Prague, 8-11 June 2009 Insulation Coordination …...Prague, 8-11 June 2009 Insulation Coordination Best Practices Leading to Improving Continuity of Supply A. Herculano P. Nunes M.T

Prague, 8-11 June 2009

Insulation Coordination Best Practices Leading to Improving

Continuity of SupplyA. Herculano P. Nunes M.T. Correia de Barros

EDP Distribuição - Portugal LABELEC - Portugal LABELEC – [email protected] [email protected] [email protected]

C. S. Engelbrecht P. HesenKEMA - Netherlands KEMA – Netherlands

[email protected] [email protected]

Pedro Nunes-PORTUGAL Session 5 Paper 0777


Introduction• EDP Distribuição is the Portuguese electricity distribution

company, supplying more than 5 million clients;• Operates at 60 kV, 30 kV, 15 kV, 10 kV and LV network; • EDP Distribuição carried out actions for improving the

quality of service.


TIEPI MV (min)638

456 420341

215 175 176

0100200300400500600700

2000 2001 2002 2003 2004 2005 2006

TIEPI MV Goals

155 145150175 162,5

0

50

100

150

200

2005 2006 2007 2008 2009

min

GOOD RESULTS WERE ACHIEVED


Introduction• In 2003 EDP Distribuição invited KEMA to conduct an

independent review and assessment• KEMA perform a QRA (Quantitative Risk Assessment)• An Improvement Program was established, encompassing

several Projects, which cover a diversity of areas, among which INSULATION COORDINATION

• Insulation Coordination project partners, was set up



Methodologies• Insulation Coordination (IC) project developed in 2 phases;• 1st Phase (2004-2005)

– Independent review and assessment conducted by KEMA ;– Root causes were established for reviewing IC practices;

• 2nd Phase(2006-2007) – identify IC best practices leading to improve continuity of

supply;– Studies were carried out by LABELEC for evaluating systems

behaviour under transient conditions;– Study by EDP Distribuição to classify and rationalize the

distribution line structures;– Conclusions and validation by EDP Distribuição, LABELEC

and KEMA



Insulation Coordination Studies

• Line Insulation Coordination

• MV/LV Transformers Insulation Coordination– Pole Top Transformers– Cable Fed Indoor Transformers– Overhead Line Fed Indoor Transformers

• HV/MV Substations Insulation Coordination









Line Insulation Coordination• MV OH Lines are mostly

involved in the technical causes of outages;

• EDP opted to insulate all MV OH Lines LIWL = 250 kV


0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400 450 500

Lightning Impulse withstand level [kV]

Line

out

age

rate

(fau

lts/1

00 k

m/y

ear)

Direct strikes

Indirect strikes

Combined Direct and indirect strikes


Line Insulation Coordination• Overvoltage Protection of Equipment on the Line

– Install surge arresters to protect vulnerable equipment

– Priority given to equipment containing non-self-restoring insulation and locations that experiences frequent flashovers


Only install arresters if location experiences frequent outages

LowIsolating switches

Only install arresters if location experiences frequent outages

LowLoad break switches

Install at both cable terminationsVery HighCable sections

Install on the MV side of MV/LV transformersVery HighPower transformers

Install on both sides of the deviceVery High Automatic reclosers (OCR)

RemarkSurge arrester priorityEquipment Type


Line Insulation Coordination• A range of

standardized structures have been designed to meet the insulation level;– Defined 73

standardized structures;

– Defined clearances between phases and phase to earth


a) Distance between phases -> 540 mm

b) Distance phase to earth -> 480 mm

a) Distance between phases -> 540 mm

b) Distance phase to earth -> 480 mm


Line Insulation Coordination• Pilot Experience









MV/LV Transformers IC









Pole Top Transformers• Proposed configuration on LV

side– Separated earths– High insulation levels in LV

cabinet

– Spark gap on LV cabinet


QGBT

TransformerMV LV

Protection earth≤20 Ω

Service earth≤20 Ω

Global Neutral earth <10 Ω

QGBT

TransformerMV LV



QGBT

TransformerMV LV



Global Neutral earth <10 Ω

18 kV8 kV----Gap in QGBT

----20 kV10 kVQGBT Cabinet

----30 kV10 kVTransformer

LIWVAC (50 Hz)LIWVAC (50 Hz)

LV-protection levelLV-insulation levels


Pole Top Transformers









Cable Fed Indoor Transformers


MV -LV

trafo

Surge arrester

MandatoryMandatoryLc ≥ 70 m

Not mandatoryMandatoryLc < 70 m30 KV

MandatoryMandatoryLc ≥ 50 m

Not mandatoryMandatoryLc < 50 m10 KV and 15 KV

Surge arresters at transformersSurge arresters at line to cable transition

Cable length Lc (m)Voltage level Un (kV)








Overhead Line Fed Indoor Transformers


Phase leads

Surge arrester

Earth leads

Insulator with protective gaps

Transformer

LV neutral

Bushing

Phase leads

Surge arrester

Earth leads

Insulator with protective gaps

Transformer

LV neutral

Bushing


Overhead Line Fed Indoor Transformers


Surge arrester

Insulator without protective gaps

Transformer

LV neutral

Surge arrester

Surge arrester

Insulator without protective gaps

Transformer

LV neutral

Surge arresterB

A

C

D

E

Maximum separation distances:

A – B: 1.0 meterA – E: 4.0 meterB – C: 0.4 meterC – D: 6.5 meter








HV/MV Substations IC

Transformer panel


Line entrance panel


HV/MV Substations IC• HV Overhead Line Entrance

Recommendations

– New substations• Tower footing resistance ≤ 30 Ω

(within 1km from the substation)• Installation of surge arrester• Surge arrester polymeric housing

– Existing substations• Same measures should be taken as

for new substations• Replace the spark gaps and install

surge arresters



HV/MV Substations IC• HV Transformer Panel

– New Substations according 2006 HV/MV substations type project


d

d2

d1+d

v S

Ures

LIWVA

d2

d1+d

v S

Ures

LIWV

Initial distances in EDP’s type project 2006:d1+d = 2,12 mdA = 1,26 md2 = 3,36 m


HV/MV Substations IC• HV Transformer Protection

– Existing installations• Remove spark gaps• Apply whenever possible the protective distances of EDP

type-project• Lengths of connection leads should be short as possible • When is not possible to apply the type-project distances:


10Cable entrance

10Double circuit overhead line entrance to different panels

7Double circuit overhead line entrance to one panel

10One or more single circuit overhead lines

Maximum protective distance d+d1+dA+d2 [m]


HV/MV Substations IC• HV Cable Entrance

– Surge arresters installed at the overhead line to cable transition

– Surge arresters are not required on substation side

– The cable sheaths are earthed on both sides

– When problems arise the cable should be earthed on the substation side only. The cable sheath on the line side should be protected by a cable sheath arrester



HV/MV Substations IC• MV Cables in the Substation

– The sheaths of the cables between the switchgear and the transformers are earthed on the switchgear side

– The cable sheath on the transformer side is protected by a cable sheath arrester

– The sheaths of the cables between the switchgear and the auxiliary transformers, reactors and capacitor banks are earthed on both sides



HV/MV Substations IC• MV OH line entrance

– surge arresters at MV-line entrance• MV cable entrance

– cable length between the transition tower and the circuit breaker ≤ 110 m

– The cable sheaths are generally earthed on the substation side only

– The cable sheath on the line side should be protected by a cable sheath arrester



Conclusions• 2nd phase of the Insulation Coordination project was successfully completed

• Insulation Coordination Guidelines to be applied throughout the HV and MV networks

• Uniform insulation coordination philosophy throughout the whole system was achieved

• A training program given to targeting key people

• Key success factors– adopted methodology– effective leadership– fruitful collaboration of the EDP Group project partners (EDP Distribuição

and Labelec) together with KEMA.




Thank you for your attention

Documents

Prague, 8-11 June 2009 Insulation Coordination …...Prague, 8-11 June 2009 Insulation Coordination Best Practices Leading to Improving Continuity of Supply A. Herculano P. Nunes M.T