Improving the reliability of energy facilities

The article analyzed and identified the main sources of interference, disrupting the work and reliability indicators of the system, which can lead to malfunction of system of microprocessor relay protection and automation for electric stations and substations, as well as elements and actuators of open distribution devices. According to official data, modern microprocessor-based relay automation systems operate with a reliability coefficient that is not lower than 0.998. Further increase in reliability requires the development of technical measures, namely, requires the use of power and signal cables that must meet the requirements for specific parameters of inductance, capacitance and active resistance, and also requires the use of special placement of cross sections of conductors inside the cable. Secondly, it is shown that to increase the reliability of information transmission it is necessary to switch to serial communication channels, but the amount of information per channel should be strictly limited. The estimation of economic indicators of the system and its dependence on the reliability of the system is given. Thus, with an increase in reliability by 1.5-2 times, it is necessary to increase the cost of design and commissioning of such a system by about 2 times. It is recommended to use in addition to the regulated maintenance procedures a mandatory assessment of the level of interference in the system in order to maintain a stable and reliable operation of the relay automation system. Experimental and calculated data confirmed that the most difficult situation to ensure the reliability of the system is associated with thunderstorms and lightning. This circumstance dictates the necessity of evaluation and measuring the parameters of a common system of earthing. The methods of evaluation and diagnosis of faulty components of the system are proposed.


Introduction
Modern power stations generating power are controlled by microprocessor-based relay automation control devices. Microprocessor devices operate under the influence of powerful fields of electric and magnetic nature, due to the high level of voltage on open switchgears (up to 1000 kV and above), as well as the presence of atmospheric phenomena (lightning discharges) [1]. All these circumstances indicate the need to develop and implement measures to improve the electromagnetic environment and thereby increase the reliability of the relay automation system [2].

Formulation of the research problem
Statement of the research problem. The scientific and technical problem of development of regulated AC drives requires solving the following tasks: To achieve the goalto increase the reliability of the system in the article the following scientific and technical problems were solved:  3  APvVGng (unshielded) -trunk line 0,4 kV from distribution unit for internal needs-0,4 kV from DC sheiled of the control building to the boxes of food and heating of circuit breakers and disconnectors;  PvVGng (unshielded) from the feed bins of the drives of the disconnectors to remote control Cabinet drives of disconnectors;  PvVbSHng (armored) -from source boxes and drive switch's heating to the central switches control cabinet, from offset drives control cabinets to the drives of the disconnectors and drive disconnector's heating, from source boxes of disconnectors drives to the heating of cabinets TN.
Under this title, the following low-voltage complete devices are installed in the distributive shield (DS) OSG-500 kV building of the control building:  automated switches' control cabinets of all 500 kV overhead lines (OL) and 500 kV shunt reactors (SHR);  basic protection cabinets of all 500 kV OL;  backup protection cabinets of all 500 kV OL;  rack locator cabinets of all 500 kV OL;  emergency events recorders cabinets of 500 kV;  cabinets ΜPA all 500 kV, SS and SHR 500 kV;  PRD, PRM cabinets of all VL 500 kV;  counters cabinets OSG-500 kV;  500 kV SHR protection cabinets;  operating current distribution cabinets.
Grounding device (GD) OSG-500 kV is made according to the requirements for the resistance of GD of longitudinal and transverse horizontal grounding of galvanized steel section 50x6 mm, laid at a depth of 0.7-0.9 m, connected to the vertical rod grounding.

Calculation of pulse resistance of the equipment
To determine the impulse resistance of the equipment on the switchgear, calculations are carried out in the program "OSG-Project". The initial data for the calculations is:  grounding scheme;  parameters of the grounding and grounding conductors;  the resistivity of the soil;  the amplitude and frequency of the RF current determined by the results of the calculation in the program "EMI analyzer"'.
The obtained values of RF current, pulse resistance and reference values of the transmission coefficient are used to calculate the interference at the inputs of microprocessor (MP) devices at the short circuit on the OSG.
When lightning strikes, the following effects of its current are possible:  reverse overlap with MD on the control cables;  field interferences on the control cables and the impact of pulsed magnetic fields on the MP device.
The lightning current flowing through the MD creates a high potential on the ground and can cause a reverse overlap of the control cable insulation. The OSG-Project programme is used to calculate this   Calculation results: 1) At single-phase short circuits at outdoor switchgear of 500 kV voltage levels with industrial frequency acting on the insulation of the control cables will not exceed 516 V that is less than the permissible value of 2000 V. Currents flowing through the screens and armor of control cables at short circuit on the OSG-500 kV, will not exceed the values for KVVGEng-401 A, VBbShVng -582 A and coaxial cable -283 A, which is less than the permissible values 460 A for cable type KVVGEng, 1800 A for cable type VBbShVng, 670 A for coaxial cable. Examples of calculation schemes with the results of calculations are shown in [7]; 2) the grounding conductor and the horizontal grounding conductor made of a steel galvanized strip of 50x6 mm meet the requirements of [8] and [9] on thermal resistance.
3) the calculated resistance of the MD OSG-500 kV is 0.04 Ohms. Considering the seasonal coefficient for the specific resistance of the soil taken equal to 5 [10], the resistance of the MD will be 0.14 Ohms, which does not exceed the permissible value of 0.5 Ohms and meets the requirements of [11,12]. 4) the maximum contact voltage on the switchgear-500 kV is 51 V, which does not exceed the permissible value of 65 V for the duration of the backup protection [13], according [14]; 5) after the end of the installation work it is recommended to carry out control measurements to confirm the calculated data [15].
The following screening factors were considered in the calculations:  coefficient of shielding of control cables with two-way grounding of screens -10 [18];  coefficients of shielding of the buried cable channel for the corresponding sections of routes of laying of control cables -10 [19].
When laying the shielded cable in the cable channel, the shielding coefficients are multiplied.
The results of the calculation of field noise at short circuit are given in the table 2: Calculation results: 1) the level of pulse emitted noise from lightning strikes at the inputs of MP devices installed in the DS of the OSG-500 kV will not exceed 1.7 kV, which does not exceed the permissible value for MP equipment tested for the fourth degree of rigidity-4 kV, according to [20]; 2) the potential induced in the cables will not exceed the permissible value for cable insulation -23 kV, according to [21].

Calculation of induced interference in short-circuit
For the calculations in the "OSG" Project used a drawing of "Lightning protection and grounding. OSG-500 kV. Plan. 122N15A-21 UA-12694-ED, L. 2". The scheme of arrangement of lightning rods and equipment OSG-500 kV is shown in [22].
In accordance with [23], to calculate the overvoltage in the MD at lightning, the current amplitude lm = 100 kA and the front duration tfr = 10 µs is taken.
The design scheme in the program "OSG-Project" is presented in [24]. The soil resistance is assumed to be p1 =20 Ohms * m, p2=18 Ohms * m, the depth of the layers h=0,8 m.
The results of the calculation of pulse overvoltages affecting the insulation of cables during lightning strikes are presented in the table 3: Calculation results: 1) Pulse voltage from lightning strikes applied to the inputs of MP devices will not exceed 1.46 kV, which does not exceed the permissible value for MP equipment tested on the fourth degree of rigidity -4 kV, according to [25]. Examples of calculation schemes with the results of calculations are shown in [26]; 2) the potential applied to the insulation of cables will not exceed the permissible value -23 kV, according to [27]; 3) the potential on the MD near the cable channel will not exceed the permissible value of the electrical breakdown voltage of 100 kV/m, according to [28].

Calculation of IF magnetic field
The sources of the magnetic field intensity of industrial frequency are power equipment and PS busbar. Calculation results: 1) the nearest source of the magnetic field intensity of industrial frequency to the distributive shield of the OSG-500 kV are flexible communication buses between the OSG-220 kV and the OSG-500 kV. In the normal mode of operation of the equipment (current 3150 A on buses 220 kV) the maximum value of the magnetic field of industrial frequency in the room distributive shield OSG-500 kV will not exceed 2.68 A/m [29,30]..
2) for MP equipment installed in the distributive shield OSG-500 kV, the magnetic field generated by the tires 220 kV flexible connection between the OSG-220 kV and the OSG-500 kV, in emergency mode (at short circuit) does not exceed the permissible value for the equipment tested on the fourth degree of rigidity -300 A/m, according to [31,32].

Determination of the levels of electromagnetic fields of RF range
Protection against external electromagnetic fields of RF range is provided by the following technical solutions:  Metal cladding of the UAV building;  Placement of MP devices in metal cabinets.
The greatest impact of electromagnetic fields of RF range on the MP device occurs when using portable radio transmitters near the MP equipment. In this case, possible sources of interference may be portable radio stations, cell phones and radiotelephones of the DECT standard.
According to the results of measurements [33] background intensity of RF electromagnetic fields in the air force building will not exceed 1.4 mV / m.

Development of recommendations to improve the electromagnetic environment
According to [34,35], portable radio stations "Vertex Standart" are used as communication devices at the Yuzhnouralskaya GRES-2. These radio stations can operate with four output power values: 5W, 2.5 W, 1W, 0.25 W. Depending on the value of the output power limits are set for the use of the radio near the MP devices. The intensity of the electromagnetic field of the RF range, created by radio stations "Vertex Standard", will exceed the permissible value (10 V / m) when used:  closer than 1.5 m from the MP devices -at a radio power of 5 W;  closer than 1 m from the MP devices -at a radio power of 2.5 W;  closer to 0.7 m from MP devices with the power of the radio station 1 watt;  closer than 0.35 m from the MP devices -with a radio power of 0.25 watts.

Conclusion
The article analyzed and identified the main sources of interference, disrupting the work and reliability indicators of the system, which can lead to malfunction of system of microprocessor relay protection and automation for electric stations and substations, as well as elements and actuators of open distribution devices. Further increase in reliability requires the development of technical measures, namely, requires the use of power and signal cables that must meet the requirements for specific parameters of inductance, capacitance and active resistance, and also requires the use of special placement of cross sections of conductors inside the cable. Secondly, it is shown that to increase the reliability of information transmission it is necessary to switch to serial communication channels, but the amount of information per channel should be strictly limited. The estimation of economic indicators of the system and its dependence on the reliability of the system is given. Thus, with an