Surya Hardi

Adaptive Mho type distance relaying scheme with fault resistance compensation

This paper describes an adaptive distance relaying scheme which can eliminate the effect of fault resistance on distance relay zone reach. Distance relay is commonly used as main protection to protect transmission line from any type of fault. For a stand-alone distance relay, fault resistance can make Mho type distance relay to be under reached and thus the fault will be isolated at a longer time. In this scheme, the relay detects the fault location using a two-terminal algorithm. By knowing fault location, fault voltage at the fault point can be calculated by using equivalent sequence network connection as seen from local terminal. Then, fault resistance is calculated by using simple equation considering contribution from remote terminal current. Finally, the compensation of fault resistance is done onto calculated apparent resistance as seen at relaying point. The modeling and simulation was carried out using Matlab/Simulink software. Several cases were carried out and the results show the validity of the scheme.

Induction motors performance under symmetrical voltage sags and interruption - Test result

Main source voltage sags are short circuit faults in power systems. These fault currents propagate entire the circuits connected with them. After the fault is removed by circuit breaker opened, the system voltage may recover to its normal value, the motor will re-accelerate during recovering process accompanied by high transient currents. This paper presents an experimental test to investigate effect of various characteristics of voltage sags such as magnitude, duration, repetitive and multistage of voltage sags on performance of induction motors. Several small induction motors were used to this purpose. Sag magnitude significantly influenced on the current peaks and speed variation whereas sag duration significantly influenced only on the speed. The motor responses to magnitude and sag duration in repetitive and multistage events are different.

Sensitivity of low voltage consumer equipment to voltage sags

Voltage sag is an issue that is becoming increasingly important to electricity consumers at all level of usage. These result from with increasing use of electronic equipment in several sectors for the reason to improve energy efficiency and performance. Customers included in low voltage environments mostly are sectors: Commercial, Residential and Light industrial. In these sectors many found equipments such as television, microwave ovens, personal computers, printer, lighting, heating ventilation air conditioners, motor contactor etc. Using with high efficiency fluorescent lighting with electronic ballast, single phase switch mode power supplies for computers, contactor for protecting motor from suddenly restarting when the voltage is recovered. These equipments are characterized as highly susceptible to voltage sags. Voltage sags are most frequent among various types of power quality disturbance faced by many consumers. Source of voltage sags are generally caused by short circuit faults associated with equipment failures on the supplying power system. Voltage sags normally do not cause equipment damage, but it can easily disrupt the operation sensitive equipment. Effects produced by voltage sags are various generally depending on its characteristics and equipment. The magnitude and duration of the sags are commonly used to evaluate sensitivity of equipment. The other characteristic such as point on wave of voltage sag initiation is significance influence to be considered. This paper presents voltage sag tolerance levels curves of three equipments sensitive to sags namely; personal computers, contactors and lightings. A Schaffner “Profline2100” has used to generate voltage sags and testing to get sensitivity of the equipment.

Photovoltaic powered uninterruptible power supply using smart relay

Uninterruptible power supply (UPS) sits between a power supply such as wall outlet and devices to prevent undesired feature that can occur within the power source such as outages, sags, surges and bad harmonics from the supply to avoid a negative impact on the devices. This paper presents a photovoltaic (PV) powered UPS using smart relay. It is a standby UPS whereas if the main power source fail to supply power to loads, a battery powered inverter turns on to continue supplying power. The battery is charged by the PV using solar charger and transfer switch controlled by smart relay. The UPS was tested to a load of 240 V, 20 W AC aquarium water pump. The test result shown that the UPS perform well, when the main power source fail, the battery could power inverter and the smart relay control the transfer switch, the load and battery current were 0.1 A and 1.56 A, respectively.

Investigation on the effect of shunt capacitor and shunt filter on harmonic in distribution system

Nowadays nonlinear loads are widely used in many consumer equipment and power systems. The main problem in using of nonlinear loads is harmonic distortion. This paper will discuss the effect of application of shunt capacitor banks and shunt filter banks to reduce harmonic distortion in the power system, which will result in the increasing of the system efficiency. With installed of shunt capacitor banks and shunt filter banks, the voltage and harmonic distortion at each bus will be improved. This research was used MiPOWER software. The results will be shown in total harmonic distortion (THD), telephone influence factor (TIF) and voltages at each bus in the system.

Harmonics Performances of Single Phase Transformer due to DC Bias

The investigation of the direct current (dc) bias effect on single phase power transformer through their harmonics performance is present in this paper. The experimental study is done by the dc bias current injected simultaneously with alternating current (ac) source to primary winding of transformer. The input ac voltage to primary winding is maintained constant during investigation and the dc currents increased gradually. Compare to pure ac power applied, the results show that the waveforms distorted when the dc bias exist. The pulsated waveforms are pushed to half cycle in which the bias current is in the same direction as magnetizing current (unsymmetrical pulsated) and even harmonics are significant.

Survey of Droop Control Technique for Parallel Inverter Operation

Increasing demand for large-scale power delivery with high reliability and quality necessitates the use of multiple distributed energy resources to be connected in parallel; for example, parallel inverters operation. Proper operation of parallel inverters requires sophisticated control techniques and many have been proposed and continue to evolve. This paper depicts the droop control techniques for the parallel inverter systems. The recent improvements and variants of this control technique are presented

Sensitivity of Induction Motor under Symmetrical Voltage Sags and Interruption

Voltage sags and interruption are one of most important of power quality problems. They can influence performance of equipment such as induction motors. They are generally caused by short circuit faults in transmission and distribution systems which propagate in entire of power systems. When their appear at a motor terminal, its effects are the speed and the torque will decrease to a level lower than values of the normal and even the motor become stall if magnitude of the voltage sags and duration exceed certain limit. The voltage can return to nominal voltage after end of the voltage sag and interruption. The motor will experience re-acceleration to normal condition is accompanied by large inrush current. A study on induction motors was carried out to confirm these effects. Single-phase and three-phase of small induction motors were used for investigating the effects caused by symmetrical voltage sags and interruption through experimental and simulation.

Investigation of influence of voltage source type on harmonic characteristics

This paper discussed about influence of voltage source types on harmonic characteristics. Usually, the voltage source is sinusoidal. But in actually, the condition of the load is has voltage sources through the elements where the output voltage of element as input to load is did not pure sinusoidal, for example at PCC between transformer and linear load and nonlinear load. The research has done with Schhafner Power Quality Analyzer. To describe the harmonic characteristic due to types of voltage source will shown as IHD, p.f., THD, and harmonic energy losses cost from measurement. As voltage source in this research are sine wave and combinations of 3rd, 5th and 7th harmonic order, and square waveform are create by means of Schhafner Power Quality Analyzer.

Laboratory Test of Current Transformer Operates under Harmonic Conditions

This research focused on the effect of harmonic to the performance of current transformer (CT) operates under harmonic conditions. Due to the increasing of harmonic in power system, the CT did not perform well. The CT may saturates due to the presence of voltage and current harmonics. In this project, a laboratory test was conducted to investigate and analyze the influence of harmonics to the CT performance. This CT has been test with different Total Harmonic Distortion Current (THDi) at primary side and constant primary current. The experiment result shows the secondary current CT errors will increases when THDi increases.