kenneth bengs, heidelberg, germany, june 2014 integrator ... · the demand for the quality and...

Integrator Partner Seminar 2014 Earth Fault protection in Medium Voltage networks

Kenneth Bengs, Heidelberg, Germany, June 2014

Earth Fault protection in Medium Voltage networks

Why will we spend time on this specific topic?

Earth faults are the most common fault types in MV

distribution networks

The demand for the quality and reliability of supply is

constantly rising

Market trends set new requirements

Earth fault protection can be a challenging area

Introduction

June 25, 2014 | Slide 2

© ABB Group

Earth Fault protection in Medium Voltage networksEarthing methods in MV

June 25, 2014 | Slide 3

© ABB Group

HV MV HV MV

HV MV HV MV

EFFECTIVELY EARTHED

COMPENSATED NETWORK, PETERSEN COIL

UNEARTHED, ISOLATED

LOW IMPEDANCE EARTHED


The earthing method is the most dominant parameter that

determines the behavior of power system during a phase to

earth fault

Earthing methods in MV

June 25, 2014 | Slide 4

© ABB Group

ParameterEarthing Method

Effectively Low impedance Compensated Unearthed

Countries

Overvoltage No No Yes Yes

Fault current High Limited Low Low

Self-clearing

arc

No No Yes Yes/No

Earth Fault protection in Medium Voltage networksBenefits of compensated system

June 25, 2014 | Slide 5

© ABB Group



Overvoltages No No Yes Yes


Self-clearing arc No No Yes Yes/No

Earth Fault protection in Medium Voltage networksBenefits of compensated system

L1

L2

L3IRES

IRES = Residual current

IL

IC IC

CO

IL

Petersen coil earthing has become

increasingly popular in MV-networks

The inductive current of the coil

reduces the capacitive fault current:

Earth-fault current is reduced

90…95%

Self-extinguishing of arcing

faults

Network operation possible during a

sustained earth fault

Faulty line section should be found

and isolated quickly, risk for more

serious faults


Regulatory authorities define targets for the continutiy of

power supply and availability of electricity for consumers

Climate change impact, e.g. in Nordic countries during last

years there has been storms leaving some consumers

without electricity for days

Distribution System Operators (DSOs) replace

overhead lines with cables and also new installations

are with cables

Change from unearthed to compensated networks is a

trend

Reduces earth fault currents -> less touch voltages ->

enables network operation during a sustained earth

fault (national regulations to be followed)

Less autoreclosings, self extinguishing of fault arcs

Trends

June 25, 2014 | Slide 7

© ABB Group

Earth Fault protection in Medium Voltage networksMV network earthing in Europe

June 25, 2014 | Slide 8

© ABB Group

No Data

No preference

Unearthed neutral

Compensated neutral without fault disconnection

Compensated neutral without fault disconnection or unearthed neutral

Compensated neutral with/without fault disconnection

Unearthed neutral or low-ohmic neutral

Compensated neutral without fault disconnection or low-ohmic neutral

Compensated neutral with fault disconnection or unearthed neutral

Compensated neutral with fault disconnection

Compensated neutral with fault disconnection or low-ohmic neutral

Low-ohmic neutralSource: Connor, STE2011 - Arten der sternpunktbehandlung in

Europa



Overvoltage No No Yes Yes


Self-clearing arc No No Yes Yes*

EF protection Easy Easy Challenging Medium

Specific

problems

Intermittent

earth faults with

cables

Ferro-

resonance

Earth Fault protection in Medium Voltage networksEarthing methods impact on E/F protection

June 25, 2014 | Slide 9

© ABB Group

Earth Fault protection in Medium Voltage networksNeed for dedicated protection

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

3I0

Uo

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Compensation delivers operational

benefits, but earth-fault protection

becomes more complex

Low fault currents

Restriking earth-faults

Risk of unselective operation

Risk of disconnection of an entire

primary substation

Need for a dedicated protection

function

June 25, 2014 | Slide 10

© ABB

June 25, 2014

© ABB


Residual

voltage Uo

Io faulty

feeder

Io healthy

feeder

Traditional solution – Wischer principle

”Wisher relay” compares the

polarities of earth fault transients

Challenges:

• Requires special

hardware

• Variation of transient

magnitude and frequency

• Disturbances in transients

Need for new and improved

solution

Earth Fault protection in Medium Voltage networksNew digital solution - overview

June 25, 2014 | Slide 12

© ABB

Patented algorithm

Latest developments in

protection algorithm design

Sophisticated filtering

techniques

Sensitive transient detection

Selective operation

Cost effective solution

Transient

detector

General

fault

detection

Uo>

Directional

evaluation

Current

magnitude

supervision

TR

IP L

OG

IC

START

OPERATE

BLOCK_EF

Io

Uo

PROTECTION FUNCTION

INTRPTEF

Earth Fault protection in Medium Voltage networksNew digital solution - performance validation

June 25, 2014 | Slide 13

© ABB

Extensively tested with actual

disturbance recordings

Wide variation of network and

fault conditions

Validated operation with high-

security and dependability

The results confirm that with

the novel algorithm, high-

security and dependability

requirements of the protection

scheme can be met!

New digital earth fault protection improves reliabilityNew digital solution - performance validation

June 25, 2014 | Slide 14

© ABB

0.5 1 1.5 2 2.5-20

0

20

40RESIDUAL VOLTAGE U0

kV

, p

rim

0.5 1 1.5 2 2.5-200

0

200

400

600RESIDUAL CURRENT 3I0

Time (sec.)

A, p

rim

0.5 1 1.5 2 2.5

BINARY SIGNALS

Time (sec.)

BlkEF_Intrptf

Op_Intrptef

St_Intrptef

0.5 1 1.5 2 2.5-20

-10

0

10

20

30RESIDUAL VOLTAGE U0

kV

, p

rim

0.5 1 1.5 2 2.5-60

-40

-20

0

20

40RESIDUAL CURRENT 3I0

Time (sec.)

A, p

rim

0.5 1 1.5 2 2.5

BINARY SIGNALS

Time (sec.)

BlkEF_Intrptf

Op_Intrptef

St_Intrptef

TEST NUMBER:104

FAULTY FEEDER HEALTHY FEEDER

DETECTED

AS FAULTY

TRIPPED DETECTED

AS HEALTHY

Earth Fault protection in Medium Voltage networksNew digital solution-Summary

June 25, 2014 | Slide 15

© ABB

The new algorithm

Highly robust and selective fault

detection during restriking and

transient earth faults

Sensitive, detects the smallest

current spikes occuring during a

restriking earth fault in today’s

extensive cable networks

Early detection of an intermittent

fault prevents it from evolving into a

more serious malfunction

This new digital approach to earth

fault protection facilitates this in a

simple and cost-effective way

Earth Fault protection in Medium Voltage networksProtection methods and functions

3I0, U0

Current based (3I0)

Power based (Po)

Admittance based (Yo)

Transient based

Io, Iocos, Iosin, ph angle

(EFxPTOC, DEFxPDEF)

Wattmetric/Varmetric

(WPWDE)

Neutral admittance

(EFPADM)

Intermittent/transient

(INTRPTEF)

f=50Hz

f>>50Hz

Harmonics basedf=n*50Hz

Harmonic based

(HAEFPTOC)

Earth Fault protection in Medium Voltage networksSolution

No matter of the earthing method or earth fault type, easy or

demanding

We have the solution with 615, 620 and 630 series with the

appropriate protection functions needed

kenneth bengs, heidelberg, germany, june 2014 integrator ... · the demand for the quality and...

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