Time synchronized switches for electric power supervising system

22nd July 2008
Posted By : ES Admin
Time synchronized switches for electric power supervising system
ELKOMTECH has chosen Westermo time synchronization R208 Ethernet switches to equip recently modernised substations within the network supervised by the Polish electric operator PSE. The network manages more than 1700 high voltage substation across the country. These distribute electricity to 35 million people and to many industrial operations – so high reliability is very important. Westermo’s R208 switches deliver the highest time stamping accuracy on the market. In the PSE project, Elkomtech also equipped them with a specific redundant power supply.
PSE has long used communications solutions based on the IEC61850 standard in its new or modernized substation systems. IEC61850 is a standard for the design of substation automation, part of the International Electrotechnical Commission’s (IEC) Technical Committee 57 (TC57) reference architecture for electric power systems. It is aiming to guarantee high reliability and easy development possibilities for the future. In 2006 Elkomtech installed WindEx, which supports surveillance centres by allowing remote access to many different substation control systems.

In the last two years, Elkomtech has ordered around 100 Westermo switches through Tekniska – Westermo’s Polish agent. It recently chose the R208 for new developments.

“We sell several brands of switches, but R208 switches from Westermo provide the best accuracy on the market in terms of time synchronization – with the highest level of reliability,” says Mr Kawale, engineer at Tekniska. “For such a critical application it is ideal. We have also added a specific redundant power supply to the switches to further increase system reliability.”

Two redundant inputs are provided. The power supply draws power from the input that has the highest potential difference when compared to the alternate supply. This allows the use of a 48V source as primary supply – with a 24VDC battery as back up. Power supply inputs have reverse polarity protection.

In industrial automation, Ethernet networks have always been limited by the latency jitter of data packet transmission inside the switches. Depending on network load, data packet size and the number of switches between the server and the client, data transmission inside an Ethernet switch can cause time latency jitter of several milliseconds. A packet that enters the switch first can even go out after one that arrives later due to switch QoS (Quality of Service) techniques.

Furthermore, a network with several off-the-shelf switches will accumulate time synchronization errors for each switch on the network path between the time server and time client. The precise data analysis needed for high- or medium-voltage substation automation then becomes impossible.

Westermo’s R208 switch allows precise time-stamping, providing a full, detailed history of data events. Sophisticated or critical industrial processes – whether or not they are in real time – can now be managed with the off-the-shelf SNTP Ethernet protocol. The R208 allows industrial Ethernet networks to be installed in a redundant ring configuration, eliminating network failure caused by either fibre or copper backbone failure. It has a reconfiguration time of 30ms.

“We are working on new solutions like synchrophasor acquisition and disturbance recording, where overall time resolution below 10 microseconds is needed,” says Mr Szaniawski, Elkomtech’s R&D Director. “This made Westermo’s 1 microsecond time synchronisation resolution a very good solution for us. We receive good technical assistance from Tekniska for our other Westermo switches. We know they will provide good levels of service on the R208 range.”

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