Enclosures continuous

For the theory of neutralization of the magnetic effect on the conductor in a non-magnetic shielding, refer to the continuous enclosures for isolated phase bus systems discussed in Section 31.2.2. As a result of non-magnetic shielding there will be no saturation of the iron core and the V-I characteristic of the reactor will remain almost linear. 

For continuous enclosure IPBs, the following ends of the enclosures are shorted to ensure continuous flow of induced current.s ... 

Figure 31.2(b) Typical layout of an IPB system in a thermal power slation, illustrating enclosure end shortings (or continuous enclosures... 

The electrodynamic and electromagnetic forces between the conductors and the structures are also reduced to only 10-15% or even less. These two advantages are not available to this extent in a non-continuous enclosure. The induced current causing the magnetic field in the space is now reduced to only,... 

Figure 31.7 Nullifying of magnetic field in space in continuous enclosures...

Since ANSI-C-37.23 is available in the FPS system, we have adopted this for ease of corroboration. Also, since continuous enclosures are more often used for their obvious advantages, we have also considered them in... 

Skeats, W.F. and Sverdlow, N., Minimising the magnetic filed surrounding isolated phase bus by electrically continuous enclosures , AIEE Trans. No. 62 (1962). 

Most continuous pressure filters available (ca 1993) have their roots in vacuum filtration technology. A rotary dmm or rotary disk vacuum filter can be adapted to pressure by enclosing it in a pressure cover however, the disadvantages of this measure are evident. The enclosure is a pressure vessel which is heavy and expensive, the progress of filtration cannot be watched, and the removal of the cake from the vessel is difficult. Other complications of this method are caused by the necessity of arranging for two or more differential pressures between the inside and outside of the filter, which requires a troublesome system of pressure regulating valves. 

If, with a vacuum equivalent to a 200 mm column of water, it is not possible to draw air 80 times the volume of the enclosure under test, the test must be continued until the value is attained. In no case must the lest be carried out for more than 8 hours. 

The electrodynamic forces between the enclosure and the conductors will be small because the enclosure, which is non-continuous, will carry much less current than the main conductors. They therefore need not be considered separately, as the metallic structure will have sufficient strength to bear them. 

Types of enclosures These may be of two types, i.e. Non-continuous, and Continuous. 

Pressurizing the bus enclosure A typical arrangement is shown in Figure 3I.I0. In this ease the enclosure is maintained at slightly positive pressure by continuously supplying it with dry and clean air or SF,s 1o prevent vapour condensation. Compressed iir is supplied at a pressure of 5-7 kg/cnr and passed through the air dryer and the flow control valve. The leakage, if any, is recom-... 

The continuous current rating of a bus system can be defined by the current at which a steady-state thermal condition can be reached. It is a balance between the enclosure and the conductor s heat gain and heat loss. If this temperature is more than the permissible steady-state thermal limit it must be reduced to the desired level by increasing the size of the conductor or the enclosure or both, or by adopting forced cooling. Otherwise the rating of the bus system will have to be reduced accordingly. 

Except for conduit or cable entries into explosion-proof enclosures containing arcing or high-temperature devices (as described in Item I above), cables that will leak gas through the core at a rate of less than 0.007 ft /hr at 6 in. of water pressure need not be sealed if they are provided with a continuous gas/vapor-tight sheath. Cables with such a sheath that will transmit gas at or above this rate must be sealed if connected to process equipment that may cause a pressure of 6 in. of water at the cable end. 

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