COMPARISON OF EVENT RECORDING SYSTEM AND SCADA SYSTEMS
Mustafa İŞBECEREN1
Nevzat ONAT2
1Telepro Energy and Electronic Systems San. Trade Ltd. Sti., 34785, Atasehir, Istanbul
2Marmara University, Vocational School of Technical Sciences, 34722, Kadıköy, Istanbul
The energy sector, which is facing an increasing demand, needs to have a suitable infrastructure to meet these demands. One of the most important issues to be considered while establishing the infrastructure is the uninterrupted and high quality delivery of energy to the final consumer. Therefore, all points from generation points to transmission, from transmission to distribution should be under the control of operators.
Data acquisition and SCADA software used for Process SCADA and Energy SCADA also differ from each other. In fact, if we consider Energy as electricity, water, steam and natural gas, the data collection equipment and SCADA software used for electrical SCADA are different from other network data collection equipment and SCADA software. due to its structure.
A 1-second pressure drop in the water network and the damage that a 1-second voltage drop in the electrical network can cause to an industrial facility are very different from each other. Therefore, when designing Mixed SCADA projects, the most sensitive network should be taken as a basis and the SCADA system should be built on this skeleton. While PLCs (programmable logic controllers) can be used to collect data from process SCADA and even water, steam and natural gas networks, PLCs should not be used for electrical SCADA. RTUs (remote terminal units) should be preferred for electrical SCADA.
A pre-written program runs in the PLC and the whole process is managed in line with this program. Since the PLCs will understand any status change when they take a picture of the field, the time of the status changes is recorded when the field is photographed. This will also differ from the actual occurrence times (depending on the length of the cycle time). In addition, all I/Os will be recorded with the same time stamp, since the PLC will take pictures of all I/Os at the same time.
The working principle of RTUs is quite different:
-Unlike PLCs, RTUs are not programmed, they are parameterized very simply.
-In PLCs, all signals must be defined and the defined signals must be processed, ie programmed, in a certain sequence for the relevant process. This is a specialist operation.
In RTUs, on the other hand, field data is defined only according to signal structures (digital or analog; single or binary status signals, etc.). No program is written to process them. Defining data according to their structure is a parameterization process. Just like parameterizing a protection relay. All the rest of the work is done in hardware in RTUs. For this reason, a loop cannot be mentioned because there is no program running in RTUs. This, unlike PLCs, ensures that the detected signals are labeled with the time they are detected, and it also eliminates the risk of not detecting any signals due to its loop-free operation. As a result, signals are all tagged as they occur, unlike PLCs. (In PLCs, since they will all be detected at the same time t0, they will all be labeled with the same time signature). This feature provides us with many advantages in electricity grid management. First of all, thanks to this feature, an accurate fault diagnosis can be made. Considering that the opening times of the breakers are between 80-100 milliseconds, which of the feeders that open at the same time opens first, and therefore which feeder causes a malfunction, can only be diagnosed with such a sensitive system. Thus, this gives us the chance to create a chronology of failures, so that we can take precautionary measures for future failures. Cycle times in PLCs can be between 40 and 500 milliseconds, depending on the size of the program they are written in. In other words, if PLCs are used as data acquisition units in electrical SCADA, there is no chance of making the above-mentioned fault diagnosis.
- Annunciators
They perform the function of announcing the fault information coming from the relays in various ways. They are functional devices used in electrical networks as well as in other areas. In the case of a malfunction, the simplest models provide the system operator with malfunction information visually and with a sound warning. Today, these devices also undertake the functions of transmitting fault information in desired detail to RTU devices, operator computers, event recorders and data collection centers with the help of a microprocessor unit and software. There are also types that have their own memory on them. Thanks to this memory, the annunciator also gains an event recorder feature, eliminating additional costs for small-sized systems. Annunciator devices can be produced with different signal input numbers according to the needs. Today, 4, 8, 16, 24, 32 and 48 input annunciator devices are commercially available in the market. There are devices in a very wide price range depending on the manufacturer, additional features and especially the quality elements in their production. Figure 1 shows an alarm annunciator with 16 inputs.
- RTU Devices
Remote Access Unit (RTU) devices have become one of the most important elements of today’s distribution center automation systems. This unit acts as a cache memory that collects the information from the announcers and stores them in various formats. It also undertakes the transmission of the incoming data to various units with software authorization according to the nature of it. RTUs are microprocessor controlled devices. Especially in recent years, models that can record data with time synchronization using GPS technology enable monitoring and control of very long distance transformer stations from a single center. This feature provides significant communication flexibility and cost savings in large area protection applications. Reducing the communication standards used in providing data to the SCADA system to a single type as IEC61850, especially in recent years, is an issue that is emphasized all over the world and in our country. This is a very costly investment as it requires all relays and measuring devices in the field to support this protocol. However, with the appropriate design of RTU units, it is possible to make a significant saving by eliminating this requirement. An example RTU model is given in Figure 2.
- Event Recorders
This unit is located in the power system control center and records all incoming data with time information. Data in the device can be accessed at various levels with software authorization. As a result of the analysis of the information, very detailed information about the behavior of the power system can be obtained. Event recorders are also included as a unit in some relays today. Depending on the system structure, they may have various physical and technical properties.