Енергетичні втрати при комутації електричної дуги

Анотація

ENERGY LOSSES IN COMMUTATION ELECTRIC ARC

V. Korobskyy, A. Siroshtan

The electric energy W, which is released in switching devices during switching, is converted into heat Q. Part of it (Q1) is spent on heating the mass of the metal, the contact detail of the stationary and movable to the melting point and partly on the melting of the metal on the working surface of the contact component; the other part (Q2) is to heat the mass of molten metal to the boiling point and to evaporate the metal part. On the other hand, this energy W has two components: one is the directly proportional combustion time of the arc t0, which is determined by the active load of the circle - WR, and the second - the constant - WL, which is equal to the energy of the magnetic field accumulated in the inductance of the electric circuit and consumed in commutative devices when switching.

The purpose of the study is to establish the relationship between the thermophysical characteristics of the contact material, the parameters of the electrical network and the magnitude of the energy costs when switching the arc.

Materials and methods of research. The objects of the experimental study were the contact details made from serial (SrM0.2 + M1) and experimental (81.3% Cu + 10% Cr + 2.0% TiB2 + 3.0% Nb + 2.0% C + 0.7% Zr) of contact materials. They were used in electromagnetic actuators PML - 1100.

The specified switching parameters (arc combustion time and average current value in the arc) were recorded using oscillograms of current and voltage. Oscillograms of current and voltage are obtained using a universal two-beam memorandum oscilloscope C8-14.

Research results. The heat conduction equation for our case will be written as a stationary nonuniform one-dimensional process. The solution of the equation makes it possible to determine the temperature at any point of the contact detail along the x-axis (longitudinal axis) at each specified time t, including the points which are located on the working surface at the end of the switching interval.

If the second boundary condition is fulfilled during the switching process, then a normal cooling process takes place.

If the known amount of heat Q released during the switching and the optimum burning time of the arc t0 are known, it is possible to determine the electric power losses and the amount of electrical erosion of the contact parts made from different materials, depending on the electric circuit parameters and the nature of the load.

The value of the electric energy W1, W2, which is allocated in the main circle of starters at the breakdown, is determined by the formulas. The calculation is made for a single trigger for one switching cycle, we use data for oscillogram calculation.

That is, with the use of starters with developed composite materials, the cost savings of electricity is almost 6%.

Conclusions

1. The energy of the arc is a function of the time of its burning, which depends on the thermophysical parameters of the contact material. Approximately 20-35% of the thermal energy of the arc, which is allocated in the contacts, is spent on melting of the material of contacts, the rest - to boil.

2. Reducing the burning time of an electric arc during switching current can be achieved by introducing into the composition of the following components C, Mo, MoO3, Cr.

3. Given the nature of the change in the wear and tear of the contacts, it is possible to determine the lifetime of the starters and to predict its commutation wear resistance. The service life of the starters is determined, first of all, by the amount of wear and tear of the electrically operated contact parts.

4. Economic efficiency of the use of starters PML-1100 with research contacts is achieved due to significantly lower cost of contact details (approximately 22-25 times). For the consumer, the loss is reduced by 6% of the electric energy, which is allocated when switching current in the contacts.