scholarly journals A way to increase the operating efficiency of admittance earth fault protection in 6–10 kV cable networks with isolated neutral

Vestnik IGEU ◽  
2018 ◽  
pp. 20-30
Author(s):  
V.A. Shuin ◽  
◽  
E.A. Vorobyova ◽  
O.A. Dobryagina ◽  
T.Yu. Shadrikova ◽  
...  
Keyword(s):  
Operating Efficiency ◽  
Earth Fault ◽  
Cable Networks ◽  
Fault Protection ◽  
Isolated Neutral

scholarly journals Dynamic stability of the functioning of current earth fault directional protection in networks with isolated neutral

Vestnik IGEU ◽  
2019 ◽  
pp. 30-41
Author(s):  
Yu.D. Kutumov ◽  
V.V. Tyutikov ◽  
T.Yu. Shadrikova ◽  
V.A. Shuin
Keyword(s):  
Dynamic Stability ◽  
Electrical Networks ◽  
Medium Voltage ◽  
Earth Fault ◽  
Fault Protection ◽  
Zero Sequence ◽  
Protection Devices ◽  
High Dynamic ◽  
Isolated Neutral ◽  
Zero Sequence Voltage

In distribution 6–10 kV networks with an insulated neutral for earth fault protection, zero sequence current directional protection devices are commonly used. According to the operation data, the main disadvantage of such kind of protection is the possibility of their functioning failures in transient conditions with the most dangerous for network intermittent arc earth faults. It is known that most earth faults in 6–10 kV networks, primarily in the initial stage of insulation damage, have an intermittent arc. Operation failures of zero sequence current directional protection in case of arc faults reduce the operational reliability of the protected network and, as a result, the reliability of power supply to consumers. Nowadays, new developments of electrical power systems relay protection devices, including earth fault protection of medium voltage distribution electrical networks, are implemented only on a microprocessor base. Therefore, the selection and justification of the implementation principles of zero sequence current directional protection which can provide high dynamic stability of functioning is a relevant objective. When analyzing the dynamic stability of the functioning of zero sequence directional current protection, regarding the complexity of transients during intermittent arc earth faults in medium voltage electrical networks with an isolated neutral, the simulation in Matlab using SimPowerSystem and Simulink was carried out. This study focuses on transient currents and voltages as the main factor influencing dynamic stability of the functioning of zero sequence current directional protection. The impact of other factors, for example, the inaccuracies of the primary zero sequence current and voltage transducers, the scheme of formation of compared quantities, etc. was not taken into account in simulation models. The study has allowed determining the causes of possible functioning failures of digital current earth fault directional protection in dynamic operation modes. It has been shown that the usage of orthogonal components of fundamental frequency of zero sequence voltage and current in current directional protection devices eliminates the failure of their operation with any kind of arc earth faults. To ensure high dynamic stability of operation under the influence of transients during arc intermittent earth faults, current directional protection for this type of damage should be performed on the basis of monitoring the phase relationships of the fundamental frequency components of 50 Hz of zero sequence voltage and current, but not their full values.

scholarly journals The influence of higher harmonics on transients during arcing earth faults in 6–10 kV cable networks with insulated neutral

Vestnik IGEU ◽  
2020 ◽  
pp. 30-40
Author(s):  
V.A. Shuin ◽  
O.A. Dobryagina ◽  
Yu.D. Kutumov ◽  
T.Yu. Shadrikova
Keyword(s):  
Root Mean Square ◽  
Fault Location ◽  
Fault Current ◽  
Mean Square ◽  
Higher Harmonics ◽  
Capacitive Current ◽  
Earth Fault ◽  
Cable Networks ◽  
Isolated Neutral ◽  
Transient Voltages

Alternating arc single-phase earth faults in 6–10 kV cable networks with insulated neutral are accompanied by over-voltages and a significant increase in the root-mean-square current value at the fault location. When evaluating the specified parameters of transient voltages and currents during arc earth faults, as a rule, the presence of higher harmonics in earth fault current is not taken into account. At the same time, in modern systems of industrial and urban electricity supply, the customers with nonlinear current-voltage characteristics are widely used. They caused a significant increase in the share of higher harmonics in earth fault currents of more than 40–55 % of the total network capacitive current determined at the fundamental frequency of 50 Hz. With such correlations between the levels of the fundamental frequency component and higher harmonics, higher harmonics can have a significant effect on the conditions of quenching and reignition of grounding arcs and, accordingly, on the parameters of transient voltages and currents in intermittent arc earth faults. Simulation in Matlab with SimPowerSystem was used to study the influence of higher harmonics in earth fault current on transient voltages and currents in 6–10 kV cable networks with insulated neutral. Modeling of alternating arc faults was carried out on the basis of existing theories of the occurrence of maximum overvoltages during arc earth faults in networks with isolated neutral developed by W. Petersen and Belyakov N.N. On the basis of computational experiments on simulation models of 6–10 kV cable networks with different values of the total capacitive current, it was shown that in the case of arc alternating earth faults the presence of higher harmonics in the earth fault current can lead to an increase in the multiplicity of overvoltages in intact phases by 13–16 % and the root-mean-square value of the current at the fault location by up to 22 %. Higher harmonics in earth fault current can have a significant effect on the conditions of extinction and reignition of the grounding arc, leading to an increase in the time of its extinction, the multiplicity of the maximum overvoltage level and root-mean-square value of fault current during alternating arc faults, which should be taken into account when evaluating the network efficiency in the isolated neutral mode.

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