Category Archive for: «Medium Voltage»

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Medium Voltage Earthing Systems – Arrangements and Comparison

Neutral point connection method First, let’s define the different medium voltage earthing systems and then compare the advantages and disadvantages of each one. Earthing systems in medium voltage can be differentiated according to the neutral point connection method. The various earthing systems in medium voltage systems are different in the way they operate and each […]

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Current and voltage sensors as an alternative to traditional CTs and VTs

Sensors as alternative As an alternative for traditional primary current and voltage measurement techniques, the use of sensor technique is gaining field. This technique is typically applied to current and voltage measurement in medium-voltage metal-enclosed indoor switchgears. There are many undeniable advantages with sensors when compared to the traditional solutions: Non-saturable High degree of accuracy […]

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Degradation of Insulation in Switchgear (What’s Really Happening)

Partial Discharge (PD) Electrical insulation is subjected to electrical and mechanical stress, elevated temperature and temperature variations, and environmental conditions especially for outdoor applications. In addition to normal operating conditions, there are a host of other factors that may trigger accelerated aging or deterioration of insulation. Both normal and accelerated aging of insulation produce the […]

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Ring Main Unit (RMU) as an important part of secondary distribution substations

RMU A Ring Main Unit (RMU) is a totally sealed, gas-insulated compact switchgear unit. The primary switching devices can be either switch disconnectors or fused switch disconnectors or circuit breakers. Different combinations of these primary switching devices within the unit are commonly used. In case a circuit breaker is the switching device, it is also […]

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Inspection, Test and Measurement Procedures for LV and MV (up to 36kV) Switchgears

Importance of checks and maintenance Installed in clean, well ventilated or air-conditioned locations, switchgear will require little routine maintenance. Major inspection should be scheduled for power plant shutdowns and concentrate for low voltage switchboards on identifying contact wear, correct operation of interlocks, correct overload settings and fuse sizes, signs of overheating, and undue dirt or corrosion. For MV […]

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The Consumer Power Substation With Metering On Medium Voltage Side

Nominal voltage 1kV – 35kV A consumer power substation with metering on medium voltage side is an electrical installation connected to a utility supply system at a nominal voltage usually between 1kV – 35kV, which for example may supply a single MV/LV transformer (exceeding generally 1250 kVA), several MV/LV transformers or one or several MV/LV secondary […]

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34 Questions And Answers To Break the Myth About SF6 Gas In Electrical Equipment

Miracle gas or not? There are many published discussions and reports on various aspects of  SF6 gas (sulphur hexafluoride) usage in electrical equipment. Most of them are based on facts and researches, but some are not. Let’s try to answer the 34 questions and break the myth about this ‘miracle’ gas. Note that most of […]

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Rating Definitions Applied to Medium Voltage Fuses

Greater than 2400V and less than 69kV The definition of low voltage fuses is equally applicable to medium voltage fuses. Medium voltage level is defined by standard ANSI C84 as containing standard system voltages from 2400 through 69,000 V, and the high voltage level contains standard system voltages from 115 kV through 230 kV. Strictly-speaking, high voltage fuse standards […]

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Rating Definitions Applied to Medium Voltage Circuit Breaker

MV protection applications The medium voltage circuit breaker is the device of choice when sophisticated system protection at the medium voltage level is required. Most modern medium voltage circuit breakers use a vacuum as the interrupting means, although sulfur-hexafluoride (SF6) based units still exist and in use. Most modern medium voltage circuit breakers are rated on […]

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Microprocessor and conventional secondary systems compared

Reliable operation of the primary system Secondary systems are all those facilities needed to ensure reliable operation of the primary system, e.g. a high voltage substation. They cover the functions of controlling, interlocking, signalling and monitoring, measuring, counting, recording and protecting. With conventional secondary systems, the various functions are performed by separate devices (discrete components) […]

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