T&D World Magazine
Automatic Circuit Recloser Protects Two-Phase, Two-Wire Spurs

Automatic Circuit Recloser Protects Two-Phase, Two-Wire Spurs

The 312 series two-phase product is based on the company’s OSM three-phase ACR but is re-engineered to meet the specific demands of customers building two-phase, two-wire spur lines.

NOJA Power has released its 312 series Automatic Circuit Recloser. The 312 series two-phase product is based on the company’s OSM three-phase ACR but is re-engineered to meet the specific demands of customers building two-phase, two-wire spur lines.

Units from NOJA Power's OSM range of medium-voltage ACRs have been installed by utilities in over 80 countries around the world but the existing range lacked an option for two-phase, two-wire spur lines.

Traditionally, spur lines to remote rural locations comprised a single-phase, single-wire with earth return (SWER) to keep down the installation costs of supplying power over long distances. But recently, SWER lines have fallen out of use in favor of two-phase, two-wire spurs as demand for power in remote location has increased. Two-phase, two-wire spurs are cheaper to construct than three-phase supplies, but offer greater capacity and are better able to spread electrical load than SWER systems.  

Utilities construct two-phase, two-wire spur lines by branching off from main three-phase distribution lines. Each spur comprises two phases from the main distribution line with a phase-to-phase voltage of either 11 or 22 kV and the phase-to-ground voltage of 6.35 or 12.7 kV (i.e. phase-to-phase voltage/√3).  Then, close to the customers’ premises, utilities tap either the two phases to create a final single-phase connection to the location.    

Previously, utilities used three-phase ACRs to protect the two-phase, two-wire spurs. Each phase would be connected to a pair of bushings on the three-phase ACR with the third (centre) pair of bushings left unused. By connecting two phases from a three-phase supply to the ACR, the utility ensured phase balance during normal operation and full availability of the ACR’s Overcurrent (OC), Earth Fault (EF) and Sensitive Earth Fault (SEF) protection capabilities. However, the utility had to cover the cost of a redundant pair of bushings.

NOJA Power’s 312 series two-phase ACR now replaces the three-phase ACR for this application. The unit is supplied with two pairs of bushings only, saving cost for the utility.  

The 312 series ACRs extend the company’s range of electricity distribution grid protection products by complementing the existing 300 and 310 series products. The 312 series has a rated maximum voltage of 27 kV, is capable of up to 800 A continuous current operation, features a fault make capacity (RMS) of 12.5 kA and an impulse withstand phase-to-earth and phase-to-phase of 195 kV. The 312 series is supplied with NOJA Power’s RC10 control and communications cubicle. The RC10 cubicle’s comprehensive feature set allows customised ACR set up and the unit’s power quality features provide an in-depth analysis of the changing state of the electrical network for smart grid applications.

The 312 series products benefit from the key features that have made the OSM38 ACR popular with utilities around the world. Notable among these are the use of a vacuum interrupt and solid dielectric insulator instead of the environmentally unfriendly oil or sulphur hexafluoride (SF6) gas used in older products. Another key feature of the 312 series is its stainless steel enclosure that forms the only solid dielectric unit with controlled arc venting on the market. The controlled arc venting design meets the requirements of IEC62271-200 Clause 6.106 and Annex A, and the efficacy of this important safety feature has been verified as part of full type testing by independent test laboratories such as KEMA in the Netherlands.

 

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