Technical sciences / 5. Power

DPhil Kaganov W. I.

The Moscow state institute of radio engineering, electronics and automatic– technical university.

Heating of wires of a contact railway system with on-power an electromagnetic wave for struggle against ice

It is known that at temperature of air from 0 to-5⁰С and the raised humidity there is an icing of bearing and contact wires of networks of railroad lines that leads to delay of speed of movement of trains on electric draft or even to their full stop. For struggle against this extremely undesirable phenomenon it is necessary at approach icing conditions to heat up wires to temperature not less 15-20⁰С..

The basic way of clearing of wires from icing consists in the following: stop movement of trains on electric draft, short-circuit close wires of a network and pass through them from traction substation of enormous force a current which is heating up wires. So according to [1] in the spent experiment for struggle against ice on a high-speed railroad line Paris-Lyons at a short-circuited contour in the extent 43km and a source pressure in 26 kV the current in a copper contact wire section 150 mm² equaled 615 A and a bronze bearing wire section 65 mm² -420 A. Hereby, the general spent capacity for heating of wires on 15-20⁰ С has made nearby 27 MW, and specific capacity - 650 W/m. Is short we name an applied method of heating of wires way of short circuit.

In [2-3] essentially new method for struggle against an icing of wires by means of the high-frequency electromagnetic wave extending on two- or three-wire line is offered. With reference to system of an electricity transmission of a railroad line the general scheme on realization of the given method is presented on fig. 1.

Owing to so-called skin-effect [4] to frequency increase there is a replacement of the current proceeding on a wire, to its periphery therefore resistance of a wire sharply increases and there is more effective transformation of electromagnetic energy of the wave extending on a line, to the thermal. So according to [3] for a copper wire specific resistance of a wire at low and high frequency accordingly:

(1)

(2)

where S - section of one of two copper wires [mm²], F - frequency of an electromagnetic wave [MHz].

According to (1) and (2) at transition to a warming up of a wire by means of electromagnetic energy of high frequency the factor of its transformation to heat will increase N = Rf / R0 time. So for example, according to (1) resistance of a wire at section S=150 mm² and length 1000m at low frequency makes 0,119W, and according to (2) resistance of the same wire at frequency F=100 MHz - 61W, i.e. increases more, than in 500 times. Hence, in the same number 500 of times there will be more effective transformation of energy of a source to heat.

Radiation of electromagnetic energy at its distribution on a two-wire line of transfer minimum as the field is concentrated basically between wires. The basic source of losses of energy in this case is теплоотдача warm wires to air by a convection, which size in the established mode:

(3)

where q [W/mm² × К] – factor heat emission (convections) of the top hot layer of a wire to air, A– the general surface of a wire [mm²], ΔT_m- average value of difference of temperatures between the top layer of a warm wire and air, t – time [c].

From (3) we will receive for capacity ВЧ of the generator demanded for heating n wires on ΔTСР of degrees:

(4)

where N=2 and more, l - length of one wire [m], S – wire section [mm²].

As the amplitude of the running wave extending along a line, decreases on экспоненциальному to the law capacity of an electromagnetic falling wave on distance x from the generator will make:

(5)

where P_G= (U₀ )²/2 ρ – capacity of a wave in the line beginning, equal to target capacity of the high-frequency generator; U₀ - amplitude of pressure of high frequency in the line beginning; a= R_f /r (1/m) – an attenuation constant; R_f– resistance of a wire at high frequency; r=276lg (a/r) – wave resistance of a two-wire line; a - distance between wires; r – wire radius.

Thus the capacity disseminated on a site of a line of small length Dx :

(6)

Difference between temperature of a wire and air depending on the races-standings, connection counted from a place high-frequency generator :

(7)

Calculation example. According to formulas (5) – (7) we will give an example calculation of heating of a two-wire line from a copper wire at the following initial data: capacity of high-frequency generator P_G=100 kw, frequency F=100 MHz, length of a line l=5000m, section of wire S=150 mm². We will accept convection factor q =16 W/mm² × К.

Schedules of capacity of falling wave P(x) and temperatures of difference DT(x) along a line, calculated under the program, are resulted on fig. 2. From them follows that in a considered example at average temperature of heating of copper wires on 15⁰ C concerning air it is required to spend capacity ВЧ of an electromagnetic wave for each meter of a line in 20 W.

Besides skin-effect it is possible to apply specially developed, simple converters to wire heating on the converter of electromagnetic energy in thermal which can be established along a line with certain step. These converters can be fixed from above a contact line, without disturbing contact of a current collector of an electric locomotive with a wire (fig. 3). Laboratory experiments on heating of aluminum wires by means of the generator capacity in 100 W frequency of 100 MHz, have confirmed substantive provisions of given article.

Fig.2 Fig.3

The conclusion.

1. Bases of a new way of prevention of formation icing on contact and bearing wires of system of an electricity transmission of a railroad line with use of two physical phenomena are developed: skin-effect and direct, discrete transformation of electromagnetic energy to the thermal.

2. The offered way in comparison with a method of short circuit applied now [1] has following advantages:

- It is not required to stop movement of trains on electric draft on-skolku an electromagnetic wave of high frequency and a current of a food elektrovo-call can extend simultaneously on a contact line (fig. 1);

- The considerable economy – on an order and more – the source of electric energy demanded for heating wires, in view of more effective transformation of electromagnetic energy of high frequency in thermal in comparison with a direct current and a current of low frequency is possible.

3. As sources of electromagnetic energy lamp radio transmitters of VHF FM of an announcement by frequency around 100 MHz can be used.

4. Full-scale check of an offered method of heating of wires of contact and bearing wires of system of power supplies on a railroad line not less than 5 km by means of the industrial sample of the high-frequency generator capacity 5 - 10 kw is necessary in the extent.

The literature:

1. System of struggle against an icing of wires of a contact network. - RWM– online - 11-2002.

2. Kaganov V. I. Struggle against ice in transmission lines by means of a high-frequency electromagnetic wave. – Elektro, 2010, №5, p.41-45.

3. Kaganov V. I. The patent №2356148 of the RF from 20.05.2009 . The way and the device for struggle against ice on transmission lines».

4. Tamm I.E. Bas of the electricity theory. – М, 1956.