Uganda completes communications installation
For the UEB, a communications system is more important than a computer for controlling the grid
By Dipl. Ing. Georg Th. Prinz
Lahmeyer International, Germany
The Uganda Electricity Board (UEB) has completed the upgrading and rehabilitation of its generation, transmission, distribution and communication systems throughout Uganda. An important part of the upgrade was the design and construction of a communication system for its electric power distribution system. A grant from NORAD, Norway, and credit supplied by the Nordic Development Fund, Finland, were used to finance the new state-of-the-art communication system for Uganda`s electric power distribution system.
The equipment is part of the communication equipment required for UEB`s new supervisory control and data acquisition (SCADA) system and operational telephone network. In addition, a new supervisory control center (SCC) at Lugogo was constructed, and eight 132 kV and six 33/11 kV substations were upgraded. ABB NERA of Billingstadsletta, Norway was the turnkey construction company, while Lahmeyer International, Frankfurt, Germany, was responsible for the design and construction management.
The new control system is used to control UEB`s electric power system throughout Uganda. Data acquisition and control is performed by remote terminal units (RTUs) and transmitted to or from the SCC at Lugogo. Because the communication system is essential for communicating data between the different parts of the SCADA system, its function, performance and reliability are very important.
The communication system includes:
– a power line carrier system,
– an optical fiber system,
– a radio system,
– a microwave system and
– an operational telephone system.
The communication system is used for transmitting speech, data and information about the teleprotection and telecontrol functions of the SCADA system. It is also used to transfer real-time data from the operating equipment to the central system via RTUs.
Power line carrier system
UEB`s 132 kV lines (Figure 1) are used for carrying speech data and teleprotection signals between Kampala North, Mutundwe, Owen Falls and Tororo. The double-circuit, vertical lines are carried on steel towers at an average height above ground for the lowest conductor of 9.11 m.
The distance between the two lines is 7.5 m and the phases on each line are 4.56 m apart. The other 132 kV lines used in Uganda are single-circuit, horizontal lines strung on wooden poles. Average phase distance on the wooden poles is 5.35 m and the average height above ground of the conductors is 7.8 m.
The ETL41/42 PLC links, supplied by ABB NERA, use single, or double, channel SSB (single-side band with suppressed carrier) equipment. Output power of the transmitters is 40 or 80 watts depending on the height of the line and its attenuation and are programmable between 40 and 500 kHz radio frequency.
A line matching unit connects the PLC equipment with the high-voltage coupling capacitors, line traps and other power engineering equipment. A phase-to-phase connection was chosen for the UEB application.
A protection signaling unit is used in connection with the terminal ETL41/42 for duplex transmission of two permissives or for direct protection commands for in-band signals.
A new 132 kV overhead line was constructed between Lugogo SCC and the substation at Kampla North. Because all communication links have to be taken through this bottleneck, it was decided to use optical fibers as the transmission medium. The optical fiber, integrated into the earthwire, has the following advantages:
– complete potential separation between the terminal equipment,
– immunity of the communication path to electromagnetic interface and
– large available bandwidth of the optical fiber.
An ABB telecommunications system FOX20 was used for the transmission system. The communications system–a modular 20-channel data, telephone and protection system–has the capability to interface with a wide selection of other users. Its built-in alarm concept conforms to CCITT G.956 and G.732 definitions.
Uganda`s SCC is located at Lugogo, a suburb of the capital city of Kampala, near Lake Victoria. In order to have reliable communication links to several small substations within the Kampala area, UEB installed a radio system for data and speech transmission. The radio system used by UEB consists of two separate systems: a microwave radio link (4 x 2 Mbits/s 15 GHz band), which connects the Lugogo SCC to Kampala Amber House via the Muyenga Hill repeater station, and the other is a UHF single-channel 400 MHz radio system, which connects the repeater station to the Queensway, Motormart, Kitante Road, Gaba, Port Bell and Kireka substations. All of the signals are connected to the microwave radio system by means of a 30-channel PCM multiplexer.
The speech and the 200 baud data signals from Lugogo to the six substations are combined into one channel. The 9,600 bit/s data channel to Amber House and UEB headquarters, and the speech channels from the Lugogo private access/area branch exchange to the Amber House private access/area branch exchange, are connected to a separate channels in the multiplexer equipment. Likewise, the speech backup system for Amber House, which consists of a remote subscriber, is connected to the Lugogo PAX. Telephone connections from Muyenga Hill to Amber House and the Lugogo SCC are connected through the service telephone system of the micro wave radio equipment.
Disc antennas for the microwave radio, which are connected to the radio unit directly, are mounted on an existing steel structure beside the repeater station building on top of Muyenga Hill. The same arrangement was chosen for the connection of Amber House and Lugogo. However, at these locations the microwave antennas and microwave radio units are mounted on the roof of the buildings.
The microwave radio has two components: a modem, which is installed in the communications room and a radio unit which is located on the antenna tower–both are connected by multiwire cables. A single-channel UHF transceiver (ASCOM type RT39-L, 400 MHz band) connects the Muyenga Hill repeater station with the substations at Gaba, Port Bell, Kireka, Queensway, Kitante and Motormart.
Because this type of radio had already been in use in Uganda, the service routine and the spare parts inventory were simplified. The RT39-L covers the 300-3,400 Hz speech band. However, the data channel is kept below 3,000 Hz. Output power of the RT39-L is 6 W, and the channel spacing is 25 Hz while the duplex spacing is 10 MHz. The RT39-L transceiver operates in continuous transmission mode.
A speech-plus-terminal type of equipment is used to interface with the microwave radio. This interface combines the four-wire speech channel of the PAX in Lugogo with the 200 baud data signals from the master device in Lugogo into one common baseband of 300-3360 Hz. The speech channel is connected to a four-wire remote subscriber unit installed in the substations and a two-wire telephone subscriber set. The connection to the PAX at Lugogo is four-wire.
Currently, the radio system is adapted to an in-band signaling system using a 50 baud signaling channel (approximately 3,300 Hz) and a 200 baud VHF channel, which are part of the terminal equipment. A 48 V dc power supplies the terminal equipment with power and is good for 48 hours.
All of the data signals between the ABB NERA communication equipment and the ABB SCADA equipment are interconnected in the main distribution panel. Alarms for the communication equipment are connected to the RTU of the SCADA system.
Operational telephone system
The rehabilitation of the national grid has shown that a reliable telephone system is very important for controlling Uganda`s electric grid system. One can do without computers, but a communication connection is essential for controlling the grid. For this reason, UEB stressed that the telephone system should have very high reliability and a minimum of maintenance.
Seven DCX 600 digital modular telephone exchanges have been installed, one at the SCC in Lugogo, and the others at the substations at Kampala North, Owen Falls, Masaka West, Tororo, Mutundwe, Kabulasoke and Nkonge. An additional link was connected to the DCX 600 branch exchange previously installed in the administration building of Amber House, (Figure 2).
Six small substations in Kampala have also been linked, via the radio repeater station on top of Muyenga Hill, to the Lugogo SCC. For safety reasons a backup telephone has been installed in each of the substations. As a result, it is now possible to communicate with the next substation even though a failure may have occurred with one of the exchanges of an adjacent station.
With the installation of the DCX 600 telephone system, UEB has a state-of-the-art communications and control system that allows it to prioritize its routing and rerouting functions, have direct access to all areas of its system, identify emergency calls and control equipment automatically.
Dipl. Ing. Georg Th. Prinz was the project manager for the SCADA and communications part of the Uganda Power Network Rehabilitation Project. He has a degree in communication engineering from Munich Technical University in Germany. Prinz has been working in the SCADA and communications field since 1971.