Design and Development of Protective Circuit against Voltage Disturbances

Transcription

1 Design and Development of Protective Circuit against Voltage Disturbances Shashidhar Kasthala 1, Krishnapriya 2, Rajitha Saka 3 1,2 Facultyof ECE, Indian Naval Academy, Ezhimala, Kerala 3 Assistant Professor (C), JNTU Vizianagaram, Andhra Pradesh, India Abstract Due to large network and varied type of loads connected, the power system often experience deviations in the prescribed voltage limits. These voltage limits can be of very minimal duration or may sustain for longer periods. The risk to the connected equipment increases with duration of voltage variation. Since this abnormal voltage is unavoidable, the onus will be on the consumer to protect the appliances. In this paper, a circuit is developed using comparators to identify if any over voltage or under voltage conditions are present in the power system. Keywords over voltage, under voltage, timer, comparator, relay. I. INTRODUCTION With the introduction of semiconductor based controlling devices, the quality of power supply plays a vital role in dealing with the operation and maintenance of electrical equipment. Any deviation in the voltage and current from the actual waveforms can be treated as poor quality in power supply. These deviations can be quantified in terms of power frequency disturbances, power factor and grounding. The power frequency disturbances also include voltage sag or swell, electrical transients and harmonics. These irregularities in power supply need to be restricted to avoid the damages in the electrical system [1]. However, this paper is restricted to only voltage sags and swells caused at least for a time period of 3 sec to 1 minute. The concepts of over voltage and under voltage can be described from the Figure 1. These over voltages can be of momentary or temporary or can be sustained for longer durations. The power supply can be considered as voltage sag, if there is a reduction in voltage level (in the range of 10% to 90% of normal voltage level) for either momentarily or temporarily i.e 3 cycles and 3 min respectively. If the voltage reduction exceeds either 3 min or 3 hours, it can be classified as long under voltage and very long under voltage respectively. The power supply can be considered as voltage swell, if there is an increase in voltage level (in the range of 110% and above of normal voltage level) for either momentarily or temporarily i.e 3 cycles and 3 min respectively. If the voltage increase exceeds either 3 min or 3 hours, it can be classified as long over voltage and very long over voltage respectively. In this paper, a system is developed based on timer ICs to compare the voltage in power supply. The comparators will verify the voltage supply and trigger the relay if there is any deviation in the power supply. The subsequent sections of this paper are organized as follows. The next section gives a brief description on the power quality. The third section of this paper describes the system architecture. The fourth section of this explains the working principle of the system. The last section of this paper discusses the improvements to be made in the system for overall improvement of power quality. DOI: /IJRTER CEJXL 25

2 Figure 1. Under voltage and over voltage classification II. Power Quality There are numerous reasons for disturbances in power quality and each cause may impact the power quality differently. The common causes and consequences of power listed below [4]. Cause Consequence Power Quality Problem Switching on/off of large loads, faults in feeders Malfunction of electronic based control devices, tripping of contractors and relays Voltage sag Switching on/off of large loads, improper power supply and transformer regulators Automatic reclosure of protective devices, insulation failure. Due to natural calamities, improper coordination between protective devices Disconnection of heavy loads, failure of power factor correction devices, Lighting strikes Unequal distribution of Large single phase loads, failure of fuse in on phase, faulty operation of power factor equipment, high reactive loads. Electromagnetic interference improper grounding, radiation due to welding machines and arc furnaces Flickering of monitors, damage to sensitive devices Damage to sensitive equipment, tripping of protective devices Stoppage of all equipment Electromagnetic interference, failure of insulation materials Presence of negative sequence currents. Excessive motor heating and increased vibrations. Disturbance to sensitive equipment Table 1. A brief on power quality issues Voltage Swell Very short interruption Long Interruptions Voltage Spike (Very fast variation in the voltage) Voltage unbalance Noise Power supply with poor power quality will damage the devices. The severity of this damage can be as simple as excessive heating and loss in the equipment or as severe as a total damage to the All Rights Reserved 26

3 Hence, for a system to operate effectively and reliably, it is important to maintain high power quality. Few of the common issues of poor power quality are Excessive heating, noise and low efficiency of rotating machines, cables, transformers, fuses etc [2]. Harmonics which will lead to premature failure of distribution transformers and force electronic components to operate in saturation [3][5]. Sudden rise in voltage/ current which will lead to failure of electronic components [6]. III. SYSTEM ARCHITECTURE In this system, a relay is connected to the load to protect it from abnormal voltage conditions. This relay is triggered by timers which act as comparative circuits. The comparative circuits acts as a control mechanism to differentiate the deviation from the normal voltage. The timers are powered by the regulated supply of rectifier circuits connected from the transformers. For the sake of simplicity, the load in this project is limited to single phase. Figure 2. Block diagram The objective of the two timers is two differentiate the voltage if they are above or below the normal voltage conditions. Out of the two timers in the circuit, one timer deals with the voltage lower than the permissible voltage limits and the other timer will operate if the voltage is more than the permissible voltage limits. IV. WORKING PRINCIPLE In this system, the load operation is controlled by the relay connected to it. This relay is in turn triggered by the two timers connected to it. These times act as comparators and will work based on the input level from the supply. The supply to this system is powered by the regulated DC power connected from the mains supply through the transformer. These timers are also connected with potentiometers for under voltage cutoff and over voltage cutoff mechanism. As shown in the circuit diagram, if the input present at the pin 2 of the first timer is less than one third value of the input dc voltage (Vcc), the output at pin 3 will be high. The scenario will be opposite of the input at pin 2 is more than one third value of the input dc voltage (Vcc). In normal operating conditions (say 230 ±10%), the timer output is set to low so that the transistor is in cutoff state. Due to this, the reset pin of timer 2 is high and consequently the output at pin 3 is high. With this the transistor 2 conducts and then the relay coil gets energized. Hence in the normal voltage conditions, the load is not All Rights Reserved 27

4 If the voltage is less than the normal operating conditions, the output of the timer 1 will be high and this changes the transistor 1 into conduction mode. Due to this, the reset pin of the timer 2 will be low and the transistor 2 will change into cutoff mode. Hence, the relay will be operated to isolate the load from the power supply. If the voltage is more than the normal operating conditions, the output of timer 2 will be high and the output at pin 3 will be low. Due to this, the transistor 2 will change into cutoff mode. Hence, the relay will be operated to isolate the load from power supply. The LED indicators are connected to the two timers to indicate the status of overvoltage and under voltage conditions. Figure 3.Circuit diagram The voltage regulator in this system is achieved using the IC The IC with this series is designed with thermal protection and discontinues the circuit when experiences the overload condition or internal short-circuit protection. This IC also as an operational amplifier to adjust the higher or intermediate values. The ICs used for the timer circuits in this system are LM 555. This is a perfect device to generate time delays. It also has an extra terminal to give triggering. In this system this extra terminal is used for the potentiometer. This IC can also be used as astable and monostable vibrators. The other applications of this timer are linear ramp generator, pulse width modulation etc. V. RESULTS AND DISCUSSIONS Over voltage and under voltages form only a part of the power quality issues. To maintain the power quality of the system, it is also necessary to identify the wave form distortions in the power supply. These distortions can be notching, harmonics, inter-harmonics, noise etc. Other issues are voltage and frequency fluctuations. This system is best operated for the over/ under voltages with a typical duration of greater than 1 min. But as said in the previous sections, there can be voltage sag or swell or interruption of duration less than 1 min and few variations in the voltage can last less than 0.5 cycles also. Thus it makes out the necessity to develop the system which can be sensitive to these minor variations. As a further extension to this work, a reliable system as to be developed with an effciennt monitoring system and control system. The data from the load centre to the control room can to be transmitted through any medium. It can be a Ethernet based system, GSM based system, power line communication etc All Rights Reserved 28

5 REFERENCES I. Shashidhar Kasthala and Saka Rajitha, Harmonic Mitigation in Ship Power Systems using Passive Harmonic Filters, International Conference on Innovations in Electrical & Electronics Engineering, Gurunanak Technical Institutions, Hyderabad, II. Shashidhar Kasthala and Krishnapriya, Fault Management of Electrical Drives Onboard Ship using Power Line Communication, International Research Journal of Engineering and Technology, Vol. 4, No. 10, III. Ramakrishna G, Shashidhar Kasthala and G.K.D. Prasanna Venkatesan, GSM Based Health Monitoring of Critical Equipments, International Journal of Scientific Research in Science and Technology, Vol. 3, No. 8, IV. Krishnapriya and Shashidhar Kasthala, Identification of Cable Faults Onboard Ship using Power Line Communication, International Journal of Advanced Research in Computer Science, Vol. 8, No.3, V. Shashidhar Kasthala, Reactive Power Management in Industries: An analysis, International Journal of Emerging Technology and Advanced Engineering, Vol. 3, No. 11, VI. Shashidhar Kasthala and Saka Rajitha, Non Intrusive Monitoring of Electrical cables in Ship Power systems, The Journal of CPRI, Vol. 12, No. 4, 2016, pp VII. Shashidhar Kasthala and Saka Rajitha, Ethernet Based Monitoring and Controlling of Real Time Security Parameters, International Conference on Innovations in Electrical & Electronics Engineering, Gurunanak Technical Institutions, Hyderabad, VIII. Shashidhar Kasthala and G.K.D. Prasanna Venkatesan, Evaluation of Channel Modeling Techniques for Indoor Power Line Communication, Progress in Advanced Computing and Intelligent Engineering, Advances in Intelligent Systems and Computing, vol 54, Springer, Singapore. IX. Shashidhar Kasthala and G.K.D Prasanna Venkatesan, Estimation of Channel Capacity for MIMO Power Line Communication using Multi-Conductor Transmission Line Theory, IEEE International Conference on Applied and Theoretical Computing and Communication Technology, Bangalore, July All Rights Reserved 29