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This paper discusses the arrangement of differential relays at the Langsa substation. The ratio of CT mounted on the transformer to the primary side is 150/1 A and on the secondary side is 1000/1 A. This result is taken with consideration of the current value calculated from 127.02 A on the primary and 952.62 A on the secondary side. For the sensitivity of the mismatch error is still good because it is still under 5% on the primary side which is 0.89% and the secondary side is 1.13%. The differential current also shows the normal condition of 0.1 A and the restraint current 1.205 A. Using the ETAP 12.6.0 simulation, relay can work well when interference occurs at the current setting indication 1.29 A is greater than the operating current 1.65 A and the relay does not work during an external fault with a setting current of 1.29 A equals to an operating current of 1.29 A.

The increase in load which increases every year causes a decrease in voltage on the line which is getting bigger. The voltage drop on the transmission line greatly affects the quality of the voltage. The voltage that arrives at the electrical equipment will decrease which in turn reduces the performance of the equipment. The power flow study uses the Fast Decoupled method, the voltage on each bus can be determined. The performance parameters observed are the value of the power factor, voltage, active power, and reactive power to determine the parameters for the location and size of the capacitor bank capacities and the static var compensator (SVC). By increasing the power factor in the range of 0.85pu to 0.95pu, the bus voltage can fulfill the SPLN standard. Parameters are designed and simulated using the ETAP programming software version 12.6.0 by testing each bus that experiences a voltage drop in turn based on the voltage limit and the power factor value ≤ 0.85pu. Furthermore, several buses with the appropriate capacity rating are selected to increase the voltage on the system. The simulation results will show the effectiveness of the capacitor bank and static var compensator (SVC) to increase the voltage value on each bus.

This paper presents the influence of distributed generation (DG) location and capacity for mitigating voltage sag caused by faults. The voltages sags are caused by the faults were simulated on the IEEE 13 bus system for single line to ground close to 650 and three-line phase faults at bus 646 using Alternative Transient Program (ATP) software. The voltages are monitored at every buss system. The DG is installed for one DG, two DG and three DG as the alternative. The DG locations are installed based on trial and error. DG total capacity is 2/3 load total installed in the system. As the alternative DGs installed viz. for one DG at Bus 611 with the capacity of 2.5 MVA; Two DGs at Bus 611 and Bus 680 with their respective capacities of 1.25 MVA; Three DGs are located at Bus 611, Bus 680 and Bus 633 with their respective capacities of 1 MVA. The results show that DG location placement in many locations gives the better results for mitigating voltage sags.

The voltage drop in distribution line unavoidable but can be reduced until the allowable limit. The voltage drop occurred due to currents flow in impedance lines. Harmonics caused by non-linear loads that are often found in the industrial used electronics devices. This study is to discuss the application of static var compensator (SVC) to improve the power quality in distribution lines. Harmonics analysis of the loads industries are modelled as arc furnace and adjustable speed drive (ASD) using software ETAP simulation. The loads are connected to the IEEE 14 busses system. Fast decoupled method was used for investigating the voltage drop at each buss. Harmonics analysis was carried out to find harmonics level contents i.e., total harmonics distortion of voltage (THDV) and current (THDI). Values of THDV and THDI resulted are evaluated by state electrical company (PLN) standard. The load flow study result shows that there are some busses have voltage below the standard and harmonics analysis beyond the allowable limit but the voltage at Bus 14 is lowest, therefore SVC is connected to it. The results show all the voltage is fulfilling the standard. The SVC installation on this case is less significant it affects on mitigating harmonics.

This paper analyzes effects caused by voltage sag types A, B, C and D on induction motor based on experimental test. The effect can be investigated in term the current peaks and speed variation. The magnitudes depend on magnitude of sag and duration, voltage sag types, during and recovery voltage sag. Several of voltage sag characteristics have been conducted in different magnitude, duration and sag types. The results show that the current peaks generated reach more than 4 times of normal current and it was achieved at recovery voltage instant. Sag magnitude has great influence on the current peak but sag duration is not significantly. Type A voltage sag only can cause the motor stop running and it was achieved when it was subjected to sag magnitude of 10% and 6s in duration. The motor stops running in shorter duration when it was subjected to interruption with sag duration of 4s. Therefore voltage sag of type A lead to more severe on induction motor if compared with other sag type. This is according to number of phase that experience sag. The magnitude and duration of voltage sags have influenced significantly on the motor speed only for low sag magnitude and long sag duration.

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.

This paper presents a study to investigate response of adjustable speed drives due to voltage sags. A small ASD of 0.39 kW, 50/60 Hz, and 400-480 V was used for testing how drives will respond to voltage sag types; A, B, C and D. The drive response is influenced by sag magnitude, sag duration and phase angle shift. Behavior of the diodes rectifier for conducting is influenced by sag magnitude and phase angle shift represented by sag of types C and D. The diodes rectifiers are reverse biased when it was supplied by voltage sags. Even though there are no charging currents to dc bus capacitor during voltage sags, the drives did not directly trip to certain sag magnitude and sag duration. Sensitivity of the ASD to voltage sag types is presented in voltage tolerance curve. Sag of type A produces highest sensitivity on the ASD and it trips for sag magnitude of 62.5% and 250 milliseconds in duration.

Faults can occurred at the transmission line due to lightning strike, broken conductor, cross arm or tower falls, danger tree, crane or animal encroachment, polluted insulator etc. Each type of fault will represents a fault resistance value. Fault resistance will affects the accuracy of protection relays in fault location and fault zone detection. Phase to phase fault is one type of unsymmetrical fault at the transmission line. This paper represents the accurate way to calculate the actual phase to phase fault resistance value by using data from both local and remote substations. From the finding, the actual fault resistance can be represented by fault resistance as seen from local substation in parallel with the fault resistance as seen from remote substation. To prove the finding, simulation has been carried out and the results show the validity of the proposed theory.

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.

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.