STABILITY ANALYSIS 0f 20 kVSYSTEMat PT PLN (PERSERO) RAYON MUARALABUH BEFORE and AFTER INTERCONECTION by IPP (PLTMH PT. SKE)

In the rapid development of the world as it is today, the electricity has a very important role in supporting people activities. PT PLN (Persero), which in this case as Government State Owned Company that directly manage the provision of electrical energy is required to be ready to face the development of electricity demand in Indonesia. In distribution system of electricity, problems often occure because of the length of line distribution system which cause voltage drop, technical losses, power losses, etc. One of them happened to PT PLN (Persero) Rayon Muaralabuh. Where the distance between the main substation (GI Solok) with the first connecting substation is ±110 KMS. This distance cause 9.62 % voltage drop during peak load. This nominal of voltage drop happens for just the first connecting substation that will be the source of division for all working areas of PT PLN (Persero) Rayon Muaralabuh. This factor encourages PT PLN (Persero) West Sumatra Area Solok to agree if Independent Power Plant (IPP) takes part in generating electricity, which will be distribute to PT. PLN (Persero) West Sumatera Area Solok Rayon Muaralabuh through interconnection system. The simulation of power flow using Etap 12.6.0 is used to analyze the stability of 20 kV system voltage at PT PLN (Persero) Rayon Muaralabuh before and after interconnection. Based on the result of simulation and Etap calculation, the highest voltage drop before interconnection by IPP is on Feeder express LubukGadang which is 13,71 %. After the interconnection by IPP, the voltage drop on that feeder becomes 4,326%, and the highest voltage drop is 4,855 %. Therefore, the voltage drop after the interconnection by the IPP already meets the standards allowed by SPLN No. 72 of 1987 which is maximum 5 % voltage drop. The precentage of technical losses in PT PLN (Persero) Rayon Muaralabuh before interconnection is 13,074 %, and after interconnection is decreased to 8,306 %.


INTRODUCTION
In the rapid development of the world as it is today, electricity has a very important role in supporting people activities. People needs electricity can be seen in daily life, such as : lighting, electronic devices, industries, communications, and etc.PT PLN (Persero), which in this case as Government State Owned Company that directly manage the provision of electricity is required to be ready to face the development of electricity demand in Indonesia.
Provision of electricity by PT PLN (Persero) to consumer through several stages. Beginning with power generation, the electricitywhich has been generated will be raised into High Voltage (HV) then transmitted through the transmission line. After that the voltage of this electricity will be reduced into medium voltage, then it will be distributted to the substation. To fulfill low voltage consumers demands electricity from medium voltage will be distributted to distribution transformator in order to reduce the voltage into low voltage.
In the distribution system of electricity, problems often occur due to the length of the distribution line resulting some impacts, including; drop voltage, technical losses, power losses, etc.These impacts encourages PT PLN (Persero) West Sumatra Area Solok to agree if Independent Power Plant (IPP) takes part in generating electricity, which will be distribute to PT. PLN (Persero) West Sumatera Area Solok Rayon Muaralabuh through interconnection system. Where the distance between the main substation (GI Solok) to first connecting substation is ±110 KMS. Before the interconnection with private power plants PT. SKE, medium voltage distribution system of PT PLN (Persero) Rayon Muaralabuh is assisted by PLTD Balun with 2 X 1 MW operating capacity. PLTD Balun is a privately-owned machine with lease status at PT PLN (Persero). The existence of 2 units of operation and 1 unit of standby of PLTD machine is not enough to help PT PLN (Persero) Rayon Muaralabuh system to fulfill consumer needs.As evidenced is the "rotating blackout" system at PT PLN (Persero) Rayon Muaralabuh.
With the interconnection on 20 kV system with IPP (Independent Power Producer) is very helpful for PT PLN (Persero) Rayon Muaralabuh to fulfill electricity needs in South Solok district which is increasing from time to time, with service voltage that meets the standard.
This study aims to analyze the stability of 20 kV System Voltage at PT PLN (Persero) Rayon MuaralabuhBefore And After Interconnection With IPP (PT SKE).

II. BASIC THEORY
The distribution system is the whole component of a power system that connects directly between large power sources (such as transmission substations) with electricity consumers (Figure 2.1) shows a series of power distribution systems. The distribution network generally consists of two parts, namely as follows: 1. Primary Distribution System Namely power system that distributes electricity from the sub transmission substation (GI) to the distribution substation (GH). This system is a medium voltage (JTM) or primary voltage system. 2. Secondary Distribution System Namely the power system that distributes electricity from the distribution substation (GH) to the consumer. This system is often called the low voltage system (JTR).

Primary Distribution System Types
In this service the primary distribution system has several variations of form, where each form of system has several advantages and disadvantages. In general there are four basic forms of primary distribution network system which are : 1) Radial primary distribution system 2) loop / ringprimary distribution system 3) Primary ring distribution system 4) Primary grid (network)distribution system 5) Spindle and clusterdistribution system.

Radial Primary Distribution System
This radial primer network is the most common and commonly used form, mainly used in load areas with low load density. This system has one power line to the load, then all the load on the channel will lose power when a channel is interrupted.
The main advantage of this radial system is its simple shape and low cost. The weaknesses of the system is the continuity of service is bad, low reliability, and high voltage drop, especially for the at the end of the distribution line. The large current density of this type of radial is found in the line between the power source and the substation and the smallest happens at the end of the line. In accordance with the level of current density, the cross-sectional area may vary. The primary radial type distribution network is represented by (Fig. 2).

Loop Primary Distribution System
Loop primary distribution system is typically used to serve loads that require good service continuity such as: Commercial buildings or factories with medium and large loads. In principle, the primary distribution line of the loop type is a line that starts from a point or rail to the load zone, then returns to the source point of the rail or the original power. In Medium Voltage Network (JTM) loop structure, enabling an alternative power supply for distribution substations, so that the system reliability is better. In case of power disturbance with one of the feeders, the load breaker in the GI will open and this will cause blackout in all distribution systems. Faced with these conditions, the action to be taken is to ensure and localize the power disturbance areas. Furthermore, areas that are not involved in power disturbance can be supplied from other feeders. Loop distribution linealso needs attention in short circuit current which is big .
Medium Voltage Line Configuration (JTM) loop structure, of course very desirable by all units of PLN. Because loop distribution linehas more advantages when compared with radial systems, the loop system can also promote to customers of PLN, especially large-capacity customers to be proposed to become a premium customer. Where one of the absolute conditions for premium customers is supported from 2 (two) different sources. The loop-type distribution network is shown by (Fig. 3).

Ring Primary Distribution System
Ringprimary distribution system is generally similar to loop type distribution line, the difference is only the number of resources more than one. In other words, The primary ring type distribution line is a loop type whose distribution substations can receive more power than a single source point. The primary line type distribution lineoften develops into a grid shape. The following is The primary line type distribution line (Fig. 4).

Grid Primary Distribution System
This system is an interconnection between some substations (GI) so that the load will receive power from various directions. Reliability of this system if there is power disturbance on one feeder, the consumer will still be supplied from other feeder so that the customer still served. Development of this type of distribution network would require large cost, because there are many substations needed. Primary grid type distribution line as in (Fig. 5).

Spindle and Cluster Primary Distribution System
In this system is often used in big cities, this system is the development of radial system. Power will be supplied from power plants or substations through some feeder or distribution substations and ends in switching substation. The specialty of this system is the presence of a free line that is not burdened by any load which will be the immediate reserve lineto reflection substation with the shortest path. For normal conditions on this system all switches on the reflection will be in open condition and if a system is not using a reflection substation, but the feeder state is primarily connected to the backup line then this is called the cluster type. While the spindle type system uses a substation reflection as it should. The primary spindle distribution line is found in (Fig. 6) and the cluster type distribution line as seen in (Fig. 7).

Voltage Drop
The voltage drop is the voltage loss between the send/source voltage and the receive voltage. The voltage drop is caused by the resistance and current on the alternating line, the magnitude dependson the impedance and the power factor at the load. Power lines generally serve loads that have lagging power factor. The factors that caused the difference of voltage distribution system are: 1. Consumers have equipment that requires a certain voltage.

Power Losses
Power loss is the amount of electricity lost during the delivery of electricity in a certain time (usually in the watthour). This loss is influenced by the amount of difference between the received power and the power sent. The magnitude of 3 phase power can be seen from the following formula:

Electric Transient and Analysis Program (ETAP)
12.6.0 ETAP 12.6.0 is a comprehensive analysis software to design and simulate a power supply system. The analysis offered by ETAP used by the authors is the voltage drop, and the network losses. ETAP also provideS a warning to undervoltage and overvoltage bus so can be known which bus is not in optimal operation.In order to analyze a series of circuitneeds complete and accurate circuit data so the calculation from ETAP can be answered.

III. ANALYSIS
To complete the data needed in the analysis and calculation required data in accordance with the purpose of the study. The data is taken in accordance with the research which from data distribution system PLN Rayon Muaralabuh. The data are as follows: 1. Data of all feeders at Rayon Muaralabuh and MuaralabuhExpress Feeder GH AlahanPanjang. 2. Table impedance JTM type AAAC 3. Transformer data of all related feeders 4. The peak load data of each related feeder.

Distribution Operation Pattern
Condition before interconnection with IPP (PLTMH PT SKE).The condition of 20 kV system at PT PLN (Persero) Rayon Muaralabuhbefore interconnection with IPP of Hydro Micro Power Plant (PLTMH) owned by PT SeloKencana Energy, Rayon Muaralabuh system assisted by two units of PLTD owned by PT. SINARINDO, as shown in Fig. 9. At GH Alahan Panjang other than incoming feeder 8 express Alahan Panjang, there is also incoming from feeder 4 MuaraPanas which is sourced from bus I GI Solok, this become supply for two outgoing feeder at GH AlahanPanjang.    From simulation and calculation results with Etap 12.6.0, so can be made data table comparison measurement and calculation of voltage drop, technical losses and 20 kV system voltage stability at PT PLN (Persero) Rayon Muaralabuh before and after interconnection with IPP ( PLTMH PT SKE) as follows: Based on the comparison table between the calculation usingetap with validation formula above, it can be shown that the difference between the two calculations does not exceed 1% (one percent). So it can be stated that the result of calculation of voltage stability with Etap 12.6.0 simulation, can be a benchmark for performing voltage stability analysis.

Saving Power
Saving Power is the amount of loss (measured by the value of power) that can be saved or reduced as a result of a program or activity, which if the activity is not executed will condition.
From the calculation of technical losses before and after interconnection with IPP (PLTMH PT SKE), it can be calculated saving power in one month (number of days