The Electromagnetic Interference in the Electrical Power Supply System. The long-term variance of the voltage specifications


Ministry of Higher Education and Science of the Russian Federation NOVOSIBIRSK STATE TECHNICAL UNIVERSITY



Vladimir Ya. Olhovskiy, Tatyana V. Myateg, Olga S. Atamanova


THE ELECTROMAGNETIC INTERFERENCE IN THE ELECTRICAL POWER SUPPLY SYSTEM




                THE LONG-TERM VARIANCE OF THE VOLTAGE SPECIFICATIONS




Approved by The Aditorial Board of NSTU as a manual





NOVOSIBIRSK

2019

UDC 621.311.018.33.78:658.26
     O-567

Reviewer:
PhD (Eng.), Assoc. Prof. D.A. Pavluchenko PhD (Phil.), Assoc. Prof. A.I. Bochkarev

The manual was prepared by the Electrical Power Supply Systems Department, the Department of Foreign Languages of Engineering Faculties




       Olhovskiy V.Ya.
O-567 The Electromagnetic Interference in the Electrical Power Supply System. The long-term variance of the voltage specifications: study guide / Vladimir Ya. Olhovskiy, Tatyana V. Myateg, Olga S. Atamanova. - Novosibirsk: NSTU Publishers, 2019. - 66 p.
          ISBN 978-5-7782-3936-4
          The introduced manual is aimed at theoretical and practical training of master students in “Power Engineering” discipline (13.04.02. - Electrical Power Industry and Electrical Engineering). One of the main tasks of the manual is to consolidate the theoretical material studied by the students in the first term of the Master Program. The manual also includes the issues of electromagnetic compatibility in electrical supply systems with the object under study - the interaction of the system “power supply network - consumer”. It allows a student to better understand the physical processes running not only during the interaction of consumer power supply systems and power networks but also during the processes of consumer’s interactions. The authors analyze the quality of consumer electrical power supply on the basis of the system operating conditions in accordance with STANDART 32144-2013.




UDC 621.311.018.33.78:658.26


ISBN 978-5-7782-3936-4

             © Vladimir Ya. Olhovskiy,

               Tatyana V. Myateg, Olga S. Atamanova, 2019 © Novosibirsk State Technical University, 2019

CONTENT


Introduction...............................................................4
1.  Voltage Deviations ....................................................8
   1.1. Main Definitions and Standards.....................................8
   1.2. Estimation of Voltage Deviations ..................................9
   1.3. Techniques of Voltage Deviation Decrease .........................10
   1.4. The Influence of Voltage Deviations on Power Consumer Operation ...10
2.  Voltage Fluctuations .................................................12
   2.1. Main Definitions and Standards....................................12
   2.2. The Ways of Voltage Fluctuations Decrease in the Power Supply Systems ................................................................17
3.  Voltage Non-Sinusoidality.............................................19
   3.1. The Main Definitions and Standards................................19
   3.2. The Currents Non-Sinusoidal of Nonlinear Loads....................22
   3.3. Oscillograms of Some Non-linear Loads Currents ...................23
   3.4. Consumer Damage due to High Harmonics.............................42
   3.5. Rationing of High Harmonics ......................................47
   3.6. The Ways of Voltage High Harmonics Decreasing .....................49
4.  Voltage Unbalance.....................................................51
   4.1. The Main Definition and Norms ....................................51
   4.2. The Ways Voltage Unbalance Decreasing.............................57
5.  Frequency Deviation...................................................61
5.1.  The Main Definition and Standards ..................................61
Conclusion ...............................................................63
Reference ................................................................64

            INTRODUCTION



    The concept of electromagnetic compatibility (EC) can be explained with Figure 1.1. Any mechanical unit, namely current-used equipment, (CUE) operates in environment, which influences its functioning. The environment (Е), with a circuit as a part of it, demonstrates different features characterized by a relevant parameters:
    • climate (temperature, pressure, humidity);
    • mechanical (vibration, impulse load);
    •     electromagnetic (frequency, voltage deviations, voltage fluctuations etc.).
    The mechanical unit is compatible with the environment, if all environmental factors don’t produce interfering effect on its operation or the mechanical component doesn’t interfere the environment. The interfering influences are such influences, which may cause the malfunction of the mechanical unit normal operation.
    The mechanical units (such as consumers) must comply with the requirements to provide compatibility with the environment: the format of climatic modification, the class of protection, reliability (including electrical safety), and also fire and explosion safety. The observation of these and many other requirements while designing, manufacturing, storing, transportation and exploitation of mechanical units provide their proper compatibility with the environment.
    The discipline “POWER SUPPLY” is to provide professional training of Master Program students (13.04.02. - Electrical Power Industry and Electrical Engineering) to meet Federal State Educational Standard of higher professional education.
    EMC is a part of general compatibility, limited by factors of electromagnetic nature (shown by a dotted line in Figure 1.1). The EMC problem can be structurally divided into three parts.
    The electromagnetic compatibility (EC) is a part of total compatibility, confined by the factors having electromagnetic nature (marked by the dotted


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line in Fig. 1.1). The electromagnetic compatibility problem can be divided into three parts.


Fig. 1.1. Electromagnetic compatibility:
          power supply system (EPSS); distribution cabinet (DC); external environment (EE); electric power quality parameters (EPQP), interference from the power network (IFN), conductive electromagnetic interference (CEI); connection (C); electromagnetic pickup (EP); electric consumer (EC); the voltage at the terminals of a consumer (CTV)

    The first of the three parts is determined by the electromagnetic interaction of ES with the power supply network and is the subject of the study for electric supply specialists.
    The second part is connected with electromagnetic fields, which can cause pick up effects in the elements of a power consumer, negatively affecting its work. This part is the basis of the problem of electromagnetic compatibility of radio electronic equipment.
    The third one is the electromagnetic compatibility of the transmission facility, telecommunication and automation.


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    This study guide is devoted to the first part of the electromagnetic compatibility problem, in which the object under study is the interaction of the system “network - power consumer”.
    Historically there can be distinguished three stages in the solution of the electromagnetic compatibility problem in power supply systems in Russia.
    The first stage lasted up to the mid-70s when the mass application of the so-called digital hardware (DH) for production and domestic purposes started. At that time EMC for traditional PCs (electric motor, electro-technological and lighting installations, etc.) was ensured by observing the requirements of GOST on the quality of electricity in 1967 [1]. In this GOST, a list of electric power quality indicators (conducted electromagnetic interference) was established and their maximum permissible values for various PCs were normalized. These interferences included: frequency deviations, voltage deviations and fluctuations, as well as indicators of non-sinusoidality and voltage unbalance.
    The second stage began with mass implementation of digital technical devices (DTD): computers, digital automation devices, telecommunications, etc., and is characterized by active works to ensure their interference immunity. The main feature of DTD in comparison with traditional electric consumers is an extremely low level of signals (voltage, current, duration) used in their logic circuits, and hence the possibility of malfunctions caused by short-term disturbances in the supply voltage. If no special measures are taken, then it is impossible to ensure the DT nonsusceptibility to short-term disturbances, which are defined as conductive electromagnetic interference in power supply (CEIP). Thus, the study of these interferences as high-frequency electromagnetic disturbances in the power supply networks, which can cause malfunctioning of a DT, began approximately from the mid-1970s [2] and is now is formulated in an engineering discipline.
    The third stage began approximately from the middle of the 80th, when the main problems of EEC were solved. Whereby, in accordance with IEC standards, power quality parameters (PQPs) and interference from the power supply network were united by the general term “conductive electromagnetic interference” (CEI) [3].
    The following list of PQPs or CEIs is established in the currently applicable Standard [5]
    The long-term changes in voltage characteristics:
    1) long-term frequency deviations,
    2) slow voltage changes,
    3) voltage fluctuations and flicker,

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    4)  non-sinusoidal voltage,
    5)  voltage unbalance in three-phase systems,
    6)  voltage signals transmitted over electrical networks.
    Random events:
    7)  voltage interruption
    8)  voltage fail and overvoltage,
    9)  pulse overvoltage.
    The first five CEIs form so-called long-term changes in voltage characteristics, which are long-term deviations of voltage characteristics from the nominal values and are caused mainly by load changes or non-linear load effect. The Standard [5] establishes their permissible values.
    The last three CEIs form random events, which are sudden and significant changes of a voltage shape, resulting in the deviation of its parameters from the nominal ones. These voltage changes are caused as a rule by unpredictable events (for example, damage of the electrical network equipment of a consumer) or external environment (for example, weather conditions or actions of the party that is not a user of the electrical network). For the last three, having a rare and random nature, the permissible parameters are not established, but their statistical characteristics obtained by surveying the existing electrical power supply system (EPSS) are given.
    Two types of permissible PQPs values are established: normally permissible (with an integral probability of 0.95) and maximum permissible ones. This means that at long observation intervals, for example, 24 hours, during 0.95 х 24 = 22.8 hours, the PQPs should not exceed the normal permissible values. The rest of the time, 0.05 х 24 = 1.2 hours, these PQPs may exceed the normal permissible values, but should not exceed the maximum permissible ones.

            1. VOLTAGE DEVIATIONS






            1.1. Main Definitions and Standards



    The difference in the U voltage value at a specific point in the network from the nominal one is characterized by 8 Uу steady-state voltage deviation: voltage deviation is the difference between the actual voltage in the steady-state operation of the power supply system and its nominal value. Voltage deviations from nominal values occur due to daily, seasonal and technological changes in the electrical load of consumers; power changes of compensating devices; voltage regulation by generators of power stations and power substations; changes in the scheme and parameters of electrical networks [5].
    Voltage deviations characterize slow changes in the power supply voltage. Indicators of EEQ related to slow changes in power supply voltage are 8 U(_) negative and 8 U(₊) positive deviations of the power supply voltage from the nominal (agreed) value in % [14, p. 6]:

⁸ U(_) =

⁸ U(+) =

U0 _ Um(_) . U 0      .

Um(+)  U0

100,

100,

(1.1)

(1.2)

U

0

where Uₘ₍_₎, Uₘ₍₊₎ are the values of the supply voltage, smaller than U₀ and larger than U₀ , respectively, averaged over a time interval of 10 minutes; U₀ - is voltage equal to the nominal or agreed values.
    In low voltage electrical networks, the Uₙₒₘ nominal power supply voltage in Russia is 380/220 V. In the electrical networks of medium and

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high voltage a Uc matched value of power supply voltage is assumed instead of a nominal one.
    For the above EEQ parameters, the following norms are established: positive and negative voltage deviations at the point of electrical energy transmission should not exceed 10 % of the nominal or matched value of the voltage for 100 % of one week time interval. The established standards for slow changes in power supply voltage refer to 1008 measurement time intervals of 10 minutes each.



            1.2. Estimation of Voltage Deviations



    Voltage deviations during long time intervals (for example, 24 hours) are shown to the utmost with a voltage deviation graph (Fig. 1.2). Two types of 8Uу (t) deviation estimates are used: estimates for limiting values and integral characteristics.

voltaae deviation

flickout

more than Iminute

Fig. 1.2. The voltage deviation characteristic.

    The estimates for the limiting values are 8U^m maximum values with the “+” sign in a minimum load mode and 8U⁽(nm maximum values with the “-” sign in a maximum load mode (Fig. 1.3). Wherein if 8Uᵢₙₘ < 10 % and T1 + T₂
—24— < 0,05, then the example shown in Figure 1.3 is permissible. Here


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Ti + т₂ is the total time during which the 5 Un (t) value exceeds ±5 % normally acceptable values, but does not exceed +(-) 10 %.


            1.3.  Techniques of Voltage Deviation Decrease


    The techniques to reduce the voltage deviations are divided into two types: voltage change in the network and voltage regulation. Measures to change the voltage are one-time in nature and influence the position of the graph relative to the ordinate axis in Fig. 1.2. They include:
    -      ET change with the help of no-load tap changing of a substation transformer;
    -     the change of the average voltage in the center of the power supply;
    -     the increase of the power of substation transformers;
    -     the increase of supply lines sections.
    These measures make it possible to reduce 5Uᵤᵥ (Fig. 1.2) and not to affect 5 Un (t) the diversity relative to the average, characterized by c₍5 Un dispersion.
    Voltage regulation measures are carried out at the pace of the process and provide a reduction in diversity5Uᵢₙ(t) relative to the average, that is, the decrease in c₍5Un dispersion.
    They include:
    -     counter load voltage control in power supply networks;
    -      voltage regulation on the 10 (6) kV distribution substation tires main step-down substation (MSDS) with the help of on-load tap-changer transformer MSDS;
    -     voltage regulation by reactive power compensation;
    -      application of individual voltage regulators for individual electrical consumers.


            1.4.  The Influence of Voltage Deviations on Power Consumer Operation


    Voltage deviations affect differently the operation of various electrical equipment. From the point of view of the analysis of this influence, all electrical consumers can be divided into three groups.


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    The first group is power consumers, replaced by constant resistance. Their power, consumed from the network depends on the square of the voltage at the terminals.
    The second one is power consumers equipped with an automatic regulator necessary to control the power consumed. For example, an automatic temperature controller to heat the parts in an electric furnace. In this case, when the voltage changes, the current consumption from the network is changed by the regulator as to ensure the required heating level of the parts. In this case, the allowed change in voltage in the electrical network is determined by the characteristics of a controller.
    The third group is power consumers designed for a wide range of power supply voltages. For example, power supply units of some electronic devices (TVs, computers, etc.) ensure the normal operation of these devices with the network voltage in the range of 100-260 V. For such power consumers, the current consumed from the circuit significantly depends on the voltage in the network.