RU2661347C1 - Over voltages in medium voltage electric networks reduction method - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to the field of electrical engineering, namely, to the over voltages reduction methods in the 10, 15 and 35 kV electrical networks, mainly with overhead lines. Disclosed method allows to reduce the consumed by the supply transformer and the load reactive current. To achieve the said result, it is proposed to connect the three-phase capacitor bank to the medium voltage busbars sections (supply transformer secondary voltage phases), assembled according to the “star with brought out zero” configuration, with connected between the zero terminal and the “ground” resistor, which together with the bank capacitors in the non-stationary modes forms a damping chain. Capacitors bank power is selected equal to the transformer power consumption.

EFFECT: reduction of the damage main type to the technically possible minimum, which is the measuring voltage transformers failure due to the emerging ferro-resonance phenomena in transient modes.

1 cl, 1 dwg

Description

In medium voltage electrical networks, the occurrence of short-term overvoltage is inevitable. The appearance of short-term overvoltages in most cases with respect to the network itself is stochastic, therefore, it is difficult to determine the time of their appearance and the duration of exposure. It is known that the occurrence of overvoltages, despite their short duration, adversely affects the state of insulation of electrical installations, the operation of electrical equipment. Single-phase earth faults (OZZ) caused by overvoltages lead to devastating consequences. In order to reduce the likelihood of an SCR and reduce the consequences of a circuit, it is necessary to use measures and devices to limit overvoltages, creating conditions for eliminating a circuit to earth. Currently, the creation of such protection systems in electric networks with a low configuration and low fault currents is associated with a number of circumstances associated with a significant increase in the cost of power, electrical and electronic equipment.

In [1], various types of overvoltages occurring in electric networks are described. To combat overvoltage in medium voltage electric networks, methods have been developed and are used to reduce overvoltages and their consequences, based mainly on the use of non-linear surge arresters (surge arresters) [2], surge arresters, RC circuits, grounding devices through a resistor, arc-compensating compensating devices . The latter, due to the high cost and complexity of control in networks with overhead lines (VL), are practically not used.

The scope of the invention relates to electrical engineering, and in particular to methods of reducing overvoltages in electric networks of 6, 10, 15 and 35 kV, mainly with overhead lines. A positive aspect of the proposed method is the reduction of the consumed power transformer and the load of the reactive current, voltage losses in the supply line.

The inventive method for reducing overvoltage in medium voltage electrical networks by connecting damping RC circuits to the phases of the electrical network. The proposed method is characterized in that capacitor banks assembled in the "star with zero" circuit are connected to the phases of the secondary voltages of the supply transformer, the zero terminal of which is connected to the "ground" by means of the resistor R.

The invention is illustrated in FIG. 1. In FIG. 1 shows the capacitor blocks Sb1 and Sb2, which are connected to the bus sections 6 kV. Similar units can be installed on bus sections 10 and 35 kV, powered by transformers T1 and T2, respectively. The total total capacity of the block SB1 of capacitors is equal to the sum of the capacities C _A1 C _B1 , C _C1 . Capacitor blocks SB1 and SB2 with resistors R1 and R2 connected in series form in turn damping RC chains. To turn on and off the resistors R1 and R2, contactors K1 and K2 are provided, which are controlled according to specified algorithms. To optimize the losses in the transformer, load, supply lines, the total power of the capacitors connected to the secondary busbars of the supply transformers is chosen equal to the reactive power consumption of the supply transformers.

Of the methods used, the closest is the connection of protective RC circuits [3], used mainly to limit high-frequency overvoltages on high-voltage electric motors that occur when they are turned on and off. The disadvantage of this method is the consumption of electricity on resistors that are constantly energized, and the inapplicability of this method to protect electrical equipment with a longer exposure time (fractions and units of seconds).

In the proposed method for reducing overvoltages in medium voltage electrical networks, a significant distinguishing feature is laid: the time constant τ of the damping RC circuit is obviously greater than the period of the current frequency of the industrial network.

The arresters of the series of arrester arresters and arresters are designed to limit short-duration surge voltages and cannot operate at frequencies comparable to an industrial network current frequency of 50 Hz [4].

Information confirming the possibility of carrying out the invention

Achievable technical result from the implementation and application of the method of reducing overvoltages in medium voltage electrical networks with low earth fault currents is to reduce to the technically possible minimum the main type of damage, which is the failure of voltage measuring transformers due to arising ferroresonance phenomena during transient conditions [5].

In order to prevent the failure of the above equipment in accordance with the proposed method, it is necessary to reduce the multiplicity of overvoltages, as well as the rate of change of voltage on the phases of the network during switching, OZZ, etc. To achieve this goal, in the developed method for reducing overvoltages in medium voltage electric networks, it is proposed to connect a three-phase capacitor bank assembled according to the "star with zero output" circuit connected between the neutral output and ground to the medium voltage bus sections (phases of the secondary voltage of the supply transformer) a resistor, which together with the battery capacities in non-stationary modes forms a damping chain.

The developed technical solution can significantly reduce overvoltage and protect the installed equipment from the effects of the OZZ, etc. An additional effect of the implementation of the proposed technical solution is to reduce the power consumption of the supply transformer and losses in power lines, obtained by compensating the reactive power consumption of the transformer, the aforementioned capacitor bank. For this, the power of the capacitor bank is selected equal to the power consumed by the transformer.

Information sources

1. Khalilov F.Kh. Overvoltage classification. Internal overvoltage. Tutorial. Publication of the NOU "Center for Energy Personnel Training", St. Petersburg, 2012. 80 p.

2. Non-linear surge suppressor. Utility Model Patent No. 145042. Published September 10, 2014

3. Combined three-phase resistive-capacitive surge suppressor. Patent for invention No. 2394326. Published July 10, 2010

4. Surge arrester containing at least one discharge element, such as a varistor. Patent for invention No. 2407087. Published 03/20/2010

5. Fishman B.C. Voltage transformers. Ways to eliminate ferroresonance phenomena // News of Electrical Engineering. 2010. No6 (66).

Claims (1)

A method of reducing overvoltages in medium voltage electric networks, which consists in connecting to the secondary voltage phases of the supply transformer an electric network of damping RC circuits, capacitor banks assembled according to the star-zero circuit, the zero output of which is connected to the ground via a resistor, characterized in that the total power of the capacitors connected to the secondary voltage buses of the supply transformers is equal to the reactive power consumption of the said transformers, as well as the constant time tim RC-chain obviously higher than the frequency of a power supply current.

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