Short Circuit Analysis on Distribution Network 20 kV Using Etap Software

Abstract In an electric power system, electricity is generated by the power plant and then channeled to a transmission line and then distributed to consumers, in the process of distributing electrical energy, the system does not always work in normal conditions, sometimes the system can experience disturbances such as one-phase, two-phase, and three-phase disturbances. This interference can disrupt the electrical system and can damage equipment if left unchecked, therefore it is necessary to install a protection device that can decide the interference so as not to damage other equipment when a disturbance occurs. Here the protection device used is a circuit breaker. In a fault condition, the circuit breaker must be able to separate the points of the fault so as not to damage other electrical equipment. In this case, to determine the capacity of the best protection device for the system, a short circuit fault simulation is performed. To simplify the calculation process here the author uses the help of ETAP software (Electrical Transient Analysis Program).


Introduction
In a broad electric power system, sometimes disturbances that come from outside cannot be avoided, therefore it is necessary to conduct an analysis of the electric power system to assist in planning and analyzing the system in order to create a system that is able to work optimally. [1].
In this paper the author will try to determine the safety capacity that is able to protect the electrical system and is able to work well in the city electrical system of Lhokseumawe, using the help of ETAP software in conducting case studies and calculations of short circuit disturbances. Figure 1 is an illustration of the form of short circuit fault that occurs due to phase and ground connection, is a short circuit fault that often occurs in electric power distribution systems. To calculate the magnitude of the one-phase fault current to ground, you can use the equation [ [4] Two phase to ground fault is a short circuit that occurs because two feeders or conductors are connected to the ground, is an asymmetrical short circuit with a fault incidence percentage of 10%. To determine the amount of short circuit two-phase ground fault current can be calculated by the formula [5]: Short circuit between phases is a short circuit that occurs because it is connected between two phases, is an asymmetrical short circuit fault with a percentage of the incidence of 15%. To determine the amount of short circuit fault current between phases can be calculated by the formula [6]: Three-phase short circuit as in Figure 2. occurs when the three phases are connected, this fault is a rare disturbance compared to the presentation of single and two-phase short circuit events with an incidence percentage of 5%, is a symmetrical disorder. To calculate the large three-phase short circuit fault current can be calculated by the equation [7]:

Tools and materials
In this study, several supporting equipment were used, including: Laptop with N2840 processor model specifications, 500 Gb HDD, 2 Gb RAM. Windows operating system 10.ETAP software 16.
The materials used in this study were data collection of 20 KV medium voltage distribution system at LancangGaram (GH) substation, Darussalam feeder (Lhokseumawe City). These data, among others: a. Power data on GH Lancang Garam

Research Steps
The research begins with a literature study on related studies as a theoretical basis for conducting this research. Furthermore, data collection is carried out and taken directly at PT. PLN (Persero) ULP Lhokseumawe City. The data taken is one line diagram data, source data, distribution transformer data, and complete load data can be seen in Figure  3.1 flow diagram.

Study of Short Circuit Interference on 20 kV Distribution Network
A reliable system is a system that is not only able to work in normal conditions but is also able to solve problems when conditions are not normal so that the resulting impact does not damage other equipment, therefore short circuit fault analysis is very helpful to determine good protection settings for the system.

Short Circuit Interference Analysis
The calculation of the short circuit fault current that occurs on the GH bus is as follows: Positive and Negative sequence source impedance calculations

Short Circuit Interference Analysis Using ETAP Software
From the calculation of short circuit fault with ETAP software, the following results are obtained : The highest fault current occurs at a three-phase fault current of 1,828 KA and the lowest fault current occurs at a single-phase fault current of 0.658 KA

Comparison of Simulation Results and Manual Calculations for Short Circuit Fault Analysis
The short circuit fault current generated by manual calculation using the formula is compared with calculations using the Etap simulation to determine the level of accuracy. The following is a comparison of the results of the two in the table 5. From table 5 the difference between simulation results and calculation results from three-phase, two-phase and one-phase faults is only a little, this proves the level of accuracy of this Etap software is very good in analyzing short circuit faults.

Determination of Disconnect Capacity and Overcurrent Relay Settings
The capacity of the power breaker is the highest amount of noise current multiplied by a safety factor of 125% according to the general requirements for electrical installations (PUIL) [8]. The following is the calculation of the breaker capacity

Conclusions
Based on the results of simulation experiments on short circuit fault studies on the 20kV distribution network of PT. PLN (Persero) Feeder Substation Kota Lhokseumawe Darussalam (GH) Lancang Garam obtained the results of short circuit disturbances that occur on the GH bus using Etap software and calculations of 1,828 and 1,723 with a difference of 0.105 KA for three-phase disturbances, then 1.599 and 1.5 with difference of 0.099 for two-phase ground fault, 1.583 and 1.582 with a difference of 0.001 for inter-phase faults, 0.658 and 0.669 with a difference of 0.011 for single-phase earth faults so that the capacity of the circuit breaker to secure the LG-02 Darussalam electrical system is 2.285 KA with overcurrent relay settings as follows: ct ratio 1: 300, current pick up 0.12 A and pick-up instantaneous at 1.75 A.