Ganiyeva N.A.
RESEARCH OF TRANSIENT PROCESSES ARISING DURING SINGLE-PHASE EARTH FAULT *
Аннотация:
purpose of the work. Research of transient processes that occur during single-phase earth faults. This article discusses neutral isolated networks, as well as networks with compensation for capacitive currents of a single-phase earth fault. In addition, the article analyzes the action of the arc quenching coil. Methods for restoring voltage in the circuit are presented. At the end of the article, a general conclusion is given
Ключевые слова:
networks, overvoltage, capacity, ground, winding
УДК 621
Ganiyeva N.A.
laboratory assistant
Azerbaijan State Oil and Industry University
(Baku, Azerbaijan)
RESEARCH OF TRANSIENT PROCESSES
ARISING DURING SINGLE-PHASE EARTH FAULT
Abstract: purpose of the work. Research of transient processes that occur during single-phase earth faults. This article discusses neutral isolated networks, as well as networks with compensation for capacitive currents of a single-phase earth fault. In addition, the article analyzes the action of the arc quenching coil. Methods for restoring voltage in the circuit are presented. At the end of the article, a general conclusion is given.
Keywords: networks, overvoltage, capacity, ground, winding.
Neutral isolated networks. The vast majority of accidents in 6-35 kV networks occur due to single-phase ground faults and overvoltages. With a long-term short circuit of one phase in networks with an isolated neutral, the voltage in healthy phases increases to a linear voltage –Ul= Uf. Such a voltage does not pose a threat to the network, which at this moment has poor insulation. The vast majority of single-phase earth faults in isolated neutral networks are caused by sparking, and in most cases this process is not permanent. The arc flashes several times until it goes out completely - the arc flash is repeated, as a result of which repeated electromagnetic switching processes occur in the networks and, therefore, extreme voltages arise. The reason for the formation of extreme voltages during repeated flashing of the arc is that when the arc is extinguished, an electric charge remains in the phase capacitances, as a result of which the neutral of the network is displaced. Thus, the magnitude and characteristics of overvoltages determine the conditions for ignition and extinguishing of the arc [1]. Networks with compensation of capacitive currents of single-phase earth fault. Analysis of the operation of the arc quenching coil. The operation of arc quenching coils can be based on two processes:
When the difference from fine tuning is within v=+-5%, the voltage recovery rate differs little from that of fine tuning. Neutral displacement in compensated networks. With fine adjustment of the arc chute, in all cases, reliable extinguishing of the arc of a single-phase earth fault is ensured. However, at this time there is a large displacement of the neutral of the network and, as a result, excess voltages in the phases. Also, this situation usually occurs with excess power and neutral displacement in the network [2]. This position can be explained on the basis of the replacement scheme shown in Fig. 1. In an isolated network with a neutral, the arcing coil is connected in series to the sum of the capacitances and slopes of the network, and the bias voltage of the network neutral is applied to the circuit - U0.
Fig.1. Scheme for compensating the voltage in the arc winding during normal operation
Voltage on the isolated neutral network:
Here:
Normally, even when the wires in the line are horizontal, the capacitances of the phases with respect to earth are not equal. With a horizontal arrangement of wires, the power of the middle phase is 10% less than that of the extreme phases [3].
Thus, if we take C1=C3=Cf and C2=0.9Cf, then according to the equation we get
Fig. 2. Dependence of the bias voltage on the degree of tuning
Neutral offset in ideal setting
at δ=0.05, the neutral bias voltage reaches Uо=0.7Uf. So, the voltage of one of the
phases is reduced to 0.3Uf, and in other phases it increases to 1.5Uf. Under such conditions, losses increase, insulation wear accelerates, and the harmful effect on communication lines increases. at δ=0.05, the neutral bias voltage reaches Uо=0.7Uf. So, the voltage of one of the phases is reduced to 0.3Uf, and in other phases it increases to 1.5Uf. Under such conditions, losses increase, insulation wear accelerates, and the harmful effect on communication lines increases. Decreasing the tuning factor slightly reduces the neutral offset. However, in this case, the state of extinguishing the arc of a single-phase earth fault worsens [4, 5].
Conclusion. Damage to the cable insulation due to irreversible damage of a non-conductive nature drastically reduces the effectiveness of arc extinguishing devices. When one phase is grounded, the insulation of the other two phases remains under the action of an excess voltage equal to the continuous line voltage. This increases the likelihood of two- or three-phase short circuits. In cable lines, in addition, the process of insulation wear also increases sharply. Due to the expansion of networks, the value of single-phase earth fault currents increases, and as a result, the value of the current in the uncompensated high-frequency circuit increases and it becomes difficult to extinguish the arc. Additional measures to limit neutral displacement in compensated networks complicate the operation of the required network.
REFERENCES:
Номер журнала Вестник науки №5 (62) том 1
Ссылка для цитирования:
Ganiyeva N.A. RESEARCH OF TRANSIENT PROCESSES ARISING DURING SINGLE-PHASE EARTH FAULT // Вестник науки №5 (62) том 1. С. 341 - 344. 2023 г. ISSN 2712-8849 // Электронный ресурс: https://www.вестник-науки.рф/article/8038 (дата обращения: 26.04.2024 г.)
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