1. Introduction

The implementation of modern technological processes in quarries, which are directly related to the growth of unit capacity of stripping and mining machines, is making increasingly stringent requirements to ensure the safety and security of the operation of electrical system [1, 2].

However, the increase in the length of electrical networks, which feed stripping and mining machines, increases the likelihood of single-phase ground fault, which, as a rule, is the main cause of the interruption of power supply. Relay protection and automation actions allow maintaining the continuity of power supply only if it is possible to control periodic insulation parameters mains phases with respect to ground.

Among the range of issues related to ensuring security of supply of electric power-electrified mining equipment and the safety of its operation, there is a

development of methodology for determining the insulation parameters, which occupies a special place, as the results of the method used are derived from the main provisions of organizational and technical measures that promote a culture of service of the internal power supply of mining enterprises. The importance of developing the method to determine the insulation value is also determined by the fact that it can be used in other industries where there is three-phase electrical network with isolated neutral with voltages up to and above 1000 V.

obsolescence of much of the equipment. Intensive increase in productivity mining leads to complication of the network configuration, which significantly affects the state of electrical networks, reducing the reliability of their operation. At the same time, there is an increase in the number of damages in electrical networks, which

Special Issues of Ensuring Electrical Safety in Networks with Isolated Neutral Voltage…

During coal mining, open-pit mining machines and equipment operate in harsh conditions, which are caused by the constant movement of the front of the mining operations, vibration, dust, and climate-meteorological conditions. This leads to the fact that during operation, the electrical insulation is subjected to a change in the electrical network, changing the properties of the electrical insulating materials. This fact affects the decrease of electrical resistance and electric strength [10]. The main factors of aging of the insulation are operating voltage, transient increase in the voltage at the external and internal overvoltages, oxidation processes caused by the ionization of air and leading to the development of a surface discharge, mechanical effects, bulk and surface contamination, heating, and humidification, influencing the quality of the voltage caused by the use of controlled semiconductor converters. Mining machines' component failure occurs due to changes in the nominal loads; data equipment failures may lead to production

The aforementioned factors intensify the process of reducing the insulation resistance phase of electrical network with respect to earth in coal extraction. Reduced insulation resistance phase electrical network with respect to earth increases the likelihood of the emergency operating modes of the operation of electrical installations, which may be a consequence of electric shocks to persons. With the exception of electric shock, it is necessary to ensure a high level of insulation in a network with an isolated neutral voltage up to 1000 V, through activities related to the systematic and effective control of the condition of insulation. This is one of the main areas to ensure electrical safety in the specific condi-

According to the "safety regulations for electrical installations," what is required is the mandatory application of the automatic control of insulation with the action off, with periodic measurements of insulation resistance phase of electrical network

In the development of coal deposits, there is a growing number of electric shocks mainly due to the weak formulation of organizational and technical measures for inspection, repair, and the condition of insulation in electrical networks and electrical equipment. Timely determination of the degree of the deterioration of the insulation can prevent equipment failure [15]. It should be noted that the operational personnel rely on protection against current leakage, which in the operation of electrical networks and electrical equipment may be damaged or artificially out

Great contributions to the definition of criteria for electrical scientists have been

In general, the analysis of research into condition of insulations and single-phase ground fault current showed that used residual current devices (RCDs) in underground coal mining and mining meet the criteria for electro security under normal

made by the Moscow State Mining Academy, University of California, Georgia State University. One criterion for electrical safety in emergency operation is the limit value of the current flowing through the human body Ih = 6.0 mA, with the contact voltage Uc = 20.0 V with the duration of the current flowing through the human body t > 1.0 s, with the main frequency f = 50 Hz, a three-phase network

are the major causes of wear and the aging network isolation [9].

DOI: http://dx.doi.org/10.5772/intechopen.81384

tions in the development of coal deposits in an open way [12].

with an isolated neutral voltage up to 1000 V [16].

with respect to earth in electrical installations up to 1000 V [13, 14].

downtime [11].

of operation.

49

For experimental studies of the state of insulation of three-phase electrical networks with isolated neutral with voltages up to and above 1000 V, a number of methods were proposed [1–9], taking into account the inherent specific characteristics in the internal power supply of open-cast mining. For the insulation parameters measuring methods, a number of requirements are presented, namely:


Based on the analysis of existing methods [1, 2], considering the aforementioned requirements for experimental research of insulation parameters of three-phase electrical networks with isolated neutral, it was concluded that the methods developed earlier are not fully met the essential requirements. Therefore, at present, in mines, previously proposed methods were not used as a primary means of prevention, ensuring uninterrupted power supply and operational safety of electrical installations.

In this regard, there are problems of further improvement of means of controlling insulation parameters of electrical networks in conjunction with the implementation of preventive measures and periodic measurements in different operating conditions. The method of determining the phase insulation parameters to earth of electrical networks must not affect the operation of the electricity system, and the calculation of insulation parameters must contain a minimum of computation.

In practice of operation of electrical networks with isolated neutral with voltage up to 1000 V and above, it is necessary to know the value of the insulation parameters by which the organizational and technical measures are developed to ensure the safety and security of the electricity supply of mining enterprises.

One of the most important issues in the mining industry is the problem of increasing the reliability of power supply systems and reduced level of electrical safety for electrical installations in mines. This condition is associated with physical

#### Special Issues of Ensuring Electrical Safety in Networks with Isolated Neutral Voltage… DOI: http://dx.doi.org/10.5772/intechopen.81384

obsolescence of much of the equipment. Intensive increase in productivity mining leads to complication of the network configuration, which significantly affects the state of electrical networks, reducing the reliability of their operation. At the same time, there is an increase in the number of damages in electrical networks, which are the major causes of wear and the aging network isolation [9].

During coal mining, open-pit mining machines and equipment operate in harsh conditions, which are caused by the constant movement of the front of the mining operations, vibration, dust, and climate-meteorological conditions. This leads to the fact that during operation, the electrical insulation is subjected to a change in the electrical network, changing the properties of the electrical insulating materials. This fact affects the decrease of electrical resistance and electric strength [10].

The main factors of aging of the insulation are operating voltage, transient increase in the voltage at the external and internal overvoltages, oxidation processes caused by the ionization of air and leading to the development of a surface discharge, mechanical effects, bulk and surface contamination, heating, and humidification, influencing the quality of the voltage caused by the use of controlled semiconductor converters. Mining machines' component failure occurs due to changes in the nominal loads; data equipment failures may lead to production downtime [11].

The aforementioned factors intensify the process of reducing the insulation resistance phase of electrical network with respect to earth in coal extraction. Reduced insulation resistance phase electrical network with respect to earth increases the likelihood of the emergency operating modes of the operation of electrical installations, which may be a consequence of electric shocks to persons. With the exception of electric shock, it is necessary to ensure a high level of insulation in a network with an isolated neutral voltage up to 1000 V, through activities related to the systematic and effective control of the condition of insulation. This is one of the main areas to ensure electrical safety in the specific conditions in the development of coal deposits in an open way [12].

According to the "safety regulations for electrical installations," what is required is the mandatory application of the automatic control of insulation with the action off, with periodic measurements of insulation resistance phase of electrical network with respect to earth in electrical installations up to 1000 V [13, 14].

In the development of coal deposits, there is a growing number of electric shocks mainly due to the weak formulation of organizational and technical measures for inspection, repair, and the condition of insulation in electrical networks and electrical equipment. Timely determination of the degree of the deterioration of the insulation can prevent equipment failure [15]. It should be noted that the operational personnel rely on protection against current leakage, which in the operation of electrical networks and electrical equipment may be damaged or artificially out of operation.

Great contributions to the definition of criteria for electrical scientists have been made by the Moscow State Mining Academy, University of California, Georgia State University. One criterion for electrical safety in emergency operation is the limit value of the current flowing through the human body Ih = 6.0 mA, with the contact voltage Uc = 20.0 V with the duration of the current flowing through the human body t > 1.0 s, with the main frequency f = 50 Hz, a three-phase network with an isolated neutral voltage up to 1000 V [16].

In general, the analysis of research into condition of insulations and single-phase ground fault current showed that used residual current devices (RCDs) in underground coal mining and mining meet the criteria for electro security under normal

development of methodology for determining the insulation parameters, which occupies a special place, as the results of the method used are derived from the main provisions of organizational and technical measures that promote a culture of service of the internal power supply of mining enterprises. The importance of developing the method to determine the insulation value is also determined by the fact that it can be used in other industries where there is three-phase electrical network

For experimental studies of the state of insulation of three-phase electrical networks with isolated neutral with voltages up to and above 1000 V, a number of methods were proposed [1–9], taking into account the inherent specific characteristics in the internal power supply of open-cast mining. For the insulation parame-

1. Measurements should be carried out without interruption in the supply of

2. The process of measurement should not cause damage to the insulation of

3. The measurements must be carried out using a small amount of electrical

4.Execution of determining the insulation parameters should be safe both for

5. Measurements of baseline values should be sufficiently accurate and if possible

Based on the analysis of existing methods [1, 2], considering the aforementioned requirements for experimental research of insulation parameters of three-phase electrical networks with isolated neutral, it was concluded that the methods developed earlier are not fully met the essential requirements. Therefore, at present, in mines, previously proposed methods were not used as a primary means of prevention, ensuring uninterrupted power supply and operational safety of electrical

In this regard, there are problems of further improvement of means of controlling insulation parameters of electrical networks in conjunction with the implementation of preventive measures and periodic measurements in different operating conditions. The method of determining the phase insulation parameters to earth of electrical networks must not affect the operation of the electricity system, and the calculation of insulation parameters must contain a minimum of

In practice of operation of electrical networks with isolated neutral with voltage up to 1000 V and above, it is necessary to know the value of the insulation parameters by which the organizational and technical measures are developed to ensure

One of the most important issues in the mining industry is the problem of increasing the reliability of power supply systems and reduced level of electrical safety for electrical installations in mines. This condition is associated with physical

the safety and security of the electricity supply of mining enterprises.

researchers and for personnel servicing electrical systems.

have a short duration of works on measurement.

6.Accuracy of the method must not exceed 10%.

ters measuring methods, a number of requirements are presented, namely:

with isolated neutral with voltages up to and above 1000 V.

electrical networks and electrical accidents.

electricity to consumers.

Industrial Engineering

equipment and appliances.

installations.

computation.

48

and emergency operating modes in a three-phase network with isolated neutral voltages up to 1000 V.

Frequent movement of flexible cables supplying mobile mining machines leads to mechanical deformation and damage. Thus, attendants are at risk of sustaining electric shocks as they work with cable, electrical equipment, and the metal structure. The number of electrical shocks in an electrical installation is in direct proportion to the frequency of damage to electrical equipment. In this way, more than 80% of electrical shocks are related to direct contact between a man and current-carrying parts, while 3–10% are related to contact between the enclosures of electrical equipment at the time of the existence of single phase-to-

Special Issues of Ensuring Electrical Safety in Networks with Isolated Neutral Voltage…

According to the mine works regulations, safety shutdown is obligatory at mining enterprises. Safety shutdown is fast-operating protection, which automatically switches off the electric equipment under 1000 V when the risk of electric shock is present [22]. This hazard can occur as a result of case-to-phase fault, reduction of phase-to-ground insulation resistance below a certain value, and live-line bare-hand touching [23]. In such cases, residual current devices provide rapid shutdown of the power section. The response time of modern residual current devices (RCDs) does

To a large extent, the reliability of the electric equipment and the safety of its services depend on the condition of the insulation of live parts of electric equipment [25]. Insulation damage is the major source of accidents and the cause of many electrical shocks with differing levels of severity, as well as fatalities. Insulation monitoring in electrical networks with insulated neutral under 1000 V at mining enterprises is carried out using automatic insulation monitoring devices, such as AIMD-380s, mining protection devices, such as MPD, devices to protect networks from leakage with automatic compensation of capacitive component of leakage current (e.g., PDAC-380), and insulation monitoring devices A-ISOMETER of

Automatic insulation monitoring devices are designed to protect people from electric shocks, continuously monitor insulation resistance, and cut off three-phase electric networks with isolated neutral of 50 Hz alternating current in the case of resistance reduction between their phases and earth up to dangerous level. Automatic compensation of the capacitive component of leakage current is used in leakage current protection devices like PDAC, unlike automatic insulation moni-

On excavators of mining, enterprises use residual current devices such as AIMD, which are designed for mine electric networks, that is, for deep mining. Mine electric networks under 1000 V contain long-distance cable lines, where total admittance of insulation measures is much like capacity admittance of network insulation and active admittance of isolation is lower than total and capacity admittance of isolation. As such, in mine networks, the current in single phase-to-earth fault exceeds the current of the RCD set point. This provides people with effective protection from electric shocks. The effectiveness of RCD in mine electrical networks under 1000 V is shown in the work of professor

In the mining industry, it is not uncommon for people to receive electric shocks during maintenance work of excavators and drill-rings when extracting minerals. There are, as yet, no causal inferences of RCD ineffectiveness to protect people from electric shocks during operation of excavators and drill-rings. In order to improve the efficiency of residual current devices, research should be conducted on the condition of insulation in three-phase electric networks with isolated neutral

earth fault [21].

not exceed the time of let-go current supply [24].

DOI: http://dx.doi.org/10.5772/intechopen.81384

IRDH575 (Bender) series as well as a number of others.

toring devices, such as AIMD [26].

under 1000 V on the excavator.

Manoilov [27].

51

In excavator mining, the electrical network voltage up to 1000 V does not contain lines more than 10 m long, and therefore, the data network is similar to the networks of electric arc furnaces, which are called short. Studies on the condition of insulations in the development of coal deposits and mining open pits in short networks up to 1000 V on excavators are not sufficient to be produced. Installed residual current devices in short networks up to 1000 V excavators have not been studied in relation to the criteria for electric normal and emergency operating modes [17].

Studying the technical parameters of the residual current devices for compliance with electrical safety criteria of normal and emergency operating modes in the three-phase electrical short network with an isolated neutral voltage up to 1000 V is necessary to research the condition of insulation.

The practice of electrical networks up to 1000 V in the development of coal deposits in the enterprise shows a lack of insulation resistance measurement techniques, and if so, then the insulation resistance measurement is made, usually very irregularly with large errors. The most widely used method to measure is found by applying the insulation resistance of the measuring device Megger [1].

It should be noted that the results of the measurements of Megger providing "electric installation code" (EIC) [18] and "rules of technical operation of electrical installations" do not correspond to the real values of the insulation resistance of the network, since the measurements are made in the absence of a working line voltage and disconnected power consumers [19].

Using a Megger measure at low values of insulation resistance in the electrical network and disconnected power consumers allows damage to be established qualitatively. It follows that the use of Megger as a means to assess the conditions of electrical safety for electrical installations is insufficient, since it is impossible to determine the resistance, reactance, and impedance of phase insulation of electrical network with respect to earth under the working voltage [1].

According to the EIC, the rate on the insulation resistance shall not be less than 0.5 MOhm ohmic resistance in the individual circuit element and the electrical network appliance. It is not possible to assess the state of the insulation as a whole. Therefore, the norm EIC relative to 0.5 MW ohmic resistance cannot be accepted as a criterion for operational insulation monitoring conditions and, therefore, as a measure of electrical safety, since from the point of view of safety production work on electrical impedes an evaluation of the insulation and its components [18].

On the basis of the foregoing information, the main task of studying the state of electrical insulation in the development of coal deposits' open method is to determine the main parameters of the insulation of the electrical networks up to 1000 V and to identify factors influencing the state of insulation in conditions of single and bucket wheel excavators and drilling rigs.

Mining companies are currently equipped with high-electrified mining machines that provide high productivity. These companies are heavy consumers of electricity. The power of the electrical installations in the modern excavators reaches 20 MW or more and can be compared with the power of a large industrial company. Indeed, in these companies, reliable and continuous power supply to the electrical receiver depends largely on the condition of the electrical equipment in operation, as well as the intensity of the electrical damage and electrical networks [20].

Special Issues of Ensuring Electrical Safety in Networks with Isolated Neutral Voltage… DOI: http://dx.doi.org/10.5772/intechopen.81384

Frequent movement of flexible cables supplying mobile mining machines leads to mechanical deformation and damage. Thus, attendants are at risk of sustaining electric shocks as they work with cable, electrical equipment, and the metal structure. The number of electrical shocks in an electrical installation is in direct proportion to the frequency of damage to electrical equipment. In this way, more than 80% of electrical shocks are related to direct contact between a man and current-carrying parts, while 3–10% are related to contact between the enclosures of electrical equipment at the time of the existence of single phase-toearth fault [21].

According to the mine works regulations, safety shutdown is obligatory at mining enterprises. Safety shutdown is fast-operating protection, which automatically switches off the electric equipment under 1000 V when the risk of electric shock is present [22]. This hazard can occur as a result of case-to-phase fault, reduction of phase-to-ground insulation resistance below a certain value, and live-line bare-hand touching [23]. In such cases, residual current devices provide rapid shutdown of the power section. The response time of modern residual current devices (RCDs) does not exceed the time of let-go current supply [24].

To a large extent, the reliability of the electric equipment and the safety of its services depend on the condition of the insulation of live parts of electric equipment [25]. Insulation damage is the major source of accidents and the cause of many electrical shocks with differing levels of severity, as well as fatalities. Insulation monitoring in electrical networks with insulated neutral under 1000 V at mining enterprises is carried out using automatic insulation monitoring devices, such as AIMD-380s, mining protection devices, such as MPD, devices to protect networks from leakage with automatic compensation of capacitive component of leakage current (e.g., PDAC-380), and insulation monitoring devices A-ISOMETER of IRDH575 (Bender) series as well as a number of others.

Automatic insulation monitoring devices are designed to protect people from electric shocks, continuously monitor insulation resistance, and cut off three-phase electric networks with isolated neutral of 50 Hz alternating current in the case of resistance reduction between their phases and earth up to dangerous level. Automatic compensation of the capacitive component of leakage current is used in leakage current protection devices like PDAC, unlike automatic insulation monitoring devices, such as AIMD [26].

On excavators of mining, enterprises use residual current devices such as AIMD, which are designed for mine electric networks, that is, for deep mining. Mine electric networks under 1000 V contain long-distance cable lines, where total admittance of insulation measures is much like capacity admittance of network insulation and active admittance of isolation is lower than total and capacity admittance of isolation. As such, in mine networks, the current in single phase-to-earth fault exceeds the current of the RCD set point. This provides people with effective protection from electric shocks. The effectiveness of RCD in mine electrical networks under 1000 V is shown in the work of professor Manoilov [27].

In the mining industry, it is not uncommon for people to receive electric shocks during maintenance work of excavators and drill-rings when extracting minerals. There are, as yet, no causal inferences of RCD ineffectiveness to protect people from electric shocks during operation of excavators and drill-rings. In order to improve the efficiency of residual current devices, research should be conducted on the condition of insulation in three-phase electric networks with isolated neutral under 1000 V on the excavator.

and emergency operating modes in a three-phase network with isolated neutral

In excavator mining, the electrical network voltage up to 1000 V does not contain lines more than 10 m long, and therefore, the data network is similar to the networks of electric arc furnaces, which are called short. Studies on the condition of insulations in the development of coal deposits and mining open pits in short networks up to 1000 V on excavators are not sufficient to be produced. Installed residual current devices in short networks up to 1000 V excavators have not been studied in relation to the criteria for electric normal and emergency operating

Studying the technical parameters of the residual current devices for compliance

with electrical safety criteria of normal and emergency operating modes in the three-phase electrical short network with an isolated neutral voltage up to 1000 V is

applying the insulation resistance of the measuring device Megger [1].

network with respect to earth under the working voltage [1].

The practice of electrical networks up to 1000 V in the development of coal deposits in the enterprise shows a lack of insulation resistance measurement techniques, and if so, then the insulation resistance measurement is made, usually very irregularly with large errors. The most widely used method to measure is found by

It should be noted that the results of the measurements of Megger providing "electric installation code" (EIC) [18] and "rules of technical operation of electrical installations" do not correspond to the real values of the insulation resistance of the network, since the measurements are made in the absence of a working line voltage

Using a Megger measure at low values of insulation resistance in the electrical network and disconnected power consumers allows damage to be established qualitatively. It follows that the use of Megger as a means to assess the conditions of electrical safety for electrical installations is insufficient, since it is impossible to determine the resistance, reactance, and impedance of phase insulation of electrical

According to the EIC, the rate on the insulation resistance shall not be less than 0.5 MOhm ohmic resistance in the individual circuit element and the electrical network appliance. It is not possible to assess the state of the insulation as a whole. Therefore, the norm EIC relative to 0.5 MW ohmic resistance cannot be accepted as a criterion for operational insulation monitoring conditions and, therefore, as a measure of electrical safety, since from the point of view of safety production work on electrical impedes an evaluation of the insulation and its

On the basis of the foregoing information, the main task of studying the state of electrical insulation in the development of coal deposits' open method is to determine the main parameters of the insulation of the electrical networks up to 1000 V and to identify factors influencing the state of insulation in conditions of single and

Mining companies are currently equipped with high-electrified mining machines that provide high productivity. These companies are heavy consumers of electricity. The power of the electrical installations in the modern excavators reaches 20 MW or more and can be compared with the power of a large industrial company. Indeed, in these companies, reliable and continuous power supply to the electrical receiver depends largely on the condition of the electrical equipment

in operation, as well as the intensity of the electrical damage and electrical

necessary to research the condition of insulation.

and disconnected power consumers [19].

bucket wheel excavators and drilling rigs.

voltages up to 1000 V.

Industrial Engineering

modes [17].

components [18].

networks [20].

50
