Verification of Power Source Grid Compliance

Over the years, we have innovated a lot, but there is still a long way to go in terms of both production and intelligent distribution (smart grid). Just think of the electricity that the waves of the sea could generate (wave energy converter). Italy could excel worldwide in this, thanks to the reuse of shipbuilding capacity and its kilometers of coastline.

Unfortunately, these technologies are almost still in the state of prototype despite the countless benefits they would bring to the community.

Several offshore wind farms - already widely used in northern Europe - have recently emerged. Here a combination of wind and wave-driven generators could stabilize the grid. Since the infrastructure represents a large part of the construction costs, taking advantage of the same network infrastructure would reduce these costs.

However, due to the continuously changing nature of the various renewable energy sources, the generators connected to the public electricity network cannot produce stable and safe electricity. Even differentiated production mixing photovoltaic, solar, wind, and wave energy does not guarantee voltage stability levels similar to thermodynamic or nuclear energy sources.

All this strengthens the need for a network of intelligent systems or smart grids. Self-balancing and -regulating grids that can deal with any instability that may lead to significant problems over large geographical areas.

If power plants reach high production powers, they are interfaced directly with the national high voltage (HV) electricity grid. At this level, any instability could affect the entire national grid. For this reason, Terna SpA - the Italian national electricity grid manager - is particularly attentive to the self-regulation of energy flows on the various exchange points.

Grid or network codes 

Grid codes or network codes are technical specifications that define the parameters any facility connected to a public electric grid must meet to ensure the safe, secure, and economically proper system functioning.

European Union network codes

Europe’s cross-border electricity networks are operated according to rules. These rules help govern the work of operators and determine how to give access to electricity to users across the EU. In the past, these rules for grid operation and trading were drawn up nationally. As electricity is increasingly interconnected between countries, the EU-wide rules effectively manage these electricity flows in the internal energy market.

The EU has introduced harmonized standards across Europe to boost the generation technology market and increase competitiveness.​ The Commission Regulation (EU) 2016/631 of 14 April 2016 establishes common EU standards that generators must respect to connect to the internal grid. It sets out detailed technical rules mainly relating to the connection of new generating installations to national electricity networks.

These rules, known as network codes or guidelines, are legally binding EU Regulations. They govern all cross-border electricity market transactions and system operations alongside the Regulation on conditions for accessing the network for cross-border electricity exchanges ((EC)714/2009). Sometimes the new rules are adopted as 'guidelines' rather than 'network codes’ but have the same status – both are legally binding regulations.

European grid codes have some similarities, but the codes of different countries and regions also differ. The European Network of Transmission System Operators for Electricity (ENTSO-E) is the organization that coordinates the transmission system operators (TSOs) in Europe. ENTSO-E has developed a set of common grid connection requirements intended to be used by TSOs across Europe. These common requirements are known as the ENTSO-E Network Code on Requirements for Grid Connection.

However, it is important to note that each country or region may have additional requirements that are specific to that area. For example, some countries may have more strict requirements for renewable energy sources, while others may have different requirements for grid stability. Additionally, different grid codes may have different requirements for the design and operation of the grid, as well as for the protection of the grid from faults

Network codes worldwide

Grid codes for other regions of the world may have similarities to European grid codes, but there may also be significant differences. For example, the North American Electric Reliability Corporation (NERC) is an organization that coordinates the transmission and generation of electric power in North America, and it has developed a set of standards for the bulk electric system in the United States, Canada, and Mexico. These standards are known as the NERC Critical Infrastructure Protection (CIP) standards.

In Asia, each country has its own grid codes and regulations. For example, the Central Electricity Authority (CEA) in India has developed the Indian Grid Code (IGC), which sets out the technical and operational requirements for the Indian power system.

The grid codes and regulations in other regions of the world will also be influenced by factors such as the specific energy mix, the level of integration of renewable energy sources, and the structure of the electricity market. Therefore, you need to be familiar with the specific grid codes and regulations that apply to the country or region you are working in - check the specific grid code to ensure compliance.

Grid compliance

There are several ways to verify grid code compliance of a power source, including

• Inspection: An inspector can physically check the grid and its components to ensure they meet the required standards and regulations.

• Testing: Tests can be conducted on the grid and its components to measure performance and ensure compliance with regulations.

• Certification process: Independent organizations can certify that a power source grid meets the required standards and regulations.

• Auditing: An audit can be conducted to verify that the power source grid is being operated in compliance with regulations and standards.

• Simulation: Using software and a model of the power grid, compliance with the grid can be verified by simulating it under different scenarios and conditions.

It is important to note that the specific method or combination of methods used will depend on the regulations and standards that apply to the power source and the grid in question.

The Italian Grid Code - Annex A.18

The Italian national electricity grid (NTG) is a complex of lines along which electricity passes between the various production plants to the main transformation nodes at lower voltage levels. The 220 kV system is powered by a non-negligible percentage of the power plants and partly performs high voltage distribution functions. The 150-132-120 kV system does the high voltage distribution task, supplying the primary HV / MV substations or directly the large power users.

All systems connected to the Italian National Electricity Grid must be tested and verified periodically as described in the Italian Grid Code. 

In this article, I will deepen the critical aspects of these checks, which are anything but trivial, and undermine most of the measurement systems available on the market.

Annex A.18 of the Italian Grid Code is a technical guide that describes how to "Verify the compliance of production plants with the technical requirements of the Operator" TERNA SpA.

The rev. 02 of February 15, 2021, incorporates the technical connection requirements deriving from the European Connection Code (Rfg).

Field of application

The requirements included in Annex A.18 apply to production plants connected to the Italian national electricity grid (NTG).

With the growth of production from renewable energy, high-capacity production plants connected directly to the National Electricity Grid increase, these systems and in particular the regulation equipment must comply with the requirements of the Grid Code and related annexes, as well as the procedures and methods for carrying out the checks themselves, which are described in Annex A.18.

Quantities to be measured

Section 8 of Annex A.18 shows all the quantities to be recorded for each type of generator:

Synchronous generation groups

• P: instantaneous group three-phase active power generated

• Q: three-phase group reactive power generated

• V: effective voltage of the generating group

• I: effective current of the generation group

• f: network frequency

• Vf: excitation voltage/field of the generating group

• w: rotor speed

• dfsim: simulated frequency error

• freg: grid frequency measured by the speed/power regulator

• Prif: active power reference

• Preg: active power measured by the speed/power regulator

• dVref: variation of the simulated machine voltage reference

• Vrif: machine voltage reference

• Vsi1: PSS frequency input where applicable

• Vsi2: PSS power input where applicable

• Vst: PSS output where applicable

• AVRo: voltage regulator output

• Vaux: auxiliary services power supply voltage

• Livq: reactive level of the SART regulation where applicable

• Qlim: SART instantaneous reactive limit (over and under excitation) where applicable

• Vrif RTS: SART RTS bus calibrator reference where applicable

Over-excitation limit trip

Limit under-excitation trip

• Paux: power absorbed by the auxiliary services

• VAT: voltage on the HV / AAT side

• PAT: active power on the HV / AAT side of the step-up transformer

• QAT: reactive power on the HV / AAT side of the step-up transformer

HV switch position

• Tap: notch2 of the variator under load on the step-up transformer where applicable

Traditional steam thermoelectric synchronous generating sets

• Turbine inlet pressure

• Turbine request

• Position of steam supply valves

• Cylindrical body level (where applicable)

• Position of bypass valves

Synchronous generation groups of the gas turbine type in the open cycle or combined cycle

• TG fuel request

• TG exhaust temperature

• TG thermoregulation temperature reference

• TG thermoregulation intervention

• IGV position

• Levels cylindrical bodies (for combined cycles)

• Position of adduction valves TV (for combined cycles)

• Position of bypass valves TV (for combined cycles)

• Environmental temperature

• Environmental pressure

• Ambient humidity

/h3Power generation parks (PPM)

• P: three-phase active power generated at the HP by the PPM

• Q: three-phase reactive power generated at the HP by the PPM

• V: effective voltage at the HP of the PPM

• I: effective current at the HP of the PPM

• f: network frequency to the HP

• dfsim: simulated frequency error

• freg: network frequency measured by the PPC

• Prif: PPM active power reference

• Pme: maximum power that the PPM can deliver according to environmental conditions

• Preg: Active power measured by the PPC

Active power limitation signal

• dVref: variation of the simulated voltage reference

• Vref: voltage reference of the PPM

• Qref: PPM reactive power reference

• Qlim: maximum reactive power deliverable/absorbable by the PPM (over and under excitation)

Reaching maximum deliverable reactive power (overexcitation)

Reaching maximum absorbable reactive power (underexcitation)

HV switch position

• Tap: notch of the variator under load on the step-up transformer where applicable

Environmental temperature

Photovoltaic systems

• Solar radiation

Wind turbine farms

• Average wind speed

• Air density

• Environmental pressure

• Ambient humidity

Minimum characteristics of the instrumentation

Most of the instruments available on the market fail to carry out the measurements as required by national grid codes.

The testing and testing procedures involve the use of several different tools:

• Voltage and current transducers

• Active power and reactive power capability

• Frequency calculations

• Average value transducer of the excitation voltage

• Quick registration system

• Function generator

• Programmable generator of voltage and current triples

• Harmonic analyzer

• Isolated network simulator

However, all functions of the tools highlighted in the bold above can be realized with just one Dewesoft instrument.

Voltage and current transducers, active power, reactive power, and frequency calculations

Annex A.18 of the Grid Code specifies the following minimum characteristics for the transducers and calculation results.

Measurement accuracy

The Annex 18 of the Grid Code requires:

• Accuracy better than or equal to ± 0.2% of full scale for voltage and current measurements

• Accuracy better than or equal to ± 0.5% of full scale for active and reactive power measurements

• Resolution on voltage, current, active and reactive power measurements better than or equal to 0.1% of the full scale

A Dewesoft SIRIUS system guarantees the accuracy of 0.03% of the reading for the measurement of direct voltage while the accuracy of the current is strictly linked to the type of current transducer that is chosen.

Voltage and current transducers always have an amplitude error and a phase shift as a function of frequency which can be compensated for with a specific sensor database function in DewesoftX.

With the calibration technology of the Dewesoft software amplitude and phase can be corrected in the frequency range from DC up to 1 MHz, e.g., ferromagnetic core clamps, AC/DC clamps, or Rogowski coils.

For electrical power analysis, high-precision amplifiers are essential. SIRIUS high-speed amplifiers for high and low voltage inputs reach new levels of accuracy. These amplifiers have a DC to 1 kHz accuracy of 0.03% of reading. This aspect is unique in the world of power analyzers or watt meters, especially measuring in the presence of frequency converters where more accurate measurement results are needed.

The resolution of the measurements and power parameters calculated for a Dewesoft watt meter/network analyzer are related to the instrument's signal/noise ratio. With DualCoreADC® technology, SIRIUS achieves a signal-to-noise ratio of over 130 dB and over 160 dB in dynamic range. These performances are 20 times better than those obtained with 24-bit systems and with the noise reduced by 20 times.

Frequency measurement

Annex 18 of the Grid Code requires:

• Accuracy better than 5 mHz for frequency measurement

• Resolution on the frequency measurement better than or equal to 5 mHz

Only with high accuracy of the mains frequency is it possible to accurately extract harmonics 

from the signal and make precise electrical power calculations.

The DewesoftX software includes a PLL algorithm that guarantees very precise measurement of the electrical frequency (1 mHz). A Dewesoft watt meter/network analyzer can also make electrical power calculations across multiple independent networks and each having its separate frequency.

Alternative frequency extraction algorithms are available to have a very quick response, e.g., frequency update every period.

Calculation interval

The Annex 18 of the Grid Code requires

• A response time of less than or equal to 50 ms

• RMS values are to be calculated no later than 40 ms for all quantities in the sinusoidal alternating periodic regime

The watt meter based on DewesoftX software allows the calculation of the periodic components of the power parameters (including the RMS values) with a freely programmable interval (up to a minimum of 0.5 ms).

Period values

We can calculate the period values = values for voltage, current, and power for:

• Periods = each = ½, 1, 2, or 4 periods can be selected from a drop-down list.

• Overlap = 0%, 25%, 50%, 75%, 95%, or 99% which can be selected from a drop-down list.

The calculation of the periodic components allows to obtain the power parameters up to ½  of the period (100 ms), and an additional data superimposition function (Overlap) allows the calculation of the relevant parameters at shorter intervals (up to 0.5 ms).

This calculation speed is well-suited for analyzing the response of HV inverters when stressed with transients.

Average value transducer

A Dewesoft system is not just a simple watt meter/network analyzer. The raw signals are always available for any mathematical processing.

Annex A.18 requires the use of average value transducers. However, with the Dewesoft watt meter, this added transducer is not needed. The signals acquired by the transducers measuring electrical power can be averaged over time. Even with periods of less than 10ms. The calculated value is available as if acquired by a dedicated sensor.

Quick registration system

Dewesoft watt meters allow the simultaneous acquisition of analog signals from 8 to 64 channels for a single system - and multiple systems can be combined.

24- or 16-bit synchronous A/D converters reaching sampling rates of respectively 200kS/S and 1MS/s acquire each channel.

The peculiarity of a Dewesoft system is the possibility of integrating signals of a different nature, including industrial buses such as MODBUS TCP/IP, OPC-UA, Siemens S7, and much more.

In this way, it is possible to compare the signals acquired by the analog sensors with those of the control devices and many other values deriving from the automation.

Subsequently, all data is exportable in various formats compatible with the commonly used analysis programs:

• MS Excel - standard spreadsheet software

• FlexPro - powerful and easy-to-use analysis software

• Text / CSV and ASCII - text file with field delimiters

• Diadem - powerful data analysis software from NI

• Famos - signal analysis software

• NSoft - NCode file format for Somat software

• Matlab - Matlab file format

• Sony - format compatible with Sony magnetic recorders

• RPC III - MTS file format used for fatigue test stands

• Comtrade - used in the power & energy sector

• UNV - universal file format

• WAV - standard audio file format

• KML - GPS export to review data in Google Earth

• BWF - multichannel wave file format

• ATI - iDeas native format for dynamic signal analysis

• SDF - used by LMS Prosig software

• WFT - Nicolet data format

• CSV - to export CAN messages

• TDF - file format defined and used by the LMS software

• ASAM ODS and MDF - Open Data Services and Measurement Data Format according to the standards of the ASAM organization

• TAFFmat - TEAC data acquisition file format

• Winplot [* .sun] - Data format compatible with Winplot, a powerful desktop graphical analysis tool that allows the user to generate views of unlimited amounts of data

Function generator

All Dewesoft systems can integrate the function generation function. This functionality is supported by a software module for programming functions and by an electronic interface with 16bit channels and ± 10 V range.

Harmonic analyzer

The Power module of the Dewesoft wattmeter allows you to calculate all the harmonic content in compliance with the IEC EN 61000-4-7 standard in force. The instrument can interface with any current transducer present in the system.

The Dewesoft network analyzer

The Dewesoft network analyzer can measure all the electrical power quality parameters according to IEC 61000-4-30 Class A. Compared to others, the Dewesoft network analyzer allows for performing more detailed power analyses, e.g., recording of waveforms, spectrum analyzer, failure behaviour, or calculation of additional parameters.

Main characteristics

It is an extremely flexible solution that combines many measuring instruments in a single device. This translates into many advantages for the measurement:

• all signals are synchronous and therefore ready for comparisons and correlations,

• all waveforms can always be saved and analyzed at any time (online and offline),

• the user does not need to learn how to use different measuring instruments, and

• lower overall cost.

Our solutions can be used for very different electrical measurements and electrical analyzes:

• Harmonics and THD up to 150 kHz

• Interharmonics and high frequencies

• Flicker, Flicker Emissions, Rapid Voltage Variations

• FFT spectrum analyzer, FFT harmonics, Waterfall FFT

• Symmetrical components

Standards implemented

Harmonics, interharmonics, and THD

The Dewesoft power analyzer can measure harmonics for voltage, current, active, and reactive power up to order 3000. All calculations are performed according to the IEC 61000-4-7 standard.

You can define the number of sidebands and half-bands for order calculation. The high frequencies can be grouped into a band from 200Hz to 150kHz. For analysis completion, the software allows the calculation of the total harmonic distortion (THD) for voltage and current up to the 3000th order and the interharmonics. These features for harmonic analysis apply to any electrical equipment.

Rapid voltage changes

The Dewesoft power analyzer detects rapid voltage changes following the IEC 61000-4-15 standard.

Electrical imbalance - symmetrical components

An electrical imbalance indicates that voltages (U1, U2, U3) and/or currents (I1, I2, I3) in a three-phase system have modules with different values. Non-synchronously charged phases are the cause of this electrical phenomenon. The Dewesoft electrical network analyzer applies the method of symmetrical components to analyze the electrical imbalance. This method divides the original system into a positive system with a rotation like the original system, a negative system rotating in the opposite direction, and a zero system.

Electric frequency

The Dewesoft electrical measuring instrument allows you to measure the frequency of the electricity grid and can be used for monitoring and testing electrical generators (eg renewable energy).

The calculation accuracy of the network frequency is 1 mHz. Calculations are done with the PLL algorithm and can be displayed over time with a Recorder graph. Faster algorithms are available to detect any quick frequency change occurring in case of fault.

Conclusion

The Dewesoft wattmeter is a perfect tool for testing electricity generators. It fully meets the requirements of Annex A.18 of the Italian Grid Code for field testing and periodic verification. And is suited for similar measurements in accordance with other national grid codes as well.

Dewesoft designs its hardware to be used in the field - very robust, with light mechanics and features, such as

• DC power supply,

• Integrated batteries,

• Self-recognition of current transducers,

• Automatic correction of sensor non-linearity, and

• Display of power calculations during the test.

Optimizing investments and staff training, the same Dewesoft instrumentation is fit for laboratory testing and the tests described in Annex A.18 of the Italian National Network Code.