Resilience is a term that distribution network operators (DNOs) will be well familiar with - in terms of building a robust grid to deliver an uninterrupted electricity supply.
In another context, resilience of communication technology infrastructure is becoming equally important to keep data flowing from the grid edge back to network operations centres.
Only a brave or financially challenged DNO relies on only one communication technology method, explains Darrell Jones, Technical Sales Manager at Cherry & White.
The UK company designs, supplies and maintains UK distribution network operator telecommunication networks to transport remote terminal unit data through SCADA systems.
Jones told the audience of an Engerati webinar that “resilience is key. Don’t rely on anyone means of communication, you will always need a backup.”
Co-presenter Richard Stamvik, Managing Ecosystem and Partnerships at industrial IoT communication device provider MultiTech, agrees that in one sense the connectivity technology is the easy bit. “The harder bit is the analysis - what connectivity do we need in place to achieve the uptime required.”
The pair work together to deliver the “most cost-effective and most efficient” solutions to UK DNOs, says Jones.
7 advantages of cellular over radio
One communication technology that both Jones and Stamvik feel has a sound business case for substation connectivity - either as a primary or secondary data transmission method - is cellular.
Jones compares the benefits of cellular communication for RTU connectivity compared to very high frequency (VHF) radio.
“While large telecommunication companies (telcos) purpose-built VHF networks to cater for utilities and RTU connectivity, these are now becoming legacy and are no longer seen as economically viable for those telcos to maintain.”
In the presentation, Jones identifies the following advantages of cellular over VHF for SCADA traffic:
1. Radio signals have difficulty penetrating thick rock or mountains. “If you have two radio towers on either side of a mountain, the chance of them communicating efficiently is slim,” says Jones. By contrast, cellular towers can work around that and maintain communication by using adjacent cells to transport the data from point A to point B.
2. The increase in network coverage from cellular towers has dramatically increased in recent years and with it an increase in data rates. An estimated 75% of the UK is geographically covered by 4G, according to UK telco operator EE.
3. Interference is another issue affecting VHF communications. If a receiver is placed in front of a transmitter, the signal coming into the receiver could interfere with the transmitting signal and therefore inhibit the communication from the tower. “Cellular networks avoid interference by each individual cell tower working on a slightly different frequency and never using the same frequency as the adjacent cell,” explains Jones.
Keeping down costs of grid connectivity
4. The business case against VHF is growing, says Jones, due to the number of VHF masts needed for a network whether regional or nationwide, and whether the structure is owned or leased by DNO. Jones adds: “VHF frequencies are also tightly regulated and licensing costs may be applicable when using them in your region. In favour of cellular, there are no associated licence costs and telcos have already built the network.”
5. In order to gain distances on VHF, power might have to be increased in order to reach especially with obstacles such as trees and buildings in the way. Wattage needed is considerable. Cellular networks are divided into cells that cover different areas with one transceiver in the middle of each piece of the network therefore keeping it quite efficient.
Securing communication for SCADA traffic
6. Security - a key and very real challenge for DNOs - is also a weak point in the VHF network where intrusions such as jamming can drown your transmission out.
Jones says: “This isn't always malicious but more often an accident where someone is transmitting on the same frequency with a higher power. This is more seen in urban environments. The way VHF gets round this is using frequency hopping or a standby clean frequency, so if other channels are compromised, this frequency is set aside to re-establish comms. Again, extensive planning and cost are considerable.”
A positive of using cellular networks, explains Jones, is using a private access point name (APN) to protect end devices from attacks from other users as well as other devices. By creating a data tunnel set-up by a cellular SIM provider this feature limits abuse and improves cost-effectiveness, says Jones.
7. Weather such as lightning strikes or high winds can also affect VHF networks causing a mast to go dark meaning that the “data path will be lost as mast A will no longer be able to contact mast B,” he explains.
By using several cells and a roaming SIM, a cellular connection is able to roam to the next available network tapping into an infrastructure already deployed by the telco.