EN 60137-2017 pdf download.Insulated bushings for alternating voltages above 1 000 V.
The test connections and their ends shall not be a source of radio interference voltage of higher values than those Indicated below. The high-voltage connections shall extend in line with the bushing axis to a point at least 0,2 L above the top of the bushing, where L is the arcing distance of the bushing. The maximum diameter of this connection shall be half the diameter of the bushing head.
The measuring circuit shall comply with CISPR 18-2. The measuring circuit shall preferably be tuned to a frequency within 10 % of 0,5 MHz, but other frequencies in the range 0,5 MHz to 2 MHz may be used, the measuring frequency being recorded. The results shall be expressed in microvolts
If measuring impedances different from those specified in CISPR publications are used, they shall be not more than 600 U nor less than 30 U. in any case the phase angle shall not exceed 20. The equivalent radio interference voltage referred to 300 U can be calculated, assuming the measured voltage to be directly proportional to the resistance, except for bushings of large capacitance, for which a correction made on this basis may be Inaccurate. Therefore, a 300 U resistance is recommended for bushings with earthed flanges.
The filter F shall have a high impedance at the measuring frequency, so that the impedance between the high-voltage conductor and earth is not appreciably shunted as seen from the bushing under test. This filter also reduces circulating radio-frequency currents in the test circuit, generated by the high-voltage transformer or picked up from extraneous sources. A suitable value for its impedance has been found to be 10 000 U to 20 000 0 at the measuring frequency.
It shall be ensured by suitable means that the radio interference background level (radio interference level caused by external field and by the high-voltage transformer when magnetised at the full test voltage) is at least 6 dB and preferably 10 dB below the specified radio interference level of the bushing to be tested. Calibration methods for the measuring instrument and for the measuring circuits are given in CISPR 16-1 and CISPR 18-2 respectively.
As the radio interference level may be affected by fibres or dust settling on the Insulators, it is permitted to wipe the insulators with a clean cloth before taking a measurement. The atmospheric conditions during the test shall be recorded. It is not known what correction factors apply to radio interference testing but it is known that tests may be sensitive to high relative humidity and the results of the test may be open to doubt if the relative humidity exceeds 80 %.
8.8.2 Test method and requirements
Bushings, one or both ends of which are intended to be immersed in mineral oil or another liquid-insulating medium, shall be appropriately immersed in liquid at ambient temperature. except for transformer bushings intended for use in mineral oil, where the oil shall be maintained at a temperature of 60 K ± 2 K above the ambient air. If the transformer is filled with another liquid-insulation medium, the temperature shall be subject to agreement.
In some applications using mineral oil (e.g. generator transformer), the transformer top-oil temperature is often restricted to values below the normal IEC limits. Subject to agreement between manufacturer and purchaser. the standard oil temperature rise of 60 K may be reduced to reflect the real transformer top oil temperature.
Bushings with a conductor drawn into the central tube shall be assembled with an appropriate conductor, the cross-section of which shall conform to 1,. When the transformer liquid is in communication with the bushing central tube, the liquid level shall not exceed one-third of the height of the external part.
The end of bushings, which are intended for immersion In a gaseous Insulating medium other than air at atmospheric pressure, shall normally be appropriately Immersed In an enclosure insulated with gas at minimum pressure, according to 3.30, the gas being at ambient temperature at the beginning of the test.
Gas-insulated bushings shall be at ambient temperature at the beginning of the test.
For transformer bushings operating in air-Insulated ducting. the air side shall be enclosed in an appropriate chamber. During the test, the air in the chamber shall be heated to 40 K ± 2 K above ambient air, either by self-heating or indirectly.
An appropriate number of thermocouples or other measuring devices shall, as far as possible, be placed along the bushing conductor, central tube and other current-carrying parts, as well as possibly on the flange or other fixing device, so as to determine the temperature rise of the bushing components in relation to the values given in table 2 with reasonable accuracy.
The ambient air temperature shall be measured with lagged thermometers placed around the bushing at mid-height and at a distance of 1 m to 2 m from it.
NOTE A 5atlsfactory degree ol lagging is obtained by placing the thermometers en liquid-filled coriLainers with a volume of approzimately 0,5 I.
The temperature of the liquid or gas shall be measured by means of thermometers placed at a distance of 30 cm from the bushing and, in the case of liquid, 3 cm below the surface of the liquid.EN 60137-2017 pdf download.