IEEE C63.13-1991 pdf free.American National Standard Guide on the Application and Evaluation of  EMl Power-Line Filters for Commercial Use.
IEEE C63.13 An EMI power-line filter is usually installed directly at the power entry point of a piece of equipment either to suppressconducted emissions that would otherwise pass from the equipment into the power distribution system, or to suppressnoise that is entering the equipment from the power line.
Since electronic equipment today is most likely to be powered by switched-mode power supplies operating atswitching frequencies from about 20 kHz to hundreds of kHz, the potential for coupling disturbances at thesefrequencies to the power line is very great.
Although often used primarily for controlling conducted disturbances, a filter also suppresses local disturbing fieldsradiated from the power line, which may act as an antenna.Most filters have performance characteristics specified upto 30 MHz.However, a filter typically will continue to suppress noise at higher frequencies.Conducted disturbances appearing on a circuit consisting of two conductors may be resolved into two components.common (asymmetrical) and differential (symmetrical) modes. An understanding of these modes will assist inanalyzing the performance of an EMI powerline filter.
Figure 2 shows the two noise modes in terms of their currents. The commonmode currents, lcw/p are identical at anyone frequency in both amplitude and phase.The differential-mode current, IM, is a single current in the loopconsisting of the two power lines.
From this simple illustration, several conclusions about the character of conducted electromagnetic noise can bedrawn. The common-mode noise currents are the same in both lines with their retum path being the groundconnection.The differential-mode noise current does not flow in the ground connection. At any one noise frequency,the total noise current in one of the lines can be expected to be larger than that in the other line, depending on theamplitude and phase of the component noise currents at that frequency.As shown in Fig 3, the total noise current inone line is one-half of the phasor sum of the common and differential mode noise currents;whereas, in the other line.IEEE C63.13 pdf download.