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- Low-voltage breakers - Confirm and/or apply settings provided by others. Perform applicable tests to determine functions and characteristics of each operating element and expected reaction; evaluate the results. Confirm correct insulation and connection.
- Characteristics of Circuit Breaker Trip Curves and Coordination Time-current curves are used to show the amount of time required for a circuit breaker to trip at a given overcurrent level.
- Primary vs. Secondary Injection Testing for Circuit Breakers The field-testing and calibration of solid-state trip units can be performed by either primary current injection method or secondary current injection method.
- Zone Selective Interlocking (ZSI) Basic Principles This guide provides a basic overview of zone selective interlocking principles and test procedures.
- Current relays - Confirm and/or apply settings provided by others. Perform applicable tests to determine functions and characteristics of each operating element and expected reaction; evaluate the results. Relays can include phase overcurrent, current balance, negative sequence, zero sequence, thermal, and ground fault.
- Applications and characteristics of overcurrent potection relays (ANSI 50, 51) 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.
- Negative Sequence Relays protects the generator and motor from the unbalanced load which mainly occurs because of the phase-to-phase faults
- Ground Fault Protection Systems: Performance Testing Basics Performance testing of ground fault systems is required by National Electrical Code (NEC) sections 230-95 (C) and 517-17 (D). Ground fault protection can be provided for 3-wire and 4-wire equipment fed from a solidly grounded 4-wire supply, wye or delta using residual or zero sequence current sensing.
- Thermal Relays when a bimetallic strip is heated up by a heating coil carrying over current of the system, it bends and makes normally open contacts.
- Directional and power relays - Confirm and/or apply settings provided by others. Perform applicable tests to determine functions and characteristics of each operating element and expected reaction; evaluate the results. Relays can include directional-power, directional-overcurrent, watt, var, and power-factor types.
- Directional Overcurrent Relaying (67) Concepts [PDF] Directional overcurrent relaying (67) refers to relaying that can use the phase relationship of voltage and current to determine direction to a fault.
- Power Directional Relays Protection against excess power flow in a predetermined direction. For anti-motoring protect on of AC generators.
- Directional Relays: Principles and Applications [Video] In this video, you will learn about the basic principles, application, and operation of directional relays in power distribution systems.
- Voltage relays - Confirm and/or apply settings provided by others. Perform applicable tests to determine functions and characteristics of each operating element and expected reaction; evaluate the results. Relays can include overvoltage, undervoltage, phase-sequence, and negative-sequence voltage types.
- Under/Overvoltage Relays 27/59 protection for generators, motors, and transformers against adverse system voltage conditions.
- Differential relays - Confirm and/or apply settings provided by others. Perform applicable tests to determine functions and characteristics of each operating element and expected reaction; evaluate the results. Relays can include line, transformer, bus, unit, and rotating machine protection.
- Differential protection principles by comparing two currents either in magnitude or in phase or both we can determine a fault and issue a trip decision if the difference exceeds a predetermined set value.
- Testing Numerical Transformer Differential Relays [PDF] This paper presentes three types of test for transformer differential protection: Transformer Differential Characteristic Boundary Test, Ground Differential Sensitivity Test, and Even Harmonic Restraint during Transformer Inrush.
- Other relay types - Confirm and/or apply settings provided by others. Perform applicable tests to determine functions and characteristics of each operating element and expected reaction; evaluate the results. Relays can include timing, reclosing, temperature, auxiliary, lockout, alarm, and control types.
- Protective Relay Testing and Maintenance Overview This guide provides a comprehensive overview of inspection and test procedures for protective relays in electrical power systems.
- Protective Relay Protection Element Tests a summary of protective relay functions and their appropriate protection element tests.
- Circuit Breaker Trip Defeat Switch [PDF] The circuit breaker trip defeat switch allows the owner to take the functional testing of the protective relay scheme and extend it all the way to the trip coil without opening the circuit breaker, thus confirming that the relay's output contacts will indeed pick up the lockout relays and that the lockout contacts will energize the trip coil of the circuit breaker.
- List of Relay Types Understand the operating characteristics of Latching, Contactor, Timing, Buchholz, Overload, and Solid-State relays.
- Relay Selection Guide [PDF] If component failure is inevitable, then it is necessary to provide a means of detecting these failures.
- Operation, Maintenance, and Field Test Procedures for Protective Relays and Associated Circuits [PDF]
- Fuses - Confirm correct type, rating and application for project use and specifications. Measure fuse resistance and evaluate.
- Fuseology: Medium Voltage Fuses Fuses above 600V are classified under one of three classifications as defined in ANSI/IEEE C37.40
- How A Fuse Operates The fuse is a reliable overcurrent protective device, primarily used as a circuit protection device for overcurrents, overloads and short-circuits.
- Selecting Protective Devices Handbook A comprehensive guide to electrical overcurrent protection and electrical design considerations.
- UL Fuse Classification Chart Safety standards have culminated in the establishment of distinct classes of low-voltage (600 volts or less) fuses, Classes RK1, RK5, G, L, T, J, H and CC being the more important.
- How to Read A Fuse Time-Current Curve A time-current characteristic curve, for any specified fuse, is displayed as a continuous line representing the average melting time in seconds for a range of overcurrent conditions.
- Tech Quiz: Fuses [PDF] Tech Quiz #79 Spring 2007 NETA World
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