Keywords

1 Introduction

A power grid is a complex system that carries electricity from generation units to consumer premises. The grid is called intelligent by the amalgamation of electrical and communication infrastructures.

As shown in Fig. 1, Smart Grid is characterized by bi-directional flow of data and electricity with self-healing capability.

Fig. 1
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Architecture of Smart Grid

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Three significant features of Smart Grid are communication technologies, distribution automation and automated control systems [1,2,3,4].

The deployment of Smart Power Grid is essential for reduced emissions, energy efficiency, reliability, outage minimization, active consumer participation and integration of renewable energy sources. The communication infrastructure of Smart Power Grid is a combination of various heterogeneous and hierarchical communication networks like home area network, neighborhood area network and wide area network. These networks are designed to facilitate various applications and services like supervisory control and data acquisition, generation and distribution network automation, real-time monitoring, energy management system, cyber security and effective spectrum utilization by spectrum sensing technology [2,3,4]. The use of numerous entities like power system components and devices, transmission lines, conductors and communication network devices makes Smart Grid network vulnerable to radiated as well as conducted electromagnetic emissions. In the existing power grid, the electromagnetic environs are considered for low to medium frequencies lower than 1 GHz. Power system components, transmission lines and conductors emit strong electric and magnetic fields. The electromagnetic interference occurs at operating frequencies and their harmonics. Partial discharges and corona due to high voltages also cause high-frequency interferences [5]. The existing standards for testing and measurements of electromagnetic interferences and compatibility are suitable for traditional power grid components and devices. In Smart Grid network, various microcontrollers, power electronic converters, renewable energy components and communication network devices will be installed. These devices and components will further increase electromagnetic interference [5,6,7,8]. The components of Smart Grid network must be compatible with electromagnetic interferences as well as safe for the operation of other devices operating in their vicinity. The innovative sets of standards are being established for safe and robust operation of Smart Grid.

2 EMI Concerns in Smart Grid

Electromagnetic interference is a disturbance which adversely affects the operation of various apparatus due to conducted and/or radiated electromagnetic radiation generated from internal or external source [6,7,8]. Smart Power Grid network is an assimilation of various electronics devices and wired as well as wireless communication networks. Integration of renewable energy resources with hierarchical and heterogeneous Smart Grid network also creates EMI and EMC issues. Smart Grid is vulnerable to conducted as well as radiated EMI. EMI can destruct or damage the power system and cause blackouts and hazards. Figure 2 shows the main causes of electromagnetic interference in Smart Grid. In this section, various causes of EMI and their impacts are discussed.

Fig. 2
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EMI concerns in Smart Grid

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2.1 High Power Electromagnetic Interference

High power electromagnetic interference can be due to excessive geomagnetic storms initiated by solar activity, intentional electromagnetic interference caused by delinquents and high altitude electromagnetic pulse. This can be referred as the triple threat [8] as discussed below.

2.1.1 Excessive Geomagnetic Storms

Solar noise is an extraterrestrial noise generated by the Sun. Under quiet conditions, the Sun constantly radiates over a very broad frequency range which is used for various communication applications. However, the Sun is a persistently changing star which undergoes cycles of peak activities which may cause electromagnetic interferences such as sunspots and corona flares. The solar cycle disturbances are repeated every 11 years. The solar supercycle is in operation when the peaks of solar cycles reach at maximum point every 100 years. An excessive electromagnetic storm is demarcated as a 1 in 100 year storm [8]. An interaction of charged particles evicted from the Sun with Earth’s magnetic field produces geomagnetic disturbances at the surface of the Earth. Geomagnetic storms induce time-varying currents in the high voltage grid through neutral of the transformer. This time-varying currents can adversely affect the power grid by heating of transformers, greater inductive load and excessive harmonics.

2.1.2 Intentional Electromagnetic Interference (IEMI)

An IEMI is the term used to indicate a premeditated attempt to damage the device or network through radiated and/or conducted electromagnetic emissions. This type of attack is used for illicit offenses. This attack can be formed by high power microwaves (HPM), non-nuclear electromagnetic pulse (NNEMP) or electromagnetic weapons [8]. Standardization work to deal with IEMI is initiated by the EMC society of IEEE, ITU-T and IEC SC 77C [8]. IEMI attack can cause jamming, denial of service or damage of equipment. It can affect solar installations, wind installations, distribution devices, smart meters and substation devices due to its high-frequency characteristics.

2.1.3 High Altitude Electromagnetic Pulse (HEMP)

HEMP is formed by electromagnetic burst at altitude above 30 km over the Earth’s surface. The burst is created by intense electromagnetic fields. There are three types of HEMP radiations [9].

2.1.3.1 Early Time (E1)-High Altitude Electromagnetic Pulse (HEMP)

E1-HEMP reaches field level of 50 kV/m in 10 ns and travels at a speed of light. It is a rapid rising short duration pulse with high frequency. These pulses can interrupt the operation of solid-state electronics devices. They can also penetrate through walls of substations and damage the devices. Smart Grid electronics devices and antennas can be adversely affected by E1-HEMP. E1-HEMP can also couple with distribution lines above the ground and can cause mechanical damage and insulator flashover [9]. It is also harmful to SCADA system located at control centers.

2.1.3.2 Intermediate Time (E2)-High Altitude Electromagnetic Pulse (HEMP)

E2-HEMP reaches field levels 100 V/m between the time interval of 1 microsecond and 1 s. On the basis of research done over the years, it is concluded that E2-HEMP is comparatively less harmful than E1 and E3 pulses due to its limited coverage, coupling efficiency and field levels [9].

2.1.3.3 Late Time (E3)-High Altitude Electromagnetic Pulse (HEMP)

E3-HEMP reaches field levels of 40 V/km between 1 and quite a few hundred seconds [6, 9]. The radial coverage of E3-HEMP is thousand kilometers which can efficiently couple with the transmission lines. It causes the saturation of transformer and potential damage to grid assets [8]. E3-HEMP can also produce severe power harmonics and destruct various devices [9]. It can also cause malfunction of devices and affect accuracy of monitoring and control units.

2.1.4 Classification of HPEM on the Basis of Frequency Bands

HPEM intentional EMI can be classified in terms of frequency bands. Band ratio is the ratio of upper frequency point and lower frequency point [9].

$${\text{br}} = fH/fL.$$

The sources creating HPEM are classified in Table 1. This classification is important for threat analysis of IEMI sources.

Table 1 HPEM classification on the basis of bandwidth
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2.2 Radiated Electromagnetic Interference

Smart Grid comprises of hierarchical and heterogeneous communication infrastructure [10]. Interoperability of diverse communication standards is unavoidable for reliable operation [11]. Amalgamation of power and communication networks makes the grid more vulnerable to EMI. The study of radiated EMI is essential for the design and development of robust Smart Grid infrastructure which can operate competently in most severe electromagnetic environmental conditions. The various sources of radiated EMI are as follows.

2.2.1 Radiated EMI from Wireless Communication Devices

Smart Grid communication infrastructure is an integration of various hierarchical networks like HANs, NANs and WANs [10]. These networks are formed by the integration of different communication standards operating at various frequencies. Smart Grid communication infrastructure also comprises of wireless sensor networks (WSNs) for sensing and communication of different parameters [11]. Numerous base stations, WSN nodes, terminals and transceivers operating at different frequency bands can cause EMI problems as they also contains inter-modulation products, harmonics and frequency conversion products. Interference is also generated from various digital electronics components, power supplies and sensor nodes. Co-existence of diverse communication standards is also a key concern for safe and reliable operation of Smart Grid.

2.2.2 Radio Frequency Radiated Interference from High Voltage Discharges

The high voltage components and apparatus operating are above 100 kV produce EMI as a result of corona discharges and surface arcing. Corona discharges produce interferences in the range of few kHz to 100 MHz [5,6,7,8]. Gap sparks also produce EMI in the range of GHz. An EMI caused by air-insulated switches is very strong in terms of frequency and magnitude. For the lines below 70 kV, gap sparks are the prime source of EMI and the spectrum is up to 1 GHz. For the lines beyond 110 kV, corona discharges as well as gap sparking are the principle sources [6,7,8].

2.2.3 Radio Frequency Radiated Interference from Inverters, Integrated Circuits, Switches and Oscillators

An integration of renewable energy resources is a promising aspect of Smart Grid. Switching operations in converters used to convert renewable power into usable form produce EMI. In solar photovoltaic system, an inverter is used for DC to AC conversion. This conversion takes place by means of fast switching by generally using pulse width modulation (PWM). The switching frequency is in terms of kHz. This switching operation causes EMI on AC as well as DC lines. Oscillatory impulses and fluctuations in voltages also cause interferences [5,6,7]. Bus bars located in substations produce damped oscillations which can potentially damage or cause malfunction on other electronic devices. Integrated circuits (ICs) processing high frequencies are also produced EMI.

2.2.4 Radiated Electromagnetic Interference from Smart Meters

Smart meter is an imperative part of advance metering infrastructure (AMI). Smart meters communicate energy consumption data to a central node. An operating environment of smart meters must be safe and secure for reliable communication of information. This communication is possible by using various licensed or unlicensed bands. Various communication standards, such as Zigbee, WLAN, Bluetooth, GSM, CDMA, GPRS, EDGE, WiMAX, LTE, [10] can be used for data communication. Use of these heterogeneous communication technologies may produce intended and unintended radiated EMI effects. Intended emissions are related to data transmission. Unintended emissions are spurious signals which may not fall into the allocated frequency bands [10,11,12,13,14]. Co-existence of various communication technologies such as Zigbee and Wi-Fi working in industrial, scientific and medical band in home area networks (HANs) can also cause EMI effects. Standardization and legal compliance are inevitable for the integrity and reliability of smart meters. The electronic devices in the vicinity of smart meters must be technically compatible with smart meters for safe operation.

2.2.5 Modeling of Radiated EMI

Radiated electromagnetic interference includes differential mode interference and common-mode interference. Differential mode radiating interference can be assumed as a small current loop by considering ground plate reflection [12] (Figs. 3 and 4).

Fig. 3
figure 3

Electric dipole radiation model [28]

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Fig. 4
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Magnetic dipole radiation model

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An equation for equivalent far-field differential mode interference strength can be written as,

$$E_{{{\text{DM}}}} = {2}.{63}*{1}0^{{ - {14}}} *f^{{2}} *\left( {AI_{{{\text{DM}}}} } \right)*\left( {1/r} \right)$$

In the equation, f is the signal frequency, IDM is differential mode current, A is the loop area size in the circuit and r is distance of measurement. From the above equation, it is evident that the strength of differential mode interference is proportional to the square of frequency, loop area and differential mode current, and it is inversely proportional to the distance [12].

As per Maxwell’s equations and radiated model of electric dipole, a common-mode model can be assumed as a shortwave dipole driven by a single voltage source. Equivalent far-field common-mode radiated interference strength can be termed as,

$$E_{{{\text{CM}}}} = {12}.{6}*{1}0^{{ - {7}}} *\left( {fLI_{{{\text{CM}}}} } \right)*\left( {1/r} \right)$$

The common-mode interference strength is directionally proportional to frequency of the signal, length of cable and common-mode current. It is inversely proportional to distance of measurement.

Furthermore, Smart Grid technology is an assimilation of various electronics and electrical devices working through the combination of hardware and software. Integrated circuit is the key component of Smart Grid network architecture for its diverse functionalities. The integrated circuit to be used in Smart Grid architecture is required to function at high frequency in terms of MHz and even more than that with tremendous processing capabilities [12]. Figure 5 shows the equivalent chip interference model. VNCLK is the transmission signal in the cable, ICM is the current and ZCM is impedance for common-mode interference.

Fig. 5
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Equivalent chip interference model

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$$I_{{{\text{CM}}}} = V_{{{\text{NCLK}}}} /Z_{{{\text{CM}}}}$$

VNCLK is a single clock frequency signal. But the processing is done at high speed so this single high frequency consists of harmonics. Thus, it is a combination of multiple signals. This can be represented as,

$$\begin{gathered} V_{{{\text{NCLK}}}} = V_{{\text{O}}} + \sum\limits_{(i = 1)}^{k} {Vi} \hfill \\ i = 1,2,3,4 \ldots . \hfill \\ \end{gathered}$$

VO is the main interference signal while rest is the multiple of main signal.

2.3 Conducted Electromagnetic Interference Due to Renewable Energy Resources and Power Electronics Devices and Converters

Conducted EMI is routed through power supplies, signal lines and cables. The coupling mechanism can be capacitive, inductive or common impedance [13,14,15,16,17]. There are enormous sources of conducted EMI. Harmonics from power line, surges due to lightning and switching transients, bursts and transients due to inductive DC circuits, etc., are some of the factors which can cause conducted EMI. Various power electronic interfaces also have an adverse interference effects on different subsystems. Integration of renewable energy resources and use of power electronics converters, interfacing between various electronics components, integrated circuits, etc., are the major contributors of conducted EMI in Smart Grid environments [14,15,16,17,18]. The amount of EMI effect depends on the type of coupling mechanism. When the solar panel is connected in a microgrid or mini-grid architecture, EMI is produced at both AC as well as DC side of the system. The specific issues related to conducted EMI caused by power electronics converters such as aggregation of multiple EMI sources, influence of EMI sources on the performance of other devices and the flow of EMI over distance circuits at input and output terminals of power electronics converter are the major issues to be addressed for electromagnetic compatibility [19,20,21,22,23,24]. The rectifiers and inverters in high voltage substations produce significant broadband EMI. There are two types of conversion technologies in practice: thyristor-based converters and voltage source converter (VSC)-based converters. The VSC-based power converters use IGBTs with faster switching [25,26,27]. Thus, the VSC-based converters have broader EMI spectrum up to few MHz.

2.4 Electrostatic Discharge

Electrostatic discharge (ESD) can be described as a phenomenon in which a transfer of electrical charge takes place between bodies of dissimilar electrostatic potential placed in vicinity or through direct contact [28]. ESD can occur when a moving electronic device comes in contact or proximity of stationary conducting object or when the equipment with cable connection is moved from one location to the other [28]. ESD can disrupt the operation of electronic devices. It occurs due to differences in static voltages of devices or surfaces [13,14,15,16, 24]. ESD effects can be mitigated by controlling the difference between static voltages of different surfaces. Data centers will play a pivotal role in Smart Grid applications. High level of humidity may cause ESD in data centers. Controlling the humidity by setting a certain threshold level can be beneficial to mitigate the occurrence of ESD.

3 EMI Measurement Procedures for Smart Grid

The primitive EMI measurement procedures can be considered as a reference but they are insufficient for the complete electromagnetic analysis of complex Smart Grid system. Smart Grid is a combination of various power electronic converters, sensors, communication standards, smart meters, renewable energy sources and electricity generation, transmission and distribution network components. A complex heterogeneous and hierarchical Smart Grid architecture require a painstaking research of EMI issues by considering even a smallest component of the network. Conducted EMI can be measured by measuring voltage at the input of the superhetrodyne receiver. The specific supplementary devices such as line impedance stabilization network, field probe, current probe, absorbing clamps can be used to convert the physical quantities like radiated power, electromagnetic field and current. The receiver parameters are normalized to ensure the comparability of results. The measurement of EMI can be conducted in frequency domain as well as time domain. The frequency-domain measurement conducted using superhetrodyne receiver determines an effect of interference on communication signal. For reliability of control system, the real-time information in time-domain information is more suitable. Frequency-domain measurement must be supplemented with statistical study of repetitive measurements as well as time-domain measurement. In time-domain measurements, the common and differential mode measurements can be used for the analysis of EMI influence on control signals. For meticulous analysis of effect of parasitic couplings on various levels of cross talk, the measurement of EMI voltage and current both are inevitable [22,23,24,25,26].

4 Standards for Electromagnetic Compatibility in Smart Grid

Some of the important standards [29,30,31] for electromagnetic interference and compatibility testing and measurements are as follows.

  • IEC 61000-6-5: This standard depicts the immunity requirements of devices and components used for generation, transmission and distribution of power and associated communication network. Equipment placed at power stations, and substations are included in this standard. High power apparatus used in primary systems of electricity network is not covered in this standard.

  • IEC 61000-4-2: This standard describes the immunity requirements and test levels for electronic devices in the presence of electrostatic discharge (ESD) from human body or metal object in the proximity of that device. According to this standard, ESD tests should be performed on fully operational and configured equipment containing all necessary hardware, software and firmware.

  • IEC 60255-26: This standard is applicable to power system monitoring and control interface devices and protection apparatus. This standard specifies electromagnetic compatibility requirements for protection devices used in power plants and substations in open-air conditions.

  • IEC 60439-1: This standard is applicable to type tested and partly type tested control gear and switch gear assemblies with low voltages up to 1 kV AC or 1.5 kV DC. This standard is developed for assemblies used for generation, transmission, distribution and conversion of energy.

  • IEC 62052-11: This standard includes type tests for indoor and outdoor metering devices for voltage up to 600 V and frequencies of 50 and 60 Hz. This standard is applicable for advance metering infrastructure (AMI).

  • ANSI C12.1: This standard provides performance guidelines for auxiliary equipment, pulse apparatus, AC watt-hour meters, and demand meters used for revenue metering.

  • ANSI C63.12: This standard provides guidelines for conducted and radiated emission levels and test levels for individual electronic instruments in controlled environment [29].

  • IEEE-C-37.90: This standard specifies testing and performance requirements, standard ratings and service conditions for relays, and relay systems used for the protection of power system equipment and control systems. A relay system may consist of communication interface, computer interface and components used for audio systems. It does not include the relay system for switching and industrial control.

  • IEEE 1613: This standard describes the guidelines for performance and testing conditions, standard ratings, environmental conditions and service conditions for communications and networking apparatus. It covers communication ports, sensors and protective relays. It does not include devices included in IEEE-C-37.90.

  • IEEE 60870-2-1: This standard is related to tele-control systems and equipment. It is applicable for encrypted serial data transmission for the management of widespread system. Moreover, it is applicable to equipment in distribution automation systems. This standard specifies minimum immunity and emission requirements and test values as well as characteristics of power supplies connected to the mentioned devices.

  • IEEE 1642: This standard describes risk levels, safety methods, monitoring techniques and experiment techniques for the protection of publicly accessible computer systems from IEMI.

  • IEEE 1909.1: This standard provides guidelines for testing and installation of Smart Grid communication equipment. It includes electromagnetic compatibility (EMC) testing for communication devices installed in generation, transmission and distribution domains of Smart Grid infrastructure [29,30,31].

  • OIML R 46-1 and 2: These guidelines are developed by International Organization of Legal Meteorology (OIML). It describes technical and metrological specification applicable to energy meters subject to legal meteorological controls. It is applicable for smart meter immunity testing.

  • CISPR-24: It is applicable to information technology-related products which use microprocessors. It is basically a product immunity testing standard. The devices at consumer premises in Smart Grid are covered in this standard. It also contains testing of DC ports as well as DC power.

5 Conclusion

Smart Grid can be described as the most revolutionary technology in the current era. Integration of communication technology with existing passive power grid is a critical and crucial aspect of this revolution. An integration of various wireless communication technologies makes Smart Grid network vulnerable to EMI threats. Adverse effects of EMI may result in severe consequences such as component failure, performance degradation or grid failure. Electromagnetic compatibility testing is essential for each and every component of the Smart Grid network for operational reliability and safety. Harmonization between different existing standards is also inevitable and can be conscientiously explored in further research. Future work may include EMC testing of various components of Smart Grid communication network. Researchers can explore various techniques to mitigate the adverse effects of EMI. Prototype EMC testing in laboratory can also provide plethora of design solutions. This survey paper is anticipated to serve as an extensive study and analysis of EMI considerations and standardization process which may lead toward enormous research problems and exploration of solutions.