A fault indicator is a device which provides visual or remote indication of a fault on the electric power system. Also called a faulted circuit indicator (FCI), the device is used in electric power distribution networks as a means of automatically detecting and identifying faults to reduce outage time.
Overhead indicators are used to visualize the occurrence of an electrical fault on an overhead electrical system. Underground indicators locate faults on an underground system. Often these devices are located in an underground vault. Some fault indicators communicate back to a central location using radio or cellular signals.
Basic principles
OHL conductor mounted fault indicator. 11 kV distribution network with compensated neutral (GFN), at Ataahua, New Zealand
Typically fault indicators sense magnetic field caused by current flows through a conductor or cable. Some of them also use measurement of electric field caused by voltage in conductor.
During an electrical fault on a grounded system, additional current flows through a conductor, inducing a magnetic field, which is detected up by the fault indicator causing a state change on the mechanical target flag, LED, or remote indication device. Ground fault indicators for isolated ground systems sense the vector sum of the current and look for an imbalance indicating a fault on one or more of the three phases.
Systems with earthing through high resistance have low phase-to-ground fault currents so require high sensitivity of FI. When there are high load currents and low earth fault levels the line mounted fault indicators should look at the differential increase of the current (di/dt) instead of the absolute value.
In insulated neutral systems and systems with earthing through a Petersen coil, ground faults cannot be located with classical FI's at all. Capacitive current appears in overall faulted system so directional fault location devices are required.
Upon energization of the lines there could be high inrush current which may lead the fault indicators to false operation. Some fault indicators can block inrush current.
Advanced fault indicators should monitor the live line to distinguish fault currents from usual current surges. They operate only after making sure of the feeding circuit breaker/fuse has cut the power flow and the line is de-energized. To monitor the live line, some fault indicators look only at the magnetic field caused by the load current. to be independent from the load current, some FI’s look at the E field to check the voltage directly. This feature is used to reset the indicator after the line is re-energized too. Such indicators can also distinguish permanent faults from transient faults.
Some modern network protection systems e.g. GFN have time to clear a fault as small as possible down to 60ms so fault indicators must not only be highly sensitive and directional but additionally very fast. Modern fault indicators can detect faults with the duration of one cycle 18-20 ms. In the networks with low earth fault levels the indicators are required to be set to low values. In such cases the user should consider the downstream capacitive discharge current to avoid false operation of the non-directional indicators.
Some overhead line fault indicators called as pole mounted fault indicators can detect the live line and the fault current from 3 to 5 meters below the conductors.
High-voltage fuses commonly drop down after operating, making it obvious where the fault is. However fuses are rarely equipped with remote communication.
History
The first fault indicators came onto the market from Horstmann (Germany) in 1946. The E.O. Schweitzer Manufacturing Company (now a division of Schweitzer Engineering Laboratories, Inc.) introduced a product to the United States in 1948. The first fault indicators were manual reset devices. Later fault indicators automatically reset on system restoration or after a set period of time. More recent fault indicators communicate their status (tripped or reset) via cell signal or radio to a central station, handheld device, or pole-mounted receiver.
Recent developments include a remotely programmable overhead line indicator, fault indication for paper-insulated lead cable, and an overhead fault indicator for mesh networks.
In electrical engineering, ground or earth may be a reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth.
A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by overcurrent. Its basic function is to interrupt current flow to protect equipment and to prevent the risk of fire. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset to resume normal operation.
In electrical engineering, partial discharge (PD) is a localized dielectric breakdown (DB) of a small portion of a solid or fluid electrical insulation (EI) system under high voltage (HV) stress. While a corona discharge (CD) is usually revealed by a relatively steady glow or brush discharge (BD) in air, partial discharges within solid insulation system are not visible.
A residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI) is an electrical safety device that quickly breaks an electrical circuit with leakage current to ground. It is to protect equipment and to reduce the risk of serious harm from an ongoing electric shock. Injury may still occur in some cases, for example if a human receives a brief shock before the electrical circuit is isolated, falls after receiving a shock, or if the person touches both conductors at the same time.
An earth-leakage circuit breaker (ELCB) is a safety device used in electrical installations with high Earth impedance to prevent shock. It detects small stray voltages on the metal enclosures of electrical equipment, and interrupts the circuit if a dangerous voltage is detected. Once widely used, more recent installations instead use residual-current devices which instead detect leakage current directly.
A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary.
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In an electric power system, a switchgear is composed of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is directly linked to the reliability of the electricity supply.
Inrush current, input surge current, or switch-on surge is the maximal instantaneous input current drawn by an electrical device when first turned on. Alternating-current electric motors and transformers may draw several times their normal full-load current when first energized, for a few cycles of the input waveform. Power converters also often have inrush currents much higher than their steady-state currents, due to the charging current of the input capacitance. The selection of over-current-protection devices such as fuses and circuit breakers is made more complicated when high inrush currents must be tolerated. The over-current protection must react quickly to overload or short-circuit faults but must not interrupt the circuit when the inrush current flows.
An electronic component is any basic discrete electronic device or physical entity part of an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components and elements.
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A test light, test lamp, voltage tester, or mains tester is a piece of electronic test equipment used to determine the presence of electricity in a piece of equipment under test. A test light is simpler and less costly than a measuring instrument such as a multimeter, and often suffices for checking for the presence of voltage on a conductor. Properly designed test lights include features to protect the user from accidental electric shock. Non-contact test lights can detect voltage on insulated conductors.
In Electrical Power Systems and Industrial Automation, ANSI Device Numbers can be used to identify equipment and devices in a system such as relays, circuit breakers, or instruments. The device numbers are enumerated in ANSI/IEEE Standard C37.2 "Standard for Electrical Power System Device Function Numbers, Acronyms, and Contact Designations".
In an electric power system, a fault or fault current is any abnormal electric current. For example, a short circuit is a fault in which a live wire touches a neutral or ground wire. An open-circuit fault occurs if a circuit is interrupted by a failure of a current-carrying wire or a blown fuse or circuit breaker. In three-phase systems, a fault may involve one or more phases and ground, or may occur only between phases. In a "ground fault" or "earth fault", current flows into the earth. The prospective short-circuit current of a predictable fault can be calculated for most situations. In power systems, protective devices can detect fault conditions and operate circuit breakers and other devices to limit the loss of service due to a failure.
Pre-charge of the powerline voltages in a high voltage DC application is a preliminary mode which limits the inrush current during the power up procedure.
Stray voltage is the occurrence of electrical potential between two objects that ideally should not have any voltage difference between them. Small voltages often exist between two grounded objects in separate locations, due to normal current flow in the power system. Large voltages can appear on the enclosures of electrical equipment due to a fault in the electrical power system, such as a failure of insulation.
High voltage switchgear is any switchgear used to connect or disconnect a part of a high-voltage power system. This equipment is essential for the protection and safe operation, without interruption, of a high voltage power system, and is important because it is directly linked to the quality of the electricity supply.
An electric power system is a network of electrical components deployed to supply, transfer, and use electric power. An example of a power system is the electrical grid that provides power to homes and industries within an extended area. The electrical grid can be broadly divided into the generators that supply the power, the transmission system that carries the power from the generating centers to the load centers, and the distribution system that feeds the power to nearby homes and industries.
In an electric power system, overcurrent or excess current is a situation where a larger than intended electric current exists through a conductor, leading to excessive generation of heat, and the risk of fire or damage to equipment. Possible causes for overcurrent include short circuits, excessive load, incorrect design, an arc fault, or a ground fault. Fuses, circuit breakers, and current limiters are commonly used overcurrent protection (OCP) mechanisms to control the risks. Circuit breakers, relays, and fuses protect circuit wiring from damage caused by overcurrent.
This glossary of electrical and electronics engineering is a list of definitions of terms and concepts related specifically to electrical engineering and electronics engineering. For terms related to engineering in general, see Glossary of engineering.
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