Vacuum breaker

Amhient Influences If cooling results in a vacuum, the design must provide for external pressure or a vacuum breaker installed also provision must be made For thermal expansion of contents trapped  [c.980]

SFg breaker 7.5 kV + 5.4 kV = 12.9 kV Vacuum breaker with copper-chromium contacts  [c.575]

Vacuum breaker with copper-bismuth contacts  [c.575]

See Splash Filling in 5-2.3.1. Dip pipes should be metallic, grounded, and permanently fixed where possible. Explosions have occurred where plastic dip pipes were used, both during filling and emptying operations. The vessels involved ranged in size from drums [8] to barge tanks [172]. The purpose of the dip pipe is either to load a vessel with minimal disruption of bottom sediment and mist production associated with splashing, or to empty a vessel. The dip pipe should extend close to the bottom of the vessel without touching it, and might be equipped with either a 45 degree cut or a tee to divert flow horizontally near the base of the vessel being filled. The design should prevent upward spraying during the initial stages of filling and this is typically achieved by using a slow start such that inlet velocity is held at less than 1 m/s until the dip pipe outlet is covered by at least 6 in. or two pipe diameters of liquid, whichever is greater. To prevent siphoning, a dip pipe may in some cases need to be equipped with an appropriate vacuum breaker such as breather holes.  [c.116]

A large distillation column in a refinery operated at high vapor loads. Just above atmospheric pressure. It was not designed for vacuum and so had to be protected if the heat input from the reboiler failed but condensation continued. An inexperienced hazop team might have accepted without comment the original design intention, which was to break the vacuum with fuel gas (or nitrogen if available). A more experienced team might have realized that the volume of gas required was enormous but that it could be reduced to a manageable figure by locating the vacuum breaker valve at the inlet to the condensers, thus blanketing them and reducing heat transfer [24].  [c.339]

P—Personnel Protection QO—Quick Opening SG—Sample Protection SO—Steam Out TSO—Tight Shut Off VB—Vacuum Breaker  [c.25]

Condensate from the low-pressure coil together with that from the flash vessel will then drain to a collecting tank, or direct to a condensate pump, for return to the boiler plant. If the pressure of the flash steam is left to find its own level it will often be sub-atmospheric. As the condensate must then drain by gravity through the steam traps these also must be sufficiently below the condensate drain points to provide an appropriate hydraulic head, and a vacuum breaker fitted above the coil. The alternatives are to allow the condensate to drain directly to a condensate pump, or to supply additional low-pressure steam through a pressure-reducing valve, to maintain a positive pressure in the coil and flash vessel.  [c.327]

Where long delivery lines are used, the water flowing along the pipe as the pump discharges attains a considerable momentum. At the end of the discharge period when the pump stops, the water tends to keep moving along the pipe and may pull air or steam into the delivery pipe through the pump outlet check valve. When this bubble of steam reaches a cooler zone and condenses, the water in the pipe is pulled back towards the pump. When the reverse flow reaches and closes the check valve, water-hammer often results. This problem is greatly reduced by adding a second check valve in the delivery line some 5 or 6 m from the pump. If the line lifts to a high level as soon as it leaves the pump then adding a generously sized vacuum breaker at the top of the riser is often an extra help. However, it may be necessary to provide means of venting from the pipe at appropriate points the air that enters through the vacuum breaker.  [c.332]

U.S. Pat. 2,357,252 (Aug. 29,1944), H. Berger, E. Nygaard, andH. Angel (to Socony-Vacuum Oil Co.).  [c.513]

IEEE, Results of an investigation on the over voltages due to a vacuum circuit breaker when switching an H. V. motor, IEEE 85 SM 370-2(1985).  [c.272]

With the availability of 3.3 and 6.6 kV vacuum contactors the control of HT motors up to 6.6 kV systems has now become easier and economical, compact and even more reliable. For 11 kV. systems, vacuum as well as SF (Sulphur hexafluoride) breakers can be used. The HT motor s switching and protection through a vacuum contactor provides a replica of an LT system. The earlier practice of using an HT OCB, MOCB, or an air blast circuit breaker for the interruption of an HT circuit is now a concept of the past.  [c.308]

The two comparatively new type of breakers, vacuum and SFg are exceptions and have gained favour in view of their reliability and durability. For details on these breakers, see Sections 19.5.5 and 19.5.6, which also deal with their switching behaviour and phenomenon of arc reignition. Figures 12.44 and 12.45 illustrate typical power and control circuit diagrams respectively, for a 6.6 kV breaker-operated motor starter.  [c.308]

The arc energy produced during an interruption is high compared to the mediums of SF j and vacuum. Figure 19.6 makes a comparison of the arc energy produced during interruption of a breaker in different mediums.  [c.633]

Figure 19.23 General arrangement of a 7.2-36 kV vacuum circuit breaker in a housing (Courtesy Siemens) Figure 19.23 General arrangement of a 7.2-36 kV vacuum circuit breaker in a housing (Courtesy Siemens)
Figure 19.25 A pole assembly of a vacuum circuit breaker Figure 19.25 A pole assembly of a vacuum circuit breaker
Hydroxyflavone [577-85-5] M 238.2, m 169-170 , 171-172 . Recrystd from MeOH, EtOH or hexane. Also purified by repeated sublimation under high vacuum, and dried by high vacuum pumping for at least one hour [Bruker and Kelly J Phys Chem 91 2856 1987].  [c.261]

Diethyl sodium phthalimidomalonate (Barger and Weichselbaum, Organic Syntheses, 1943, Coll. Vol. II, 3B4) (6.52 g) was dissolved in boiling methyl ethyl ketone (BO ml) and a solution of p-nitrobenzyl chloride (3.44 g 1.0 mol) in the same solvent (20 ml) was added. Sodium iodide (ca 0.5 g) dissolved in hot methyl ethyl ketone (10 ml) was introduced, and produced an immediate precipitation. The mixture was refluxed for 1.5 hours, cooled, filtered, evaporated under vacuum and the residual gum crystallized from ethanol. The di-ethyl-p-nitrobenzyl-phthalimidomalonate formed colorless prisms (B8%), MP 103° to 105°C, sharpening to 104° to 105°C on recrystallizing from ethanol.  [c.925]

Concerning condensing turbines, be sure to obtain an adequately sized vacuum breaker for the condenser. There are no words to describe the agony of watching a turbine or the driven compressor tear itself up.  [c.291]

Consideration shonld also be given to the possibility that the flame arrester may ping, which conld prodnce a vacnnm condition in a low-pressnre tank when the tank is primped out, and implode (collapse) the tank. This may reqnire the installation of a vacnnm breaker or a pressnre-vacnnm conservation valve. If the tank contents are flammable and admission of air may resnlt in an ignitable mixture, it may be necessary to install an inert gas blanketing system on the tank, actuated by a pressnre controller, which would admit a sufficient flow of inerting gas when a vacnnm condition is detected.  [c.139]

Agitator Dyers. Increa sing iaterest ia iadirect-heat dryiag has brought out a variety of relatively slow speed, batch, and continuous agitator dryers. These combine the advantages of low purge gas flow, characteristic of all iadirect-heat dryers, with a material handling versatility lacking ia fluid beds and an ease of gas-tight operation lacking ia rotary dryers. Material holdup may be varied from a few minutes to several hours. Figure 22 is an example of this dryer type, called a porcupiae dryer. It may have one or two parallel shafts and, as shown, can be provided with stationary, lump-breaker bars that intermesh with the moving paddles. Other types may provide scrapers for both jacket and agitator heating surfaces. Most can be operated under vacuum or well above atmospheric pressure and at temperatures up to 400°C usiag hot oil, steam, and water. The vessels are stationary and shaft seals are small to minimise leakage.  [c.254]

Results of an investigation on the overvoltages due to a vacuum circuit breaker w hen sw ilching an H.Y, motor. IEEE A ,5. SA7 370-2 (1985).  [c.585]

When a live circuit is interrupted, an arc is invariably formed between the parting contacts, the intensity atid magnitude of which would depend upon the quantum and the quality (p.f.) of the current being interrupted. The arc, due to its excessive heat, under high pressure or vacuum (the medium in the breaker is maintained thus), fortns a plasma in the medium which causes decomposition of the insulating and the quenchitig medium to a few gases atid vapours. The gases so formed then ionize into electrons and protons, which are charged particles conducting in nature, and make the arc conducting as well. How to disperse the heat of the arc plasma quickly for a successful interruption of the circuit is the theory of arc extinction. The types of gases produced and their behaviour, as a consequenee of ionization of the insulating and quenching mediums are as follows  [c.629]

The arc i,s caused during an interruption of the live contacts, and also just before closing the contacts, when the contact gap falls. short of the required dielectric strength to withstand the impressed voltage. When an tire is caused the gases present in the arcing chamber, under the influence of high temperature of the arc plasma and the high pressure or high vacuum maintained within the arcing chamber, become ionized. They liberate protons (positive ions, positively charged, heavier particles) and neutrons (uncharged particles) surrounded by electrons (negatively charged lighter particles (Figure 19.3)). The theory of arc extinction relates to the physics and behaviour of these elecfrically charged particles that are responsible for a restrike of the TRV even after a current zero. The effectiveness of the medium and the design of the arc chamber to diffuse these electrically charged particles to neutrons as quickly as possible determines the ability of one type of breaker over others. In fact, the theory of arc extinction is the theory of deionization (neutralization) of the electrically charged protons and electrons. The theory may be briefly explained as follows.  [c.631]

The electrical breaking capacity in vacuum has been long known. But it was not until 1970 that it was tisetl in the making and breaking of currents at high voltages. It has been a widely recognized and accepted breaker, leaving behind all other techniques ofarc breaking and extinction in its voltage range. In vacuum, a 10 mm gap at about l/IO mm vacuum of mercury iscapable of w ithstanding a peak voltage up to around 240 kV (Figure 19,1 >. These breakers require no maintenance and are very compact.  [c.643]

Vacuum is finally judged to be the best medium to quench the arc plasma and interrupt a circuit undci the most adverse conditions. Figure 19,24 gives cross-sectional views of one pole of a vacuum circuit breaker and a typiciil construction of the arcing contacts and Figure  [c.643]

With advances in technology in the field of circuit interruption, fast to extremely fast interrupting devices have been developed, aided by high-performing arc quenching and extinguishing mediutns, as discussed above. While such techniques have helped in the interruption of system currents, particularly on faults (at very low p.f.s), they have also posed some probletns in certaiti types of circuit breaking. For instance, an air blast circuit breaker and a vacuum circuit breaker are both extremely fast operating. When interrupting on a fault, their operation is as desired but at much lower currents than rated, such as at no-load, they may operate rather faster than desired and interrupt the circuit before a natural current zero. Premature interruption of a circuit stich as this is termed current chopping and may occur just before a natural current zero when the current is stnall. In a VCB it is of the order of. 5-5 A.  [c.646]

Telander, S.H., Wilhelm M.R. and Stump, K.B., Surge limiters for vacuum circuit breaker switchgear , CH 2279-8/86/0000-003751.00, / (1986)  [c.656]

On supply failure capacitors must drop out and should not switch on automatically on resumption of the supply to avoid an overvoltage as a result of the trapped charge. Even sudden voltage dips may cause the charged capacitors discharge into the terminal equipment and damage them. On LT, to achieve the required protection, the capacitors may be switched through contactors which have a novolt coil and drop out on failure of the supply. On HT an instantaneous undervoltage relay, with a low drop-off value (say, 30-60%) may be used with the interrupting device, which may be a breaker or a vacuum contactor. Reclosing may be through a lockout relay with a time delay, for at least the safe discharge time or less, if the control is by a p.f. correction relay, whose time setting is low and the capacitors are provided with suitable discharge devices.  [c.834]

See pages that mention the term Vacuum breaker : [c.162]    [c.20]    [c.675]    [c.325]    [c.634]    [c.644]    [c.460]    [c.568]    [c.575]    [c.9]    [c.357]    [c.430]   
Compressors selections and sizing (1997) -- [ c.291 ]