Power Substations Monitoring and Control System
The designed system is intended for the remote monitoring and control of distribution power substations of SPP or similar types. This system has been applied to the open pit in Bełchatów Poland. It is one of the largest brown coal mines all over the world, with the coal output of 38500000 Mg and overlay output of 125 Mm3 per annum. The coal is conveyed to a 4320MW power plant. The SPP substations are of movable construction and they consist of a 30kV switchgear, a transformer, a 6kV switchgear and compensating capacitors. Those stations supply power to basic machines working in the open pit. Considering their designation, the stations are non-stationary and their location changes as mining advances. They are situated within an area of the radius not exceeding 20km.
Remote measuring points (ZPP) located within the SPP stations are the basic components of the structure shown on the diagram. They are provided with measuring modules processing the selected signals to digital form, and data transmission equipment (RM radiomodem) intended for the transmission of the acquired information to the central station for further processing. First of all, the data from ZPP are transmitted to a remote data concentrator (ZKD), that includes a communication server (SKOM) and a monitoring and control system server (SWIZ). Communication between ZKD and ZPP is provided by data radio transmission system. In order to ensure the required operational reliability, information is protected against accidental changes occurring due to disturbance during transmission.
In the designed system there are used SCADA - Supervisory Control and Data Acquisition stations (WIZ), which are to illustrate the current state of signals at the SPP stations under monitoring, to record events in time and to make control of selected signals possible. The WIZ station is connected to the system at an optionally selected place by means of the existing plant computer network. In practice, any number of stations of that type can be connected owing to the adapted solutions. The SCADA (WIZ) station currently:
- shows the status of the station, i.e. illustrates the values of recorded signals in a graphic and numerical way on a display of a very great resolution;
- shows information connected with the inspection of the correct functioning of measuring points (ZPP) and data transmission systems;
- records signals and alarm status in time;
- makes remote control of selected signals possible;
- precludes access to control functions of non-authorized persons;
- prepares reports on alarm status.
Manual portable control unit (RSW) is of vital importance for maintenance and diagnostic procedures. It is meant for local visualization of current values of signals, diagnostics and configuration of measuring systems and data transmission equipment. If the system functions properly that station is useless. But it is indispensable to configure and test the operation of ZPP on the occasion of extending the list of signals to be monitored, repair, modification of parameters, check on the operation of transmitting and receiving devices, etc.
System Main Functions
Communication with substations is provided via data radio transmission system (as described below) whose operational frequency and signal strength have been selected basing on a computer simulation using a digital map so as not to interfere with the equipment in use and to ensure required reliability of the whole system. Current signal values are monitored by SCADA stations (WIZ) connected to the network. Data delivered thereto ensure:
- recording of data;
- acoustic signalling of any alarm status to the operator;
- processing of measurements in the form of tables and diagrams;
- possibility of report printout;
- monitoring of DC power intended as backup supply for station local control circuits;
- 6kV voltage measurement;
- monitoring of the position status of 30kV and 6kV switches;
- tripping of differential current, temperature and overcurrent protections for 30kV;
- tripping of overcurrent and earth fault protections for 6kV;
- remote switching on/off of capacitor battery.
The system has been designed in such a way that, in future, it can be developed with regard to:
- an increase in the number of signals to be monitored;
- an increase in the number of substations connected to the system;
- an increase in the number of SCADA stations.
System of Data Digital Radio Transmission
Data radio transmission is provided by radiomodems manufactured by MDS (Microwave Data Systems), working within the frequency band of 350-512MHz. To get reliable evaluation of radio system coverage there is used a computer propagation analysis which makes it possible to allow for factors affecting the propagation of radio waves, including, especially, land configuration. The computer program used implements various propagation models, among others Okumara's, ITU-370, Lee's, Ibrahim-Parsons' ones. For computing, the program uses a digital map of land configuration and development as shown in the figure below.
To determine usable range there has been selected Okumara's area model, which is generally used within the frequency band and application types under consideration. Additionally, there is used an adjustment for so called angle of path shading as developed by EBU (European Broadcasting Union), which enables better regard to land configuration details than the original Okumara's model does. It is of vital importance considering diversified earth surface within the Bełchatów Brown Coal Mine. Results of the simulation are shown on the drawing.
Additional assumptions have been made for the design in order to reduce costs of operation and to increase the functionality:
- the system includes functions for the management and control of functioning of its individual elements, especially the data radio transmission system;
- local data reading from any SPP station is also possible by means of an additional mobile control device;
- the existing communication infrastructure such as fibre optic lines, computer network, etc. have been used to the maximum extent.