Eskom Distribution ERTC `09

Durban, South Africa, 18th November 2009

Bare Jumpers-

lead to bird

electrocutions

Replacement of LDPE pipe using PVC Covered Jumper Conductor

S. Nayager C. Shunmugam Engineer in Training - T&Q Department Technical Engineering Investigator, T&Q Department

Phone: 072 6231205, Email: nayages@eskom.co.za Phone: 031 710 5416, Email: shunmuc@eskom.co.za

Abstract – On MV overhead networks, bare aluminium jumpers

are used to connect auxiliary equipment such as transformers,

voltage regulators and reclosers to the system. Due to the number

of bird/wildlife deaths caused by these bare jumpers, the

Endangered Wildlife Trust (EWT) required that Eskom structures,

especially the equipment structures, be bird/wildlife friendly. One

of the ways this was achieved was to use an insulated covering

over the bare jumper to mitigate the problem and reduce the

number of wildlife fatalities. The low density polyethylene (LDPE)

pipe was chosen as the best solution to cover the bare jumpers

thereby making the equipment structures, “environmentally

friendly”.

Although the LDPE Pipe was an excellent environmental solution,

it has created three engineering problems which will be discussed

further in this paper. These engineering problems have affected

our networks performance creating a poor quality of supply to

Eskom customers. Due to this our SAIDI and SAIFI targets were

being negatively impacted. To improve our plant reliability an

alternative to the LDPE pipe had to be researched. This paper

explains the newly designed Polyvinyl Chloride (PVC) covered

jumper which was piloted on two feeder networks namely

Esikhawini NB 17 (North Coast Empangeni) and Marina Beach

NB 78 (South Coast). The results of the pilot study are discussed

and recommendations are made on the proposed way forward.

I. INTRODUCTION

In habitats where natural nest substrates are limited, power

line structures have become a common nesting site for many

birds such as vultures and raptors. Likewise other birds also

use these power lines and poles for perching, roosting and

hunting. Due to this, bird electrocutions on power lines has

become a concerning issue for both Eskom and wild-life

groups. The biological and environmental components that

influence electrocution risk include the following:

� Body size

This is the one of the main causes for bird fatalities on both

sub transmission and reticulation lines. Birds with large wing

spans come into contact with the energized conductors when

either flying in or taking off from power line structures and

auxiliary equipment such as transformers.

Figure [1]

The picture above shows an example of a vulture sitting at

the top of a pole structure. It can be seen that this bird has a

large wing span which causes a short circuit on the power

system and thus making it susceptible to electrocutions.

� Habitat

In open areas lacking natural perches, power utility poles and

auxiliary equipment provide sites for hunting, resting,

feeding, roosting or nesting. A habitat with an abundance of

prey will attract a variety of birds.

� Cable/Jumper Configurations Configurations with closely spaced energized phase

conductors and grounded wires as shown below are being

readily bridged by birds. The arrow shows potential danger

for birds: on the auxiliary transformer the jumpers coming off

from the main line are in close proximity from one another.

Figure [2]

In 2007/2008 a total of 18 bird electrocutions had occurred

with about 89% of the deaths taking place on reticulation

lines.

Bird Electrocutions 2007/2008 Eastern Region

0

2

4

6

8

10

12

14

16

18

Reticulation Sub transmission

Power Lines

Nu

mb

er

of

ele

ctr

ocu

tio

ns

Figure [3]

II. ENDANGERED WILDLIFE TRUST(EWT)

ENVIRONMENTAL REQUIREMENTS

In 2002 the Endangered Wildlife Trust (EWT) required that

Eskom make all their jumpers terminating on auxiliary “bird

friendly” due to the high fatality rate. According to standard

DST 34-1191 titled ‘General Information and Requirements

for Overhead lines up to 33kV’ the details for a covered

jumper was specified. The conductor’s jumper insulation is

defined below:

“Jumpers for auxiliary structures and line equipment shall be

made from conductor that is covered with a suitable

insulating material to minimize the risk of birds being

electrocuted. Terminations shall be shrouded in particularly

sensitive areas and if insulating jumper material is bared for

the purpose of applying earths, these bared areas shall be

staggered vertically to ensure that simultaneous contact of

two bared sections by a bird is not possible.”

From this specification the low density polyethylene (LDPE)

pipe was chosen as the most cost effective method to provide

the insulating covering on all jumpers to auxiliary equipment.

This will reduce the number of bird electrocutions as well as

provide the jumper with protection from the natural elements.

However over the past few years the LDPE pipe has become

problematic causing more damage to jumper conductors than

protection. The problems with LDPE involve:

� Increased fatigue failure- In windy areas LDPE pipe

chaffs into jumper conductor and over time the

conductor breaks off

� Water accumulation in LDPE pipe could lead to

accelerated degradation of the aluminium conductor.

� Fault finding has become more difficult for TSC

operators since the jumper conductors are enclosed in the

LDPE pipe hence compromising visibility.

A sample of a damaged jumper containing the LDPE pipe

was obtained from Marina Beach (NB78). From analysis it

can be seen that strands of the jumper has been damaged

before the crimp fitting canceling any uncertainty of incorrect

crimping.

Figure [4a]

Figure [4b]

III. STATISTICS

Jumper failures have impacted largely on customer delivery

and System Average Interruption Duration Index (SAIDI),

System Average Interruption Frequency Index (SAIFI)

values. As it can be seen below, a total of 947 jumper failures

in general had occurred in the year 2008 for the Eastern

Region. The latter half of the graph shows a high failure rate

due to high winds and summer rains.

Figure [5]

0

20

40

60

80

100

120

140

160

Number of failures

January April July October

Month

Jumper Failures-2008

Series1

In terms of jumper failures, Marina Beach NB 78 and

Esikhawini NB 17 were rated as two of the worst performing

networks in the Eastern Region. At the Technology Forum

Change Control (TFCC), a decision was taken to pilot a PVC

covered ACSR aluminium conductor. This was done on

Marina Beach NB 78 on August 2008 and on Esikhawini NB

17 on July 2007. The graph below shows the qualitative

comparison of the jumper performance on Marina Beach NB

78. The number of jumper failures is inclusive of the LDPE

pipe damaged jumpers.

0

1

2

3

4

5

6

7

8

Number of

failures

2004 2005 2006 2007 2008 2009

Year

Marina Beach NB 78

Figure [6]

Taking a look at the figures from the chart it can be seen that

from 2008 to 2009 there has been a reduced failure rate. From

the end of August 2008 (when PVC covered jumper was

installed) to the current period jumper failures had dropped

substantially. Marina’s Beach Technical Service Officer has

confirmed that there has been no PVC covered jumper

failures to date. The energy charges (cents per kW/hr) over

the last six years were obtained from the pricing and tariff

department for home power users. A calculation for the loss

of revenue was determined using the following tariff costs

per year and an assumption of a unity power factor: 2004

(27.95c kW/hr); 2005 (30.16c kW/hr); 2006 (31.70 c kW/hr);

2007 (33.57 c kW/hr); 2008 (45.05 c kW/hr); 2009 (57.46 c

kW/hr). The total loss in revenue over the past 5 years was

R114382.10 due to jumper failures. This does not cover

repair team labour and transport costs.

0

5000

10000

15000

20000

25000

30000

Rands

2004 2005 2006 2007 2008 2009

Year

Marina Beach NB78 : Loss of Revenue

Figure [7]

Looking at Esikhawini NB17 it can be seen that 2007

contained the highest amount of jumper failures. After the

installation of the PVC jumpers it was noticed that there was

a significant drop in failures which has improved Eskom’s

SAIFI and SAIDI values.

0

1

2

3

4

5

Number of jumper

failures

2004 2005 2006 2007 2008 2009

Year

Esikhawini NB 17

Figure [8]

Using the same tariff prices from the previous page the

following figures were calculated showing the loss of revenue

for Esikhawini Network breaker 17 over the past 5 years. The

total loss is R 36842.13 with the lowest loss being in 2009

which shows that there has been an improvement on this

network with the use of the covered jumpers

0

5000

10000

15000

20000

25000

Rand

2004 2005 2006 2007 2008 2009

Year

Esikhawini NB17-Loss of Revenue

Figure [9]

IV. TESTING AT VIBRATION RESEARCH TEST

CENTRE-UKZN

In order to determine if the LDPE pipe was the root cause of

jumpers failing, an overhead to auxiliary transformer

simulation was setup at the University of Kwa- Zulu Natal’s

Vibration Research Test Centre (VRTC). For the test an

Electrodynamic Vibration Tester (shaker) was used to imitate

the vibration created by wind on the LDPE pipe. Fox

conductor was chosen for the test since it’s the most widely

used on reticulation lines for jumpers. The top half of the Fox

conductor was connected to an attachment beam in the

ceiling using a preform dead end and the bottom half was

1

x: 8, y: 0.0956147

x: 49.0383, y: 0 .102629 Locked

8 10 20 50 60

0.05

0.1

0.2

m/s

(Lo

g)

Hz (Log)

A Sine m/s [Control] B Sine m/s [CH 2]

1 x: 49.0383 y: 0.102629

L D P E

P ip e

S h a k e r H e a d

S h a k e r

terminated in the shaker head. To obtain an accurate

simulation, a LDPE pipe of larger diameter than the

conductor was fitted over the conductor. The final setup is

shown in the picture below:

Figure [10]

Two sensors were used in the experiment; the sensor below

the shaker head measures the excitation frequency generated

and the sensor on the LDPE pipe measures the amount of

vibration that the pipe experiences.

Figure [11]

A sweep test was carried out using the PUMA control system

which is responsible for determining the highest resonant

frequency acting on the LDPE pipe. The range was chosen

between 8Hz and 60Hz to determine the highest points of

vibration, ideally to 50Hz to match normal load conditions.

To provide an extra force to simulate vibration created by

wind an amplitude distortion of 6mm from the conductor and

LDPE was maintained. When the excitation frequency

matched the natural frequency of the pipe, the maximum

vibration was obtained. The test was run over 3 days, with the

first day running at 11Hz and the remaining days at 49Hz

with both set at 9.9G to simulate wind. These frequencies

were chosen from the sweep test graph shown below:

Figure [12]

The test had run for 20 hours over a 3 day period after which

the jumper was examined under a microscope at Pfisterer.

The images below showed that the LDPE pipe had chaffed

the conductor which could eventually lead to jumper failure.

Figure [13a]

Figure [13a]

V. RESEARCH AND DEVELOPMENT

At the Technology Forum Change Control (TFCC) a decision

was taken to pilot an alternative to the LDPE pipe. A pilot

PVC covered jumper project was run in 2007 in two areas,

Esikhawini NB 17 (July 2007 installed) and Marina Beach

NB 78 (August 2008 installed). These network breakers were

chosen as they were the worst performing networks in the

eastern region in terms of jumper failures. The PVC cover

jumper (manufactured by Aberdare) was designed to use a

Fox conductor (ASCR) and was to be greased according to

CASE 3 ie “All the conductor is greased including the outer

layer”. In 2009 IARC Power Plant Technology Department

requested that the installed samples from the inland and

coastal areas be removed and tested to determine the

following:

� To establish the effectiveness of the water blocking

of the cover

� To determine the flammability of the cover material

if exposed to an open flame

� To determine what temporary insulation the material

can provide

The test results showed:

The greased PVC covered jumper when analysed showed no

indication of water ingress or dirt. When the cover material

was placed under an open flame, it immediately reacted to the

heat by changing texture and colour. However, the material

did not continue to burn once the flame was removed. When

the sample was exposed for more than 5 minutes to the flame,

the damage was limited to the area that was within the flame.

Withstand and flashover tests for the PVC covered jumper

were conducted at Simmerpan’s HV lab. The test voltage was

gradually increased up to 36 kV and maintained for 60

seconds; thereafter it was increased gradually until flashover,

i.e. puncturing of the PVC cover occurred. All samples had

an insulation thickness of 1.6mm and eventually flashed over

above 50kV. After drawing up a final specification for the

PVC covered jumper, Aberdare had informed Eskom that

they had a problem manufacturing the jumper according to

CASE 3 greasing. The greased outer strands made the

extrusion process difficult as the PVC covering did not

adhere to the greased conductor. The only solution was to

grease the conductor according to Case 4: The inner

interstices will be completely filled with grease and the outer

interstices will be fully extruded by the PVC covering.

VI. CONCLUSION

Performance of the piloted PVC covered jumpers on feeder

network Marina Beach 78 and Esikhawini Network Breaker

17 has without a doubt proved to be the most cost effective

alternative to the LDPE pipe. The Technology Forum Change

Control has had positive feed back from Field Services

personnel. Accordingly the Regional Engineering

Management has authorized the use of PVC covered jumpers

on all auxiliary equipments for medium voltage overhead

lines. Using this PVC covered jumper as an alternative would

definitely eliminate the engineering challenges that was

experienced with the LDPE pipe. Standardisation of PVC

covered jumpers on MV networks would make a positive

impact on network performance and plant reliability. Hence

our quality of supply to Eskom’s customers would be

siginificantly improved.

ACKNOWLEDGMENT

1]. D.R. Rossouw Theron- IARC Chief Engineer,Power Plant

Technology

2]. Jacques Calitz- IARC Material Specialist

3]. Vibration Research Test Centre (VRTC) –Pravesh

Moodley

4]. Megan Diamond(Endangered Wild Life Trust(EWT)

5]. Cyril Shunmugam-Technical Engineering Investigator

(TEI)

6]. MV Standard-DST 34- 1191- “General Information and

Requirements for Overhead lines up to 33kV”

7]. IEEE-Transaction on Power Delivery, VOL 19 No 4,

October 2004, R Sundarajaran et.al and others-

“Preventive Measures to Reduce Bird Related Power

Outages- Part 2: Streamers and Contamination”

8]. Nivan Pramjeeth- Technical Service Officer- Marina

Beach

9]. Brett Goosen- Works Co-ordinator Empangeni Technical

Centre

10]. Kevin Bower-Data Analyst-Plant Department

11]. Pfisterer- Brian Murry- Mechanical Engineer