While we talk about the power distribution systems, we are talking of a system which comprises of the distribution substations, the primary and secondary feeders, distribution transformers and other secondary networks. Despite the rapid advancements in power systems, the worth of distribution networks is sky-high and there is a need for sophisticated protection schemes which ensure safety against menacing overcurrents. In this regard Engineers and technicians have developed various protection zones and complex schemes which involve various configurations of protection elements. 7 types of such protection elements are:
- Lightning arrester
- Circuit breakers
- Line sectionalizer
- Circuit reclosers
- Load-break switch
Let’s talk the basics of all these elements one by one.
While it comes to the protection devices, the fuse tops the list. Small sized wire and glass fuses are common and are employed in the protection of our laptop chargers. On the other hand, power fuses are large in size, the HV fuses in distribution systems are known as distribution cutouts. A protection engineer carefully selects the fuses and keeps various factors in mind while selecting a system. Such factors involve voltages, scope, and magnitude of fault current that might occur in any system.
The relay is an electrical switch which is actuated by an electromagnet coil. Relays are discrete protection components which have two states of working, “on” and “off”. They are very useful devices since multiple relays can be connected together to achieve various on and off function. Various types of relays having different switching functionality and working are available. The entire list includes SPST, SPDT, DPDT.
A lightning arrester is used to protect the equipment from lightning surges. They are used above 1 kV and are connected with power systems against thunders and other faults. When lightning occurs the arrester is activated and diverts the path of lightning down the earth. Jonthan Woodworth has an amazing video in which he concisely explains the working and construction of lightning arresters:
The circuit breaker is an automatic current interruption device which is most commonly available protection i our homes as well. Circuit breakers are rated in rms symmetrical value and they operate on inverse time to current curves.
Automatic Line sectionalizer
The line sectionalizer is an automatic device which is installed with backup circuit breakers and reclosers. It counts the number of interruptions that occur and automatically interrupts the circuit after a preset number is exceeded. The sectionalizer contains a built-in circuit, connects in series with the circuit and obtains power via CT.
Automatic Circuit reclosers
The automatic circuit reclosure is a current protection device which automatically trips the circuit under the temporary fault and again connects the circuit after some time. Circuit reclosers are employed in overhead distribution lines and systems for protection against momentary faults and they ensure the continuity of surface by providing the automatic power restoration.
Load-break switches are the manually operated switches that are designed to interrupt the load currents.