Load-break switches ensure reliability of modern distribution networks

The reliability of interconnected distribution networks with wind and solar power suppliesis a growing challenge. Network designers seek ways to keep the complex system in balance, particularly in fault situations. New compact overhead load-break switches can increase the reliability significantly, and offer additional features to support network automation as seen at SP EnergyNetworks

The sales manager at Ensto UK, Iain Strachan, said: "In the event of an outage, utilities can no longer afford to have personnel visiting remote sites to open load-break switches. This pressure will only increase in the future.

"Today, it is possible for a smart load-break switch to work in conjunction with upstream fault-break devices to detect and isolate a faulty section and automatically reconfigure the network. With these functionalities, the switch increases the selectivity of a protection plan and quickly restores supply for the majority of customers."

Smart features for supporting network automation are refined in the compact modular design of the AugusteSF6 Load Break Switchfrom Ensto. This overhead load break disconnecting switch is designed to allow a load interruption of up to 630A for a medium voltage up to 36kV. Motorised versions use the existing adaptable manual control mechanism to secure a fail-safe operation. With the Ensto control box they can be easily integrated into any remote SCADA controlled networks.

You still see what you get

When reliability, functionality and safety are packed in a closed case, it is not possible to visually confirm open isolation points. Instead, the Auguste has an indicator mechanically and solidly linked to the contact operation shaft, much like in a sub-station switch. It clearly shows the load-break switch position and is visible from the base of the pole. Rugged design and more than a decade of operational experience have proven this to be a true indication at all times.

The constraints of existing networks are never a problem, because the modular Auguste switch range can be adapted to different modes of operation and future network evolutions. The remote control is compatible with standard protocols and a variety of communication interfaces. The sectionalising function is electrically operated and automatically triggered by the fault detector. All this can be monitored via SCADA and seen real-time in the control room monitor.

Durable and frost-free

"Durability starts with good design and time-proven performance to give decades of maintenance-free operation," Iain Strachan said.

"Each unit we deliver undergoes individual tests during manufacturing as well as routine testing before despatch."

"For us, durability means that our product demonstrates true capability to operate in really harsh climatic conditions," he continued.

"As part of a specific customer application, a new version of Auguste was developed to operate at a minimum temperature of -50°C. Mechanical-climatic tests were performed in a french laboratory, and these new frost-resistant versions are installed in Russia."

Any work relating to durability and reliability must also cover installation, which, in the case of Auguste, can be done using live line techniques. High-level safety characteristics allow switchgear to be installed and used in full confidence.

Proven reliability at SP EnergyNetworks

SP EnergyNetworks, with its 30,000 substations and 31,000km of overhead lines, now has eleven years’ experience of Auguste switches. Today, the company has 1,174 of them employed inits SP Distribution (Scotland) and SP Manweb (England and Wales) networks.

The lead engineer of technical risk, Alan MacGregor, summerised: "Good reliability is invaluable for telecontrol and automated supply restoration.

"We have gained considerable savings in regulatory penalties by minimising customer minutes lost in fault incidents."

According to MacGregor, Auguste SF6 load break switches are especially useful in the telecontrol of 11kV overhead line network switching points using the sectionalising function for spur-line protection.

"In future networks, these type of switches will continue to be crucial for telecontrol, but will probably also carry out load-monitoring and recording over SCADA", Alan MacGregor said. "That could include fault detection data to measure amps in each phase and earth fault element plus the duration of the fault".

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