Meeting the telemetry needs for power supply automation in Ghana, Africa
Lucy Switchgear, a trading name of Lucy Electric UK, has more than a century of experience within the power distribution industry, providing switching and protection solutions for electrical distribution systems. Headquartered in Thame, Oxfordshire, with manufacturing facilities in Dubai, joint ventures in Saudi Arabia and India and a number of licensees globally, the company offers support to customers across the world.
In 2005 Lucy Switchgear began a pilot automation programme in Accra, Ghana's capital city, with the objective of reducing electricity revenue losses, improving overall efficiency, minimising customer outages and reducing operational and maintenance costs for the Electricity Company of Ghana (ECG).
With ECG committed to a planned three phase roll out programme, 33kV radial overhead feeders are now automated across the regions of Bogoso and Tokuse, as are the 11kV underground metropolitan networks within Kumasi and Accra. The current second and final third phases will extend the network across the entire country, including the Volta region, encapsulating over 200 sites with a control centre in each of the eight separate districts acting as a communications node. To achieve this Lucy Switchgear has installed a variety of automation products including its own standalone Gemini-Scada 2 package.
Bill Carlyle, business development manager (automation), Lucy Switchgear, said: "Completing the project is a major engineering challenge in terms of reaching across remote locations all the while dealing with extreme equatorial terrain encompassing mountain and jungle. This is all exacerbated by the relatively poor road infrastructure, which is needed to gain basic access to power equipment for maintenance.
For this reason high performance radio data communication links were required, with the Ghanaian government allocating a regulated frequency band Lucy Switchgear could use.
For these critical radio links, Lucy Switchgear required a supplier of quality products that could understand and fulfill the ECG's requirements and would represent value for money. For three particular reasons Lucy Switchgear chose independent manufacturer of professional radio solutions, Wood & Douglas and its Sentinel ER450 UHF radio modem.
Firstly The ER450's specifications made it feasible to use throughout the hot, humid conditions of Ghana. Its ability to store and forward messages would be crucial when spanning terrain and finally it delivered a complete onboard diagnostics and management package that would help overcome the problematic issues of field maintenance.
"The general level of co-operation from Wood & Douglas has been great. It is a huge logistical challenge to pre-engineer a system on the back of extensive radio surveys," said Carlyle. "But being able to engineer the system in the UK and pack in Dubai made transferring the ‘ready to go' solution to Ghana in containers much simpler, and it makes the process of service roll out far more efficient."
Wood & Douglas' Sentinel ER450 outstation radio, deployed by Lucy Switchgear, is housed in a compact die-cast enclosure, ideal for the rigours of Ghana. This digital data radio is designed for data transmission applications within SCADA systems and features two RS232 user ports. This dual user port feature opens the opportunity to deploy Sentinel in communications networks using concurrent yet independent data streams.
Crucial to the ECG SCADA infrastructure was the ability to use the Sentinel ER450 to store and forward messages in range-extending repeat transmissions, enabling the sending and receiving of messages to far distant remote terminals. At every remote terminal unit (RTU) location, whether ground mounted 11kV ring main units, or overhead air break switches for 33kV transmission, as well as at all repeater sites, Lucy Switchgear deployed a Sentinel ER450 using up to four ‘hops' for retransmission of signals and up to 5W maximum RF output. At the extreme, from a control centre, to high mountain repeaters and on down the valley, the furthest of these single hops covered a distance of 50kms.
The Sentinel ER450's onboard remote diagnostics and network management system, which requires no operational break in the Scada data flow, supported Lucy Switchgear's monitoring of its own Gemini range of Scada equipment. The ER450 network management enables comprehensive monitoring of individual radios across the network, independent of the transmission of Lucy Switchgear's Scada messaging relating to current, load flows and the condition of switchgear. These features enable the control centre to quickly identify, localise and sectionalise a line fault remotely in order to reduce the number of users affected by a supply failure.
This is made possible using Lucy Switchgear's automated field devices, such as the remotely controlled 33kV air break switch disconnectors (Rapier RX-RC36), which incorporate the fault passage indicators and RMU actuators interfaced with the Gemini-RTUs/ communication modems. Using over the air (OTA) configuration with the switchgear, a line can be remotely switched, rerouting power flow to enable reconfiguration. The ability to remotely identify line faults also enables a repair crew to get to the fault point faster for quicker restoration.
"Despite the extremes, deploying UHF telemetry with the Sentinel ER450s delivers tremendous flexibility in the field," says Carlyle. "Ultimately that saves a huge amount of time and money for the electricity company, which is absolutely what automation should be about."
