Industrial automation company Streamworks recently installed an automated control system at Katse Dam in Lesotho. Katse Dam is one of the highest dams in Africa and one of the largest concrete arch dams in the world. This automated control system ensures a safe supply of electrical power to the dam. From implementation and commissioning, the project took three months to complete. Streamworks' staff provided training on site to ensure that Katse personnel were familiar with the system.
The electrical power utilised at Katse Dam is generated from three sources: Lesotho Electricity Commission (LEC), Katse Hydro Power and three Barlows' generators.
Monitoring the breakers of each power supply allows Streamworks to verify that the combination of power is safe. An operator will select which power supply is going to be used via a scada interface. The scada verifies that the power supplies are an acceptable combination and the PLCs permit these choices to be implemented.
System functionality
If LEC is selected and connected, the minihydro can also be requested to come into operation and synchronise with the main grid. Once switched, the system will be running in a grid connection mode.
If LEC is no longer available, the minihydro will keep on supplying the load in an isolated mode without a power failure being experienced. If the minihydro is requested to shut down when it is grid connected, the stopping sequence will be initialised and the load will be reverted back to LEC.
If neither LEC or minihydro is available, or if the operators choose to select the generators, they can be requested to start up, synchronise and share the load.
The generators are monitored via a special screen where information like voltages, current, frequencies, active power, apparent power and engine speeds are displayed.
Software
Wonderware's InTouch Version 7 running under WindowsNT was used. Siemens Step 7 programming software was used for programming the PLC's. PC Anywhere software was used for the remote dial-in link. The Gencon II communicator converts the signals from the Gencon controllers which controls the generators from a RS485 protocol to an RS232 base protocol on which a Modbus software protocol then functions.
Drivers
Two drivers were used in the system. A Siemens/InTouch driver which allows the PLCs and scada to communicate. A Modbus driver was implemented to interface between the GenconII communicator and the InTouch scada.
Animation
The scada was animated to show the live switching status for every reticulation breaker. This ensures that the operator knows which power supplies are being used at any given time.
Bitmaps
Pictures of actual equipment (diesel generator, mini hydro generator etc) were taken and imported into the InTouch scada.
Workstations
The system comprises one workstation, which is situated in the operator control room in the Katse Dam wall. A link to Johannesburg is established via a dial-in modem. This link allows any changes in the system development to be made and then downloaded. The dial-in also allows access to the Gencon II control system, which allows Barlows to remotely view the full status of generators from Johannesburg.
PLC
Siemens' S7 PLCs, using 314 IFM CPUs, were used. They are networked using a Siemens proprietary system which limited the communication between PLCs to 100 m. A distance of 750 m was needed between the PLCs so Streamworks implemented copper to fibre converters and solved the communication limitation problem. The PLCs interface with the InTouch scada system using the IFM port of the CPU. A Siemens interface card (CP 5412 ISA) resides in the scada workstation which provides a full Profibus network. The advantage of this card is that it enables the system integrator to program the PLC and see the changes on the scada immediately. These PLCs are programmed to act autonomously should the scada system shut down, ie the PLCs remember the last combination of power supplied and by using the network, they interlock with each other to ensure the power switching is safe.
Management information
Reports are printed displaying generator usage and efficiency information. All other events are time stamped and logged. This allows traceability of actions as all operators have to log on and off with passwords. Every time a circuit breaker trips, the information is stored in the PC for further inspection. This information serves as a 'tendency' report showing management when and why breakers fail.
Unique features
The system acts as a policeman to ensure the safety of personnel and equipment at Katse Dam. Electrical feedback can have devastating effects should the incorrect reticulation combination be switched.
Safety improvements
Only specified power sources may be connected at any given moment to ensure a safe reticulation at all times.
Streamworks
(011) 803 4376
© Technews Publishing (Pty) Ltd | All Rights Reserved
printer friendly version