RU2465702C1 - Method to melt glazed frost on wires of three-phase overhead power transmission line - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to melting of glazed frost on three-phase overhead power transmission lines (OL). Alternately within serial time intervals not exceeding 20% of the total expected melting time, DC is sent via a wire (7) of the main phase of the OL and two wires (8 and 9) of other phases, connected in parallel, at the same time as the main phase they cyclically use each phase of the OL, and its wire heating capacity is controlled by variation of ratio of duration of the time interval, in which this phase is used as the main one, to the total duration of the cycle. Serial time intervals are separated with current-free pauses.

EFFECT: reduced power consumption and less melting time on three OL phases without use of complex conversion equipment for melting of glazed frost.

2 cl, 2 dwg

Description

Technical field

The invention relates to the electric power industry, in particular to ice smelting on three-phase overhead power transmission lines (VL).

State of the art

For smelting ice on three-phase overhead power lines, a direct (rectified) current is used, which is generated using rectifier units based on AC to DC converters. Rectifier installations are located in areas with a standard ice wall thickness of 20 mm or more at substations adjacent to overhead lines of different voltage classes, usually 220-500 kV, of different lengths, with different cross-sections of wires and the number of wires in phase. Ice smelting can be carried out under different weather conditions - air temperature and wind speed. These differences make it necessary to conduct ice melting with adjustable heating capacities of wires, including unequal in the phase wires of one overhead power transmission line, since, as a rule, ice deposits on the leeward and leeward phases of overhead lines are different.

Simultaneous (not alternate) icing in all three phases of overhead lines with independent regulation of the melting current in each phase requires sophisticated converting equipment with several controlled thyristor groups (it can be performed, for example, by installing a separate thyristor converter for each phase) and therefore could not find wide application.

Known and widely used, the prototype method of melting with a direct current of the rectifier installation with connecting the OHL phase wires according to the “phase-two phases” scheme, in which the current is alternately passed through the main phase wire and the wires of the other two phases connected in parallel, and, having completed the melting ice on the next main phase, connect another phase as the main one. Such a melting sequence is used, in particular, in the method [RU 2309522 from 06.24.2006]. In the prototype, ice melting on a three-phase line is performed for three time intervals, and in the second and third intervals, the melting current passes through the wires of those phases in which the ice is already melted in the first and second time intervals, respectively. As a result, the heating energy is used inefficiently, because the phase-free wires of ice are uselessly heated, and accordingly the total (total) melting time increases, during which the overhead line remains out of operation.

Used in the prototype, the regulation of the melting current of a controlled rectifier installation does not eliminate this drawback, since the procedure for melting ice of a three-phase line in three time intervals is preserved - one time interval for each phase.

SUMMARY OF THE INVENTION

The technical result of the invention is the reduction of energy consumption and the reduction of the melting time in the three phases of overhead lines without the use of complex converting equipment for smelting ice.

The subject of the invention is a method of melting ice on wires of a three-phase overhead line, which consists in the fact that alternating during successive time intervals not exceeding 20% of the expected total melting time, direct current is passed through the wire of the main phase of the overhead line and two wires of other phases connected in parallel, this, as a main phase, each phase of the overhead line is cyclically used and the heating power of its wire is controlled by changing the ratio of the duration of the time interval in which this phase is used as TBE main, to the total cycle time.

This set of features allows to solve the problem of the invention.

The development of the invention provides for the separation of consecutive time intervals without current pauses.

This makes it possible to further simplify the conversion and switching equipment used for melting.

The implementation of the invention in view of its development

The implementation of the proposed method is illustrated by the structural diagram in figure 1 and time diagrams of currents in the phases of the overhead line in figure 2.

Figure 1 shows a bipolar controlled thyristor rectifier, consisting of a three-phase cathode group 1 and a three-phase anode group 2, a bridge switching device with four thyristor arms - 3, 4, 5, 6, three phases 7, 8, 9 VL, on the wires of which carry out melting ice; a fusion control unit 10, a rectifier power supply 11 with a three-phase alternating voltage.

The method is as follows.

On the side of the overhead line removed from operation, remote from the rectifier (direct current source of melting), the phase wires are short-circuited.

During the first time interval t ₁ (see figure 2) include with a control angle close to zero, the thyristors of groups 1, 2 and arms 3 and 4 of the thyristor switching device. In this case, a direct smelting current flows through the phase 7 wire, which in this interval is the main one, and two other phases 8 and 9, connected in parallel, and the currents of the corresponding phases are I ₇ = I, I ₈ = 0.5 · I, I ₉ = 0.5 · I, where I is the current in the main phase of the overhead line. At the end of the first time interval, the thyristors of groups 1, 2 and arms 3 and 4 are turned off. After a dead time pause Δt = 5 · τ, where τ is the decay time constant of the overhead line current (5 · τ <1 s), turn on with the control angle, thyristors of groups 1, 2 and arms 3 and 6 are close to zero. During the second time interval t ₂ , the melting current passes through a phase 8 wire, which is the main wire in this interval, and two other phases 7 and 9 connected in parallel, and the currents the corresponding phases are I ₇ = 0.5 · I, I ₈ = I, I ₉ = 0.5 · I. At the end of the second time interval, the thyristors of groups 1, 2 and arms 3 and 6 are turned off. After a dead time, Δt is turned on with a control angle close to zero, the thyristors of groups 1, 2 and arms 4 and 5. During the third time interval t _{3, the} current melting passes through the wire of phase 9, which in this interval is the main one, and two other phases 7 and 8, connected in parallel, and the currents of the corresponding phases are I ₇ = 0.5 · I, I ₈ = 0.5 · I, I ₉ = I. After the third time interval, through a dead time pause Δt, the process is cyclically repeated and continues until the ice is melted at all phases of the overhead line. Commands for turning on and off the three-phase thyristor groups and the corresponding arms of the thyristor switching device are provided by the control unit 10. The thyristor converter is powered by a three-phase alternating voltage by a power source 11.

The ice melting time at each phase of the overhead line is determined by the square of the current value

;

;

;

;

.

.

The fraction of the total heating power given to the wire of each OHL phase is determined by the relative duration of the intervals t _i = t _i / T, where the cycle duration is T = t ₁ + t ₂ + t ₃ + 3Δt, and i = 1, 2, 3.

The duration of the cycle in practice varies from several tens of seconds to several minutes.

The greatest energy savings and the minimum melting time is ensured while melting ice on the wires of all phases of the overhead line.

With the same thickness of the ice wall at all phases of the overhead line, the ice will melt almost simultaneously at t _{1 *} = t _{2 *} = t ₃ and the relative durations of all intervals, approximately (if we neglect the short current-free pauses Δt) equal to 1/3.

If the wall thickness of the ice is different on the phases of the overhead line, then for the simultaneous melting of the ice on them set in the control unit 10 intervals duration in accordance with the expressions

;

;

;

;

,

,

where k _B , k _C are the unevenness coefficients of the currents in the phases of the overhead line, which are determined by the ratio of the icing wall thicknesses taking into account weather conditions - air temperature and wind speed and can be calculated using icing control data obtained, for example, using an automated system [ Information system for icing control on overhead power lines / A.F. Dyakov, I.I. Levchenko, A.S. Zasypkin, etc. // Energetik. - 2005, No. 11, p.20-25].

When melting ice on short lines, the melting current can be reduced to an acceptable value by increasing the duration of dead time pauses Δt (figure 2).

To control each thyristor shown in FIG. 1, a circuit known, for example, from [Handbook of converter technology. Ed. I.M. Chizhenko. K., "Technics", 1978], which provides the inclusion of a thyristor with a control angle close to zero, and turning off the thyristor in a dead time.

The reduction in energy consumption and the reduction of ice melting time in relation to the prototype is practically manifested in cases where the total cycle time T does not exceed 20% of the total expected (according to the icing control system) melting time, i.e. the expected ice melting time is divided into at least five cycles. Moreover, the duration of one cycle is usually 5-10 minutes.

Claims (2)

1. The method of melting ice on the wires of a three-phase overhead power line, which consists in the fact that alternately during successive time intervals not exceeding 20% of the expected total melting time, direct current is passed through the wire of the main phase of the overhead line and two wires of other phases connected in parallel, in this case, each phase of the overhead line is cyclically used as the main phase and the heating power of its wire is controlled by changing the ratio of the duration of the time interval in which this phase is used as TBE main, to the total cycle time. 2. The method according to claim 1, in which consecutive time intervals are separated by dead time pauses.

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