RU2569318C1 - Method for melting ice on wires of overhead electric line - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: fault short circuiting is generated at the end of overhead electric line, current in the wire and air temperature are controlled directly and temperature of the wire is also controlled at the section of overhead electric line free from icing, and overhead electric line is switched off when temperature of the controlled wire reaches maximum permitted value. The overhead eclectic line is switched on again at lowering of the controlled wire temperature at no-current condition at the moment of time when not instantaneous value but average value of the wire temperature at current and no-current intervals will become equal to the rated value. At that, in order to define the moment for reconnection of the overhead electric line steady-state value of the wire temperature is calculated by extrapolation and against current of the wire and voltage of the power supply source at the beginning and ending of current interval relative length of ice head and when it is more than zero the above process of the overhead electric line disconnection and connection is repeated until ice head is eliminated completely. Wire block of the power supply source installed at the substation is used as a section of the overhead electric line free from ice as far as its wires correspond to wires of all overhead electric lines melted from this power supply source.

EFFECT: reduced time for iced melting at wires of overhead electric lines and reduced power consumption.

3 cl, 2 dwg

Description

The invention relates to the electric power industry, in particular, to smelting ice on wires of overhead power transmission lines (OHL) in intermittent mode with direct current pulses and alternating current pulses in cases when the active resistance of the overhead line at 0 ° C is at least 20% from the total inductive resistance of the current circuit, i.e. when a thermal drop in current occurs.

To melt ice on overhead lines, when the melting current exceeds a long-term allowable value according to the condition of heating the wires, high-voltage melting is used in sections of overhead lines free of ice, which is characterized by alternating short-time operation, characterized by alternating current flow time intervals (current intervals) with dead-time pauses.

A melted overhead line is connected to a power source for the duration of the current interval, during which the ice clutch melts at a surface temperature of the wire close to zero, and the wire temperature rises in a section free of ice. The permissible value of the maximum wire temperature at the end of the current interval for AC grade wires is taken to be 130 ° C. After the current interval, the overhead power line is disconnected and the wire is cooled to the minimum temperature in a dead time pause. The permissible value of the average temperature of the wire during the repeatability period (current interval and current-free pause) is normalized. For example, for AC grade wires, the normalized average temperature is 90 ° C. If the icy clutch is not melted during the period under review, this process is repeated until the icy clutch is completely removed, after which the melted overhead line is disconnected from the power source.

The methods of melting ice in the intermittent mode are distinguished by the method of choosing time points in each repetition period: disconnecting the overhead line from the power source and reconnecting, as well as finally disconnecting after the icy clutch is completely removed.

Known and widely used is the method of melting ice in the intermittent mode, according to which the time of disconnection, connection and final disconnection is determined by calculating the duration of the current interval, dead time and the total time of melting ice. The calculation of the durations recommended in [Methodological guidelines for glaze ice melting with alternating current] / Burgsdorf VV, Nikitina LG, Nikonets LA, Khrushch P.R. - Soyuztekhenergo, 1983. - 114 p., P. 88-105] and performed for the average melting conditions characteristic of specific overhead lines.

The disadvantage of this method is the large inaccuracies in the calculation, leading to an increase in the time spent by the melt overhead line under current and electricity consumption.

The specified methodology for calculating the indicated durations is described in the book [Rudakova R.M., Vavilova I.V., Golubkov I.E. Methods of dealing with icing in electrical networks of energy systems. - Ufa, USATU, 2005, - 187 p., P. 68-86].

The disadvantage of this method is an approximate result due to the need to take into account a large number of factors, including changes in current during the current interval due to changes in the temperature of the wire in areas without ice, and also due to the use of a fixed value of the minimum temperature of the wire without ice, which is recommended + 10 ° C.

The well-known "Method of melting ice on overhead power lines 6 (10) kV" (RU 2478244, publ. 03/27/2013), taken as a prototype.

In the prototype, an artificial short circuit is created at the end of the overhead power line, the wire current, air temperature, wind speed are directly controlled and indirectly, the temperature of the wire is calculated on the part of the overhead power line free of ice using a thermal model of the wire, and the depth is also calculated clutch penetration using a mathematical model of ice penetration. After the indirectly controlled temperature of the wire reaches the maximum permissible value, the overhead power line is disconnected. Reconnecting the overhead power line is performed by lowering the indirectly controlled temperature of the wire to a set lower instantaneous value. The process continues until the indirectly controlled penetration depth of the ice clutch becomes equal to the user-defined depth at the beginning of the melting.

The disadvantages of the prototype are: low accuracy of the calculation methods, especially the penetration depth of the icy clutch, which has different diameters and densities in different sections of the overhead power transmission line, which requires the introduction of substantial reserves and an increase in the melting time; reconnecting the overhead power line at a given instantaneous value of the wire temperature leads to a decrease in the wire current compared to the maximum allowable one, which creates an average wire temperature over the period of repeatability of the short-time mode, close to the normalized value.

The objective of the invention is to increase the reliability and efficiency of electric power systems in the conditions of ice-wind situations.

The technical result of the invention is to reduce the time of smelting ice on the wires of an overhead power line and reduce energy consumption.

The problem is solved due to the fact that they create an artificial short circuit at the end of the overhead power line, directly control the current of the wire and air temperature, and also control the temperature of the wire in the section of the overhead power line free of ice, the overhead power line is disconnected after reaching the maximum temperature controlled wire permissible value, and then reconnected to the power source when the directly controlled pace is reduced to a dead time atures of the wire at a time when the average value of the temperature of the wire during the current interval and the current pause becomes equal to the normalized value, extrapolate the steady-state value of the temperature of the wire to determine the time of reconnection of the overhead power line, control the current of the wire and the voltage of the power source in at the beginning and end of the current interval, calculate the relative length of the ice clutch, and if the relative length of the ice clutch is greater than zero, indicate This process, disconnect and connect the overhead line continued until the complete removal of glaze sleeve.

The first development of the invention involves monitoring the current of the wire, the voltage of the power source and the temperature of the wire at the beginning and end of the current interval during trial melting in the absence of icing.

The second development of the invention involves the use of ice-free overhead power line section installed on a substation in the power supply circuit of a block of wires corresponding to the wires of all overhead power lines smelted from this power source.

In FIG. 1 shows diagrams of wire current and wire temperature in a section without ice.

In FIG. 2 presents a variant of a functional circuit for melting ice with alternating current, which implements the proposed method. When melting ice with direct current from a controlled rectifier, the switching and measurement scheme is modified, but the method remains the same as when melting ice with alternating current in an intermittent mode.

In FIG. 2 shows: the power supply of the ice melting circuit 1, current sensors 2 in the phases of the power supply 1 and simultaneously in the wires of one of the melted OHL connected to the power supply 3. The OHL is connected when the shorting disconnector 4 is turned on, creating an artificial short circuit at the end of the overhead power line , and a linear disconnector 5 with a three-phase switch 6. The composition of the switched wire block 1 included in the power supply circuit Г includes temperature sensors for wire 8 and disconnect the single-pole (Recorded as the temperature of the disconnected wire temperature unit 7), the voltage transformer 10, voltage unit 11, the current block 12, the wires 13 and air temperature: and 9. For fixing and processing of information about the parameters of ice melting modes are used. Blocks 11, 12, 13 are connected to the computing unit 14, which gives the command “enable-disable” to the control unit 15 with a three-phase switch 6.

, то средняя температура провода превысит ϑ_норм, что опасно для провода, если позже - при $${\vartheta }_{\min }^{\prime \prime }<{\vartheta }_{\min }$$

, то бестоковая пауза увеличится, и время плавки возрастет.Consider the implementation of the method. At the end of the overhead power line 3, an artificial short circuit is created with a short-circuit disconnector 4, the line disconnector 5 is turned on and the overhead power line 3 is connected with a three-phase switch 6 to the power source 1 at time t _on1 , the voltage is controlled in power source 1 using a voltage transformer 10 and a unit voltage 11, wires _etc. I via current sensor 2 and the current of the current unit 12, and at a site free from ice, - _straight wire temperature θ and θ _in air temperature from sensor rate Aturi wire 8 and the wire temperature and air block 13. After reaching the controlled temperature of the wire the maximum value θ _ppm computation unit 14 delivers the command to "turn off" the control unit 15 and the air line 3 power is disconnected from the three-phase power supply 1 when the switch 6 time t _{off 1} . Calculate by extrapolation the steady-state value of the wire temperature ϑ _y1 in the calculation unit 14. When the controlled temperature of the wire decreases to a dead-time pause to ϑ _min, the calculation unit 14 sends a “turn on” command to the control unit 15 and the three-phase switch 6, the overhead power line 3 is reconnected to the power source 1 at time t _on2 , determining the end of the first dead time pause. The temperature ϑ _{min is} calculated in real time in the calculation unit 14 so that the average temperature of the wire ϑ _srd for the current interval and the subsequent non-current pause is equal to the normalized value ϑ _norms . This is an essential feature of the invention. If you connect the overhead power line 3 earlier - at $${\vartheta }_{\min }^{\prime }>{\vartheta }_{\min }$$

, then the average temperature of the wire will exceed ϑ _norms , which is dangerous for the wire, if later - at $${\vartheta }_{\min }^{\prime \prime }<{\vartheta }_{\min }$$

, then the dead time will increase, and the melting time will increase.

For use in the method is defined as a first approximation ϑ _min from the expression

, $${\vartheta }_{\min }^{\left(\mathrm{one}\right)}=2{\vartheta }_{n\mathrm{about}Rm}-{\vartheta }_{m.d}$$

,

with subsequent refinement by the formula (1):

(see formula (14) in the article Zasypkin A.S., Zasypkin A.S. Heating of OHL wires by electric current during ice melting in the intermittent mode / Izv. Universities. Electromechanics. 2014. No. 4).

, по формуле (1): ϑ_min=53°C.For example: провода _ppm = 130 ° C; ϑ _normal = 90 ° C; measured _at θ = -5 ° C and θ values _etc. for the current interval, which is calculated by extrapolating the steady-state temperature θ _y = 220 ° C. In a first approximation $${\vartheta }_{\min }^{\left(\mathrm{one}\right)}=2\cdot 90-190={\mathrm{fifty}}^{\circ }C$$

, by the formula (1): ϑ _min = 53 ° C.

With a second current pulse from t _on2 to t _off2, the wire temperature increases from ϑ _min to ϑ _ppm , calculate by extrapolation in the calculation unit 14 the steady-state temperature ϑ _y2 and a new refinement ϑ _min .

Using the values of the voltage of the power source 1, the current of the wire, and the temperature of the wire recorded at the beginning and end of each current interval in the section without ice, the change in the active resistance of the overhead power line 3 as a result of heating all sections of the overhead power line 3 without ice is calculated, and the relative length thereof icy clutch. The smaller the relative length of the icy clutch, the greater the decrease in current in a known range of changes in the temperature of the wire due to the heating of sections without ice - a thermal decrease in current.

Let us explain this essential feature.

The active resistance of the overhead power line sections 3 without ice at 0 ° C is

R _VL.0 (1-l _{gm *} ), where l _{g * *} is the relative length of the icy clutch. Due to the heating of these sections by the wire current during the current interval, the active resistance increases by ΔR _VL :

where α is the temperature coefficient of resistance of the overhead lines.

The actual value of ΔR _{VL is} calculated from the values of the voltage of the power source and the current of the wire recorded at the beginning and end of each current interval (when melting with alternating current, the phase shift between them is taken into account). Therefore, from (2):

In the first current interval in FIG. 1 ϑ _min = ϑ _c . In subsequent current intervals, with a decrease in the length of the icy clutch, the value of l _{gm ∗} decreases, and when l _{gm ∗} = 0, the melting stops.

The first development of the invention consists in experimental refinement for each overhead power transmission line 3 of the active resistance R _VL.0 in formula (3) in the absence of _ice formation (l _{gm ∗} = 0), for example, when conducting a “trial” melting, which is provided Requirements for the organization and implementation of ice melting on wires and lightning protection cables of power transmission lines, JSC System Operator of the Unified Energy System, 2011.

By (3) for l _{gm ∗} = 0:

,

,

where the index (PP) means trial melting.

The second development of the invention consists in using ice-free as an overhead transmission line section 3 installed on a substation in the power supply circuit of a switched block of wires 7 corresponding to the wires of all overhead power transmission lines smelted from a single power source. The composition of the switched wire block 7, included in the power supply circuit 1, includes temperature sensors for the wire 8 and single-pole disconnectors 9. The ice from the ice of the switched wire block in the substation is carried out by known methods (mechanical, artificial heating in the off state or others). The creation of conditions for the worst cooling of wires, possible on the melted overhead power lines 3, is provided by the fencing block of wires.

The claimed technical result of the invention is realized when ice is melted on OHL wires in the intermittently short-term mode by DC pulses, as well as by AC pulses in those cases when the active resistance of the OHL wire at 0 ° C is at least 20% of the total inductive resistance of the current circuit, those. when a thermal current drop occurs (Guidelines for the calculation of short circuit currents and the selection of electrical equipment / Edited by B.N. Neklepayev. - M.: Publishing House NTs ENAS, 2002. - 152 p., p. 68).

Claims (3)

1. The method of melting ice on the wires of an overhead power transmission line, which consists in creating an artificial short circuit at the end of the overhead power transmission line, directly controlling the current of the wire and air temperature, and also monitoring the temperature of the wire in the section of the overhead transmission line free of ice, air the power line is disconnected after the temperature-controlled wires reach the maximum permissible value, and then reconnected to the power source, I distinguish Take into account that the reconnection of the overhead power line is performed when the directly controlled temperature of the wire is reduced to a dead time pause at a time when the average temperature of the wire during the current interval and the dead time is not equal to the normalized value, and the established value of the wire temperature is calculated by extrapolation determine the time point of reconnecting the overhead power line, control the wire current and voltage of the power source at the beginning and end of the current interval, calculate the relative length of the ice clutch and, if the relative length of the ice clutch is greater than zero, the indicated process of disconnecting and connecting the overhead power line continues until the ice clutch is completely removed. 2. The method according to p. 1, in which the wire current, the voltage of the power source and the temperature of the wire at the beginning and end of the current interval during trial melting in the absence of icing are directly controlled. 3. The method according to p. 1, in which a block of wires installed on a substation in the power supply circuit is used as a section of an overhead power line free of ice, which corresponds to the wires of all overhead power lines smelted from this power source.

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