A case study in distribution automation

This case study assesses the various elements of project implementation that ensured a successfully, delivered Distribution Automation (DA) project on the continent of Africa. The first phase implementation concentrated on the second largest city in Ghana, Kumasi, with a population of over 1.5 million and some 250 kilometres from the capital Accra.

“We have a successful history of the design, manufacture and delivery of power distribution equipment to ECG and this project was no exception”
-Graham Pryce, International Sales Manager for Lucy Switchgear

Lucy Switchgear first approached the Electricity Company of Ghana some five years ago, with a view to introducing them to the benefits of DA across their distribution network. It was felt that a proof of concept was necessary in the first instance and a pilot project was commissioned to fulfill this requirement. The pilot network would need to be representative of the network as a whole and it was decided to automate 33kV radial overhead feeders across the regions of Bogoso and Tokuse and, in addition, parts of the 11kV underground network in Accra itself. In order for the pilot to have been deemed successful, a number of objectives were clearly defined from the outset, namely:
➢ reducing electricity revenue losses
➢ improving overall efficiency
➢ minimizing customer outages due to system faults
➢ reducing operational and maintenance costs (OPEX).

Lucy Switchgear installed a variety of automation products and systems to meet these objectives, which included own brand and some third party manufacturer’s equipment and these included:
➢ Standalone GEMINI-SCADA 2 package
➢ GEMINI-DC (Data Concentrators) to integrate the secondary RTUs into the existing DMS/ SCADA systems
➢ Automated field devices such as the remotely controlled 33kV air break switch disconnectors (RAPIER RX-RC36) complete with fault passage indication and current monitoring.
➢ Retrofit RMU actuators for Lucy ring main equipment and third party RMUs interfaced to GEMINI-RTUs/ communication modems
➢ High power radio communication links incorporating “store and forward” techniques at repeater locations to enhance the distances covered
➢ In-house system design, integration, system testing and technical training services

Phase 1 - Kumasi
After the completion of the pilot evaluation period, ECG took the decision to substantially increase the scope of DA to be applied and chose their second largest city, Kumasi, as the location for a Phase 1 roll-out programme.

In partnership with Lucy Switchgear, approximately 50 locations were identified as strategic points in the distribution network at 11kV and 33kV. These proposed automated locations, including underground and overhead feeders, were spread across the city boundary and up to a radius of 45 kilometres from the city centre. One of the main ECG offices in Kumasi was also chosen as the main Control Centre.

Much of the installation work at the various automated sites was undertaken by Ghanaian contractors under the joint supervision of the Lucy Switchgear project team and the ECG project manager.

Communication Considerations
A radio survey was commissioned to ensure robust radio communications were permissible to all the 50 locations and it also served as a general site survey. The use of GPS coordinates allowed desk-top radio modeling to be undertaken prior to the actual site survey and immediately identified potential problem areas in terms of line-of-sight radio transmission coverage. It was clear that a number of radio repeater stations would need to be established to encompass all 50 locations. Actually acquiring suitable sites for radio repeater masts is, in itself, fraught with difficulties, bearing in mind the requirement for road access and establishing a power supply connection. Solar-powered alternatives were also considered. Modern digital radio modems can achieve line of sight transmission distances of over 25km given the correct choice of antenna and radiated power setting (up to 5W). The “store and forward” function within the repeaters means RTU messages can be retransmitted to the appropriate RTU and, in theory, doubling the original transmitted distance. This functionality proved invaluable in securing the necessary radio coverage area.

Automation Technology
Much of the Lucy Switchgear technology utilised on the original pilot project was replicated for the phase 1 project. At the 11kV/LV substation level, full use was made of retrofit systems for the motorization of ring switches, EFIs and RTUs on the oil-insulated ring main units. Pole-mounted switchgear in the form of remotely controlled air break switch disconnectors, equipped with fault passage detection devices, were deployed on both the 11kV and 33kV overhead systems. Each overhead structure being suitably accessorised with voltage transformers for the RTU auxiliary supply (protected via expulsion drop-out fuses) and supplemented with surge arrestor protection. Remote terminal units and radio modems were factory pre-configured to minimize commissioning time on site.

Although the central SCADA system was based on a readily available Windows operating PC platform, it was felt appropriate to build redundancy into the system architecture. This principle was also extended to the radio communication base station.

The duplication of hardware and software for the main PC servers meant that any hardware failure on the main server would invoke an immediate transfer to the standby server and continued SCADA data processing without loss of crucial data. A battery-backed Uninterruptible Power Supply protected the system against loss of AC power and, if the power failure was sustained for an extended period, then a controlled shutdown of the SCADA system could be initiated.

The radio manufacturer had also developed a piece of software that provided an overall radio network management system accessible directly from the operator’s two monitor station. Any problems with radio communication could be quickly diagnosed and effective remedial action taken given the real time monitoring of the operation of the radio modems. Changes to the configuration of the radio units such as addressing or perhaps boosting the device output power could be carried out “over the air” and hence eliminating site visits.

The nature of modern SCADA systems enables the network operators to easily access alarm and event data through the click of a mouse and pan and zoom features to navigate the network screens. Trending and database management can be added and accessed through other client stations on the same corporate Local Area Network.

Ongoing Support
It may sound like stating the obvious, but once the DA had been handed over to the client, a dedicated team of staff needed to be allocated to the task of on-going maintenance and future upgrading of the system. Lucy Switchgear insisted that nominated ECG staff were trained comprehensively in the operation and maintenance of the product and systems installed. The advances in Internet technology has provided a means of directly accessing the SCADA control systems and remote terminal units for remote diagnostics and trouble-shooting. This facility will assist in ensuring a cost-effective maintenance strategy going forward for the client.

DA Project Legacy
From the initial inception of the pilot project to the phase 1 implementation, Lucy Switchgear and ECG worked closely together to formulate the best Distribution Automation solutions and taking into account ECG’s current operational practices. The successful completion of the pilot project, as a proof of concept, gave ECG the confidence in the technology deployed and allowed a period of time to adapt to a different network control philosophy through an extension of remote control and monitoring of their distribution networks. Forward project management techniques, with no stone left unturned, ensured the turnkey project was delivered as smoothly as possible given the logistical and general terrain issues.

Distribution Automation has given ECG the tools to more effectively control and supervise day to day operations, providing better information for future planning and overcoming the limitations of Ghana’s road infrastructure and at times fragile generation capacity. Future system design of the networks will regard DA as an integral part of the electrical design and not just a “nice to have” aspiration.

Lucy Switchgear has since secured a further substantial contract from ECG to extend the benefits of automated distribution networks to other parts of Ghana. Distribution Automation facilities are now well and truly embedded in the networks and minds of ECG personnel.

In the meantime, a number of pilot projects are in progress in the Middle East, including customers such as ADWEA and DEWA in the United Arab Emirates and SEC in Saudi Arabia. These pilots are focused on the automation of the urban, underground networks involving the ring main units and the use of modern wireless, packet data networks. It is early days, but it is expected that these customers will experience the same benefits that DA has brought to ECG’s distribution networks.