DESIGNING AND MANUFACTURING CURRENT TRANSMITTER ON MV SYSTEMS FOR SMART GRID APPLICATIONS

Transcription

1 DESIGNING AND MANUFACTURING CURRENT TRANSMITTER ON MV SYSTEMS FOR SMART GRID APPLICATIONS Saeed ABACHIZADEH Tabriz Electric Power Distribution Co. Iran ABSTRACT Power Systems have developed rapidly in the last years. Therefore, we need precise and confident control and protection systems to protect them. Entrance of digital control equipments could improve precision and reliability of control systems. Considering to the requirement of power system, medium voltage and high voltage transmitter with ability of monitoring of factors has been designed and manufactured. In this system, transmitter uses magnetic field. However this transmitter differs mainly with traditional Current Transformers (CTs). The advantages of this CT are high precision, less weight and dimension, and capability of measuring of Direct, harmonic and frequency. This CT has been designed and tested in Ansys and Proteus software. Then prototype model has been manufactured and test during 9 months on 20 kv network. 1. INTRODUCTION Nowadays, measurement is done with magnetic field measurement. Magnetic field could not be measured directly. So it must be converting to force such as light converter, such as transformer converter, voltage with Hall Effect converter. Comparing three laws and models show that light converters are expensive with complex technology. Transformer convertors could not measure DC and transient modes. Thus Hall Effect law is only law that is used in AC and DC s. However heat and saturation highly effect on Hall Effect sensors. So, this converter is used only in low amperes and some industry like communication, aerospace and medical. Proposed system emits these constrains on MW and HV networks. Also, some facilities are added to it. 2. HALL EFFECT THEORY Hall Effect theory discusses that if a conductor that carries, locates in magnetic field according to Lorentz law, magnetic field forces and disturbs its monotonous, figure(1). Therefore a voltage is created between two points of conductor that this voltage is proportional with magnetic field and. ( ) (1) Where: V h : Voltage Arman AMINI BADR Islamic Azad University-Sardroud Branch Iran arman.amini.badr@gmail.com I: B: magnetic flux density Figure (1): Hall Effect sensor 3. SYSTEM DESIGN (SKETCH) This transmitter system has a transmitter unit and receiver unit. Figure (2) and (3) show two block diagrams. Transmitter unit has a sampling unit, processor and coupling converter with optical transfer. Sampling unit changes high s to signals which are useable in digital equipments. Control unit includes anti-saturation circuits to improve performance and temperature controller to reduce temperature effect on output of system. Transmitter unit has a supply unit to supply all electronics equipments. Figure (2): block diagram of transmitter system CIRED /5

2 Receiver unit includes processor units, factors displayer, OC/EF relays, output modules, coupling unit with optical transfer. Coupling unit with optical transfer gets data from transmitter by optical cable. Process unit have a PIC16F84 micro controller that is SMD type which processes input data and creates output. Displayer unit is a complete metering of factors such as peak, effective, phase angle, THD of and frequency. OC/EF relays has been designed to protection of feeders that the type of these relays is inverse-time with 0.05 to 1 TMS. 5. REDUCTION OF THERMAL EFFECT ON THE SENSORS Semiconductors are sensitive to temperature variations, and output error increases at high temperature and s. Thus Hall Effect sensors are not used on high voltage lines. A new manner to solve this case has been shown in figure (5). While Hall Effect sensor is on air gap, a sensor of same type is located at 0.5 cm distance and 90 angle location to first sensor. Temperature effect and noise for two sensors are same and output of second sensor will be zero. The Outputs of two sensors are subtracted, and then net output amount is sent to the next step. This sensor is located in a bismuth box so that magnetic field was minimised. Hall Effect Sensor Figure (3): block diagram of receiver system According to figure (4), the prototype is made of a cast iron core with relative permeability 44 and a B type ferrite core with relative permeability In low s, the sensor of ferrite core is active and in high s, the sensor of cast iron core. This is done with a control system [1], [2]. For high accuracy in very low s, extra high permeability cores are used. On the other words, non linear area is changed to several linear areas. Bismuth Box SecondHall Effect Sensor Figure (5): Reduction of thermal effect on the sensors 6. ANTI-SATURATION UNIT Figure (6) shows model which is used for prevention of saturation in ferrite core. In this model, the output power of sensor is reinforced by push-pull circuits, then it is applied on winding which is wrapped on the core in the reverse direction of main cable. Thus a flux is made contrary of main flux, and it restricts core saturation. Consequently, measurement range is increased in the system. Figure (4): the circuit of the sensor and micro-controller 4. REDUCTION OF ELECTRIC FIELD EFFECT OF LIN To reduction of electric field effect on the sensitive equipments, a system like to the faraday cage is used. So all of electronics equipments are located in two aluminium foil with 0.45 mm thickness and from two sides connect to earth system. Therefore, the electric field effect on electronic equipments has been reduced. [3], [4] Figure (6): Anti-saturation unit 7. MICROELECTRONIC SYSTEMS In system designing, it has been tried to the software of system carries more role than hardware. CIRED /5

3 It causes that industrial production of CT would become worthwhile and flexible. Also, the changing of the system properties will be easy and inexpensive. System hardware includes micro controller, sensor, interface, I/O unit, and power supply. The type of microcontroller is atemga 32. A reason to select this micro is its internal analogue to digital facility that is 10 bit ADC. Noise effect on system is minimized. Consequently when ADC does sampling and conversion, internal ENTRABAT is activated automatically and all parts are off except RAM. It causes that high frequency of CPU and other equipments does not effect on ADC function. PIC controllers which have similar architecture and is adaptive with fibre optical transfer system, has been used on the receiver side. All units that are supplied by CT could be simulated by different programs. Therefore factors displayer, adaptive unit with SCADA, OC, and EF relays and computer converter are designed and implemented. Three ways are used to send output signals to control room in the power substations: direct, wireless, optical fibre cable. Direct way is applied less because of intensive signal drop and noise. Wireless manner is complex and expensive. Thus third way is the best which is used in DCS substations; figure (7) shows equipment installation arrangement. All of them connect together by RS 485. One of them is sender that collects data and sends them. 8. INSTALLATION Figure (7): data transmission Installation of the conventional transformers has some problems. For example, the down core CTs confront to local saturation or the center of gravity of top core CTs is near the top of the instrument. The proposed system solves two mentioned problems, because it is lightweight and even it can be installed without structure and supporter.[5] 9. ELECTROMAGNETIC FIELD ANALYSE WITH ANSYS To analyse the noise effect on the output of the system, simulation has been done with ANSYS software. According to figures (8), and (9), magnetic and electric field distribution at sampling unit is monotone. Figure (8): Electrical Field Distribution Figure (9): Magnetic Field Distribution 10. SIMULATION OF ELECTRONIC PARTS Electric parts have been simulated with Proteus software. PCBs have been designed in two different models. Transmitter unit has been made with two layer PCBs, which causes to decrease system dimension. PCB of receiver unit has been designed in one layer form. To eliminate noise effect on CPU, RS 232 transmission unit has been isolated from the other parts. All particles have been chosen to SMD form to reduce system dimension. This issue is important in compact substations CPU simulation This unit includes an atemga 32 microcontroller which digitalizes all received data, then these data are coupled by RS232 to optical transducer, [6]. Figure (10): Processor unit simulation CIRED /5

4 10.2 Sampling unit simulation This unit includes a differential unit with an ideal rectifier. All ICs are supplied by AC source and diode bridge rectifier. Figure (11): Sampling unit simulation 10.3 Control unit simulation This unit includes a main Hall Effect sensor, a Hall Effect sensor which control temperature, transistor amplifier, DC capacitor filter; push-pull resistor and anti saturation feedback. [7] Figure (12): Control unit simulation 10.4 receiver unit simulation This unit includes an atemga 32 micro controller that processes all receiving data and on a LCD displayer shows all information about graphically, for example, RMS, Peak, Phase angle, frequency, and harmonics. Also, this unit have an auxiliary relay that stimulated on over and earth fault condition. Figure (13) shows this unit. Figure (13): Receiver unit 11. LABORATORY TESTS Current transmitter of high and medium voltage was tested at four sections according to IEC-60, IEC-185, IEC-296, IEC-156, IEC-290, and IEC-519. These sections are: metering test, protection unit test, insulation test, and accuracy test Metering test Metering test has been done by injection RTU 125, 500 A, and 220 V power supply during one week and three steps. A LCD displayer and a injection unit have been used for evaluation. Table (1) shows conclusion of third step. Comparing the measured and injected s show that difference is about hundredth Ampere. The percentage of difference between s is about percent. According to the standards, this amount is applicable. Table (1): conclusion of third step For THD test, an available network which has harmonic, has been chosen. Table (2) shows the results in three steps with 48 hours time interval. The percentage of difference between the proposed system and data logger is about and percent respectively. This is applicable according to IEEE 519. Table (2): THD test Theory Data Transmitter Logger I rms I 1 I 2 I 3 THD THD THD Accuracy test This section shows the accuracy test results at two temperatures, 5 C and 40 C. Table (3) and (4) shows test results. The percentage of difference is and for two mentioned temperature respectively. 12. CONCLUSION The CT has been designed and tested by software.in system designing, it has been tried to the software of system carries more role than hardware. The advantages of this CT are high precision, less weight and dimension, and capability of measuring of Direct, harmonic and frequency. It causes that industrial production of CT would become worthwhile and flexible. Also, the changing of the system properties will be easy and CIRED /5

5 23 rd International Conference on Electricity Distribution Lyon, June 2015 inexpensive. PIC controllers which is adaptive with fibre optical transfer system, has been used on the receiver side. All units that are supplied by CT could be simulated by different programs. Therefore factors displayer, adaptive unit with SCADA, OC, and EF relays and computer converter are designed and implemented. Current transmitter of high and medium voltage networks was tested at four sections. Figure (14), (15), and (16) show the hardware of system. Table (3): accuracy test resultss at 5 C an Optimized Magnetic Circuit", Allegro Microsystem, [7]C. Kühnel, 2003, Programmieren der AVR RISC Mikrocontroller mit BASCOM-AVR, ISBN , Germany. Figure (14): Receiver unit of system Table (4): accuracy test results at 40 C REFERENCES [1] Lawrence H.van vlack, 1982, Materials for Engineering Concepts and Applications, Addison- Wesley. [2] J. Gilbert and R. Dewey, , " LINEAR HALL-EFFECT SENSORS", Allegro Microsystem, 1-9. [3] T.G. Gustavsson, 2000, Outdoor Aging of Silicone Rubber Formulations in Coastal Environment, Publisher, Department of electric Power Engineering, Chalmers University of Technology, Goteborg, Sweden. [4] A H Luxa,A B Mueller,T J Noble, 1998, " Sensors and non-conventional V.T and C.T for medium voltage switchgear", IEE Conference publication, No.459. [5] C. Teyssandier, 1995, From transformers to hybrid sensors in HV", Merlin Gerin, Cahier technique. No. 170, [6] R. Dickinson & S. Milano, 2002, Isolated Open Loop Current Sensing Using Hall Effect Technology in Figure (15): Installation on overhead line (20kV) Figure (16): Displayer CIRED /5