RESEARCH ON BUILDING FOR DEPENDENCE OF INSULATION PARAMETERS OF THE 6kV GRID WITH THE ENVIROMENT AND STRUCTURAL PARAMETERS OF OPEN-PIT MINES IN THE QUANG NINH AREA

Http://www.ijetmr.com©International Journal of Engineering Technologies and Management Research [56] RESEARCH ON BUILDING FOR DEPENDENCE OF INSULATION PARAMETERS OF THE 6kV GRID WITH THE ENVIROMENT AND STRUCTURAL PARAMETERS OF OPEN-PIT MINES IN THE QUANG NINH AREA Tran Quoc Hoan , Ho Viet Bun , Nguyen Anh Nghia 3 *1 Department of Electrical Engineering and Automation, College of Industry and Trade, Viet Nam 2, 3 Department of Electrification, Ha Noi University of Mining and Geology, Viet Nam Abstract: Medium voltage insulation indicators depend on many factors such as environment, length of feeders, numbers of transformers and motors connected on the grid. The values determined by experimental measurements will be used to build up maths distributions. Base on these results, an experimental equation will be formed for determining capacitance and impedance of 6kV grid to ground in QuangNinh open pit coalmines.


Introduction
Building a 6kV grid model of open-pit mines in the Quang Ninh area, used to investigate the transient process in switching of short-circuit switches in fault phases so as to ensure safety when there occursingle-phase earth faults, need take into accountthe effect of insulation resistance,the capacitance, loads, compensate capacitors and potention transformers.
The insulation resistance and capacitance of the 6kV open-pit minegrid in the Quang Ninh area depend on the operating environment such as temperature,humidity,... and the structural parameters of the grid. Based on the measured datas, it is possible to determinethe dependenceof the environment and the open-pit mine 6kV grid's structure such as: the supply line length, the number of low-voltage transformers, the number of high-voltage motors.Therefore,this results are the basic factors for the grid modeling.

Research On Selection Of Measuring Methods To Identify Insulation Parameters Of
Open-Pit 6kv Mine Grids In The Quang Ninh Area

Elementary Theory
Research on the analysis and comparision of measurable methods enable to choose a three-volt meters method for determination the capacitance (С) and the conductance(G) of the grid to the ground. This method has the outstanding advantage, such as no creation artificial short-circuit causing insecurity, in complex measurable techniques and instruments. Although calculations are complex, it is extremely convenient to program by a computer. The principle diagram is shown in Figure 1 [1,4].

MC
The secondary transformer 35/6kV  q-the certain standard is the confidence probability function. If consider that the value (q) corresponds to the probability value if P = 0,95 then q = 1,96 P = 0,99 then q = 2,58 -vectors of phase-to-ground voltage before connecting to Cph.
Suppose there has a phase-earth fault on phase A, the complete earth fault current of phase A before and after connecting to Cph: To ensure accuracy, it is necessary to select the auxiliary capacitance (Cph) so that the groundphase voltages fluctuate minimum, about (10-20) %. Ufđm  Based on the measured datas, it is possible to identify Gcd and Ccd. The results are listed in Table  1.

Frequency of the Capacitance (Cf) and the Insulating Conductance (Gf)
Identify the number of capacitance intervals [4]:  The diagramillustrates that the frequency of insulation capacitance C f and insulating conductance Gf has only one peak, closingto the standard form. Therefore, it is reasonable to examine the insulating parameters of the open-pit mine grids in the Quang Ninh area by months of the year.

Testing the Normal Distribution of The Capacitance and The Insulating Conductance
According to the results of the capacitance Cf and the conductance Gf measurement, the testing of the compatibility between the experimental distribution and the theoretical distribution, based on the distribution standard χ2 [2], is carried out. The characteristic parameters which arerepresented by the line graph of the theoretical standard distribution density function (dash-dottedline) and the experimental distribution function (solid line) are calculated by using the Descriptive Statistics tool in Excel (Figure 4). After testing the standard distribution of the capacitance Cf and the insulating conductance Gf found that it is reasonable to investigate the dependence of the capacitance Cf and the insulation conductance Gf of phases to ground with environmental parameters (temperature, humidity) and the structure of grid during the year.

Building Dependence of insulating Capacitance Cf And Insulating Conductance Gf with Environment and Structural Parameters of Open-Pit Mine 6kv Grid
Based on the calculated results (Table 1), the least squares method is an effective and resonable to build the relationships between the conductance Gcd and insulating capacitance of phase to ground with parameters of environment (temperature, humidity) and the grid structure (the grid conversion length, the number of low-voltage transformers, high-voltage motors).
Through the results of the variance testing of Cf and Gf measurements and the regression results of Cf and Gf, the equations indicating the dependent relationship are received as follows: In the experimental formulas , besides the grid's structural effects (the supply line length, the number of transformers and high-voltage motors), it also takes into account the impact of open-pit mine environment such as humidity and temperature, environmental temperature of the year • Based on the experimental relationships, it is possible to simulate the actual working status of the grid in order to give necessary conclusions ensuring safety when operating open-pit mine grid as well as accuracy and efficiency calculation, calibration of the single-phase earth-fault protection.