Expansion of electric vehicles (EVs) is rapid, and it has led to the introduction of numerous EV models. The harmonic current emissions of the on-board chargers of EVs are analyzed in this article based on a large collection of measurement data from public charging sites. The objectives are to discover the emissions of the variety of EV models and to estimate their aggregated emissions in future scenarios. This article utilizes the measurement data of 109 EVs at rated power and 27 below rated power. The recent development of aggregated emissions is observed with a four-year measurement data of a 40-spot charging site. Aggregated emissions in the future are simulated in scenarios of the years 2030 and 2040. In the results, many EVs can be divided into groups based on the emissions. The emissions increase the steepest when below 10 A charging current. The highest harmonics are the 5th, 7th and 11th order, yet compared to the standards, the problematic harmonics are the 11th–19th order. The future scenario simulations indicate no problems with emissions. The major harmonics are the 3rd, 5th and 7th order and the years 2030 and 2040 have similar results. The simulation studies provide charging site-specific summation coefficients for the harmonics. This article contributes to the development of emission standards and methods to control and monitor the emissions of EV charging sites and gives guidance to estimate the emissions of a charging site for stakeholders involved in charging site design and operation.

On-site partial discharge (PD) measurements have turned out to be a very efficient technique for determining the insulation condition in high-voltage electrical grids (AIS, cable systems, GIS, HVDC converters, etc.); however, there is not any standardised procedure for determining the performances of PD measuring systems. In on-line and on-site PD measurements, high-frequency current transformers (HFCTs) are commonly used as sensors as they allow for monitoring over long distances in high-voltage installations. To ensure the required performances, a metrological qualification of the PD analysers by applying an evaluation procedure is necessary. A novel evaluation procedure was established to specify the quantities to be measured (electrical charge and PD repetition rate) and to describe the evaluation tests considering the measured influence parameters: noise, charge amplitude, pulse width and time interval between consecutive pulses. This procedure was applied to different types of PD analysers used for off-line measurements, sporadic on-line measurements and continuous PD monitoring. The procedure was validated in a round-robin test involving two metrological institutes (RISE from Sweden and FFII from Spain) and three universities (TUDelft from the Netherlands, TAU from Finland and UPM from Spain). With this round-robin test, the effectiveness of the proposed qualification procedure for discriminating between efficient and inappropriate PD analysers was demonstrated. Furthermore, it was shown that the PD charge quantity can be properly determined for on-line measurements and continuous monitoring by integrating the pulse signals acquired with HFCT sensors. In this case, these sensors must have a flat frequency spectrum in the range between several tens of kHz and at least two tens of MHz, where the frequency pulse content is more significant. The proposed qualification procedure can be useful for improving the future versions of the technical specification TS IEC 62478 and the standard IEC 60270.

The insulation condition of HVDC grids consisting of cable systems, GIS, and converters should be monitored by partial discharge (PD) analysers using artificial intelligence (AI) tools for efficient insulation diagnosis. Although there are many experiences of PD monitoring solutions developed for the supervision of the insulation condition of HVAC grids using PD analysers, there are no standardised requirements for their qualification available yet. The international technical specification TS IEC 62478 provides general rules for PD measurements using electromagnetic methods but does not define performance requirements for qualification tests. HVDC and HVAC PD analysers must be tested by unambiguous test procedures. This paper compiles experiences of using PD analysers with HFCT sensors in HVAC grids (cable systems, GIS, and AIS) to define a qualification procedure for HVAC systems. This procedure is applicable to HVDC grids (cable systems, GIS, AIS, and converters) because the particularities related to the insulation behaviour under HVDC voltage are also considered. Representative PD sources are discussed in HVAC and HVDC positive and negative polarity. The PD pulse trend of representative insulation defects in HVDC cable systems is quite different from that of HVAC grids. Special attention should be paid to the acquisition of PD signals in HVDC grids since few pulses appear in solid insulations, mainly during voltage changes (polarity reversals or surges), but rarely in continuous operation with constant direct voltage. A synthetic PD simulator has been developed to reproduce trains of PD pulses or noise signals, similar to those that can appear in the power network. A set of three functionality tests has been developed for qualification of the diagnostic capabilities of PD analysers working up to 30 MHz addressed to HVDC or HVAC grids: (1) PD recognition test, (2) PD clustering test, and (3) PD location test. This qualification procedure has been validated by means of a round-robin test performed by five research institutes (RISE, FFII, TUDelft, TAU, and UPM) using commercial and in-development AI PD recognition and clustering tools to demonstrate its robustness and applicability. Applying this qualification procedure, two PD methods for electrical detection and prevention of insulation defects have been approved, one for HVAC and the other for HVDC grids.

Often the accuracy or reliability of the time stamps of power quality data coming from different measurement locations is not adequate for certain analysis tasks. This paper studies improving the accuracy and reliability of the time stamps by utilizing the mutual correlations of the measured signals. Especially the electricity grid fundamental frequency estimated using a reliable and stable high performance adaptive method is almost the same everywhere in a synchronized power system. That enables accurate identification of clock time differences and drifts. The paper compares the results with the time stamps given by time managed local metered data preprocessing and concentrator servers. The results show that the identified time differences agree well with the time stamps given by the servers, but also reveals that the identified timing difference makes it possible to detect and correct the large timing errors that occasionally appeared in the time stamps added by the server.

In this paper, the impact of LED lighting systems to the power quality (PQ) of the electrical network are analyzed. The paper compares the effect for PQ in respect with the old fluorescent tube lights (FTL). Moreover, the alternative installation methods for LED lights are analyzed and recommendations for the installations of LED lights will be given to achieve the expected energy efficiency.

The increasing usage of power electronic devices and changes in time domain characteristics of power generation and electricity markets motivate the studies of this paper. The electrical energy system of a modern office building is comprehensively monitored with advanced power meters and the influence of solar power plant and various load types is examined on power flows and voltage and current distortion. The study presents the behavior of active and reactive power with several time averages considering separately measured loads and solar power plant. In addition, Fryze’s power theory is discussed with the aid of total distortion measurements. The results offer an overview of the effect of time averaging on power measurements and a case study, in which distortion is included in power quantity.

The suitability of 0.1 Hz VLF tangent delta (TD) and three different partial discharge (PD) measurement methods for condition assessment and commissioning measurements of MV underground cable systems were studied. On-site measurements were conducted in MV networks of 12 Finnish distribution network operators (DNOs) on a total of 100 three phase cable systems of different ages and 5 different cable types. Based on the TD measurement results the limits given in IEEE Std400.2-2013 seem too high for Finnish cable systems. No clear correlation between the PD and TD measurement results or the age of the cable and TD was observed. It could be concluded that the measurements complement each other revealing different degradation mechanisms. TD measurement does not reliably reveal the presence of PD and thus, for cable commissioning, PD measurement is recommended.

Secondary substations' earthing systems are connected to each other via metallic screens of the 20 kV underground cables also in suburban and rural areas nowadays. Topology is different from the earthing systems in city centres, where earthings are connected via multiple mesh connections forming a solid ground level. The standards EN 61936-1, EN 50522 and the Finnish SFS 6001 (high-voltage installations) do not clearly consider the case of connected earthings. In 2015, studies were launched to investigate this issue. According to results of the studies, the connected earthings should be evaluated as a whole, and not separately as in the overhead networks. There is a need for renewing earthing network design principles because at the moment, the connections between the secondary substations are not systematically taken into account in the non-urban areas' earthing design. Results show that the resulting impedance was typically 50–80% lower than the secondary substations' individual earthing resistances. It means that there is great potential for savings in the earthing network without risking the safety. Furthermore, there is a need to develop earthing impedance measuring methods. Methods that are used for overhead network earthing measurements are not often suitable for cable network.

Networks of medium voltage have spread over a long distance through underground cables. The aim to prolong the life span of existing network assets increases the need for condition monitoring to prevent unplanned and long lasting interruptions. Continuous on-line partial discharge (PD) measurement is an excellent way to determine the overall health of the medium voltage (MV) components and to detect developing faults in underground cables. A sensor is an essential part of the PD monitoring system which measures the high frequency PD signals. PD sensors can be used to measure power frequency current and harmonic currents on the MV side to estimate the thermal loading of transformer or incoming cable provided that the sensors have a suitable frequency response for measuring low frequency signals as well. A novel inductive sensor is described in this paper which allows both PD measurements as well as power quality (PQ) measurements at frequency range below 2.5 kHz. Authors did experiments on different ferrite cores in order to design the best possible sensor which can be used for both PD and PQ measurement. Characteristics of the sensors, including sensitivity, saturation current, and frequency bandwidth, as well as relative errors are provided and analyzed under laboratory conditions. At the end, developed sensors are compared with a commercial HFCT sensor, the Rogowski coil and power quality current sensors to show the capability of the sensors to be used for PD and PQ measurements.

Smart grid concept substantially increases the need of monitoring devices in the future for efficient and flexible power delivery. Secondary substation is an ideal location for monitoring both LV and MV networks which can be used to improve the power grid resilience. This study presents the key features and practical experience gained from the deployment of novel wideband high-frequency current tr...

Smart Grid concept substantially increases the measurement need in the future for efficient and flexible power delivery. Distribution network monitoring has been traditionally focused on primary substation (i.e., high voltage/medium voltage), whereas least attention has been given to secondary substation (i.e., medium voltage/low voltage). Distribution network operators are facing considerable network investments in the near future due to the renewal of aging cable networks in cities and renewal or replacement of overhead lines by underground cables in rural areas. To focus on the network renewals at the correct places to decrease the occurrence and duration of unplanned power interruptions and to maintain good power quality despite the proliferation of e.g. distributed generation and electronic loads, the need for proactive network monitoring is ever increasing. Secondary substation is an ideal location for data acquisition because both MV and LV network can be monitored. This paper proposes a novel cost-effective secondary substation monitoring concept for smart grids which can be installed permanently at secondary substation for partial discharge (PD) monitoring, power quality (PQ) monitoring and disturbance recording. No sensors having expensive high voltage insulations are needed, which makes the solution cost-effective and reliable.

This paper presents new findings on phenomena contributing to flicker and voltage variations caused by grid-connected photovoltaic (PV) inverters. The voltage variations caused by two different 6 kW single-phase grid-connected PV inverters were studied during climatic variations by varying their grid-coupling impedance. Two different methods for characterizing the PV-plant induced voltage variations were studied: the short-term flicker index (Pst) and the 10 minute very-short voltage variation value (VSV). The results clearly indicate that PV inverter power fluctuations induced by cloud shading and enhancement have a significant effect on the VSV value, but not on Pst. PV inverters have a clear effect on the Pst as well, but the main contributors are related to the inverter design rather than the power fluctuations caused by clouds. The main contributor in the elevated Pst values could be traced back to the poor design of the maximum power point tracking (MPPT) of the inverters. The MPPT caused subharmonic current variations at a frequency of approximately 8 Hz which is close to the most sensitive frequency of human eye. Another factor causing rapid voltage variations in low irradiance conditions was the current transients related to the inverter start-up and shut-down. Harmonic current distortion is also a potential PV inverter related power quality (PQ) issue. This study indicates that although the current total harmonic distortion (THD) may be very large at low power levels the total demand distortion (TDD) of the PV inverters is almost constant regardless of the output power and the harmonic current had only a very limited effect on the voltage quality even at the weakest network having a short-circuit current of Isc=250 A. Thus, voltage variations caused by the PV inverters were the main PQ issue in the studied networks. The investigations also clearly show that a part of the power quality problems found in the PV plants are caused by the poor design of the PV inverters.

Smart Grid concept substantially increases the power measurement need in the future for efficient and guaranteed power delivery. The medium voltage (MV) cable is an important asset of a distribution network and it must guarantee a stable operation of the supply. With the increasing age of the underground MV cables in power grids, the accident and failure arising from insulation degradation is becoming one of the main challenges against power system reliability. It is also essential economically to extend the life span of the medium voltage cable. Continuous on-line partial discharge (PD) monitoring is an excellent way to determine the overall health of the MV components and to detect incipient faults in underground cables. However, continuous on-line PD monitoring is not widely used primarily because no adequate cost-effective solution is available for permanent installation. This paper presents the development of a versatile solution for continuous on-line PD monitoring of MV cables at secondary substation. The laboratory tests and data analysis exhibit the capability of the proposed system to detect PD signals successfully.

The electric utility industry is going through significant changes caused by new regulation models, distributed generation, increased competition and requirements for continuous improvement in the quality of power supplied to the customers. To minimize outages and supply interruptions, utilities must be able to monitor and locate faults more quickly and to develop condition monitoring in a more preventive direction. On-line continuous partial discharge (PD) measurement is an excellent way to determine the overall health of the medium voltage (MV) cables. Essential parts of a PD monitoring system are the sensors for measuring the high frequency PD signal. The continuous on-line PD monitoring of MV cables is a problem, primarily because no adequate costeffective sensor solution is available for permanent installation. The goal of this paper is to develop a lowcost, sensitive and robust sensor solution for continuous on-line PD monitoring of MV underground cable networks.

The new legislative requirements and all the time tightening economic regulation cause a great pressure for Finnish distribution system operators to improve the security of power supply. Underground cabling has been seen in many cases basically the only but at the same time very expensive solution to solve this problem. This paper presents that with the help of reserve power solutions it is possible to fulfill the requirements especially in sparsely populated rural areas. The results show the profitability of utilizing reserve power generators instead of investing in the cabled network. In addition, the calculations support the fact that customers should at least consider purchasing own reserve power.

According to Finnish legislation, at least 80% of the energy meters had to be remotely readable and provide hourly based data by the end of 2013. The expansion of AMR system has certainly set higher demand for the reliability of the communication link when hundreds of meters establish communication link with data concentrator. This paper discusses the architecture of different Automatic Meter Reading (AMR) systems and gives some insight to the level of conducted disturbances which may cause PLC communication problems in commonly used AMR systems. It also proposes potential solutions to overcome the PLC communication problems. On-site measurements have been carried out to study the behavior of different system in real networks with various electronic loads. The results indicate that large number of PLC links failed to operate in the field due to the high frequency noise generated by electronic loads at frequencies close to the PLC carrier frequency. The presence of high frequency disturbances in the PLC frequency range caused by customer loads obstructed the communication of AMR systems which is a matter of concern for DNOs.

The interference of touch dimmer lamps due to PLC signals has found to be a common interference problem in Finland after the installation of smart meters that use PLC. One reason for this is the lack of equipment immunity standards for voltage frequencies below 150 kHz. This paper will study controlled discontinuous high frequency signal burst effect to two touch dimmer lamps in the laboratory environment. Both lamps were disturbed due to these signals. Based on the results it is possible that interference problems can occur even if the distance between lamp and the PLC device is close to 100 m. Paper will also show the measurement results on how one plug-in type filter improve interference situation. Results show that the amplitude of the signal burst will decrease at lamp side but filter also affects signal levels at mains side.

According to Finnish legislation, at least 80 % of the energy meters have to be remotely readable and provide hourly based energy data by the end of 2013. In April 2011 Tampere University of Technology (TUT) in co-operation with Finnish Energy Industry conducted a questionnaire to Finnish distribution network operators (DNOs) to map the installation status of the remotely readable meters, the communication technologies used in the meters and the interference problems experienced so far, related to, especially, PLC (power line communication) systems. The questionnaire dealt with both the interference caused by customer apparatus to PLC and vice versa. On-site measurements to study common customer apparatus disturbing the PLC were also conducted in 2012 in the networks of a few DNOs. Most common disturbance sources were frequency converters and switch mode power supplies. The measurements indicate that in addition to the lack of emission standards below 150 kHz the aging of customer equipment may be a relevant cause of interference problems.

This paper proposes the design and development of a novel, portable and low-cost intelligent electronic device (IED) for real-time monitoring of high frequency phenomena in CENELEC PLC band. A high speed floating-point digital signal processor (DSP) along with 4 MSPS analog-to-digital converter (ADC) is used to develop the intelligent electronic device. An optimized algorithm to process the analog signal in real-time and to extract the meaningful result using signal processing techniques has been implemented on the device. A laboratory environment has setup with all the necessary equipment including the development of the load model to evaluate the performance of the IED. Smart meter and concentrator is also connected to the low voltage (LV) network to monitor the PLC communication using the IED. The device has been tested in the laboratory and it has produced very promising results for time domain as well as frequency domain analysis. Those results imply that the IED is fully capable of monitoring high frequency disturbances in CENELEC PLC band.

Characteristics of partial discharges (PD) caused by trees in contact with covered conductor (CC) lines have been studied. A tree in contact with a CC distorts the electric field around the conductor and causes partial discharges. According to tests conducted in a high voltage laboratory the rise time of the PD current pulses caused by the trees is relatively long, in the order of 60 ns...0.8 mus. The fault impedance and PD magnitude caused by a tree in contact with a CC and the propagation attenuation of PD pulses was studied in different seasonal conditions in September, November and March on a full scale 110 kV CC trial line. In case of an intact CC the fault impedance is several MOmega. After breakdown of the conductor covering the fault impedance collapses in summer to tens and in winter to hundreds of kOmega. The average PD magnitude measured in March was approximately one fifth of that in September. On a 9.3 km line portion the observed propagation attenuation of the PD signal was 0.37...3.7 dB. The variation in the attenuation is attributed to the variation in the rise times of the PD pulses and the modal composition of the PD signal. The results indicate that PD measurements can be used to detect trees fallen on CC lines.