The Urban DA research Case study

The Urban FA project was initiated in 2005 to develop additional pilot systems and to determine the technical and financial feasibility of FA technology. The scope of the Urban FA project included the enhancement of the Rawsonville and Machadodorp FA pilot systems, and the establishment of a new FA pilot system on the Magaliesburg reticulation network.

During the initial stages of the Urban FA project, it became apparent that an underground urban network wasn’t really ideal to demonstrate FA technology. Reasons included the risk of interrupting high revenue urban areas to the fact that the system would take a long time to prove itself because of the relatively low frequency of faults on cables compared to overhead lines.

Subsequently the Magaliesburg – Hekpoort 11kV feeder was proposed, a dense rural feeder with a poorer than average performance, as the candidate site for the FA pilot system. The proposed network was analysed in terms of the pre-defined selection criteria for FA systems and it passed all the requirements.

The Magaliesburg FA system was successfully commissioned on 9 December 2009. The system has operated as expected for the five sustained faults, which occurred during the analysed period (9 December 2009 – 31 January 2010).The FA system resulted in significant technical improvements for the analysed period.

Though the Rawsonville and Machadodorp FA pilot systems forms part of the Urban FA case study, but we will focus on the Magaliesburg pilot system as a complete new FA system was implemented and to avoid comparison and duplication.

4.1.1.1 Magaliesburg – Hekpoort 11kV feeder FA Pilot system

Selection of Magaliesburg – Hekpoort 11kV feeder

The project relied on criteria developed during the original “Distribution Automation” project (Project no. RJLNEW844, started in 1998) to develop selection criteria for the new “Urban FA”

pilot site. Table 1 provides a summary of the selection criteria that the candidate networks had to meet in order to be considered for the Urban FA pilot project. This criterion was discussed with Central Region stakeholders, who subsequently identified three possible candidate networks.

As shown in Table 1 below. The Magaliesburg - Hekpoort 11kV feeder met (and in some cases exceeded) all the requirements. As a result its nomination was fully supported by the Distribution Control Technologies Research Steering Committee.

Table 1: Selection criteria for the Urban DA pilot site

Category Requirement

Overview of Magaliesburg – Hekpoort 11kV feeder

As mentioned earlier the Magaliesburg – Hekpoort feeder, situated close to the Magaliesburg town, was selected as the site for Eskom’s fourth FA pilot site. A simplified single line diagram of the Magaliesburg / Hekpoort 11kV feeder is shown below in Figure 12.

Figure 12. Magaliesburg - Hekpoort single line diagram (simplified)

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The main characteristics of the feeder is summarised in the table below.

Table 2: Characteristics of the Hekpoort 11kV feeder (2005)

An analysis of the power network revealed that the network has three potential back feed sources, namely:

• Alberta feeder at location MH123/4

• Alberta feeder at location MH90/3

• Brandvlei feeder at location MH10/71

Parameter Value

Feeder length 48.5 km

Backbone length 14.2 km

Installed capacity 14 465 kVA

Maximum demand 3 300 kVA

Number of Customers 188

75% Agricultural 10% Residential 10% Commercial 5 % Industrial

No. of CTs/VTs 3

Backbone conductor 95Al, Mink ; 120 Cu Fox

Thermal loading 79.31%

Optimistic load growth 4% per year (4170 kVA in 2010) Pessimistic load growth 2 % per year (3825 kVA in 2010) Customer profile

Historic Performance of the Magaliesburg – Hekpoort 11kV feeder

The historic performance of the Magaliesburg – Hekpoort feeder was analysed to determine how the FA system could improve the reliability and availability of the network.

The main KPIs of the network are summarised in Table 3.The figures suggest that the performance of the Magaliesburg – Hekpoort is about 50% worse than the Eskom Distribution average – which means that the network presents an ideal opportunity for FA to improve the network’s performance. An improvement target of 50% for the SAIDI, SAIFI and SLI KPIs were set.

Table 3: KPIs of the Hekpoort 11kV feeder

KPI Current value Desired value % improvement

SAIDI 82.46 hours 41.23 hours 50%

SAIFI 51.26 25.63 50%

SLI 3.63 1.82 50%

The information in Table 3 was however not sufficient to understand the reasons for the poor performance. Consequently data from the Network Performance System (NEPS) was analysed for the period January 2002 to March 2005. The following data was extracted:

• The number of supply interruptions per emergency or fault interruption

• Customer minutes interrupted per emergency or fault

• The average restoration time per supply interruption (Table 4)

• The number of momentary vs. sustained interruptions

• Causes of momentary and sustainable faults (Figure 14)

• Distribution of faults along the main feeder (Figure 15)

As indicated some of these analyses are illustrated in figure 13 below to provide more insight into the value and need for these types of analyses. For instance figure 13 indicates that 56.1% of all the faults on the Hekpoort feeder are momentary in nature (i.e. lasting less than 5 minutes). The focus of the FA system is therefore to reduce the outage time of the remaining 44% of faults through automatic fault location and isolation.

Figure 13. Average supply interruption restoration times (Jan 2002 – Mar 2005)

Figure 14. Causes of sustained faults (Jan 2004 – Jul 2005)

The value of the analysis into the causes of sustained interruptions is that it shows a very wide distribution of causes, which any single conventional technology wouldn’t be able to address.

FA technology is a prime candidate to limit the impact of such a wide variety of failures.

Figure 15. Distribution of sustained faults (Jan 2004 – Jul 2005)

Illustrates the distribution of faults on the feeder. This is very useful, as it allows informed decision making as to the best locations to install FA devices. The specific analysis also enables the calculation of the performance improvement that could be achieved as a result of the FA system.

A specification for the Magaliesburg FA system was developed based on the following inputs:

• The current network configuration

• Installed power and control plant on the network

• Historic performance of the network, in particular the distribution of network faults.

• Equipment available to the contractor based on Distribution National Contracts

• Applicable equipment standards and specifications

Performance evaluation Methodology

The Magaliesburg FA system was analysed from the date of commissioning 9^th December 2009 till the 31^st of January 2010. Although this period may not be considered sufficient to give an estimation of the technical and financial benefit to Eskom over the entire project life cycle, this was the maximum time allowed between system installation and the contracted Urban FA project end date.

The performance improvements analysed were:

a) Customer minutes saved, due to:

i. Automatic restoration of the healthy sections of the feeder;

ii. Faster restoration of the faulty sections of the feeder due to automatic isolation and the time saved during fault location;

b) Number of customer interruptions saved due to automatic restoration of the healthy sections of the feeder;

c) MVA hours saved, due to:

i. Automatic restoration of the healthy sections of the feeder;

ii. Faster restoration of the faulty sections of the feeder (isolation is automatic and time is thus saved during fault location)

Sustained interruptions during the analysed period occurred on the network, nine faults were sustained interruptions which caused recloser lockout, i.e. 41%.

Table 4: FA operations on Magaliesburg for the period 9 December 2009 – 31 January 2010 No Date Description FA restoration time

It should be noted that, according to the historic performance of the Magaliesburg – Hekpoort feeder , the majority of faults on this feeder occur during December and January. This is due to the stormy wheather in the area during this time of the year. The number of faults analysed in this report is therefore more than the expected average number of faults on feeders, considering a twelve month period.

Performance improvement

The customers and load interrupted during each of the 5 successful operations, with and without the FA system, are summarised in Table 5.

Table 5: Event data for each of the Magaliesburg FA operations for the period 9 December 2009 – 31 January 2010

The FA system also has an operational benefit, since less labour and travelling is required to repair sustained feeder faults. The isolation time was assumed to be 15% of the total

Table 6: Performance improvements of the five analysed events

No Date Customer

The MVA hours saving is based on the installed MVA. The actual MVA saved can be calculated from the installed capacity, assuming that the maximum load is 50% of the installed capacity and a load factor of 25%. The actual MVA hours saved during the analysed five events is therefore 9.17 MVA.

The effect of the customer minutes saved on the Magaliesburg, Central Region and Eskom SAIDI is shown in Table 7.

Table 7: Summary of Magaliesburg, Central Region and Eskom SAIDI saved

The CAIDI for each event, with and without FA, is given in Table 8 below:

Table 8: Summary of Magaliesburg CAIDI for each event, with and without FA

No Date CAIDI without

FA [hours]

CAIDI minutes with FA [hours]

1 19 December 2009 2,61 2,42

2 21 December 2009 4,09 3,79

3 26 December 2009 4,69 4,69

4 18 January 2010 1,59 1,59

5 20 January 2010 5,96 5,80

Total 4,28 3,48

The FA system resulted in the following technical improvements of the Magaliesburg – Hekpoort feeder:

A comparison between the customer minutes lost and MVA hours lost with and without FA is shown from the graphs respectively.

Customer minutes lost with and without FA MVA hours lost with and without FA Figure 16. Customer minutes lost and MVA hrs lost with and without FA.

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19 December 21 December 26 December 18 January 20 January

Cusotmer minutes lost

Interruption date Customer minutes lost with DA and potentially lost without DA

Customer minutes potentiall lost without DA

19 December 21 December 26 December 18 January 20 January

MVA hours lost

Interruption date

MVA hours lost with DA and potentially lost without DA

MVAh potentially lost without DA MVAh lost with DA

4.2 C

This chapter was aimed at presenting the research that was prepared by Eskom to develop a business case study for FA technology in Eskom, determining technical and financial feasibility of FA technology. We only presented the Magaliesburg-Hekpoort case as it was the only one out of the other two case, were a new FA system will be implemented and to avoid duplication of work. We divided the Magaliesburg-Hekpoort case into three sections: the selection of the Magaliesburg-Hekpoort 11kV feeder, the implementation & operation of FA, and lastly the results obtained from the research.

The proposed methodology discusses how one should consider implementation of FA technology on a feeder, and the presented case demonstrates how FA was implemented on feeder. From this presented case, it can be seen that a certain approach was used to implement automation on the Magaliesburg-Hekpoort feeder. That is, there were some planning principles that were taken into consideration prior implementation of FA, even though there was no method or guideline followed to discuss these issues prior any work.

In the next chapter we will discuss the presented case study with respect to the FA planning methodology proposed in chapter 3 of this research. This discussion will analyse how Magaliesburg – Hekpoort was conducted with respect to the proposed methodology, which steps of the method were taken into consideration and to what extent were they applied.

For those steps of the method that were not considered we will look at what was considered and why. We will further discuss modifications that can be done to improve the FA planning methodology.

5 CHAPTER 5: DISCUSSION ON ESKOM CASE STUDY &

THE PROPOSED METHODOLOGY

5.1 I

A

O

The aim of the study is to define a way or systematic approach on how one should consider or plan for implementation of Feeder Automation on an electrical distribution network. This is done by first defining the problem statement i.e. on what will the method be based.

Furthermore literature on what other researches have done in finding ways of planning for FA was also considered in defining the proposed method.

A case study was presented in the previous chapter. The main reason for presenting this case study was to demonstrate how Eskom has approach the implementation of FA on the Magaliesburg-Hekpoort feeder. From the case study it could be noticed that there was an approach or methodology used to implement FA, though the approach was not a strategic approach or preliminary defined.

Therefore now we need to analyse the proposed methodology with respect to the presented case study. This will enable the improvement or better modification of the method.

We will not develop a new case study neither do any comparison, but we will discuss the similarity and differences in Eskom’s approach to implementation of FA on the Magaliesburg –Hekpoort feeder and what the FA planning methodology suggests.

On the analyses we will also analyse the outcomes if the FA methodology is implemented, to show what would have been the benefit or difference of implementing FA using the proposed method.