T&D World Magazine
Reclosers Working In Sub Zero Temperatures

Reclosers Working In Sub Zero Temperatures

NOJA Power standard recloser products have been supplied to electrical utilities worldwide for use in almost every type of environment, from Bhutan nestling in the Himalayas to the equatorial Amazon region of South America or closer to home in the arid outback of northern Queensland, Australia where temperatures can reach +50°C.

The OSM range of vacuum reclosers have been tested and proven to work in the harshest of environments and extremes of temperatures using NOJA's own environmental test chamber together with independent testing at KIPTS (Koeberg Insulator Pollution Test Station) in South Africa and the ultimate test, trouble free service experience.

Extremes of temperature are no more evident than in Sweden, a country that is 1574Km long and where the temperature in the far northern Lappland region can drop to -53°C in February and in the South can reach +38°C in June. Typical specifications for outdoor switchgear for use in the Northern region stipulate that products need to withstand temperatures of -40°C to +55°C whereas in the south this would typically be -25°C to +55°C.

NOJA Power has been supplying the OSM range of vacuum reclosers and RC10 control units to the Swedish utilities via our exclusive distributor, Techinova AB, who are experts in communication and automation solutions, based in Karlskrona.

The Swedish utilities of Ljusdal Energi in Ljusdal, Elektra Networks AB in Edsbyn and Hofors Elverk AB in Hofors are all in the Gävleborgs Län region which has an area of 18,000 Km2 and a population of approx. 276,000. It has a sub-Arctic climate where temperatures have been recorded at less than  -30°C in Winter and a balmy 25°C in Summer with 60-80mm of rain in the Summer months, so a very challenging environment for any product but one we know the NOJA Power recloser and RC control cubicle has been more than capable of meeting.

In Sweden, the entire distribution network is of a high impedance compensated type i.e. an arc suppression coil is used to connect to the transformer neutral to limit the capacitive earth fault current flowing when an earth fault occurs on the system, typically it is matched with a 3-5k ohm resistor. The consequence of this is that a fully developed earth fault current is very low at about 0.5-1.0 Amps in a 10 kV network.

In the Swedish overhead network about 75% of all faults are earth faults, typically a tree or a branch hanging on one of the phases. The most important feature of the NOJA Power recloser is therefore its ability to be able to detect and determine the direction of low value earth faults and after that perform subsequent reclosing operations.

The vacuum circuit breaker pole mounted reclosers supplied are the standard OSM15 products with the RC10 control cubicle with in-built RTU. Since Swedish utilities are required to monitor the electricity distribution network over vast areas, Techinova AB have installed their long distance radio systems within the RC10 control cubicle with the RTU acting as the IEC60870-5-101 master that constantly polls the data from the recloser. If the status of the recloser has changed (indication or analog values) then a radio message is forwarded through the radio network. It does not transmit unless there has been a status change. This gives a very fast and responsive radio system with very long range capability (typical distances in one jump are 10-25km) since all radio RTUs have built in repeater functionality. Techinova also use Tetra radio as a data carrier over SDS (Short Data Service) and have developed a gateway between IEC60870-5-101 and Tetra SDS which is used throughout Sweden and in NOJA Power reclosers for EON.

The Swedish utilities are very forward thinking, none more so than Eon in Kisa, Östergötland region which is in the South of Sweden where they are evaluating a "Smartare Nät" or "Smarter Grids" looking for the best solution for their future needs. They have installed a trial system using a fully automated back feed restoration scheme with two normally open points (two normally open reclosers with ABR enabled) between two feeders. On each outgoing line, two reclosers with full directional protection settings have been installed. 

There are four companies being evaluated but the NOJA Power/Techinova solution is the only one that isolates a fault in two directions and automatically restores power from two directions. Techinova were also the only one to think of an "emergency stop" in SCADA, one graphical button that turns reclosing off on all units within the system.  Since these reclosers have been installed, NOJA Power have further enhanced the product range with the launch of the new RC15 with improved communications including Wi-Fi, GPS, 3G/4G modem and SIM card making it the most advance recloser product on the market today.

 

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