Category Archive for: «Energy and Power»

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Let’s analyse phase-to-earth faults in a single-incomer power system

Detect and isolate… Power-system protection should detect faults and isolate the faulty parts of the power system while keeping the fault-free parts in operation. Protection units are chosen according to the power-system configuration (parallel operation of generators or transformers, loop or radial power system, neutral earthing arrangement…). Resistance earthing on the transformer Earth fault protection units […]

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18 Key Terms Defined In NEC System Grounding Requirements

System Grounding Arrangement The topic of system grounding is extremely important, as it affects the susceptibility of the system to voltage transients, determines the types of loads the system can accommodate, and helps to determine the system protection requirements. The system grounding arrangement is determined by the grounding of the power source. For commercial and industrial […]

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An Example of the Effectiveness of Directional Overcurrent Relays (ANSI 67, 67N)

When fault currents can flow in more than one direction… When fault currents can flow in more than one direction with respect to the load current it is often desirable to determine which direction the fault current is flowing and trip the appropriate devices accordingly. This is usually due to the need to de-energize only those parts […]

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Applications and Characteristics Of Overcurrent Relays (ANSI 50, 51)

50/51 and 50/51N relays Overcurrent relays are the most commonly-used protective relay type. Time-overcurrent relays are available with various timing characteristics to coordinate with other protective devices and to protect specific equipment. Instantaneous overcurrent relays have no inherent time delay and are used for fast short-circuit protection. Figure 1 below shows the timing characteristics of several typical […]

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What Is Earth And Why And How Do We Connect To It?

Zero Potential The thin layer of material which covers our planet – rock, clay, chalk or whatever – is what we in the world of electricity refer to as earth. So, why do we need to connect anything to it? After all, it is not as if earth is a good conductor. It might be […]

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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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Energy Efficiency Aspects of Electric Motors

Load Efficiency Three-phase squirrel-cage induction motors comprise a considerable percentage of the electrical load in the United States. Design, operation, and maintenance of these machines is well described in some of the articles already published. This technical article focuses on their energy efficiency aspects. Induction motors typically range in full load efficiency from about 87% […]

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Maintenance Management Of Electrical Equipment (Condition Monitoring Based) – Part 6

Read previous parts of this serie – Part 1 | Part 2 | Part 3 | Part 4 and Part 5 Content: Proper Use of Predictive Technologies Merits and Demerits of CDM program Advantages Disadvantages CDM is more than maintenance Conclusion Proper Use of Predictive Technologies System components, such as circuit breakers, transformers, cables, etc. are an integral part of the electrical system […]

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The need for electric energy is never ending

Distributed generation As you guess, yes, the need for electric energy is never ending. Along with the growth in demand for electric power, sustainable development, environmental issues, and power quality and reliability have become concerns. Electric utilities are becoming more and more stressed since existing transmission and distribution systems are facing their operating constraints with […]

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Rating Definitions Applied to Low Voltage Molded-Case Circuit Breaker (MCCB)

For system protection 600V and below The molded-case circuit breaker is the “workhorse” for system protection 600V and below. A circuit breaker is a device designed to open and close by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating. The following terms apply […]

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