Electrical

What is an autorecloser?

The recloser is used in overhead power lines as a protective device, basically, it is used for electrical protection. These devices are used in overhead lines, distribution systems so that they can prevent or interrupt faults. The auto recloser is a protective device that would automatically trip and reclose for a preset number of times. The autorecloser is composed of a relay that would automatically close the recloser after clearing the fault. By using the recloser we can improve the continuity of the service, due to the ability of the recloser to restore the line power automatically after clearing the temporary faults.

What are the uses of autorecloser?

  • Protection of overhead lines
  • Transformer protection
  • It is used to protect the distribution equipment from damage
  • It would be useful for quick restoration of the power after a transient fault

What are the required constructional features for an autorecloser?

  • The construction of the autorecloser must be triple pole and all three phases must be driven by a simple operating mechanism
  • The autorecloser cabinet must be constructed in a way that it should be capable to handle the weather
  • The external parts such as nuts and bolts must be hot-dip galvanized
  • Metal parts that are not part of the electrical circuit should be earthed
  • These devices must have auxiliary switches, and they should also have an indication mechanism
  • The auto-reclosers should have a power supply unit for the control, metering, and also for the protection

What are the major features of an autorecloser?

  • It can be used for pole-mounted application or as an autorecloser
  • Personal safety
  • It has operation modes such as RTU or MAN
  • Installation is simple
  • Good fire retarding capability

What is the dead time, reclaim time, and the number of shots in an auto recloser?

Deadtime

This is the time that is taken by the auto-recloser to detect and clear the fault, so this is the time between fault detection and auto-reclosing after clearing the faults. The required time for the auto-recloser will be depended upon the system voltage, nature of the fault, weather condition, and also the fault clearance time.

Reclaim time

This is the time required from closing the contact in an autorecloser till the completion of another circuit. The autorecloser relay shouldn’t reset before the protection has got the time to operate. The reclaim time will be dependent on the continuity of the supply, fault incidence, and switchgear rating.

Number of shots

This is the number of attempts which is done by an auto reclosing scheme to remove a permanent faulty.

How to choose the dead time and reclaim time in an auto-recloser?

The dead time for the longer lines will be more due to the phase capacitance and this would result in high de-ionizing time in case of single-phase faults. In order to quench the capacitance arc NGR’s are used so that proper auto reclosing can be achieved. The dead time for an extra-high voltage system, the lower limit will be according to the de ionizing time and the upper limit is by transient stability and synchronism.

Reclaim time

The reclaim time shouldn’t be set too low because it would cause a major problem. If the reclaim time is low then the operation time of this A/R will be more if two faults occur close together.

How to do the selection of an auto recloser?

We must consider certain factors before selecting an auto-recloser and they are

  • Deadtime
  • Reclaim time
  • Number of shots
  • High speed or low speed
  • Single shot or multi-shot

How does auto recloser operate?

If there is a fault in the overhead line then the protected relay would operate the breaker tripped power-off fault. The autorecloser relay would command the breaker to reclose, so when the breaker recloses then the power will be restored. The autorecloser can provide a maximum of five shots. When the phase or earth fault occurs then the dead time will be started and the reclaim time would start after the dead time.

What is the major requirement of an autorecloser relay?

  • The breaker should be reclosed by an auto reclose relay if it is initiated by the protective relay
  • If the initiation takes place during the reclaim time, then the autorecloser relay should not reclose the breaker
  • In the single-pole mode, the auto recloser relay must only reclose the breaker for a single phase to earth fault
  • The breaker must be closed by the autorecloser relay in case of the line-to-line fault under the control of the synchro check relay.

What are the requirements of a circuit breaker in an auto-reclosing scheme?

  • In case of the high speed reclosing the breaker must close after 0.3 seconds and it should regain its whole breaking capacity
  • The breaker must be capable to withstand the reclosing onto permanent fault without any damage
  • The breaker operating time must be short to permit short deionizing time

What are the advantages of autorecloser?

  • The supply interruption to the customer can be reduced
  • Restoration of the critical system interconnection
  • The capacity of the system can be restored with fewer outages and also with less manpower
  • System stability and synchronism can be maintained
  • Service to critical loads can be easily restored
  • The chances of recovery from the multiple contingency outages are improved
  • The duration of the fault is limited and due to this less damage
  • The substation can be operated with less manpower
  • Chances of permanent damage will be reduced

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