Category Archive for: «Transformers»

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5 conditions for perfect parallel operation of single phase transformers

Parallel operation of transformers // In perfect parallel operation of two or more transformers, current in each transformer would be directly proportional to the transformer capacity, and the arithmetic sum would equal one-half the total current. However, there are 5 conditions for operating transformers in parallel and they are: Any combination of positive and negative […]

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Measurement of residual currents on a distribution feeder

Residual currents (earth fault) The measurement of the earth fault or residual currents on a distribution system feeder can be done by the so-called summation connection, where the three current transformers, one in every phase, are connected and the summated current is brought to the inputs of an earth fault protection relay. This is a […]

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Underground substations – Out of sight, out of mind

Underground substations // Underground substations help to bring high voltage electricity directly into the city center. The stations are environmentally friendly, almost unnoticeable, and have none of the planning problems encountered by surface-built solutions. Building new transformer substations in inner-city zones or expanding existing facilities is a challenging remit: Due to the lack of acceptance […]

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The Worst Transformer Inrush Current Occurs When…

Possibly 40 times the full-load current // When a transformer is first energized or reenergized after a short interruption, the transformer may draw inrush current from the system due to the core magnetization being out of sync with the voltage. The inrush current may approach short-circuit levels, as much as 40 times the transformer’s full-load […]

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HV/MV/LV Transformer Protection Schemes

Transformer protection // Transformer protection should take into account the power, voltage, vector group and the importance of the unit within a particular system. Depending on these factors, the transformers can be assigned to one of the two groups: MV/LV transformers HV/MV/LV transformers and autotransformers MV/LV transformers The protection of these units should include overcurrent […]

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Stop Transformer Noise With These Rules and Techniques

Precautions to minimize transformer noise There are a number of basic installation precautions and transformer mounting techniques which if carefully noted and followed, will minimize the audible sound level (noise) of energized transformers. Some of the more pertinent ones are noted below. 6 rules to limit transformer decibels 6 transformer installation techniques Transformer decibel limits // Proper […]

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8 Recommended Periodic Inspections of a Substation Transformer

Medium power transformer routine maintenance The following periodic tests and inspections are recommended for routine maintenance of the medium power substation transformer. Gauge readings Cooling fans Control wiring Paint finish Fluid dielectric test Bushing and surge arrester insulators Bushing terminals Gaskets 1. Gauge readings One month after initial energization and annually thereafter Gauge readings, ambient […]

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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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