IEEE 436:1991 pdf download.IEEE Guide for Making Corona (Partial Discharge) M easurements on Electronics Transformers.
This guide covers the detection of corona (partial discharge) and the measurement of its magnitude in electronics transformers. Test conditions, test apparatus, calibration, and test requirements are included.
Corona (partial discharge) is an ionization phenomenon that can cause detenoration in certain insulation systems. Its presence in electronic equipment can be harmful through its manifestation as circuit noise, spurious voltage or current pulses, or other undesirable effects that lead to circuit malfunctions. Transformers and inductors used in electronic circuits at high voltages can be locations where this harmful phenomenon onginates. Even in instances where discharges are not of concern in circuit performance, they may be of concern because of their adverse effect on component life. It is, therefore, essential that the insulation system be free of corona discharges at operating voltage stresses. The magnitude or intensity of these discharges is usually of such a low level that very sensitive electronic measuring apparatus and techniques are required to detect them.
This guide presents a uniform procedure for making corona (partial discharge) measurements by electrical means on electronics transformers. Methods of applying voltage stress, the use of a sine-wav voltage to sirnulate dc and ac combintions, the types and limitations of voltage stresses encountered, and the acceptable limits of discharge pulse energy are included. Recommended test conditions and the need for negotiation of special tests are discussed.
5.1 Application of This Guide. The test con di- Lions applicable to electronics transformers include all the configuration and circuit arrangements used in power transformers and, in addition, include a large number of inductive devices with special circuit characteristics and with electrical stress on insulation covering the entire range of frequencies from dc through microwave and all combinations of these frequencies. At the present time, this guide will be limited to detection and measurement.s with sine-wave applied voltage ranging in frequency from zero to approximately 2000 Hz. The detection and measurement of corona discharges with applied voltages at. higher frequencies or with nonsinusoidal wave shapes requires special techniques, since the discharge pulse itself also has a wide frequency spectrum, a portion of which may fall within the operating frequency range.
52 Conditions for Acceptable Corona Test.. The duplication of the exact voltage stresses that occur in service, including frequencies and transients, is acknowledged to result in the most accurate corona discharge measurements; however, insistence on exact condiLions may be impractical. The fundamental conditions for acceptable corona tests are based on the assumptions and limitations that follow.
5.2.1 Frequencies at Which Corona Measurements May Be Performed. Corona discharges are a function of the peak-to-peak voltage, provided the voltage contains no intermediate peaks and is applied long enough for ionization to take place. Corona measurements may be performed at any frequency under 2000 Hz; they need not be made at the operating frequency. However, discharges are affected by the test frequency; as the frequency is increased, variations occur in the response times of ions within the insulation to the rapidly varying externally applied electric field. The resulting nonuniform internal electrical stress leads to a decrease in the corona inception voltage. Care must therefore be taken in interpreting the results of tests performed at other than the operating frequency.IEEE 436 pdf download.