Category Archive for: «Transformers»

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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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Do Not Energize Oil-Filled Transformer Without Performing These 15 Tests and Checks!

Obligatory Checklist The following tests and checks should be performed at a minimum to ensure that the transformer is ready to be energized. Do not energize the transformer without performing these tests and checks. If any of below explained tests fail and transformer is energized anyway, it may lead to the serious hazard, and that’s […]

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Basic Transformer Routine Test – Measurement of Winding Resistances

Purpose of the measurement The resistance between all pairs of phase terminals of each transformer winding are measured using direct current. Furthermore the corresponding winding temperature is measured. The measured resistances are needed in connection with the load loss measurement when the load losses are corrected to correspond to the reference temperature. The resistance measurement […]

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4 Essential Features of Transformer On-Load Tap Changer (OLTC)

Done on the HV winding On-load tap changers (or circuit tap changers), as the name suggests, permit tap changing and hence voltage regulation with the transformer on-load. Tap changing is usually done on the HV winding for two reasons: Because the currents are lower, the tap changer contacts, leads, etc., can be smaller. As the […]

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An Example Of Transformer Overload and Short-Circuit Protection

NEC Article 450 // Transformers Vaults Transformer protection consists of both overload protection and short-circuit protection. Overload protection is usually accomplished via proper selection of the secondary overcurrent protective device. NEC Article 450 gives specific primary and secondary overcurrent device ratings that may not be exceeded. These vary depending upon the accessibility of the transformer […]

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Why cooling is essential for long transformer life?

Pushing loads over design limitations As you already know, cooling is really essential for long transformer life. Most transformers are designed for 55°C or 65°C rise. Using newer insulations such as Nomex, temperatures of 95°C and higher can be achieved. These temperatures can only be maintained if the transformer operating conditions do not exceed the […]

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