Overhead lines - reclosers, load break switches (sectionalizers) and indicators

Object definition

Recloser - this is a switching device used in power distribution grid, which is capable to switch off and on again the power lines under short circuit (reclosing). Mostly they are placed on the overhead line poles at the beginning of sections behind substations (if they are not already equipped with the switching device on the branch), to divide long sections of the power line, or at the critical points, where power switching may be needed, including short-circuit currents. It can be for example a connection point of two different substations used for network reconfiguration, important customer location, etc. From the quality point of view, reclosers are the top level switching devices with the possibility of switching off short-circuits using the different types of insulation (SF6, vacuum, mechanical), thus they are most expensive type of switching devices.

Load brake switch (LBS) - this is a switching device in the power distribution network, which is capable to switch off the power lines under nominal load. It is used to divide the power line into smaller sections, hence its second designation as a sectionalizer. If reclosers and LBSs are remotely operated, then during the short circuit, a manipulation (LBS switching off and on) is done in cooperation with a recloser in non-voltage pauses (when recloser is off) to protect the LBS from higher currents than nominal. When the LBS is manipulated in standard conditions with nominal load, they occur the arc discharges. Therefore, load break switches are mostly equipped with various types of arc discharges extinguishers (spring, oil, vacuum, etc.).

Indicator - it is a device indicating the states of voltage and current at a given location. The power line is not manipulated and therefore it is a cheaper device designed to mark an affected area as accurately as possible, so a repair can be done in the shortest time.

Description of the situation

With the gradual development of automation in power distribution, more and more elements in the network are equipped with remote monitoring and control. The aim of these investments is to ensure the supply for as many users as possible during a network failure and to reduce the SAIDI and SAIFI indicators, therefore the network is segmented by reclosers and LBSs. Together with meeting these needs, the network intelligence and number of measurement points grow, which also meets the requirements of the projects SMART GRID or SELF HEALING GRID. Using basic considerations or more complex network analyzes, it is possible to define the optimal number of switching elements in the power network - a compromise between costs and revenues during operation of a power distribution network.

ELVAC RTU solution

The Basic RTU Features

  • Remote monitoring and control of reclosers and sectionalizers (LBS),
  • independence on switching elements manufacturer – we have solutions for all types of sensors (measuring transformers, capacitive and resistive sensors, Rogowski coils),
  • failure indication (overcurrent, short-circuit, earth-fault, (including directional and time depending), current asymmetry, over-voltage, under-voltage, frequency),  reclosers and load break switches use them for activation of automation functions (protection relay functions),
  • automation functions for reclosing, switching-off in non-voltage pauses and another programmable principles for use in SMART GRID and SELF HEALING GRID.

This topic is covered in more detail in the application guide

Another advantages of ELVAC RTU

  • All-in-one device - powering, battery charging, communication, indication, measurement, control, protection relay,
  • wide range of communication interfaces and protocols,
  • optional two communication lines to superior systems - backup routes or two different SCADA dispatching centers that can represent each other for different areas,
  • measured voltage directly from power supply transformers - voltage indication in front of switch (from power supply) and behind switch (via measuring sensors),
  • web interface or free SW for remote parameterization of RTU,
  • remote download of voltage and current waveforms records for failure analysis,
  • logging all events in RTU,
  • highest technical standard and reliability, products are made under strict control directly in the Czech Republic.

Searching for places affected by earth faults

One issue is an identification of a problem in the network and switch off the power lines, the second issue is to find and remove it as soon as possible. It is the task for service teams, which go to the field. The common problem on overhead lines are earth faults, usually in forests, where branches can touch the lines. The finding of such a place can be difficult and time consuming, because these areas are not easy available.

An excellent helper for earth fault searching is our handheld earth fault locator ELF7, which can significantly reduce the necessary time for finding of the problem cause. The device indicates whether the fault is behind or in front of the measurement point. It is possible to identify quickly a section at easy available places. For more detail please visit ELF7 product pages.