fault location system for radial mv underground...

Fault Location System for Radial MV Underground Distribution Cable Networks

71st Texas A&M University Relay Conference

Lifeng YangABB Inc.

Lake Mary, FL



What issues faced with cable fault localization?▪ Conventional fault location technique such as distance based approach might not work due to the

unique characteristic of cable fault current.▪ Not visually accessible (buried underground or in conduit) .

Aim of this paper▪ Introduce the cable fault detection technique.▪ Present faulty cable branch localization system.

Water

Zs xZl (1-x)Zl

Zld

CB

Relay



What is cable fault?▪ Short duration▪ Self clearing▪ Relatively high magnitude



Field recorded data:



Approaches published to deal with cable fault current:• Travelling wave• Transient signal analysis• Wavelets analysis• Neuro net• Short window DFT• Etc.



Cable Fault Detection Function:• Short window DFT based (as result from the DOE

research project)• Separate Phase and ground • Pickups can be fixed setting or adapt to load• Able to detect as short as a quarter cycle pulse• Intend to identify early stage of faulty cable to avoid

unplanned power outage• Field proved technology• Wont indicate fault location

Cable Fault Detection

Inputs:Ph & Gnd currentsBreaker position

Outputs:CFD indicationCFD counts



M1 M2

TIE1

DG Load

Source 1 Source 2

Motor

MT1

Motor

MT2

Load Load Load

F1F2

F3F4

F5

N.O.

Typical Simple MV Cable Network Configuration

▪ A fault occurs downstream F3, multiple relays upstream could also seethe fault▪ Need not only to detect the fault but

identify the faulty branch



Local tier

neighborhood tier

Fault Branch Localization strategy:

▪ Divide and conquer from bottom up

▪ Three tiers system: Local, Neighborhood and Central

▪ Local decision reports to neighborhood, and neighborhood reports to central

Laptop

Ethernet Switch

IEC 61850 8-1 Laptop

Ethernet Switch

IEC 61850 8-1



Neighborhood Tiers

Central Tier

Load Load

F1 F2 F3 F4

Ethernet Switch

Laptop

PCM600

Relay

Non-

Conventional

VT/CT

B1

Load Load



Local Tier

▪ Radial ▪ Close to load▪ Lowest in the hierarchy ▪ Master processing unit on top branch▪ GOOSE communication

GOOSE



Local Tier Implementation:

▪ Five inputs on left are the cable fault indications from the relays (four feeders and one branch)

▪ Five outputs on top are the faulty branch indications.

▪ Output on right indicates whether the fault is within this local tier .

B1 FI

F1 FI

F2 FI

F3 FI

F4 FI

B1_F F1_F F2_F F3_F F4_F

B1_FT

M1 M2

TIE1

DG

Source 1 Source 2

Motor

MT1

Motor

MT2

N.O.

B1 B2DG



Neighborhood Tier

▪ May not a simple STAR formation dependent on tie breaker position.

▪ Contain some local tiers.▪ Mid level in the hierarchy ▪ Master processing unit can be any of

main branches and tie breaker. For redundancy, can be implemented on both main branches.

▪ GOOSE communication

Local TierLocal Tier



Neighborhood Tier Implementation:

▪ Inputs on left are the cable fault indications from the relays (local tiers, DG, Motor loads, Mains and tie breaker)

▪ Outputs on top are the faulty branch indications for each breaker involved.

▪ …

B1_FT

MT1_FT

B2_FT

MT2_FT

DG_FT

B1_F MT1_F DG_F B2_F MT2_F

M1 FI

T1 Close

M2 FI

M1_F M2_F



Neighborhood Tier Implementation:

▪ Fault indication within this neighborhood tier .

B1_FT

MT1_FT

B2_FT

MT2_FT

DG_FT

B1_F MT1_F DG_F B2_F MT2_F

M1 FPI

T1 Close

M2 FPI

M1_F M2_F

NH1_F



Conclusions:

▪ Faulty cable branch can be identified with a hierarchy fault location system.▪ Local and neighborhood tiers can be implemented on the existing relay that has

user configurable logic gates.▪ Logic needed is relatively simple and easy to implement.▪ Logic can be easily scaled up or down according to the network topology.▪ No extra cost.▪ Faulty cable branch can be immediately identified once a cable fault is detected

in the tiers.▪ No need to manually determine the faulty branch, save time and money.▪ Early faulty cable branch identification to avoid unplanned power outage,

reducing down time and increasing power distribution network reliability.▪ The fault location system presented here can be used for generic fault

localization.

fault location system for radial mv underground...

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