Protective relay

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In electrical engineering, relay protector is a relay device designed to guide circuit breakers when errors are detected. : 4 The first protective relay is an electromagnetic device, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as overcurrent, overload, flow power back, excess frequency, and low frequency.

Microprocessor-based digital protection relays now mimic the original device, as well as provide a type of protection and oversight that is not practical with electromechanical relays. Electromechanical relays provide only a basic indication of the location and origin of an error. In many cases, a single microprocessor relay provides functions that require two or more electromechanical devices. By combining multiple functions in one case, numerical relays also save capital costs and maintenance costs through electromechanical relays. However, due to their very long life span, tens of thousands of "silent sentinels" still protect the transmission lines and electrical equipment around the world. Important transmission lines and generators have dedicated chambers for protection, with many individual electromechanical devices, or one or two microprocessor relays.

The theory and application of these protective devices is an important part of the education of an electrical engineer specializing in power system protection. The need to act quickly to protect circuits and equipment as well as the general public often requires protective relays to respond and trip breakers in a few thousandths of a second. In some cases, the timing of this permit is determined by law or operating rules. A maintenance or testing program is used to determine the performance and availability of a protection system.

Based on the final application and applicable law, various standards such as ANSI C37.90, IEC255-4, IEC60255-3, and IAC set the relay response time to potential disturbance conditions.

Video Protective relay

Principle of operation

Electromechanical protective relays operate with either magnetic attraction, or magnetic induction. ^{: 14} Unlike type of electromechanical relay switching with fixed operating voltage threshold and usually unclear and operating time, the protective relay has the operating characteristics, time, and defined operations, can be selected, and can be adjusted properly (or other operating parameters). Protective relays can use arrays of induction, shaded-pole, magnetic, operation and coil restrictions, solenoid type operators, contact telephone relays, and phase transfer networks.

Protective relays can also be classified by the type of measurement they make. ^{: 92} The protection relay can respond to magnitudes such as voltage or current. Induced relays can respond to a two-quantity product in two field coils, which can as an example represent the power in the circuit.

"It is impractical to create a relay that develops the same torque as the result of two ac quantities, but this is not important: the only condition necessary for the relays is the arrangement and the arrangement can be made to fit the ratio regardless of the value of the component over a wide range. "^{: 92}

Some rolls of operation can be used to provide a "bias" to the relay, allowing the sensitivity of responses in one circuit to be controlled by another. Various combinations of "operating torque" and "retaining torque" can be produced in relays.

By using permanent magnets in magnetic circuits, relays can be made to respond to currents in one direction different from the others. Such a polarized relay is used on a direct-current circuit to detect, for example, reversing the current into a generator. These relays can be made bistable, maintaining closed contacts without coil currents and requiring a backflow to reset. For an AC circuit, this principle is extended with a polarization winding connected to a reference voltage source.

The light contact makes the sensitive relays operate quickly, but the small contacts can not carry or destroy heavy currents. Often the measuring relay will trigger an additional type of armature phone relay.

In large installations of electromechanical relays, it would be difficult to determine which device derived signal is tripping the circuit. This information is useful for operating personnel to determine possible causes of errors and to prevent re-occurrence. Relays can be equipped with a "target" or "flag" unit, which is released when the relay operates, to display different colored signals when the relay has been disconnected.

Maps Protective relay

Type according to construction

Electromechanical

Electromechanical relay can be classified into several types as follows:

"Armature" -the relay type has a rotating lever supported on a hinge or a blade-edge pivot, which carries a moving contact. This relay can work on alternating or direct current, but for alternating current, shading coil on ^{pole 14} is used to maintain the power of contact throughout the cycle alternating current. Since the air gap between the fixed coil and the armature move becomes much smaller when the relays are operated, the current required to maintain the closed relay is much smaller than the current to operate it first. "Return ratio" or "differential" is a measure of how much current should be reduced to reset the relay.

Application variations of the principle of attraction are plunger-type or solenoid operators. The reed relay is another example of the principle of attraction.

"Moving coil" meter using a wire loop transforms into a stationary magnet, similar to a galvanometer but with a contact lever rather than a pointer. This can be done with very high sensitivity. Another type of moving coil retains the coil from two conductive ligaments, which allows a very long coil trip.

Overflow current from disk induction

"Induction" disk meters work by inducing currents in a rotating disk; disc rotary movement operates contacts. Induced relay requires alternating current; if two or more coils are used, they must be on the same frequency if no net operating style is generated. This electromagnetic relay uses the principle of induction discovered by Galileo Ferraris in the late 19th century. The magnetic system in the overcurrent disk induced relay is designed to detect excessive currents in the power system and operates with a predetermined delay time when a certain overcurrent limit has been reached. To operate, the magnetic system in the relay produces a torque acting on a metal disc to make contact, according to the following basic torque/torque equation:

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Di mana ${\ displaystyle \ phi _ u}} Â$ dan ${\ displaystyle \ phi s}} Â Â$ adalah second flux dan $Â\; ÂÂ\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â?Â\; Â\; Â\; Â\; Â}Â\; Â\; ÂÂ\; Â\; Â\{\backslash \; displaystyle\; \backslash \; alpha\}\; Â\; Â$ adalah sudut phase antara flux

The following important conclusions can be drawn from the above equation.

• Two alternating fluxes with phase shift are required for torque production.
• Maximum torque is generated when two fluxes alternate 90 degrees apart.
• The resulting torque is stable and not a function of time.

The primary relay winding is supplied from the power system current transformer via a plug bridge, called the plug setting controller (psm). Usually seven braking or tape operations are equally spaced determining the relay sensitivity. The primary winding is located in the upper electromagnet. The secondary winding has connections on the upper electromagnet that is energized from the primary winding and connected to a lower electromagnet. Once the upper and lower electromagnets are energized they produce an eddy current induced into the metal disk and flow through the flux path. This eddy and flux current relationship creates torque proportional to the input current of the primary winding, since the two flux paths out of phase are 90 °.

In overcurrent conditions, the current value will be achieved which overcomes the control spring pressure on the spindle and magnetic braking, causing the metal disk to rotate toward fixed contact. The initial movement of the disk is also retained to the current critical critical value by the small slot that is often cut to the side of the disc. The time required for rotation to make contact depends not only on the current but also the backstop spindle position, known as the time multiplier (tm). Time multipliers are divided into 10 linear divisions from full rotation time.

Providing free relays of dirt, metal discs and spindles with contacts will reach fixed contacts, thereby sending signals to trips and isolating circuits, within designated time and current specifications. The relay current decrease is much lower than the value of its operation, and upon reaching the relay will be reset in reverse by the pressure of the control spring set by the braking magnet.

Static

Electronic amplifier applications for protective relays were described in early 1928, using vacuum tube amplifiers and continued until 1956. Devices using electron tubes were studied but never applied as commercial products, due to the limited amplitude of the vacuum tube. A relatively large standby current is required to maintain the temperature of the filament tube; an uncomfortable high voltage is required for the circuit, and the vacuum tube amplifier has difficulty with the wrong operation due to noise interruption.

Static relays have no or some moving parts, and become practical with the introduction of transistors. Measuring elements of static relays has been successful and economically constructed from diodes, zener diodes, avalanche diodes, unijunction transistors, pnp and npn bipolar transistors, field effect transistors or their combinations. ^{: 6} Static relays offer the advantage of higher sensitivity than pure electromechanical relays, because the power to operate the output contacts comes from a separate supply rather than a circuit signal. Static relays remove or reduce disconnected contacts, and can provide fast operation, long life, and low maintenance.

Digital

Digital protective relays were still in its early stages during the late 1960s. Experimental digital protection systems were tested in the laboratory and in the field in the early 1970s. Unlike the relays mentioned above, digital protection relays have two main parts: hardware and software ^{: 5} . The first commercially available digital protective relay in the world was introduced to the power industry in 1984. Apart from the development of complex algorithms to perform protective functions, microprocessor-based relays marketed in the 1980s did not integrate them. Microprocessor-based digital protection relays can replace the function of many discrete electromechanical instruments. This relay converts the voltage and current into a digital form and processes the measurements generated using a microprocessor. Digital relays can mimic the function of many discrete electromechanical relays in a single device, simplifying the design of protection and maintenance. Each digital relay can run a self-test routine to ensure readiness and alarm if an error is detected. Digital relays can also provide functions such as communication interfaces (SCADA), contact input monitoring, measurement, waveform analysis, and other useful features. Digital relays can, for example, store several sets of protection parameters, which allow the relay behavior to be changed during the maintenance of attached equipment. Digital relays can also provide protection strategies that are impossible to implement with electromechanical relays. This is especially true in high-voltage or multi-terminal circuits over long distances or in lines that are series or shunt compensation ^{: 3} They also offer benefits in self-testing and communication for supervisory control systems.

Numerical

The difference between digital and numerical protection relays lies at the point of good technical detail, and is rarely found in areas other than ^{Protection: Ch 7, pp 102} . Numerical relays are the product of technological advances from digital relays. Generally, there are several types of numerical protection relays. Each type, however, shares the same architecture, allowing designers to build entire system solutions based on relatively few flexible components. They use a high-speed processor that executes the appropriate ⁵¹ algorithm. Most numerical relays are also multifunctional and have several settings groups each often with dozens or hundreds of settings.

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Relay by function

The various protection functions available on a given relay are indicated by the standard ANSI device number. For example, a relay including function (51) will be a surge protector overcurrent time.

Overcurrent relay

Overcurrent currents are a type of protective relay that operates when the load current exceeds the pickup. The ANSI device number is 50 for instant over current (IOC) or Definite Time Overcurrent (DTOC). In a typical application the current relay is more connected to the current transformer and calibrated to operate at or above the specific current level. When the relay operates, one or more contacts will operate and energize for the circuit breaker (trip). Over time current relays must have been used extensively in the United Kingdom but the problem is inherent in slower operation due to errors closer to the source leading to the development of IDMT relays. ^{: pp 30 -31}

Default minimum time

A definite minimum time-shielding relay (IDMT) has been developed to address the shortcomings of the Time Great Time Relay. ^{: pp 30-31 : 134}

If the source impedance remains constant and the fault current changes significantly as we move away from the relay it will be advantageous to use IDMT overcurrent protection ^{: 11} to achieve protection speed on most protected circuits. ^{: 127} However, if the source impedance is significantly greater than the feed impedance then IDMT relay characteristics can not be exploited and DTOC can be utilized. Secondly if source impedance varies and becomes weaker with fewer generations during light load then this leads to a slower opening time so as to negate the destination IDMT relay. ^{: 143}

The IEC standard 60255-151 sets the IDMT relay curve as shown below. The four curves in Table 1 are derived from the English Standard BS that is now withdrawn 142. The other five, in Table 2, are derived from the ANSI C37.112 standard.

While it is more common to use IDMT relays for current protection it is possible to use the IDMT mode of operation for voltage protection ^{: 3} . It is possible to program the adjusted curves in some protective relays ^{: pp Ch2-9} and another manufacturer ^{: < span> 18} has a special curve specific to their relays. Some numeric relays can be used to provide more inverse voltage protection when : 6 or more negative current sequence protection. ^{: 915}

I _r = is the noise current ratio for current relay settings or Plug Setup Multiplier. ^{: pp 73} "Plug" is a reference of the era of electromechanical relays and is available in discrete : pp 37 step. TD is the Call Time setting.

                   P         S         M         =                                             P               r               yang               m               a               r               y               Ã,               f               a               u               yang               t               Ã,               c               u               r               r               dan               n               t                                       R               dan               yang               a               y               Ã,               c               u               r               r               dan               n               t               Ã,               s               dan               t               t               yang               n               g               Ã,               ÃÆ' -               Ã,               C               T               Ã,               r               a               t               yang               atau                                           {\ displaystyle PSM = {\ frac {Primer \ kesalahan \ {saat ini} Relay \ saat ini \ settings \ \ kali \ CT \ rasio}}}  Â

The above equation produces a "family" curve as a result of using different multiplex time settings (TMS). It is evident from the relay characteristic equation that larger TMS will result in a slower cleaning time for the given PMS (I _r ) value.

Distance relay/Impedance relay

The distance relay differs in principle from other forms of protection in that the performance is not regulated by the amount of current or voltage in the protected circuit but rather the ratio of these two quantities. The distance relay is actually a double-drive quantity relay with one coil energized by voltage and other coils by the current. The current element generates a positive torque or takes while the voltage element generates a negative torque or reset. The relay only operates when the V/I ratio falls below a predetermined value (or value specified). As long as the fault on the transmission line the noise current is increased and the voltage at the fault point decreases. The ratio V/I is measured at CT and PT. The voltage at the PT location depends on the distance between the PT and the error. If the measured voltage is smaller, it means the error is closer and vice versa. Therefore protection is called Distance Relay. The load flowing through the line appears as an impedance to the relay and the load is large enough (because the impedance is inversely proportional to the load) can cause the trip to relay even in the absence of error. ^{: 467}

The current differential protection scheme

The differential scheme acts on the difference between the currents entering the protected zone (which may be the bus bar, generator, transformer or other equipment) and the current leaving the zone. Errors outside the zone give the same interruption current as it enters and exits the zone, but errors in the zone appear as differences in currents.

"The protection of the differential is 100% selective and therefore only responds to errors within the protected zone.The boundary of the protected zone is uniquely determined by the location of the current transformer.Payment times with other protection systems are therefore not required, allowing to trip over without additional delay.Therefore protection differential fits as a fast main protection for all important plant items. "^{: 15}

Differential protection can be used to provide protection for zones with multiple terminals and can be used to protect channels, generators, motors, transformers, and other power plants.

The current transformer in the differential scheme should be chosen to have an almost identical response to the high current surplus. If "through error" produces a set of current transformers that saturate before the other, the zone differential protection will see the wrong "operation" and may be mismanagement.

GFCI circuit circuit breakers (basic fault circuit breakers) combine overcurrent protection and differential protection (not adjustable) in commonly available standard modules.

Directional relay

The direction relay uses a polar source or additional polarization current to determine the direction of the interference. Directional elements respond to phase shifts between the quantity of polarization and the quantity in operation. Fault can be found in the upstream or downstream relay location, allowing suitable protective devices to operate inside or outside the protection zone.

Sync check

Synchronization checking relay provides close contact when frequency and phase of two sources are similar to tolerance limits. A "harmonized counter" relay is often applied in which two power systems are connected, such as the switchyard that connects two power grids, or on the generator circuit breaker to ensure the generator is synchronized to the system before connecting.

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Resources

Relays can also be classified on the type of resources they use to work.

• The self-powered relay operates on energy derived from a protected circuit, through a current transformer used to measure the channel current, for example. This eliminates the cost and reliability issues of separate supplies.
• Additional power relays depend on the battery or external ac supply. Some relays can use AC or DC. Additional supplies must be very reliable during system errors.
• Multiple powered relays can also be powered, so that all batteries, chargers, and other external elements are made redundant and used as a backup.

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References

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External links

• Silent Sentinels 1949 online text edition

Source of the article : Wikipedia