or claim 2.

5. A sealing arrangement according to claim 1 and substantially as hereinbefore described with reference to, and as shown in Figures 1 and 2 of the accompanying drawings.

6. A sealing arrangement according to claim 1 and substantially as hereinbefore described with reference to, and as shown in Figures 3 and 4 or 3 and 5 of the accompanying drawings.

7. Any novel feature or combination of features described herein.