Temperatures switchgear assemblies

The temperature rise limits of the various parts of a switchgear assembly during continuous operation at the rated current must conform to the values in Tables 14.5 and 14.6. 

The rating of an indoor or outdoor switchgear assembly is referred to at an ambient temperature of 40°C. For a higher ambient temperature the rating of the assembly will be reduced in the same proportion as for the busbar systems and as shown in Table 28.3. 

The ambient temperature should be measured during the last quarter of the test by at least three thermometers or thermocouples placed equally around the switchgear assembly, at almost the centre level and at about I metre from the body of the enclosure. The ambient temperature to be considered must be the average of these readings and should be within 10-40°C. To ensure that the ambient temperature is unaffected by ntagnetic field, alcohol thermometers must be used and not mercury thermometers. 

Testing of metal-enclosed switchgear assemblies 14/427 Table 14.5 Temperature rise limits for buses, bus connections and other parts of a switchgear assembly... 

Figure 14.2 Temperature rise test on a switchgear assembly...

T Other parts of the switchgear assembly and the aiixiliaiy components, for which limits have been specified, will not exceed the hot spot temperature rise, as recommended in Table 14.5. 

Figs 6.72 and 6.73). Sparking components (e.g. fuses, contactors, circuit breakers) inside or parts not complying with the temperature class of the assembly are individually protected by an independent type of protection (for the most part in a flameproof housing). More recently, attempts have been made to introduce pressurized switchgear assemblies onto the market (Fig. 6.19). In the USA, the classic solution has been a flameproof enclosure with the conduit technique, see Fig. 6.83. 

If such fasteners are stove-enamelled (which is normally not done), the trapped hydrogen is removed automatically while being stoved. Since the fasteners are used only for the assembly of switchgear or busbar systems, they are used at room temperature only. Therefore, if they are electroplated, they must be tampered, which is time consuming and adds to the cost of production. Moreover this has no technical advantage. The HT hardware must therefore be used as they are. When it is absolutely necessary to electroplate them, tampering will be essential. 

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