CSA C88.1-96 pdf download – Power transformer and reactor bushings.
4. Ratings 4.1 Bushings shall be rated by performance characteristics, as follows: (a) Rated voltage — the rated voltage of the bushing is the maximum design voltage from the line terminal to ground (U). Refer to Table 1 . (b) Rated current — the rated current (IN) is the rms value of the current that the bushing can carry in continuous operation at the rated frequency without the temperature rise of the hottest spot of the bushing exceeding the limits specified in Clause 9.1 . The rated current of the bushing need not necessarily be identical with the rated current of the complete apparatus. The permissible operating current will be in accordance with Figure 1 . The permissible continuous operating current under other loading conditions shall be as described in IEEE C57.1 .9.1 00. This shall apply to both bottom-connected and draw-lead bushings. (c) Rated frequency — the rated frequency is the frequency at which the bushing is designed to operate. (d) Rated dielectric strength — the rated dielectric strength of a bushing is expressed in terms of the values of voltage withstand tests specified in Clauses 8 and 1 0.
5. Operating Conditions 5.1 Altitude This Standard covers bushings suitable for operation at altitudes not exceeding 1 000 m. Note: The air density at high altitudes is lower than at sea level. The dielectric strength of the air is thus reduced, and air clearances that are adequate at altitudes not exceeding 1 000 m may be insufficient at higher altitudes. The puncture strength and the flashover voltage in the immersion medium of a bushing are not affected by altitude. Although the insulation level refers to sea level, bushings specified in accordance with this Standard are designed for operation at any altitude not exceeding 1 000 m. In order to ensure that the external withstand voltages of the bushings are not reduced at altitudes exceeding 1 000 m, the air clearance normally required must be increased by a suitable amount. It is not necessary to adjust the radial thickness of insulation or the clearances of the immersed end. The air clearance of a bushing designed to operate at altitudes exceeding 1 000 m shall be such that, if the bushing could be tested at an altitude of less than 1 000 m, the air clearance would withstand the application of higher test voltages. Owing to the limitations of puncture strength and flashover voltage in the immersion medium, it may not always be possible to check the adequacy of the increased air clearance by actual tests at any altitude lower than that of operation. In such a case, the supplier may demonstrate by any other means that the air clearance is adequate. The amount by which the insulation level, on which the air clearance is based, should be increased is (for general guidance) 1 .0% for each 1 00 m in excess of 1 000 m above sea level. Example: Altitude of installation: 2800 m Increase in insulation level required =(28—1 0)xl.0 =1 8% 5.2 Temperature of the Cooling Media Bushings conforming to this Standard shall be suitable for operation under the temperature limits specified in Clauses 5.2.1 to 5.2.4.
5.2.1 Ambient Air (a) The maximum temperature shall not exceed 40°C. (b) The average temperatures in any one-day period shall not exceed 30°C. (c) The minimum temperature shall not be less than —50°C. 5.2.2 Immersion Media The average temperature in any one-day period shall not exceed 95°C, and maximum temperature in one day shall not exceed 1 05°C. In addition, bushings shall be suitable for any specified requirements for loading of the equipment beyond nameplate rating. 5.2.3 External Temperature The temperature of the external conductor when operated alone shall not exceed a 30°C rise above the ambient air temperature. 5.2.4 Special Ambient Condition In the special case of bushings used inside of bus duct, users shall advise the bushing manufacturer of the higher ambient temperature conditions expected. 5.3 Angle of Mounting 5.3.1 Liquid-filled bushings shall be designed for mounting at any angle of inclination not exceeding 30° from vertical. Where liquid level gauges are supplied, the gauge mechanism shall be adjustable (self-correcting) to compensate for the mounting angle.CSA C88.1-96 pdf download.
