Category Archive for: «Protection»

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Miniature Circuit Breakers (MCBs) For Beginners

Dual functions of a switch and a fuse This technical article focuses on the widely used miniature circuit breakers rated for 240 V or less. These are smaller and lower-rated versions of industrial-grade molded-case circuit breakers rated for 600 V or less. These miniature breakers, called air circuit breakers, are based on thermal, magnetic, or […]

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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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Lightning and surge protection of multi-megawatt wind turbines

Importance of protecting wind turbines There is an unabated trend for the utilisation of regenerative energy gained from wind turbines, solar, photovoltaic and biogas plants or geothermal heat. This is an enormous market potential not only for the energy industry but also for the suppliers and the electrical trade and that worldwide. In Germany meanwhile about 19,000 wind […]

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Danger And Control Of Static Electricity Buildup

Troubles that you can run into… The following are the dangers posed by static electricity: Ignition causing fire or explosion Damage to sensitive electronic components Electric shock to humans followed by accidents such as a fall Damage to mechanical components such as bearings due to sparking through the oil films on bearing surfaces. It is necessary […]

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When customer complains on equipment failure caused by overvoltage…

Customer explanations… While voltage sags and momentary interruptions cause the most widespread power quality problems, several other power quality disturbances can damage equipment, overheat equipment, disrupt processes, cause data loss, and annoy and upset customers. Often, customers complain of equipment failures, especially following power interruptions. Is it lightning? Voltage swells during faults? Some sort of […]

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4 Essential Qualities Of Electrical Protection

Fundamental Protection Requirements In generating stations, all electrical circuits and machines are subject to faults. A fault is generally caused by the breakdown of insulation between a conductor and ground or between conductors due to a variety of reasons. The result is a flow of excess current through a relatively low resistance resulting in severe […]

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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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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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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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