IEEE C57.13-2008 pdf download IEEE Standard Requirements for Instrument Transformers
4. General requirements
4.1 Service conditions
4.1.1 Usual temperature and altitude service conditions
nstrument transtormers conforming to this standard shall be sutable for operation at their thermal ratingsprovided that the altitude does not exceed 1000 m.
4.1.1.1 30·C average ambient temperature
If the transformers are air cooled, the ambient temperature of the cooling air does not exceed 40 °C and theaverage ambient temperature of the cooling air for any 24-h period does not exceed 30 °Co
The minimum ambient air temperature is -30 C
41.1.2 55°C average ambient temperature
Instrument transforers may also be given ratings for operation in 55 °C average ambient temperature.
with maximum ambient air temperature not exceeding 65°C.
4.1.2 Unusual temperature and altitude service conditions
Instrument transformers may be applied at higher altitudes or higher ambient temperatures than specified in4.1.1, but the performance may be affected and special consideration should be given to these applications(see 4.4).
4.1.3 Other conditions that may affect design and application
Where unusual conditions other than those discussed in 4.1.1 or 4.1.2 exist, they should be brought to theattention of those responsible for the design and application of instrument transformers. Examples of theseconditions are as follows:
aDamaging fumes or vapors, excessive or abrasive dust, explosive mixtures of dust or gases.
steam, salt spray, excessive moisture or dripping water, etc.
bnormal vibrations,shocks, or tilting6)
Ambient temperatures above 55 C or below -30C
dUnusual transportation or storage conditions
e) Unusual space limitations or restricted ventilation
f) Unusual duty, frequency of operation, difficulty of maintenance, poor wave form, unbalanced voltage, special insulation requirements, etc.
g) Applications in switchgear assemblies, including metal enclosed bus
h) Applications with high-voltage power circuit breakers
i) Applications with power transformers
j) Applications with outdoor bushings
4.2 Effect of air density on flashover voltage
The effect of decreased air density is to decrease the flashover voltage for a given flashover distance. See IEEE Std 4 7 for use of a correction factor with sphere gaps.
The dielectric strength of air decreases as altitude increases. Dielectric strength that depends on air should be multiplied by the proper altitude correction factor to obtain the dielectric strength at the required altitude (see Table 18 ).
IEEE C57.13-2008 pdf download
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