Source: International Wroclaw symposium on electromagnetic compatibility "EMC 2000", Wroclaw, Poland, 2000.
The operation of the electric power equipment is always accompanied by its own intensive electromagnetic radiation with wide frequency band. For instance, it was experimentally found, that the electromagnetic field, which is emitted by electric equipment outdoor substation by voltage >220 kV, is observed up to frequencies of hundreds and even thousands megahertz. The spectrums and the radiation levels of different parts of equipment essentially differ from each other. Sources of radiation are partial and corona discharged, breakthrough at switching, thunderstorm overvoltage.
Thus, the overwhelming number of high-voltage and electric power equipment is a source of radio interference. Despite of small power compared with radio station these man-made interference substantially determine an electromagnetic environment in a radio-frequency range. The dependence of the investigated well enough. Devices, which emit the signals of continuons and discontinuons operation, create the interferences with a frequency spectrum usually up to several megahertz. The single signal with a steep front has wider spectrum. The grouped together impulses create the interferences in the widest frequency band.
The detection and elimination of electromagnetic noises from different industrial equipment is one of the main problems in support in a normal conditions of acntivity of radio electronics equipment. The majority investigations in the field of electromagnetic compability is devoted to this problem.
On the other hand electromagnetic symbols, emitted by high-voltage and electric power equipment, can show a serviceability or faults of this equipment. The circumstance allows to generate a new direction in the field of an electromagnetic compability, namely diagnostics of an electric power equipment on the basis of measurement and analysis of high-frequency electromagnetic noises. The main advantage of suggested method is the minimum meddling in the technological process. The data of regular or periodical measurements can be the base for early warning about the tendencies of the state of the technical equipment.
The analysis of availability index of product of the object presupposes the creation of a diagnostic model. For its creation it is necessary to study the following problems: 1) physical nature of interfering sources; 2) influence of environmental conditions of intensity and levels of signals; 3) the paths of propagation of interferences from a source to a receiving antenna. It is necessary to distinguish the elements of the equipment and elements of the diagnostic model. So, the transformers and switches are the elements of the equipments of electric substation. But their parts, whose faults are coupled with appearance electromagnetic noises, select as elements of diagnostic model.
The study of the processes of creation of signals in the elements of diagnostic model by classification of these parameters.
The main source of electromagnetic radiation at substation is the capital equipment. Let us assume that the registered signal is a linear function of its source. The total equivalent circuit shown in figure 1 corresponds to the model where e1(t), ei(t) … en(t) are electromotive forces of n equivalent sources of electromagnetic radiation, u1(t), ui(t) … um(t) are voltages of m electromagnetic radiation measures in different parts of substation.
The complex resistances correspond to the real electrophysical characteristics of air and to the presence of large number of units of connections. The analysis of the sources of radiation can be presented as a generalized equivalent circuit.
The connection between sources of electromagnetic radiation and measures voltages must be written down in the matrix form
Where 
and 
are spectrum vectors of voltages and sources respectively, 
is matrix pf complex factor of a transfer.
The spectrum voltages provide possibility to determine the spectrum of sources of a signal. The dynamics of change of voltages are connected with serviceability state of elements of the electrical equipment, spectrum voltages were measured:
a - near the autotransformer of 500 kV
b – near the current transformer of 500 kV
c – outside of power equipment.
One of the main problems for the creation of a diagnostic model is determing of the elements of matrix. Theoretically, this problem can be solved by method and diagnostics of multipolar circuit. The number of sources of signals is usually more than number of measures voltages, that is n > m. Then the test methods of diagnostics are expedient for the decision of the task. According to these methods it is possible to make changes in the circuit of the power equipment at the substation. Including models of complete switching-off. Then in this case it is possible to find test matrix for p > m/n experiments, based on the various circuits of electric equipment. Its elements are zero if the equipment is switched-off. The new test equation
Can also be solved regarding a vector of sources of radiation. The inexactitudes of measurements of high-frequency signals, variation of meteoconditions and other factors can interfere with the reception of reliable results. The regular supervision, accumulation of databank and use of statistical methods of diagnostics of electric power equipment.