Category Archive for: «Transformers»

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Practical Considerations of Transformer Heat and Noise

Unwanted electrical effects // In addition to unwanted electrical effects, transformers may also exhibit undesirable physical effects, the most notable being the production of heat and noise. Transformer noise is primarily a nuisance effect, but heat is a potentially serious problem because winding insulation will be damaged if allowed to overheat. Heating may be minimized by […]

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12 Transformer Factory Tests Briefly Explained

Factory tests The remainder of the twelve factory tests are briefly summarized below. The details of the test set connections and formulas of some of the listed tests are already described in separatly published articles, and for the rest you are directed to ANSI/IEEE Standard C57.12.90 for these details. This list is not complete, there […]

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Take Into Account the Losses When Purchasing Power Transformer

Transformer Price and Losses The Connection Losses and purchase price should be considered when deciding which transformer to purchase. The purpose of this technical article is to present a uniform approach that can be used to determine the dollar value of these losses over the life of the transformer. Below is typical wording of a transformer loss evaluation clause […]

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Procedure for Transformer Lightning Impulse Test

Purpose of the test The purpose of the impulse voltage test is to secure that the transformer insultations withstand the lightning overvoltages which may occur in service. Testing equipment Impulse generator Where: C1 – Impulse capacitor Rc – Charging resistor Rs – Series resistor Ra – Low-ohmic discharging resistor for switching impulse, Rb – High-ohmic discharging resistor for […]

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Understanding The Ratios Of Magnetic HV Instrument Current Transformers

Primary & secondary windings The primary winding is a part of the network, carrying the actual load current. The transformer’s secondary circuits usually consist of several units, each of them having its own magnetic core and winding. The transformer has a rated current transforming ratio, like for example 200/1 A, stating the rated primary current […]

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What to do if transformer has an excessive moisture content

Moisture measurement The term “moisture” in the transformer industry is commonly used to indicate water which is absorbed in the paper or dissolved in the oil. Occasionally, the terms “water” or “water content” are used as an alternative way to describe the same substance. Water in transformers can be found in different parts of the […]

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4 Power Transformer Protection Devices – Explained In Details

Oil Transformer protection The power transformer protection is realized with two different kinds of devices, namely the devices that are measuring the electrical quantities affecting the transformer through instrument transformers and the devices that are indicating the status of the physical quantities at the transformer itself. An example of the former could be current-based differential […]

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Network Distribution Transformers – Serving Grid and Spot Networks

Housed in vaults Network transformers, the distribution transformers that serve grid and spot networks, are large three-phase units. Network units are normally vault-types or subway types, which are defined as (ANSI C57.12.40-1982): Vault-type transformers // Suitable for occasional submerged operation Subway-type transformers // Suitable for frequent or continuous sub-merged operation Network transformers are often housed in vaults. Vaults […]

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Maintenance of Load Tap Changers (LTCs)

Regulating transformer’s level of reliability LTC maintenance is the basis for the regulating transformer’s high level of reliability. The background for maintenance recommendations is as follows: Oil // For LTCs where oil is used for arc-quenching, the arcing at the arcing switch or arcing tap switch contacts causes contact erosion and carbonization of the arcing […]

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6 Transformer Types You Can See In Commercial Installations

Transformer Types and their Characteristics Transformers in commercial installations are normally used to change a voltage level from a utility distribution voltage to a voltage that is usable within the building, and are also used to reduce building distribution voltage to a level that can be utilized by specific equipment. Applicable standards are the ANSI […]

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