Running a hydroelectric power plant requires appropriate electrical equipment, starting from generators through auxiliary equipment and transmission lines. Generators convert mechanical energy into electric one which is transmitted afterwards to the receivers via electric transmission lines. Transmission lines are developed as over-head and underground ones. The so called sub-hanged lines – with a transmission cable hanged at the electrical poles. In order to lower the transmission losses transmission lines are erected for voltages higher than that of the generator. In such cases transformers enabling matching the voltage generated by the unit to that of the electrical grid are necessary. Furthermore, transmission of electrical energy requires auxiliary equipment and switchgears. The auxiliary equipment includes the devices that are necessary for power plant operation, but don’t take part in the process of electricity generation – e.g. oil or dewatering pump engines. The switchgears allow proper distribution electricity onto individual circuits and electrical system operation (connecting activi-ties). The electric equipment includes also measurement instrumentation as well as protection and control de-vices.
Electricity generation requires proper control of all devices taking part in this process. Currently, the staff is sup-ported by relevant control systems facilitating power plant operation. The widely conceived control system con-sists of measurement instrumentation as well as protective and control devices. Interaction with the staff/user is also enabled. Finally, the appropriately developed control systems allow unmanned power plant operation and/or remote control. Integration of all above-mentioned tasks contributes to facilitating the staff work, in-creasing the electricity supply safety and dein-creasing the operational costs – e.g. by introducing the predictive maintenance and diagnostics components preventing major failures.
The contemporary control systems are usually featured by multilevel structure - that is the individual devices are furnished with dedicated control systems (e.g. turbine governor) which are incorporated into the control system of equipment groups (e.g. block controller) and then into the power plant supervisory control system.
The PLC controllers are of substantial significance in the control systems. The controllers are furnished with ap-propriately selected set of analog and digital inputs and outputs and allow data transmission between the de-vices. Ever more frequently the control systems of individual devices are also furnished with operator panels allowing monitoring or changing their operating parameters.
Visualisation and control of power plant operation are generally conducted from the level of operator station connected to the supervisory control system. Generally, the system allows monitoring the condition of the equip-ment and their technical parameters as displayed in the technological schematics (Figure 57). The system tasks include also reporting current events, such as surpassing the alarm or trip values, recording the events and pa-rameters, survey of archived records. Typical examples are shown in form of screen shots taken from a control and supervision system in one of Polish hydropower plants furnished with 2 Kaplan and 1 Francis turbine units.
The violet, green and yellow panels in Figure 57 denote start-up, shutdown, and emergency shutdown, respec-tively. The isle operation start-up panel can be seen additionally in case of unit 2. Improper pressure in the spiral case immediately after shutdown is shown in red in Figure 58.
The general trend is to perform most of activities in an automatic mode, after occurrence and fulfillment of some specific requirements. For instance, the start-up process should be preceded by attaining the state of start-up readiness (including no safeguard excitation). Next, the operator issues the start-up command. After this time point the consecutive steps of the start-up procedure are performed with each subsequent step commenced only after the necessary conditions are fulfilled (e.g. the required speed is reached prior the synchronization process starts). Any disturbance in the unit operation or the sequence course is reported to the operator (with the problem source indicated) and the system undertakes the activity adequate to the situation having occurred.
The essential component of the generally conceived control system are protection devices which task is to take care of safe operation of the equipment, to minimise probability of a failure and minimisation of their conse-quences. In contrary to the previous situation in the electrical power protection automation with individual pro-tective functions ascribed to separate devices, the contemporary market is dominated by digital devices fulfilling a number of protective functions which allow the user configuring their parameters by means of the relevant software. For instance, the respective list of generator safeguards includes among others the over current, ground-fault, under and over frequency, over and under voltage, reverse power protection. In addition to the complex protection they provide also communication with the supervisory monitoring and control systems and deliver the measurement data. In case of hydromechanical part the protective function (e.g. against tempera-ture, too high or too low oil level) is fulfilled by controllers of separate devices or the supervisory system.
In order to increase the electricity generation reliability, lower the operational costs and improve the staff work comfort the control systems are subject to continuous development. Their stage of advancement and complexity is demonstrated by the number of process variables in a hydraulic unit control system, often as high as several hundred. Of course, the unsupported staff would be unable to monitor such a number of parameters. The com-puterised monitoring systems facilitate the faultless power plant operation preventing the operator from actions not allowed in a given situation. The significance of automatic control systems for power plant safety and faultless power plant operation can be easily demonstrated at an example of synchronisation process which can lead to severe consequences if improperly conducted. The proper "manual" synchronisation has always required sub-stantial expertise. Today, even the first synchronisation (during unit commissioning) is often conducted by means of an automatic synchroniser, as this technique is considered a more safe solution. The control systems allow automatic regulation of the hydraulic unit/power plant/electrical grid operating parameters such as water level, power and voltage. Contemporary control systems allow also increasing the use of hydropower potential and decreasing the electricity generation operational costs by introducing control algorithms taking care of the opti-mum running of devices.
Figure 57: Electrical system schematic of an SHP power blocks in Southern Poland. A screenshot taken at standstill from the power plant supervision and control system (Courtesy of PGE EO SA)
Figure 58: Unit 1 hydraulic control system schematic of an SHP of Figure 53. A screenshot taken immediately after shutdown from the power plant supervision and control system (Courtesy of PGE EO SA)