IV DAS Pilot Project

5. Analysis of DAS Introduction Benefits

Benefits following DAS introduction break down into quantitative ones translatable into financial value and qualitative ones representing operational efficiency improvement, etc.

First of all, quantitative benefits include reduction of on-site electrical engineering manpower because of decrease in on-site workload following replacement of site trip by remote monitoring and control capability, decrease in supply failure for reduction of interruption time, more balance in distribution line load and optimization of firm tie point location leading to reduction of line loss, uniform increase in distribution line supply capacity resulting in decrease in distribution line construction requirement and reduction of distribution line addition, increase in facility service life by reducing frequency of substation circuit breaker activation with recloser, etc.

Introduction of distribution automation simplifies and reduces on-site workload of distribution electrical engineer, but, requires new additional tasks such as administration of computer system, communication network, control circuit of automated switches, etc. Therefore, it is true that even though on-site workload decreases, workload increases in other fields.

TDAS functions are as follows:

1. Automatic detection and recovery of distribution line fault
2. Real time acquisition of distribution facility operation information
3. Remote monitoring and control of switch
4. Optimization of distribution system load

5-1 Quantitative Benefits of TDAS Introduction

5-1-1 Decrease in Supply Failure

Basically, automation of distribution allows for remote control of switch via computer and communication without site trip. Notably, as it is possible to control distribution line switches without site trip in areas where heavy traffic delays site trip or rural area where distance to site is long, distribution automation system receives favorable response from on-site staffs and customers as well. After the introduction of TDAS, time spent on fault recovery by as-is manual switch and time spent on fault recovery by remote control including determination of load transferability between distribution lines has been reviewed as described below on the basis of actual fault data and interruption time, etc. collected in Semarang in 2006.

[Table 4-5] shows statistics on the number of faults and interruption time per fault type for TDAS-installed lines of Sayung substation in 2006, which is used for comparative analysis with actual fault data in 2007 after TDAS installation.

As for classification, if interruption time is longer than 5 minutes, a fault is classified as permanent one and, if interruption time is 5 minutes or shorter, a fault is classified as temporary one.

[Table 4-5] 2006 Faults Status

In addition, in the past, if fault occurred in distribution system equipped with manual switch, substation circuit breaker was opened to interrupt all sections in step 1, engineers were dispatched to fault site to investigate fault section in step 2, fault section was located and switches were manipulated to separate fault section in step 3, power was supplied to normal section on power side and switched to other line in normal section on load side in step 4 and fault section was recovered completely by engineers dispatched to fault site and switches were manipulated manually to provide power to the entire lines and complete fault recovery finally.

Time spent on fault recovery from step 1 to 4 was found out to be 39.3 minutes on average (total time spent 60,049 minutes/1,530 faults).

However, if TDAS switches are installed, all switches are controlled remotely without manual operation and engineers are dispatched to locate fault and wrap up fault recovery. In other words, interruption time (substation circuit breaker opening time) attributable to site trip and switch control from step 2 to 4 which is unnecessary in case of manual switch can be minimized. When F.I is displayed by system upon fault occurrence, operator can determine fault section, separate it remotely in accordance with manipulation sequence and resume power supply to normal section on power side and load side promptly. As the whole process takes 3.3 minutes on average, all in all, TDAS installation saves control and interruption time by about 36 minutes. With TDAS in place, it is possible to separate fault section remotely without site trip and supply power to normal section from other line, which saves interruption time. Then, energy sales volume increases as much as interruption time shrinks, which is one of the direct benefits of distribution automation. Increase in energy sales volume for distribution automation is calculated as below.

Increase in power sales volume attributable to reduction of power supply interruption was calculated by multiplying aggregate annual number of interruptions by 36 minutes of interruption time reduction, average interrupted customers in normal section where interruption time per fault was reduced and annual average customer load per household. Therefore, annual power supply interruption volume calculation formula is as below.

[Table 4-6] below shows reduction of load interruption volume and cost for Semarang branch attributable to distribution automation calculated by the following formula in reference to 2006 annual report of PLN Distribution Java.

[Table 4-6] Reduction of Supply Interruption Volume

No. of TDAS-recovered households (household/fault) was calculated as below and the fault status in [Table 4-5] was referenced for interrupted load.

In reference to [Table 4-6] above, annual power interruption volume reduced directly by introduction of distribution automation is 3,241MWh and annual power interruption cost is estimated to be 2,028,866,000Rp. if power interruption volume not supplied by distributor is multiplied by unit sales price to calculate loss resulting from interruption. However, from customer’s and nation’s perspective, it is true that the impact of interruption lasting even for a moment is much more significant than the above.

For example, interruption lasting less than 1 minute may lead to loss of data to be saved in computer, interruption lasting several hours disposal of much food, some factory having to dispose of all products in production for a moment of interruption. Therefore, in other countries, power interruption cost is multiplied several dozens of times to calculate power supply interruption reduction amount. For one thing, KEPCO multiplies it 2 to 14 times, Japan 31 to 33 times, France and Canada 35 times or even more.

In conclusion, loss of power supply amounting to 39.3 minutes inevitable for fault recovery by manual switch can be compensated by gains from automated switch installation in terms of improvement in profitability of distributor resulting from increase in power sales volume and enhancement of distributor’s corporate image as well, promising huge intangible benefits hard to be expressed in financial value.

5-1-2 Reduction of Loss in High Voltage Distribution Line

1. Loss of High Voltage Distribution Line
   If distribution loss rate of Semarang branch which is 7.59% according to the power loss volume analysis in the 2006 annual report of PLN Distribution Java is compared with power sales volume (2,665,157MWh), aggregate distribution loss volume is 218,900MWh. Assuming the application of the loss rate of KEPCO which is 2.23%, loss in high voltage distribution line is about 66,333MWh, which translates into 41,524,458,000 Rp. per year.
2. Loss Reduction of Optimization of Fixed Interconnection Point
   As distribution system takes radial shape, power loss differs, depending on location of switch defined as fixed interconnection point. To find how much high voltage line loss can be reduced by optimization of fixed interconnection point, references in actual system operation cases of Japan (8%), the US (8.8% and 14.6%) and Korea (15%) were studied and consolidated and approximately 10% can be applied although such actual references vary, depending on voltage, capacity, line length and switch quantity.
3. Loss Reduction Estimate for 5 years to Come
   Loss reduction amount as of a certain point of time can be calculated by the following equation. However, in case of estimation for 5 years in the future, aggregate generation volume, high voltage line loss rate, loss reduction rate and unit sales price will all change. Therefore, all such factors must be considered in calculation.

1. Aggregate power supply volume
   Actual power supply volume for all customers of Semarang branch per year and estimation for 5 years to come are as in [Figure 4-6] below.
   
   [Figure 4-6] Actual Annual Generation Volume & Estimation
2. High voltage line loss rate
   It is impossible to estimate future line loss accurately. However, as the transmission/ distribution loss rate fell from 8.0% in 2005 to 7.59% in 2006, the same reduction rate was applied to the high voltage line loss for 5 years and the loss was calculated to be reduced from 2.23% assumed for 2006 to 1.51% by 2012 by phase.
3. Loss reduction rate
   As explained with references from Japan, the US and Korea in the Loss Reduction Rate by Optimization of Fixed Interconnection Point section in the above, about 10% was applied.
4. Unit sales price
   Unit sales price per 1kWh is assumed to increase from 592.39Rp./kWh in 2005 to 626Rp./kWh in 2006 at 3.2% at annual average. It is highly difficult to forecast how unit sales price will change because of several economic, social and political implications.

[Table 4-7] shows the consolidation of line loss reduction amount constituents in the above and, according to the result, loss reduction amount of high voltage line for 5 years to come will amount to 21,673,031,062Rp.

[Table 4-7] High Voltage Line Loss Reduction for 5 years to Come

5-1-3 Suppression of Distribution Line Construction Requirement

Distribution line’s ability to respond to fault determines its supply capacity. In other words, the driver of determining whether to construct a new line or manage with existing facilities to supply increasing load in a certain line is whether adjacent interconnection line has enough extra supply capacity to support load transfer and normal section of fault-impacted line on load side is transferable to adjacent interconnection line in case of fault occurrence. A key variable in evaluating the fault recovery capability of line is accurate maximum load per section. To sum up, knowledge of maximum load per section allows you to service increase in load without increasing facilities and securing load transfer capability in preparation for fault by changing fixed interconnection point as load increases.

As improving utilization ratio of distribution line is the most primary goal of distribution automation system and all functions of such system are deemed to be implemented to serve the goal, distribution automation system is believed to contribute to about 50% achievement of the goal which is estimated to be equal to saving about 5,000,000,000Rp. on the assumption that 10,000,000,000Rp. is to be required for new/additional construction of distribution lines in preparation for load increase for 5 years to come.

5-1-4 Saving Operational Costs

Controlling switches remotely in case of fault occurrence can save 36 minutes necessary for site visit and manual switch manipulation, which will lead to reduction of manpower requirements and operational costs. On the assumption that the unit labor cost of distribution electrical engineer is 50,000Rp. in Indonesia and reduced interruption time is 55,080 minutes for the number of faults and 4 site engineers are mobilized per fault in 2006 according to [Table 4-5], total annual labor cost saving will be:

5-1-5 Extension of Substation CB Service Life

Upon comparison between substation protective relay activation status per line in [Table 4-5] and [Table 4-3-2] in the above, as for the number of faults in lines equipped with reclosers during the trial run period, 11 faults in total occurred in SYG.5 and 27 in total in SYG.6 as described in [Table 4-3-2]. Among the faults, 4 and 22 faults were recorded since September when reclosers were placed in operation actually. However, substation circuit breakers were activated with just 4 times because of the faults occurred on the source side of recloser, which implies that recloser utilization and protection coordination saved activation of substation circuit breakers 22 times effectively thanks to recloser operation.

Such result may indicate that most of the faults occur in the two lines on the terminal side where loads are concentrated. Although it is a bit premature to judge simply on the basis of faults recorded during the trial run period, it can be assumed that automatic separation of fault section by recloser saves 9.1%(SYG.5) and 78%(SYG.6) of aggregate faults per line respectively.

Then, assuming that the number of faults that occurred in the two lines in 2006 is 21 (SYG.5) and 19 (SYG.6) respectively, distribution automation system is expected to save about 2 or 15 faults leading to activation of substation circuit breaker and also assuming that the total number of activations of substation circuit breaker indicating its service life is 10,000 times, distribution automation system is believed to extend its service life by about 11% (10,000 times/21 cases = 476.2 vs. 10,000 times/19 cases = 526.3).

5-2 Qualitative Benefits of TDAS Introduction

Benefits of TDAS introduction was reviewed only from quantitative perspective based on economic benefits translated from comparison of investment and financial gains in the above section. However, qualitative benefits such as decrease in customer damage from reduction of interruption time or improvement in site engineer’s working conditions are too huge to be translated in financial terms. In addition, there will be significant gains in terms of site business advancement as voltage/current measurement or other site activities which were difficult to conduct effectively or even at all in the past will be supported.

5-2-1 Improvement of Responsiveness to Fault

As distribution automation system eliminates the needs for site trip to manipulate switches manually, it can save distribution electrical engineer’s workload involving site visit. Notably, line faults occur in adverse weather conditions such as typhoon or rain, road conditions are usually not good on such days, requiring a lot of time to reach fault site. In addition, maintenance crews had to climb up electric poles in bad weather conditions or at night to manipulate switches or separate line manually in the past. However, as distribution automation system supports such operation remotely, it results in significant improvement in site operation and manipulation.

5-2-2 Acquisition of Line Information Assures Optimization of Distribution System Operation Efficiency

Application to Nzed and other application programs, it is now possible to understand and monitor line status remotely. As Nzed program provides line load, voltage, current, maximum fault current and power factor, etc. in real time, it is now possible to optimize distribution system operation by balancing loads across distribution lines and improving distribution line utilization ratio, line voltage regulation, reducing loss and resolving imbalance across lines, etc. Notably, AgOLD application program displays fault information such as fault type and fault current in real time as fault occurs in a line and Nzed program stores and maintains such information, which will provide valuable inputs for fault analysis and resolution development in the future.

5-2-3 Advancement of Distribution Electrical Engineer’s Work Quality

As repetitious on-site activities such as switch manipulation or voltage/current measurement are simplified, distribution operation office staffs can have more room for working on some other tasks.

5-2-4 Scientific Distribution Line System Operation

Planning mid/long-term investment in distribution line depended unscientifically on empirical experience in line operation of engineers in charge in the past. However, distribution automation system acquires a variety of line information, fault log data and event data and enables scientific analysis and investment planning. In addition, distribution operators will be able to enhance their professional knowledge and skills for distribution system operation and IT technologies as well.

5-2-5 Prevention of Customer Complaint & Improvement of Service Quality

As improvement in standard of living increases dependence on electric power, outage inflicts more impact on society in general and the general public takes prolonged outage simply as unacceptable justifiably. Notably, some customers dependent on electrical power to run their business suffer huge damage from extended outage and raise strong complaints, which aggravates into social issues when severe. However, distribution automation system reduces such outages and improves customer service quality dramatically, delivering benefits that are too huge to translate in financial terms. Such benefits will provide a momentum to supply electric power of high quality and realize customer satisfaction, which are the ultimate goals of all electrical companies.

5-3 Conclusion

The greatest economic benefit expected at the introduction of distribution automation was reduction of power supply interruption volume thanks to the ability to understand fault status and control site facilities remotely without site visit and reduce interruption time and fault section promptly thereby. However, if investment in distribution facilities continues for several dozen years and reduces the number of faults drastically, it will be obvious that reduction of interruption time does not have significantly greate effects. In other words, KEPCO’s experience has revealed that the economic benefits of distribution automation system are far greater than its investment cost at such point of time in terms of reduction of distribution system loss and delay of facility investment. To that end, it is concluded that the goal of distribution automation must not be limited to remote monitoring and controlling of distribution line but extended to optimization of distribution system operation.