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Voltage transformer

A voltage transformer, also known as a potential transformer (PT), is an instrument transformer designed to step down high voltages in electrical power systems to lower, standardized levels—typically 115 V or 120 V on the secondary side—for use with metering, protection relays, and control equipment, while providing electrical isolation for safety.^[1]^[2] Unlike power transformers, which handle bulk energy transfer, voltage transformers prioritize accuracy and low burden to ensure precise voltage representation without significantly affecting the primary circuit.^[1]^[2] Voltage transformers operate on the principle of electromagnetic induction, with a primary winding connected in parallel to the high-voltage line and a secondary winding linked through a magnetic core, producing a proportional output voltage based on the turns ratio.^[1] The core is typically made of high-permeability magnetic steel to minimize exciting current and operate in the linear region below saturation for accuracy, allowing continuous performance at up to 110% of rated voltage.^[2] They exhibit low impedance and are engineered to handle burdens up to 400 VA, with phase angle and ratio errors tightly controlled to support reliable measurements.^[3]^[1] Classified under standards like IEEE C57.13, voltage transformers are grouped by overvoltage withstand capability (e.g., Group 1 for 125% overvoltage for up to 8 hours, Group 5 for 140% for 1 minute), insulation class matching system voltages (e.g., 60 kV BIL for 7.2 kV systems), and accuracy classes such as 0.3 or 0.6 for metering (error ≤0.3% at rated conditions) and 0.6 or 1.2 for protection.^[3]^[2]^[1] Construction types include wound-primary (for low and medium voltages) and capacitor voltage transformers (CVTs) for high-voltage applications above 115 kV, often using capacitive dividers for cost efficiency.^[1] In power systems, voltage transformers are essential for revenue metering to ensure accurate billing, protective relaying to detect faults like overvoltages, and load surveys for demand management, enabling safe monitoring of systems from distribution (e.g., 7.2 kV) to transmission levels (e.g., 500 kV).^[2] They reduce risks by isolating low-voltage instruments from high-voltage lines and support standards from ANSI, IEC, and CSA for global interoperability.^[1] Modern advancements include optical and digital variants for enhanced precision in smart grids, though traditional inductive types remain dominant for their reliability.^[2]

Fundamentals

Definition and purpose

A voltage transformer, also known as a potential transformer, is a type of instrument transformer designed to step down high voltages from electrical power systems to low, standardized levels suitable for safe measurement, monitoring, and control applications.^[2] It reproduces the primary voltage in its secondary circuit in a definite and known proportion, typically providing isolation between high-voltage lines and low-voltage equipment to prevent hazards.^[1] This enables accurate replication of voltage signals without direct exposure to the full system voltage, which can exceed hundreds of kilovolts.^[4] The primary purposes of voltage transformers include voltage metering for billing and load monitoring, relaying for protective functions such as fault detection and circuit breaker operation, and supplying isolated signals to instruments, relays, and control devices in substations and power networks.^[5] In metering applications, they ensure precise voltage readings for energy consumption calculations, while in protection schemes, they provide scaled-down signals that trigger responses to abnormalities like overvoltages or short circuits.^[6] These roles are essential in high-voltage transmission and distribution systems, where direct measurement would be impractical or dangerous.^[1] Unlike power transformers, which are engineered for efficient bulk energy transfer across voltage levels with high power ratings and minimal losses, voltage transformers prioritize measurement accuracy and operate at low power outputs, typically in the range of 25 to 500 VA, to avoid influencing the primary circuit.^[2] This design focus on precision and isolation distinguishes them from power transformers, which handle megavolt-amperes for grid interconnection rather than signal reproduction.^[1] Voltage transformers are rated for primary voltages up to 765 kV in modern transmission systems, accommodating extra-high-voltage applications, while secondary voltages are standardized at 120 V for primaries up to 24 kV and 115 V or 110 V for higher ratings to interface with conventional instrumentation.^[1] These ranges align with industry standards like those from IEC and ANSI, ensuring compatibility across global power infrastructures.^[7]

Principle of operation

Voltage transformers operate on the principle of electromagnetic induction, where an alternating current in the primary winding, connected to a high-voltage circuit, generates a varying magnetic flux in the core that induces a proportional voltage in the secondary winding connected to a low-voltage measurement or protection circuit.^[8] This process allows safe isolation and scaling of high voltages to levels suitable for instrumentation without drawing significant power from the primary side.^[8] In an ideal voltage transformer, the relationship between the secondary voltage V_s and primary voltage V_p is given by the turns ratio:

\frac{V_s}{V_p} = \frac{N_s}{N_p}

where N_s and N_p are the number of turns in the secondary and primary windings, respectively. This equation derives from Faraday's law of electromagnetic induction, which states that the induced electromotive force (EMF) in a coil is \mathcal{E} = -N \frac{d\Phi}{dt}, with \Phi as the magnetic flux. For the primary winding, V_p \approx N_p \frac{d\Phi}{dt}, and for the secondary, V_s \approx N_s \frac{d\Phi}{dt}, assuming the flux \Phi is the same through both windings due to the shared core and neglecting resistance; dividing these yields the voltage ratio.^[9] In practice, non-ideal behavior arises from the magnetizing current, a reactive component of the no-load current that creates the magnetic flux and lags the voltage by 90°, leading to a small voltage drop across the primary impedance.^[8] Core losses, including hysteresis and eddy currents, further deviate from ideality by dissipating energy as heat, influenced by the flux density and core material properties.^[10] To minimize these losses, voltage transformers employ laminated cores made of silicon steel, a soft magnetic material with high permeability and low hysteresis that concentrates the magnetic flux while reducing eddy currents through thin laminations and silicon's resistivity.^[10] This design enhances efficiency by limiting energy dissipation in the core during flux reversals.^[11]

Key parameters

Voltage ratio

The voltage ratio of a voltage transformer defines the proportional relationship between the primary voltage, which is connected to the high-voltage system, and the secondary voltage, which provides a standardized low-voltage output for measurement or protection devices. This ratio is typically expressed as a fraction or nominal value, such as 14,400:120 V for distribution systems or 115,000:115 V for higher transmission levels, ensuring the secondary output remains proportional to the primary input under nominal conditions.^[1]^[12] The voltage ratio is calculated as the nominal primary voltage divided by the nominal secondary voltage, yielding a dimensionless value that represents the transformer's scaling factor; for instance, a 480:120 V transformer has a ratio of 4:1. Standard secondary voltages are set at 120 V for systems up to 24 kV and 115 V for higher voltages to align with metering equipment compatibility, as specified in industry norms. This calculation assumes ideal linear behavior, where the ratio directly corresponds to the turns ratio of the primary to secondary windings.^[1]^[12]^[8] Ratio errors arise primarily from non-linearities in the magnetic core, such as saturation effects that cause deviations in the magnetizing current and flux distribution, leading to inaccuracies in the secondary voltage output relative to the expected proportional value. These errors, quantified as a percentage deviation from the nominal ratio (e.g., ±0.15% for high-precision metering classes), can degrade measurement precision, particularly at voltages exceeding 90–110% of the rated value, where core non-linearity amplifies the discrepancy between primary and secondary voltages. Such impacts are critical in applications requiring exact scaling, as even small errors can propagate in protective relaying or revenue metering systems.^[12]^[8] Selection of the voltage ratio depends on the system's nominal voltage level, with lower ratios (e.g., 7,200:120 V) suited for distribution networks operating at 15 kV and higher ratios (e.g., 230,000:115 V) required for transmission lines up to 765 kV to match insulation classes and ensure safe, proportional voltage reduction. Criteria emphasize compatibility with the line-to-line system voltage, where the transformer's primary rating must exceed the maximum system voltage by a safety margin, such as 110% continuous operation capability, to prevent overexcitation while maintaining ratio integrity across varying load conditions.^[1]^[12]

Burden

In voltage transformers, the burden refers to the total electrical load connected to the secondary circuit, encompassing the impedance of devices such as metering instruments, protective relays, and interconnecting cables. This load is quantified as the apparent power in volt-amperes (VA) that the transformer can deliver under rated primary voltage conditions while adhering to its specified accuracy class.^[13]^[8] Standard burden classes for voltage transformers are designated in VA ratings, with common values including 10 VA, 25 VA, 75 VA, 100 VA, and up to 500 VA, as defined by international standards such as IEC 61869-3. These ratings ensure the transformer operates within performance limits at a specified power factor, typically 0.8 lagging, and are selected based on the aggregate secondary load to prevent performance degradation.^[13]^[8] The maximum allowable burden is determined by the equation:

\text{Burden (VA)} = \frac{V_s^2}{Z_\text{load}}

where V_s is the rated secondary voltage and Z_\text{load} is the total impedance of the connected load. Exceeding this rated burden results in voltage drops across the secondary winding, amplified ratio and phase errors, and potential overheating due to increased Joule losses in the windings and core, which can compromise insulation integrity and reduce the transformer's operational lifespan.^[14]^[15] Excessive burden also interacts with the transformer's accuracy limits, leading to measurements outside the intended error bounds.^[16]

Accuracy

Accuracy of a voltage transformer refers to the degree of closeness between the secondary output voltage and the ideal proportional representation of the primary voltage, with deviations primarily quantified as percentage errors in magnitude and phase.^[1] This precision is critical for applications requiring reliable voltage measurement or relaying, ensuring the transformed signal remains faithful to the input within specified limits.^[8] Voltage transformers are assigned accuracy classes based on international standards, such as those outlined in IEC 61869-3 (formerly IEC 60044-2), which define maximum permissible errors under rated operating conditions. For metering purposes, common classes include 0.2, 0.5, and 1.0, where the class number corresponds to the maximum percentage ratio error (e.g., 0.2% for a class 0.2 device) at 80–120% of rated primary voltage and 25–100% of rated burden, enabling precise energy billing.^[8] In protection applications, classes like 3P and 6P permit higher errors of up to 3% and 6% respectively, prioritizing transient response over fine precision to support fault detection at voltages as low as 5% of rated.^[8] The connected burden influences these errors, with accuracy guaranteed only within the specified load range to account for variations in secondary circuit impedance.^[8] The principal sources of error in voltage transformers are ratio error and phase angle error, both arising from non-ideal magnetic and electrical characteristics. Ratio error quantifies the discrepancy between the actual secondary voltage and the nominal value derived from the primary voltage divided by the marked transformation ratio, expressed as a percentage of the true ratio.^[1] Phase angle error measures the deviation in the angular position of the secondary voltage relative to the primary, where the ideal is a 180-degree opposition; this error, typically in minutes or degrees, affects power factor calculations and relay timing.^[1] These errors stem from factors like core magnetization, winding resistances, and leakage fluxes, which cause the secondary voltage to deviate from perfection.^[8] Testing methods for accuracy involve direct comparison of the device under test with calibrated standard reference transformers to isolate and quantify errors under controlled rated conditions of frequency, voltage, and burden. Techniques such as the inductive voltage divider or comparative null method connect the test and reference units in opposition, using detectors to balance voltages and derive the ratio correction factor (indicating magnitude error) and phase displacement (for angular error), achieving precisions down to parts per million in ratio and microradians in phase.^[17] Such procedures, performed in accredited laboratories, ensure compliance with class limits by simulating operational burdens and verifying performance across the specified voltage range.^[8]

Design and construction

Physical construction

Voltage transformers, also known as potential transformers, feature a core constructed from high-permeability silicon steel laminations to ensure efficient magnetic flux conduction while minimizing core losses and hysteresis.^[18] The windings consist of a primary coil designed for the high-voltage input, typically with more turns of insulated copper or aluminum wire, and a secondary coil with fewer turns to step down the voltage to a standard low level such as 110 V or 120 V. These windings are arranged concentrically around the core, with the secondary often placed closer to the core for better magnetic coupling and ease of insulation.^[19] Insulation systems in voltage transformers are critical for high-voltage isolation and vary by design to suit environmental and operational needs. Oil-immersed types use mineral oil combined with paper insulation to provide dielectric strength, cooling, and protection against partial discharges, commonly applied in outdoor installations up to high voltages. Dry-type constructions employ cast epoxy resin, such as hydrophobic cycloaliphatic epoxy (HCEP), which offers resistance to arc tracking, ozone, and ultraviolet degradation without the risk of oil leaks, making them suitable for indoor or polluted environments. Gas-insulated variants utilize sulfur hexafluoride (SF6) for superior insulation in compact, high-voltage applications, though they require sealed enclosures to contain the gas. However, due to SF6's high global warming potential, regulations in regions like the US (CARB phase-out from 2025) and EU (F-gas bans from 2026) are promoting alternatives such as g3 or clean air insulation. Emerging alternatives include fluoronitrile/CO2 mixtures (e.g., g3) for reduced environmental impact, compliant with 2025+ regulations.^[20]^[21]^[22] Enclosures for voltage transformers are engineered for safety, durability, and accessibility, differing between indoor and outdoor use. Indoor models are typically compact and dry-type, housed in non-conductive resin or metal casings with plug-in terminals for switchgear integration. Outdoor designs incorporate weatherproof housings, often with porcelain or composite polymer insulators, and feature high-voltage bushings for secure connections to overhead lines or busbars, ensuring creepage distances meet pollution level requirements. These bushings protrude from the enclosure to isolate the internal components from external voltages.^[19]^[23] Size and weight scale with voltage ratings to accommodate insulation thickness and structural integrity. For medium-voltage applications like 11 kV, units are relatively compact, often weighing around 25-35 kg with dimensions under 1 meter in height for indoor models. High-voltage transformers rated at 220 kV require larger enclosures for extended insulation paths, typically weighing 100-200 kg or more, with heights exceeding 2 meters to support elongated bushings and robust mounting bases. External markings on these enclosures, such as rating plates, indicate voltage class, accuracy, and serial numbers for identification and maintenance.^[24]^[25]

Markings and labeling

Voltage transformers are equipped with standardized markings and labels to ensure safe installation, proper connection, and compliance with operational specifications. These markings typically appear on a durable nameplate affixed to the transformer's enclosure, often on the side or top for easy access during inspection and maintenance. The exact requirements vary by regional or international standards, such as IEC 61869-3 for inductive voltage transformers and IEEE C57.13 for instrument transformers in North America.^[26]^[12] Under IEC 61869-3, the rating plate must include the manufacturer's name or trademark, type or designation, serial number, year of manufacture, rated primary voltage (U_Pr), rated secondary voltage (U_Sr), rated output (S_r), rated voltage factor (F_V) and its duration, accuracy class, rated frequency (f_r), insulation level, and total creepage distance where applicable. Similarly, IEEE C57.13 mandates nameplate information such as the manufacturer's details, serial number, year of manufacture, rated primary and secondary voltages, basic impulse insulation level (BIL), rated frequency, thermal burden rating, accuracy class, and confirmation of compliance with the standard, including no detectable PCB levels for oil-filled units at production. These elements provide essential data for verifying the transformer's suitability for metering, protection, or other applications without needing internal disassembly.^[26]^[12] Polarity markings are critical for correct phasing and to prevent phase reversal during connections, which could lead to measurement errors or equipment damage. In IEC 61869-3, primary terminals are labeled "A" for line and "N" for neutral or earthed, while secondary terminals use "a" for line and "n" for neutral, with additional windings marked sequentially (e.g., "b," "c"). Under IEEE C57.13, high-voltage (primary) terminals are designated "H1" and "H2," low-voltage (secondary) as "X1" and "X2," with H1 and X1 indicating the same polarity; multiple secondaries use "Y" or "Z" suffixes. These labels are permanently applied near the terminals or on the nameplate for visibility.^[26]^[12] Safety labels, including high-voltage warnings and handling instructions, are also required to mitigate risks during operation and maintenance. Both standards emphasize durable, weather-resistant labels cautioning against high-voltage exposure, often with symbols for grounding and isolation procedures. The date of manufacture is explicitly noted on the nameplate to track aging and compliance with evolving safety regulations. These markings collectively facilitate traceability, interoperability, and adherence to electrical safety protocols.^[26]^[12]

Types

Inductive voltage transformers

Inductive voltage transformers, also known as potential transformers, operate on the principle of inductive coupling using a ferromagnetic core to step down high primary voltages to proportional secondary voltages for measurement and protection purposes.^[26] The device functions similarly to a small power transformer, with the secondary voltage being substantially proportional to the primary voltage and featuring a small phase displacement, ensuring high efficiency in replicating system voltages.^[27] In construction, the primary winding consists of multiple turns designed to handle elevated voltages, wound around a laminated ferromagnetic core operated at low flux density to limit the magnetizing current and enhance linearity.^[27] The secondary winding, with fewer turns, provides the output, often with turns compensation to correct ratio errors. Insulation is typically oil-immersed for cooling and dielectric strength in units above 36 kV, while dry-type designs suffice for lower ratings; single-phase configurations predominate for higher voltages to manage mechanical stresses.^[27] These transformers offer high accuracy at standard power frequencies of 50/60 Hz, achieving error classes as precise as 0.1 for metering applications, making them reliable for both indoor and outdoor installations up to 145 kV or higher, depending on design.^[26]^[27]^[28] However, their ferromagnetic core and inductive nature result in larger size and weight compared to alternative designs, particularly at elevated voltages, which limits scalability. Additionally, they are prone to ferroresonance—a nonlinear resonance interaction with system capacitances during switching—that can produce overvoltages up to 3.5 per unit and damage insulation.^[29]

Capacitor voltage transformers

Capacitor voltage transformers (CVTs), also known as coupling capacitor voltage transformers, are specialized devices employed in high-voltage applications to measure and step down voltages from transmission lines. They operate by using a capacitive voltage divider, consisting of a stack of high-voltage capacitors, to initially reduce the line voltage to an intermediate level, typically 5-20 kV, which is then further stepped down by an inductive transformer to standard metering or protection levels. This configuration allows CVTs to interface safely with relays, meters, and control systems while providing isolation from the high-voltage environment.^[30]^[31] The primary components of a CVT include the capacitor divider head, which houses serially connected capacitor elements (often made of polypropylene film or paper impregnated with oil) within a porcelain insulator for high-voltage withstand; an intermediate step-down transformer, typically filled with mineral oil and enclosed in a base housing; and a tuning or compensating reactor connected in parallel with the divider to achieve resonance at the system frequency (50 or 60 Hz), thereby minimizing phase errors. Additional elements, such as a ferroresonance suppression circuit (either passive or active), damping devices, and sometimes a high-voltage terminal for power line carrier (PLC) coupling, are integrated to enhance stability and functionality. The capacitor stack forms the high-impedance arm (C1, around 100 pF) and low-impedance arm (C2, around 2000 pF), with the reactor inductance calculated as L = \frac{1}{\omega^2 (C_1 + C_2)} to compensate for the capacitive reactance.^[30]^[31]^[32] CVTs offer several advantages over inductive voltage transformers, particularly for extra-high-voltage (EHV) systems rated at 132 kV and above, up to 765 kV or higher. Their capacitive design results in lower weight and smaller dimensions, facilitating easier installation and reduced foundation requirements in substations. They are also more economical to manufacture and better suited to harsh environmental conditions due to their robust porcelain construction, which provides high creepage distances (44-55 cm/kV) for pollution resistance. Additionally, the inherent capacitor divider enables direct coupling for power line carrier communication systems, allowing simultaneous voltage measurement and data transmission over the same line without extra hardware.^[30]^[31]^[33] Despite these benefits, CVTs have notable limitations, including reduced accuracy at frequencies deviating from the nominal 50/60 Hz, where detuning of the resonance circuit can introduce phase and magnitude errors. They are also sensitive to environmental factors, such as temperature variations (e.g., a ±40°C change can alter capacitance by up to 3.2%, affecting dielectric constants in materials like polyester or polypropylene) and humidity or pollution, which impact surface resistance and overall performance. Other drawbacks include poor transient response during faults (with oscillations lasting 1-2 cycles) and potential for ferroresonance, necessitating suppression circuits. CVTs can be designed to meet specific burden and accuracy requirements, akin to those for inductive types, though their capacitive elements require compensation for optimal performance.^[30]^[32]

Applications and standards

Metering and protection uses

Voltage transformers are essential in metering applications, where they step down high system voltages to standardized low levels, such as 11 kV to 110 V, for use by energy meters in substations.^[34] This scaling enables precise measurement of electrical energy consumption, supporting accurate billing, load monitoring, and power quality analysis in utility systems.^[35] By isolating high-voltage lines from metering instruments, these transformers ensure operator safety while providing reliable data for revenue collection and grid management.^[35] In protection roles, voltage transformers deliver proportional voltage signals to protective relays, allowing detection of faults such as overvoltage, undervoltage, and phase imbalances in power systems.^[34] These signals enable relays to respond rapidly by triggering circuit breakers or other isolation mechanisms, thereby preventing equipment damage and maintaining system stability during abnormal conditions.^[35] Designed to handle transient stresses, voltage transformers in protection setups prioritize responsiveness over metering precision, though sufficient accuracy is required to avoid false trips.^[34] Voltage transformers integrate into electrical systems in single-phase or three-phase configurations, depending on the application scale and grid requirements. Single-phase units are typically deployed for monitoring individual phases in smaller distribution setups or dedicated fault detection.^[34] In contrast, three-phase configurations offer compact, efficient measurement for balanced systems, commonly used in medium-voltage (1–72.5 kV) distribution grids to oversee busbars, feeders, and switchgear simultaneously.^[34] For instance, in urban distribution networks, three-phase voltage transformers provide synchronized voltage data across phases, facilitating coordinated control and anomaly detection in interconnected lines.^[35] In smart grids, voltage transformers support real-time monitoring by interfacing with digital systems for advanced metering and protection. Optical voltage transformers, in particular, integrate seamlessly into digital substations, offering electromagnetic interference resistance and enabling continuous data streaming for predictive fault analysis and dynamic load balancing.^[35] This deployment enhances grid resilience, as seen in modern utilities where they contribute to automated responses during peak demand or disturbances.^[34]

International standards

The primary international standards governing voltage transformers, also known as instrument voltage transformers, are the IEC 61869 series developed by the International Electrotechnical Commission (IEC) and the ANSI/IEEE C57.13 standard from the Institute of Electrical and Electronics Engineers (IEEE).^[7]^[36] The IEC 61869 series, first published in the early 2010s as a replacement for the older IEC 60044 standards, provides a comprehensive framework for instrument transformers, with IEC 61869-1 outlining general requirements applicable to voltages over 1 kV AC or 1.5 kV DC, IEC 61869-3 specifying additional requirements for inductive voltage transformers, and IEC 61869-5 addressing capacitor voltage transformers.^[7]^[37] In North America, IEEE C57.13-2016 establishes requirements for both current and voltage instrument transformers, including electrical, mechanical, and safety characteristics for systems up to 115 kV and above.^[36]^[12] These standards mandate rigorous testing protocols to ensure reliability and safety, focusing on dielectric strength, temperature rise, and partial discharge measurements.^[38] Dielectric strength is verified through power-frequency withstand tests, such as the wet applied voltage test in IEC 61869-1 for transformers rated up to 245 kV, and induced voltage tests in IEEE C57.13 that simulate operational stresses.^[38]^[36] Temperature rise tests evaluate thermal performance under rated load conditions, limiting allowable increases to prevent insulation degradation, as specified in both IEC 61869-1 and IEEE C57.13.^[39] Partial discharge testing, guided by IEC 60270 and referenced in IEEE C57.13, measures insulation integrity by detecting discharges below 10 pC at rated voltage.^[3]^[40] Key differences between the standards include their emphasis on accuracy limits and additional qualifications. IEC 61869 prioritizes defined accuracy classes (e.g., 0.1 to 3 for metering) with strict limits on ratio and phase angle errors under harmonic conditions, ensuring compatibility with protective relaying and measurement applications.^[41] In contrast, IEEE C57.13 incorporates seismic qualification requirements for transformers in high-risk areas, alongside more stringent dielectric test levels compared to IEC, such as higher induced voltage durations.^[38]^[42] Post-2000 updates to these standards have addressed modern challenges like harmonic distortion and digital metering integration. The transition to IEC 61869 around 2011 introduced provisions for low-power instrument transformers (LPITs) in parts 6, 10, and 11, enhancing compatibility with digital interfaces and harmonic-rich environments up to the 50th order.^[43] IEEE C57.13 revisions, including the 2016 edition, aligned with harmonic assessment needs by referencing IEEE 519 limits and supporting non-conventional transformers for smart grid applications.^[36]^[44]

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Oct 4, 2010 · Change with load: When temperature and voltage are held constant, a change in the magnitude of the positive polarity pulses between light ...
[39]
CT Accuracy Standards - Continental Control Systems, LLC
The IEC 60044-1 and IEC 61869-2 accuracy limits are simpler than C57.13, only defining allowed ratio (accuracy) and phase angle errors. For the Accu-CT, we meet ...
[40]
[PDF] Differences & Similarities in IEC and IEEE Standards for Current ...
This paper is the first part of the two part series and discusses mainly on similarities and differences in specifying Current transformers to IEC – 61869 and ...
[41]
10 AND IEC 61869 –11 PASSIVE SENSORS AND THEIR ...
IEC 61869-10/11 standards define requirements for low-power transformers (LPCT/LPVT) connected to IEDs, and the connection must not affect low voltage levels.
[42]
Understanding the IEEE 519 – 2014 standard for Harmonics | Elspec
Mar 7, 2024 · The IEEE 519-2014 standard defines the voltage and current harmonics distortion criteria for the design of electrical systems.Missing: 2000 | Show results with:2000