Page 51 - Energize August 2022

TECHNICAL

Parameter Urban network Rural network
Typical trip time reclose sequence Fast-slow-slow Fast-slow-slow-fast
First reclose time 200 ms to 2 s 200 ms to 2 s
Second reclose time 5 to 10 s 5 to 10 s
Third reclose time (if used) 5 to 10 s 5 to 10 s
Table 1: Typical ARC settings

Sectionalisers count the number of operations of the recloser sectionaliser opens during the dead time of the recloser.
during fault conditions. After a preselected number of recloser Sectionalisers are available in single-phase or three-phase
openings, and while the recloser is open, the sectionaliser opens variants. Commonly used sectionalisers have either hydraulic
and isolates the faulty section of line. This permits the recloser to or electronic operating mechanisms. The hydraulic contacts are
close and re-establish supplies to those areas free of faults. If the opened by pre-tensioned springs. Most of these sectionalisers have
fault is temporary, the operating mechanism of the sectionaliser is the provisions for manual opening and closing using a hook stick.
reset. Electronically controlled mechanisms are more flexible and easier to
In case of a temporary fault, the fault often disappears before set than hydraulic mechanisms are. They usually offer both manual
the electronic sectionaliser reaches the number of counts for which and automatic motor-controlled opening and closing options.
it was set. The sectionaliser’s memory is reset after a current lower Single-phase selectionalisers are also available in stand-alone
than the actuating current flows through the sectionaliser for versions, i.e., without a separate control unit. The electronics are
more than the reset time. After this, it remains prepared for a new contained on the body of the sectionaliser, as shown in Figure 8.
counting operation.
Electronic sectionalisers are designed to coordinate with Applications
MV distribution networks. The use of electronic sectionalisers in Reclosers and sectionalisers can be used anywhere on a system
branches and service connections, instead of a fused sectionaliser, where the ratings are adequate for the system requirements.
allows better coordination in the event of faults. This results in a Reclosers are used in radial distribution, ring feed and meshed
decrease in both operating costs and the number of power outages. networks. Common locations are:
The load switch, which has the function of isolating the fault, • In substations as the primary feeder protective device.
cannot open and close a short-circuit current, but can open and • On the lines at a distance from a substation to sectionalise long
close the rated current and close the short-circuit current. It is feeders, and thus prevent outages of the entire feeder when a
generally matched with recloser or fuse, connected in series with permanent fault occurs near the end of the feeder.
the load side of recloser, and automatically opens when there is • On the taps of main feeders (lateral), to protect the main feeder
no voltage or current. The corresponding controller can locate the from interruptions and outages due to faults on the taps.
line fault and isolate the fault section. In contrast, the cost of a • Reclosers are available as pad-mounted units to provide simple,
sectionaliser is lower than that of a breaker and recloser. direct connections to underground cable systems.
Some ACR models on the market can be configured to function • Mixed cable and overhead line networks encountered in
as intelligent sectionalisers as well, since the price differential some distribution systems which present a problem for
between the two functions is claimed to be too low to justify reclosing. Recloser systems have nonetheless been successfully
separate units. implemented.

Sectionaliser operation References available on request
A sectionaliser operates by counting the number of recloses and
opening the circuit after a set number has been reached. The Send your comments to rogerl@nowmedia.co.za

Figure 7: Sectionaliser operation (Sustech) Figure 8: Stand-alone sectionalisers (ABB)

energize | August 2022 | 49