Technical Articles

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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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Automation Migration Strategy in 3 Phases

Evolving the manufacturing systems Owing to competitive pressures in the marketplace, a company often needs to introduce a new product in the shortest possible time. The easiest and least expensive way to accomplish this objective is to design a manual production method, using a sequence of workstations operating independently. The tooling for a manual method […]

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Guidelines to Maintenance of Low Voltage Switchboard

Maintenance Benefits and Facilities A. Maintenance Program A well-executed maintenance program can provide the following benefits: Longer life of switchboard and fewer replacements; Reduced time on repairs and overhauls, and the option of scheduling them at an opportune time; Fewer failures with unexpected outages; Timely detection of any undesirable operating conditions which require correction; Improved plant […]

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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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14 energy-efficiency improvement opportunities in pumping systems

Detailed energy assessment Pump systems consist of pumps, driver, pipe installation and controls (such as ASDs or throttles) and are a part of the overall motor system. Below some of the energy efficiency opportunities for the pumping system are presented. Also, American Society of Mechanical Engineers (ASME) has published a standard that covers the assessment […]

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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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