Corona (partial discharge) is an ionization phenomenon that can cause deterioration 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 originates. Even in instances where discharges are not of concern in circuit performance, they 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 sine-wave voltage to simulate dc and ac combinations, 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.