POWER QUALITY AND RELIABILITY IMPLICATIONS OF UTILITY FEEDER RECLOSING PRACTICE

Paulo Meira, Walmir Freitas

Department of Electrical and Computer Engineering, University of Alberta

Department of Electrical Energy Systems, University of Campinas (Brazil)

Impact of auto-reclosing on power quality

Objectives

Figure 1. The impact of automatic reclosers.

This project investigates the impact of feeder auto-reclosing, a standard utility fault-clearing practice, on the power quality and power reliability of distribution systems. Auto-reclosing is very useful to increase the reliability of a distribution feeder. However, it can create momentary interruptions to a large number of customers, adversely affecting the power quality. Thus, the objectives of this project are:

• Determine the impact of auto-reclosing on power quality; • Investigate a scheme of selective auto-reclosing; • Develop a method to quantify the efficiency of a certain recloser or group of

reclosers.

All the analyses were conducted using an 6-year data based of a Canadian distribution utility.

Figure 3. Four situations to be considered when designing a reclosing scheme.

Since the feeder reclosing scheme does not always lead to the best outcome on reliability and power quality, a selective application of the scheme is the natural choice. Selective application means to design and apply the reclosing scheme based on the characteristics of feeders and customers involved. Figure 3 illustrates the broad situations of interest to utility companies when designing a reclosing scheme. This figure considers two most influential factors – the ratio of temporary versus permanent faults and the ratio of PQ sensitive versus less-sensitive customers.

Substation

A

B

CB

C

A

C

A1

A2A3

A4

B1

B2B3

C1

C2C3

C4

C5

ABC2

ABC3

ABC1

F

R1

R2

The impact of auto-reclosing practice on power quality can be understood using the sample system shown in Figure 1. The feeder has two reclosers R1 and R2. For the fault at point F, the recloser R1 will open one or two times, each for about 2 seconds, before the fuse of the faulted section could operate. This operation, even if limited for one shot, will result in the following power quality consequences:

• All customers located downstream of R1 would experience an interruption lasting at least 2 seconds. The power quality of these customers is therefore much worse off than the cases without recloser.

• The power quality at C1 and C2 could be improved since the fault is cleared faster than those provided by the fuse. The same conclusion applies to other upstream customers.

• The number of customers affected could be reduced if only the phase A recloser operates.

One can therefore conclude that the practice of automatic reclosing is not generally helpful for power quality. The larger the area covered by a recloser, the more adverse effect the recloser will have on power quality.

Impact of feeder reclosing on power quality and reliability indices

Determination of feeder characteristic and recloser efficiency

A complete scheme of selective feeder reclosing selection

Period Permanent Temporary

January 42.1% 57.9%

February 36.7% 63.3%

March 44.1% 55.9%

April 42.9% 57.1%

May 47.9% 52.1%

June 60.3% 39.7%

July 53.5% 46.5%

August 48.3% 51.7%

September 55.0% 45.0%

October 47.3% 52.7%

November 58.9% 41.1%

December 54.5% 45.5%

Total 52.1% 47.9%

Period (A)

Direct Sustained

(B+C) Progressive

(D+E) Momentary

(D+E)* Momentary Related to Fast Trip

Reff (D+E)*/(B+C+D+E)

January 11 13 33 30 65.2%

February 19 25 76 63 62.4%

March 32 20 66 51 59.3%

April 22 2 32 27 79.4%

May 14 9 25 21 61.8%

June 54 22 50 43 59.7%

July 47 14 53 47 70.1%

August 53 19 77 66 68.8%

September 48 23 58 54 66.7%

October 18 8 29 23 62.2%

November 68 64 92 73 46.8%

December 228 172 334 291 57.5%

Total 614 391 925 789 60.0%

Permanent failure

rate (faults/km/year)

Temporary failure rate

(faults/km/year) Customers

Length (km)

Switching time

(hours)

Repair time

(hours)

Feeder sections 1 to 32

0.25 0.75 80 0.75 0.5 3

Taps 1 to 32 0.1 0.3 25 0.25 – 1.5

Number of reclosers SAIDI SAIFI MAIFI

0 1.05 3.38 0.39

1 0.95 1.97 6.72

2 0.91 1.44 9.38

Scheme of selective feeder reclosing selection

Weighted PR

performance

Weighted PQ

performance

Design parameter (such as the number of reclosers)

Ob

ject

ive

fun

ctio

n Optimal

(or tradeoff)

solution

• Step 1: Data collection from OMS and Sentry logs • Step 2: Data analysis

o Temporary versus permanent faults o Efficiency of reclosers

• Step 3: Combined PR and PQ Assessment • Step 4: Identification and evaluation of potential solutions

Figure 2. The impact of location of the automatic reclosers on SAIDI, SAIFI and MAIFI.

SAIFI: System Average Interruption Frequency Index (RI) SAIDI: System Average Interruption Duration Index (RI) MAIFI: System Average Momentary Interruption Frequency Index (PI)

The momentary and sustained interruptions frequencies are inversely related, i.e., when one decreases the other increases. Therefore, the reliability and power quality indices cannot be simultaneously minimized using reclosers, so a compromise between momentary and sustained interruptions must be found (a Pareto efficiency solution must be obtained).

In order to eliminate or not a recloser, aside from the customer characteristic, the following aspects must be analyzed based on the utility databases:

• The feeder characteristics must be determined (permanent versus temporary faults) • An index for recloser efficiency must be used

A Canadian utility provided the following two sets of data from November 2003 to May 2009:

1. Outage Management System (OMS): containing sustained interruption data, as well as detailed information such as the outage causes, duration, number of affected customers, protection operation, etc. 2. Sentry device logs: containing data from sustained and momentary interruptions of a selected number of customers spread over the system without further information such as outage causes, protection operation, etc.

Based on techniques of filtering and classification, all the data was treated so that the relationship between permanent and temporary faults can be determined (Table I shows the results for 1 year). Table I. Permanent versus temporary faults

Table II. Recloser efficiency index

To assess how effective the recloser usage is, one needs to determine the relationship between successful (fuse-saving) and unsuccessful (not fuse-saving) recloser operations. Thus, a new index was developed to measure this efficiency as shown in Table II.

....0

30

20

1

E

E

MAIFI

MAIFIw

SAIDI

SAIDIw

SAIFI

SAIFIwf

Figure 4. Data filtering and classification

Feeder characteristics

Customer characteristics

More temporary faults

PQ

sen

siti

ve

Q1: sensitive customers served by feeders with high temporary faults

Q3: less sensitive customers served by feeders with high permanent faults

Q4: less sensitive customers served by feeders with high temporary faults

Q2: sensitive customers served by feeders with high permanent faults