Category Archive for: «Energy and Power»

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8 important definitions to quantify Load Diversity

Load Details The most vital, but often the last to be acquired, pieces of information for power system design are the load details. An important concept in load planning is that due to non-coincident timing, some equipment operating at less than rated load, and some equipment operating intermittently rather than continuously, the total demand upon the power source […]

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Applications and Characteristics Of Differential Relays (ANSI 87)

Differential relays categories Differential relays generally fall within one of two broad categories: Current-differential and High-impedance differential Current-differential relays Current-differential relays are typically used to protect large transformers, generators, and motors. For these devices detection of low-level winding-to-ground faults is essential to avoid equipment damage. Current differential relays typically are equipped with restraint windings to which the CT […]

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What NEC says about design constraints for grounding systems

Design constraints Several key design constraints for grounding systems from the NEC are as follows. These are paraphrased from the code text: Ø Electrical systems that are grounded must be grounded in such a manner as to limit the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines and that will stabilize the […]

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9 Most Common Power Quality Problems

Description, Causes and Consequences The most common types of Power Quality problems are presented below along with their description, causes and consequences: Voltage sag (or dip) Very short interruptions Long interruptions Voltage spike Voltage swell Harmonic distortion Voltage fluctuation Noise Voltage Unbalance 1. Voltage sag (or dip) Description: A decrease of the normal voltage level […]

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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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