Merus™ ESS with Reclose technology revolutionizes electricity supply security

Merus™ ESS Energy Storage Solution is a cost-efficient and elegant solution for protecting rural electrical networks’ supply security instead of carrying out construction works and installing underground cabling. During network faults, the Merus™ ESS is able to restore the voltage for the customers in an instant. When the fault is cleared, the Merus™ ESS automatically reconnects the island network into the supplying grid. While everything is working normally, the Merus™ ESS helps in frequency regulation and local voltage support.

The importance of electricity supply security

We are increasingly dependent on electricity in our daily lives. Not only do we use household appliances, computers and charge our mobile devices at home, we use the same equipment at the office. Often our heating or cooling systems are dependent on electricity, and so are our fridges and freezers. Full electric vehicles and plug-in hybrids need to be charged at the right time, so that we can get going when we need to. Industries and public infrastructure are equally – if not more – dependent on electricity supply.

Electricity supply security is vital for us to be able to lead our daily lives and to power our businesses. The supply security is dependent on the reliability and stability of the electricity transmission system, and closer to the customer, reliability of the local distribution network.

The electricity supply security requirements are typically governed by national or regional regulation – in Finland, for example, the law governing electricity markets. It states that the network infrastructure should be built with the target that power outages caused by weather phenomena do not last longer than six hours in population centers and 36 hours in rural areas. On top of this, the customers are eligible for compensation from the distribution companies for power outages.

The distribution companies are responsible of providing this security to the electricity consumers. In many rural areas, this presents problems, because the electricity distribution is traditionally physically taken care of with overhead lines which are vulnerable to weather phenomena: storms, trees falling, lightning and so on.

A typical way of improving the supply security is to build underground cables, which are not vulnerable to weather phenomena. Underground cables may also be more practical for example in cities, where the space for overhead lines would be limited. The downside is that underground cabling is 1.5-2 times more expensive. Is there a way to provide the required supply security more cost-effectively?

Innovative concept for network protection

Merus Power’s answer is backing up the electricity supply with batteries.

Merus Power, Elenia and Fortum have started a joint innovation project where Merus™ Energy Storage Systems are installed to network branches feeding remote areas in Finland as a more cost-effective and elegant option to changing the overhead lines to underground cables. In this venture, Merus Power supplies the complete Merus™ ESS, but the power conversion system is owned by Elenia and the batteries by Fortum.

In this scheme, Elenia is able to utilize the power conversion system for voltage control during normal network operation. The voltage is supported by the dynamic reactive power control that the Merus™ ESS is able to carry out at the same time with charging or discharging the battery.

Fortum is able to use the battery capacity in the frequency regulation reserve to create revenue from the electricity markets and help the transmission network in maintaining power balance. During a power outage, Elenia is able to use the battery capacity as a service from Fortum to be able to supply electricity to the protected network area.

Reclose – Resynchronize – Reconnect

Merus™ ESS is able to detect a failure in the distribution in an instant. In an event of such failure, our sophisticates energy storage with Merus™ Reclose technology is able to instantaneously separate the protected network into its own island and quickly restore the voltage for the customers. The electricity consumers will only experience a short interruption – comparable to automatic recloser operation time.

The Merus™ ESS feeds the loads in the island grid while Elenia has time to fix or selectively isolate the failed branch in the distribution network. The Merus™ ESS is in charge of network protection in both grid-connected and islanded modes of operation. When the network fault has been cleared and the upstream voltage has been restored, the Merus™ ESS automatically synchronizes the island grid with the supplying network and closes the islanding breaker – the customers will not notice a thing!

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