Radial Feeder Protection using Arduino

Transcription

1 Available online at International Journal of Innovative and Emerging Research in Engineering e-issn: p-issn: Radial Feeder Protection using Arduino Ishant Sharma, Tarak Patel a, Prof. Dhaval Tailor b a B.E. Student, Electrical Department, ADIT, New Vidhyanagar b Assistant Professor, Electrical Department, ADIT, New Vidhyanagar Abstract: The main purpose of this project is to provide backup protection and overcurrent protection in radial feeder transmission system using microcontroller. In the constituted system, if fault occurs then it is sensed by microcontroller via current sensor and the controller commands immediately isolates the faulty part. In case the C.B in zone 2 fails to operate, then the previous C.B, i.e., the relay of zone 1 provides backup protection against the fault resulting in the isolation of both zones. In this project, we are giving backup protection as well as overcurrent protection to the system. The overcurrent indicates that the relay operates and the contacts are closed when the current exceeds the predetermined value. The microcontroller is programmed to sense whether the circuit breaker has operated or not in case of faulty conditions and provide the backup protection and overcurrent protection by the logic deduction and hence giving trip signal to the contactor after the specified time delay. Keywords: Radial Feeder, Overcurrent protection, Arduino, current sensor I. INTRODUCTION The conventional Overcurrent relay fails to respond to this misuse, unless the set points or pick up values are changed appropriately by human intervention, often the locals influence the substation personnel to keep the set points in such a way that the misuse is not reported. This, at times, may cause cascading disasters in the power system. [8]. The radial transmission line is protected by various protective device like distance relay, directional relay, differential relay and overcurrent relay. The radial feeder scheme has many disadvantages like shutting down whole line in case of fault. So reliable and speedy (in decision making) protection must be used so that mal-operation is avoided and to contain disconnection of line as small as possible. Here we are providing protection by overcurrent relay but instead of conventional relay which is slow, costly and inaccurate we use microcontroller for giving tripping command and isolating faulty section. The arduino is used for making decision by acquiring value of current flowing from the line by using current sensor ACS712 and generating tripping command if current exceeds some value. Overcurrent protection and overcurrent relay: An Over Current Relay is a type of protective relay which operates when the load current exceeds a preset value. In a typical application the over current relay is used for over current protection, connected to a current transformer and calibrated to operate at or above a specific current level. This thesis will attempt to design and fabricate over current protection relay using microcontroller [5]. In overcurrent protection the protective relay checks whether the current passing through line exceeds some value or not and according to current flowing the relay is energized after some time delay which depends upon how much current is flowing through line to be protected. According to time delay the relay are classified as 1. Inverse time overcurrent relay 2. Definite time overcurrent relay 3. Inverse definite time overcurrent relay And current value at which the relay operate depends on location of relay i.e. the current value at which relay operates near generating end is high and load end is least. The current at which the relay operates is determined by plug setting. And time delay is determined by time dial setting. [3]. The current required by relay to operate or to move contact (connected to current coil) against restraining force given by spring is called Pickup Current. The pickup current of a particular relay is constant. It depends on restraining coil or spring. 17

2 Figure 1. Working of electromechanical relay [3] The current required for operating or moving contact against restraining force also depends on number of turns of current coil. If we reduce number of turns of current coil, then current required for actuating relay increases. So tapings are provided on current coil on mechanical relay. This is current setting of a relay. Current Setting = (Pick up current Rated secondary current of CT) 100% The ratio fault current by-product of pickup current and current setting is called Plug setting Multiplier of a relay. The current flowing from operating coil is directly proportional to fault so PSM determine force produced by operating coil. PSM = Fault curret in relay coil pickup current = Fault cuurent in relay coil Rated CT secondary current Current setting Here in overcurrent relay there is some time delay required for moving contact near to each other. The time delay depends upon distance between to contacts and moving speed (which is proportional to PSM). The distance between contacts can be varied thus time required for actuating contact can be varied. This is called Time dial setting of a relay. [1] By knowing PSM and TDS of a relay we can calculate time of operation. The graph of PSM vs. Time delay is plotted we get various characteristics by varying Current setting and TDS. As discussed earlier the relay follows various characterises like 1. Inverse time overcurrent relay 2. Definite time overcurrent relay 3. Inverse definite time overcurrent relay In inverse time overcurrent relay the time of operation is inversely proportional to fault current. But also the characteristic depends on Plug Setting of relay. Inverse time overcurrent protection In a system for which the fault current is practically determined by the fault location, without being substantially affected by changes in the power source impedance, it is advantageous to use inverse definite minimum time (IDMT) over current protection. This protection provides reasonably fast tripping, even at a terminal close to the power source where the most severe faults can occur [6]. Given below the figure shows characteristics of Inverse time overcurrent relay Figure 2. Characteristics of inverse time overcurrent relay [2] 18

3 And in DMT characteristics we see that at the relay operate at certain value of current according to position of relay i.e. time of operation will increase at near generating end and vice versa. Figure 3. Graph of DMT relay [3] And in IDMT relay we have inverse characteristics and DMT also. The relay will operate instantaneously at some threshold value of current. Protection based on microcontroller: Here arduino is used as brains for decision making. Here CTs are bypassed and instead we use current sensor, ACS712 hall-effect sensor. They are used for converting current signal to voltage signal. As arduino only measure voltage at ADC port so we need current sensor to convert current value to proportional voltage value. The output of current sensor is feed to A0 and A1 port. And value of voltage measured at ADC is converted into digital form and value of maximum value of voltage is determined and maximum value of current is determined. The arduino will be programed in such a way that it will give backup protection to relay at load end if it will fail to operate The current signal is converted to voltage signal, but here voltage signal will be of AC form so we need something to convert in DC form so that arduino will measure a constant value. So here we use rectifier circuit. The current setting and TDS at source end is set higher than load end. And time of operation is calculated. Figure 4. Diagram of radial feeder prototype About current sensor: The current sensor is basically a hall sensor. This converts current value to proportional voltage value. The current sensor used here is ACS712 which can measure current upto 30 A. The voltage generated at output of current sensor is 66mV/A so this relation is used to determine value of current by arduino. But here 2.5V offset at zero current is present at output of current sensor. 19

4 Figure 5. Current sensor (4) So we need to compensate this offset inside the program of arduino. As current to measure is in AC form thus the output voltage signal is in AC offset form at 2.5 volt. So we need rectifier to convert this AC signal to proportional DC signal and then output is given to Arduino or we can determine maximum value of voltage and maximum current is determined. And rms value of current is determined OR by using rectifier circuit for converting AC value to DC value. II. WORKING A current transformer is used to measure the over current. The current is reduced to a lower value using a current divider. The reduced AC current is converted into a smooth DC value by using an IN4007 diode and a 10μF capacitor. This DC current is fed to microcontroller which activates the relay [7]. As from the circuit diagram we can see that current sensor is in series with load. Thecurrent is sensed by the current sensor and its output is in AC form. Thus we have to convert it in Dc form by rectifier which is mounted in PCB along with relays and auxiliary relay. Therefore, the PCB circuitry along with arduino is called control circuit of the radial feeder protection model. The arduino is program in such a way that if current is more than some fixed value (plug setting) it will send tripping signal to auxiliary relay on control circuit and then it will trip main relay which in turn disconnect the faulty line. The main idea of project is that the arduino will sense the status of two switches in both zone and if zone 1 switch is on the zone 1 relay will give instantaneous protection and for off it will give backup protection and if zone 2 switch is in on condition the it will be remain/give off/instantaneous protection. Transmission line 12 volt relay Current sensor 5 volt relay Program rectifier Arduino Switch states Figure 6. Block diagram of radial feeder protection scheme using Arduino 20

5 Figure 7. Simulation of radial feeder protection Figure 8. Working model III. ALGORITHM AND PROGRAM: Here as we know that rectifier is not used instead of we are determining maximum value of current. This is possible by program. Here maximum value of voltage is determined and then maximum value of current is determined by using relation of 66mV/A. And then RMS value of both current is calculated. The secondary current referred to primary is calculated. Both current is compared and then ratio is calculated which in turns determines tripping action and then 9 pin is set high. 21

6 Figure 9. Flow Chart RESULTS AND OBSERVATION TABLE Table 1. N.L at load 2 Zone 1 (no load at load 2) Voltage1(A1) Current 1 (I1) Top 1 Top 1'

7 Table 2 zone 2 N.L at load 1 Zone 2 (N.L at load 1) Voltage1 (A1) Current I1 Voltage2 (A2) Current I2 Top 1 Top 1' PSM 2 PSM 1 TDS Top Table 3. Zone 1 at constant load and zone 2 at variable load Zone 1 at constant load and Zone 2 at variable load Voltage1 PSM 1 Current Voltage2 PSM PSM 2 Current TDS 1 Top 1 Top 1' Top 2 (A1) I1 (A2) 1' I

8 Figure 10. screenshot of serial monitor IV. CONCLUSION Thus we have successfully provided backup and instantaneous protection for zone 2 and zone 1respectively. We also come in conclusion that using Arduino is cheaper because it can have different types of characteristics as all we have to do is to change the algorithm in ROM rather than changing the whole relay in case of conventional mechanical relay. It is also cheaper and also efficient. And also we have concluded that at internal fault current at both winding differ by a huge value which can be measured accurately by current sensor. And we have derived very reliable protection as Current transformer is bypassed and it is only for small size transformer. For bigger size either current sensor with high rating is used or simply current is stepped down by CT. 24

9 References [1] N.G.C. Protection and Switchgear. [book auth.] N.G. Chothani. Protection and Switchgear. s.l. : Oxford Pub. [2] wikipedia. wikipedia. [Online] [3] electrical4u. electrical4u.com. [Online] [4] [Online] [5] International Journal of Scientific & Engineering Research, Volume 6, Issue 2, February [6] Overcurrent protection relay using PIC microcontroller [7] Fault Detection and Control in Power System Equipments using Atmega 16 [8] Adaptive overcurrent relay for the rural Agricultural feeder Based on Niranthara Jyothi Yojana 25