



































International Journal of Biological Engineering and Agriculture


American Journal of Science and  

Learning for Development 
 

Volume 1 | No 2 | Dec-2022 

 

 

 
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Methods of Protection against Single-Phase Short Circuit to Earth in 

Networks with Isolated Neutral 

 
 
1
Nurov Xomid,

 2
Amrullayev Behzod  

 

 
1 

Lecturer at Bukhara Institute of Natural Resources Management 
2 

Student of Bukhara Institute of Natural Resources Management 
  
  
 

Abstract: With the development of the energy industry, various types of problems began to arise 

related to the transmission, distribution, consumption, improvement of the quality of transmitted 

energy, as well as the problem of protecting networks from various types of damage. One of the 

problematic tasks of the power transmission system in networks with isolated neutral is protection 

against single-phase short circuits to earth. 
 
Keywords: Isolated neutral, single-phase earth fault, neutral mode, zero sequence, protection, 

overhead lines. 

 

Methods:  One of the most common types of damage on power lines is a  single-phase earth fault - 

this is a type of damage when one of the phases of a three-phase system is shorted to earth or to an 

element electrically connected to earth. The processes occurring in the network during such a short 

circuit largely depend on the mode of operation of the neutral of this network. 

Cases of single-phase earth faults can be very different, but they all occur due to a violation of the 

transmission equipment of electrical installations, especially on cable or overhead power lines. 

Insulation failure can occur due to its aging, as well as mechanical consequences at the electrical 

installation, most often this occurs during significant earthworks or a tree branch falling on overhead 

lines, etc. 

In the CIS countries, in networks with a voltage of 6-35 kV, the neutral mode isolated from the 

ground is used. 

Methods of the last century 

Individual protections are the simplest, but at the same time they have a high percentage of false 

positives. 

1. Zero sequence current protection. 

The simplest and most common of the protection against SPZ is the current individual protection of 

the zero sequence, which reacts to the zero sequence current (hereinafter referred to as NP) of the 

operating frequency. However, to ensure the conditions of selectivity of action, these protections 

must have a detuning from the feeder's own capacitive current, taking into account the surges of the 

capacitive current at the moment of switching on, it limits the sensitivity of the protection. 

 



 

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Figure 1. 

Zero-sequence equivalent circuit of a transformer with a star-delta connection of the transformer 

windings 

In general, an individual non-directional overcurrent protection against SPCA can only be effective 

in installations with a large number of connections connected to the section, each of which has a 

small capacitive current. Then detuning from this current will not lead to an unacceptable decrease in 

sensitivity. This case is typical, for example, for workshops of enterprises with a large number of 

low-power electric motors connected by short cables. However, if an arcing reactor is installed in 

such a network, then protection built according to this principle is not able to ensure stable operation, 

since the capacitive current of 50 Hz of the damaged connection will be compensated. 

 

 

 

 

 

 

 

 

Figure 2. Neutral grounding through resistance 

2. Current directional zero sequence protection. 

Protections using only one PV current signal, despite their simplicity, are significant phenomena that 

lead to their non-selective actions. In the course of a consistent increase in efficiency, two protective 

signals began to be used - the current and voltage of the NP to determine the directions. A large 

number of directional protections react to the direction of the zero sequence power in the set mode. 

The sensitivity of such protections is higher than non-directional ones, since their current is 

disconnected only from the unbalance current in the maximum operating mode, and detuning of 

protection from its own capacitive current line is not required, since it is globally detuned from this 

current. A common disadvantage of the protective type is non-selective actions or failures in actions 

during intermittent arc faults. 

3. Zero sequence active power protection. 

1. Another method for determining a faulty connection from the current and voltage signals of the 

LP is the calculation of the active power of the zero sequence in the steady state. Protections 

implemented according to this principle have a higher stability of operation in modes with an 

intermittent arc at the fault site and are more tuned against capacitive current surges in transients. It 

is possible to ensure the stable functioning of such protections mainly in networks with resistive 

neutral grounding. 



 

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4.  Zero sequence protection for higher harmonic currents. 

Since the main disadvantage of protections that use currents and voltages of industrial frequency NP 

is that they are not able to work in networks with a compensated neutral due to the lack of a stable 

useful signal with a frequency of 50 Hz, protections against single-phase earth faults have been 

developed that respond to higher harmonics of electrical quantities. During arc faults, the content of 

higher harmonics in the network increases sharply, especially in the current of the damaged line, 

where their proportion is much greater than in the zero sequence currents of undamaged lines. These 

processes are observed in networks of all types of neutral grounding. 

General disadvantages of devices made using higher harmonics: 

 probability of detection in case of SP by transient resistances; 

 Instability of the composition and the highest level of harmonics in the NP current. 

Features of detecting non-excitability when detecting ground faults and excitation in case of 

violations of the absolute measurement organs, the harmonic increases mainly at large substations 

and power plants with a large number of connections. 

5.   Protection that reacts to the imposed current. 

To increase the stability of protection against single-phase earth faults that respond to a non-

commercial frequency fault current, protection has been developed that responds to an imposed 

current. The superimposed current can be either above or below the mains frequency. To create a 

current of increased frequency, you can use a non-linear resistance connected between the network 

neutral and earth. However, such an arrangement greatly increases the cost of such protections and 

may reduce the reliability of the protection. It can also be noted that a significant high-frequency 

component may be present in the connection currents in normal mode. First of all, this applies to 

networks associated with industries that have a non-linear load. In such cases, the described method 

of protection is unsuitable. In addition, as some studies show, harmonics with a frequency of 100 Hz 

appear almost 2 times more often than, for example, with a frequency of 25 Hz and their amplitudes 

are much larger. 

 

Figure 3. 

Network with isolated neutral - short-circuit currents on ground phase L3 

The main disadvantages of protections that respond to an imposed current with a frequency below 

the industrial one include the need to include a special device in the network neutral to create a 

control current, as well as the impact on stability. Protection that increases with decreasing operating 

frequency, complication of the primary switching circuit due to the need to connect a superimposed 

current source and the complexity of connecting an auxiliary current source when using several in a 



 

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network installed at different sites. Also, there are difficulties in detuning from its own harmonic 

components at external arc currents of discontinuous circuits, in which the current spectrum depends 

on the parameters of the network and the mode of grounding its neutral. 

References 

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kommutatsionnyh-ustroystv article/n/izuchenie-kommutatsionnyh-ustroystv 

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https://cyberleninka.ru/article/n/izuchenie-kommutatsionnyh-ustroystv
https://cyberleninka.ru/article/n/izuchenie-kommutatsionnyh-ustroystv/viewer
https://cyberleninka.ru/article/n/izuchenie-kommutatsionnyh-ustroystv/viewer

