Preventing Power Outages from Happening Again

KOMPAS/RIZA FATHONI

The Senayan area of Central Jakarta is dark against the background of buildings along Jl. Jendral Sudirman during a blackout on Sunday (4/8/2019). The major power outage that hit Jakarta and its surrounding area disrupted transportation and economic activities for millions of residents.

Sunday, 4 August 2019, became a dark day for state-owned electricity company PLN and people in the western part of Java Island. Disturbances in the Ungaran-Pemalang 500 kilovolt extra-high voltage electricity transmission system in Central Java caused a major power outage in Jakarta, West Java and parts of Central Java.

Because of the blackout, President Joko Widodo had to visit the PLN office to discover its cause and encourage the problem be solved, both in the short and long term. The wide-scale blackout happened relatively close to a previous incident where on 5 September 2018 disruption to the Paiton-Grati extra-high voltage electricity transmission system in East Java caused a power outage of about 2,400 megawatts, which spread partly across Java and almost the whole Bali.

Causes and system condition

Looking at the chronology presented by PLN, these two events had a similarity in that they were both preceded by a disturbance (short circuit) that caused the transmission lines to be cut between the eastern and western parts of Java. This channel outage caused a disruption of load balance (demand) and generation (supply). In the western part of Java Island, because the load exceeded generation the system frequency dropped beyond the permitted limit. In contrast, the eastern part of Java experienced oversupply, which caused the frequency to rise.

As a result of the sharp frequency changes, the defense scheme worked by releasing the loads (load shedding) and or releasing power plants (generator shedding). This was done to achieve load balance and new generation to avoid wider blackouts and damages on the generators.

Power outages cause huge losses. Shopping centers and offices have to turn on generators at a much more expensive cost per kWh. Factories would suffer losses from wasted materials caused by stalled production processes or even fines from production delays. The country\'s reputation has fallen (meaning a significant decline in the Composite Stock Price Index on the Indonesia Stock Exchange) at a time when the government is striving to improve the investment climate. Moreover, there were material casualties and fatalities from fires that were an indirect impact of the power cuts.

At present, the peak load of the Java and Bali electricity systems is about 27,000 MW with an installed power generation of about 35,000 MW. At a glance, the capacity of the generators is far exceeding the load. However, if calculated more carefully, the installed capacity of the plants would shrink drastically when we pay attention to the level of readiness of the generating units. Not all power plants are ready to operate because of maintenance or because of the unavailability of primary energy, such as may be caused by a scarcity of reservoir water in the dry season for hydroelectric power (PLTA). Moreover, most of the power plants in Java are steam-driven power plants (PLTU) with low electricity generation costs, but have a slow response to the occurrence of load imbalances and generation.

In general, the electricity load in the western part of Java is greater than the electricity load in the eastern part of Java because a larger number of factories are located in the western part of Java. In the western part of Java, the electricity load exceeds the electricity generation. On the other hand, power generation exceeds the load in the eastern part of Java. As a result, electricity needs to be sent from the eastern to the western part of Java. As an impact, the western part of Java is vulnerable to a decrease in frequency and voltage (which results in blackouts) if supplies from the east of Java are stopped, both when the transmission system is cut off or when the power plants abruptly stop operations. Moreover, transmission line losses are relatively higher and have the potential to increase the cost of the power generation.

The electricity system of Java and Bali is supported by a 500 kV transmission system that runs from east to west and consists of north and south transmission lines. For channel reliability, each channel consists of two circuits. At present, the electric power that is channeled to several transmission lines has exceeded the reliability limit of the N-1 channel. As a result, if one circuit is cut off, there is a possibility that the second circuit will be overloaded and potentially be interrupted as well.

Planning up to maintenance

Although two large-scale power outages occurred in the past year, this incident could not be separated from the electrical system planning in the past. There are many considerations in the planning of plant development. Some of them include system reliability (plant availability), plant locations and types of power plants. First, the generators must be available in an adequate quantity. It means that the total generating capacity must exceed the peak load. In the Java and Bali system, the reserve capacity should at least be 30 percent of the system\'s peak load. However, the construction of power plants, which is frequently delayed, means that the minimum reserves could not to be reached. Moreover, the low quality of the plants reduces the plants’ readiness and capacity. This condition is exacerbated by the fact that hydropower plants do not operate during the dry season. As a result, the system reliability is getting lower.

The generator should be located near the substations (GI) that have high LMP values and the load should be connected to the substations with low LMP values.

Second, the plants must be built in the right locations. Proper placement can reduce the generation and load imbalance in an area, both when the system is running normally and when the system is experiencing disruption (contingency). Proper placement can also reduce the flow of electric power in the transmission line. Therefore, congestion on the power transmission will decrease (congestion relief), the voltage profile improve and channel losses decrease. One of the techniques used for plant placement is the use of locational marginal price (LMP) indicators. These indicators can show the effect of the location of the plant (or load) on the cost of electricity generation, especially those related to power transmission, voltage and line losses. If the LMP value on each bus is the same, the cost of electricity generation tends to be cheaper. The generator should be located near the substations (GI) that have high LMP values and the load should be connected to the substations with low LMP values.

Third, the type of generators influences the system response when a disturbance occurs. Certainly, a generator with a fast response is more desirable. However, the faster the generator’s response, the higher the generation costs. For example, a gas powered plant (PLTG) has a fast response, but the cost of generation is high. In contrast, coal-fired power plants (PLTU) have a slow response, but the cost of generation is low. Because the price of cheap electricity is still a reference, PLTU still dominates in the Java and Bali system.

With the greater burden and complexity of the electrical system, ordinary operating methods that only consider the cost of cheap electricity generation must be abandoned. In conventional operating methods, anticipation of the possibility of disruption (contingencies) gets less attention. As a result, the system becomes less ready to deal with interference. There are three categories of actions that can be taken in dealing with contingency conditions, namely preventive control, corrective control and a combination of the two of them.

Preventive control, an action taken before the disturbance occurs (pre-interference), is generally carried out by regulating the power output of the plants that operate by considering the minimum cost of generation and anticipating the possibility of disruption. When interruptions occur, the system remains safe without the need to do the post-disruption actions. However, regulating the power output of these generators can cause a shift in power generation from cheap to expensive plants. Therefore, on preventive measures, the power generation costs tend to be more expensive.

Meanwhile, corrective action is taken after the disturbance occurs. Generally, corrective action is the release of the load and/or release of the generator with the aim of restoring the balance of the load and generation rapidly. Other more complex repair actions can be carried out by using flexible AC transmission systems (FACTS) that aim to engineer the flow of power in the transmission line. Corrective action by releasing the load causes huge losses from a power outage. However, this action can prevent power outages on a broader scale. Meanwhile, the combination of the actions of prevention and repair can reduce losses by reducing the load or the plants being released.

However, when compared to losses from power outages, the maintenance costs are smaller.

If it was true that Sunday\'s blackout was caused by trees under the transmission towers that were too high, this shows that maintenance is an important factor. This power outage could have been avoided by cutting tall trees. This is not easy as it requires funds since the transmission lines stretch for thousands of kilometers and are located in areas that may be difficult to reach. However, when compared to losses from power outages, the maintenance costs are smaller.

Next steps

In the short term, PLN will need to utilize safer electrical system operation techniques by considering the anticipation of disruptions even though operating costs will be a little more expensive. Moreover, maintenance of transmission lines also needs to be done more effectively to prevent unwanted interference.

In the long run, PLN must continue to maintain a minimum capacity reserve of 30 percent above peak load by building plants in the right locations and with the type of power plant suitable for operating needs, both under normal and contingency conditions. Since they need funds, all of these efforts will tend to increase the cost of generation. For this reason, PLN\'s optimal efforts to continue to make the electricity system efficient and the community\'s willingness to the increase of tariffs are very much needed. Jer Basuki Mawa Beya (Achievements are only won through sacrifice).

Rony Seto Wibowo, Electrical Engineering Lecturer of Sepuluh November Institute of Technology