ABB ArcLimiter Benutzerhandbuch

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TECHNICAL AND APPLICATION GUIDE

ArcLimiterTM

Arc flash mitigation solution for low

voltage equipment using UFES (ultra-

fast earthing switch)

2ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES

—

Many industries are facing internal

or external deadlines to implement

arc flash (AF) mitigation solutions

within their facilities. ABB now

offers ArcLimiterTM, an arc flash

mitigation solution that is unique

in the industry. It solves the LV arc

flash problem at the MV or LV

system level.

TECHNICAL AND APPLICATION GUIDE 3

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Table of contents

004 – 005 Introduction

006 Solidly grounded MV systems

007 – 008 Low resistance/grounded MV

systems

009 – 010 High resistance/grounded MV

systems

011 – 012 Ungrounded Delta MV systems

013 Summary of ArcLimiterTM solution

application scenarios

014 MV-LV transformers fed by MV

breaker

015 ArcLimiterTM solution application

at LV system level

016 Available UFES ratings

4ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES

Abbreviations used in this document

AF: arc flash

AWG: American Wire Gage

CLF: current limiting fuse

FLA: full load amperes

LV: low voltage

MV: medium voltage

PSE: primary switching element

QRU: quick release unit (of the UFES)

REA: ABB’s dedicated arc flash detection relay

SCC: short circuit capacity

SUS: secondary unit sub, MV-LV

51G: AC inverse time earth overcurrent relay

(residual method)

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This solution is appropriate for:

- Light and heavy industrial

- Commercial facilities

- Educational campuses

- Any facility applying primary

loop fed transformers with

fused MV switches (36 kV

limit), new or existing applica-

tions

- Facilities having MV to LV

transformers in the range of

750 KVA – 5000 KVA

To prove this solution concept, tests were per-

formed at a third-party test laboratory. During an

actual LV arc flash event (performed per IEEE

C37.20.7), the REA detected and responded to the

AF event, sending a closing signal to the UFES.

The REA is advertised to detect and close its out-

put trip contact within 2.5 milliseconds (ms). With

the current setting at 1.5x the CT primary rating

and the light detection adjustment at mid-range,

this third-party test proved the REA responded

within 1 ms.

This response placed negligible voltage on the

transformer primary, extinguishing the LV arc

flash quickly (approximately 4 ms). Test results in-

dicate the incident energy level peak was 0.5 cal/

cm2, which is well below the AF threshold of 1.2

cal/cm2, where PPE is required.

A note on the CLF application is in order. A fuse

will become current limiting when the magnitude

of amperes through it is large enough to fully in-

terrupt in ¼ cycle or less, i.e., the fault waveform’s

peak is never reached. In general, for each appli-

cation with an applied UFES and MV E rated fuse,

the applying engineer needs to obtain the SCC (in

amperes) available at the upstream MV BUS. The

MV E rated fuse will reach its current limiting

threshold (¼ cycle interruption) when the ratio of

SCC to fuse full load ampere rating is 25 times at

a minimum. If the ratio is less than 25, the fuse

will take many cycles to fully interrupt. With the

UFES closed, the MV BUS is now at zero volts,

negatively impacting plant operations.

—

ArcLimiterTM

Introduction

Many industries are facing internal or external deadlines to implement

arc flash (AF) mitigation solutions within their facilities. ABB now

offers ArcLimiterTM, an arc flash mitigation solution that is unique in

the industry. It solves the LV AF problem at the MV or LV system level.

Many industries have internal distribution system configurations as

shown in Figure 1. The REA and UFES are ABB product additions to

this typical configuration that comprise the ArcLimiter AF mitigation

solution.

UFES

MV “E” RATED FUSE

MV BUS

OIL or DT

XFMR

LV EQUIPMENT

MV SWITCH

(normally closed)

REA

BONDING JUMPER

TECHNICAL AND APPLICATION GUIDE 5

LV starters can drop out while we are waiting for full

fuse interruption. The CLF interruption time deter-

mines when the MV BUS returns to nominal operat-

ing voltage.

Consider the following two examples for illustration

(in either case, the LV AF problem is solved equally

well):

• System SCC= 10,000A; CLF is a 150E; ratio of the

SCC to the fuse FLA rating is 67. Fuse will inter-

rupt in ¼ cycle. Operations should not be im-

pacted.

• System SCC= 4,600A; CLF is a 200E; ratio is 23.

Fuse will interrupt in cycles. Operations could be

impacted and the plant needs to be informed up-

front.

—

01 Internal distribution

system configuration

Post testing analysis revealed that MV system

grounding has an impact on overall system behavior

in case of an AF and applying a UFES. This applica-

tion note addresses system grounding configura-

tions and how to technically apply the UFES, mini-

mizing any reliability issues for customers’ plants.

Each MV grounding method is addressed.

UFES

MV “E” RATED FUSE

MV BUS

OIL or DT

XFMR

LV EQUIPMENT

MV SWITCH

(normally closed)

REA

BONDING JUMPER

6ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES

On a solidly grounded MV system, shown in Figure

2, the ArcLimiter application for LV AF mitigation is

proven very effective by test. The UFES closes all

three phases to ground simultaneously with some

minor contact bounce. At this point, the LV AF is

over.

Depending upon UFES closing time and phase se-

quence, phases A and B fuses melt in 1 ms (MV sys-

tem voltage recovery starts) with full CLF interrup-

tion by 1.5-2 ms. The actual CLF interrupting time is

dependent upon the MV system fault availability

(many times referred to as SCC). The higher the

SCC, the faster the CLF interruption, the shorter du-

ration of the fault induced voltage dip, the less im-

pact on other on-going operations.

When phases A and B CLF fully interrupt, the entire

phase C current briefly appears as a zero sequence

current on the traces. The only path for fault current

is through the phase C fuse, to UFES phase C PSE,

to transformer grounded neutral. Since there is no

impedance in that path, the fault current flow is

high, only limited by the transformer’s short circuit

impedance.

Since phase C is delayed by 120 degrees, about 5

ms (assuming a 60 Hz system), in order for the

phase C fuse to melt, those amps will not flow via

phases A and B fuses, which are already open, but

back to the source neutral. The UFES to ground

bonding jumper can be small thermally, approxi-

mately #2 AWG, since it only has to carry current for

5 ms.

Upon UFES operation, all three fuses should be re-

placed, since the phase C fuse may be damaged by

microsecond internal arcing, along with all three

PSEs.

—

Solidly grounded MV systems

On a solidly grounded MV system, the ArcLimiter application for LV arc

flash mitigation is proven very effective by test.

—

02 solidly grounded

MV system

—

UFES

MV “E” RATED FUSE

MV BUS

OIL or DT

XFMR

LV EQUIPMENT

MV SWITCH

(normally closed)

REA

51G

BONDING JUMPER

UFES: 3 PSEs

(CLOSED)

MV “E” RATED FUSES

MV BUS (3 PHASE)

OIL or DT

XFMR

LV EQUIPMENT

(3 PHASE)

MV SWITCH

(normally closed)

REA

BONDING

JUMPER

51G-2

51G-1

GROUND

FAULT

PATH

TECHNICAL AND APPLICATION GUIDE 7

If the MV system is not solidly grounded, but low

resistance neutral grounded (Figure 3) the applica-

tion of the ArcLimiter solution needs to change.

The UFES closes all three phases to ground, simul-

taneously, when triggered. At this point, the LV AF

is essentially over.

Depending upon UFES closing time and phase se-

quence, phase A and B fuses melt in 1 ms (MV sys-

tem voltage recovery starts) with full CLF interrup-

tion by 1.5-2 ms (SCC dependent). When phase A

and B CLF clear, the entire phase C current appears

as a zero sequence current on the test traces. There

is a large reduction in phase C fault current once

phases A and B CLF open.

The only path for fault current is through the phase

C fuse, to UFES phase C PSE, to the transformer’s

neutral, but is now limited by the source neutral re-

turn path’s resistance (Figure 4).

—

Low resistance/grounded MV

systems

If the MV system is not solidly grounded, but low resistance neutral

grounded, the application of the ArcLimiter solution needs to change.

—

03 MV system is not

solidly grounded,

but low resistance

neutral grounded

—

04 Path for fault current

is through the phase C

fuse, to UFES phase C

PSE, to the transformer’s

neutral, but is now lim-

ited by the source neutral

return path’s resistance

—

8ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES

Typically, in industrial plants, that ground fault

value can be limited to 200-600 A and in power

plants up to 1200 A. Phase C could remain energized

to the transformer primary for an extended time

and since most of the plant’s SUS are delta-wye, all

three transformer phases have the same evenly ap-

plied potential. Since there is no potential differ-

ence between the delta windings, there is no cur-

rent flow, therefore, there is no induction to

generate secondary potential. With no supporting

secondary potential, the LV AF collapses in micro-

seconds.

However, a sustained bolted line-to-ground phase C

fault on a low resistance grounded system will be

detected and tripped by the upstream 51G-1 or

51G-2 protection relay “x” seconds later. Review the

ground return path in Figure 4. This action shuts

down the entire MV BUS resulting in poor reliability

for customers’ plants. The 51G-1 or 51G-2 will be

faster than a sustained high ground fault value (say

1200 A) through the CLF.

To prevent this reliability issue, the MV SWITCH

should be installed (or retrofitted) with a shunt trip

activated by one of the QRU1’s trip out contacts

Phase A and B CLF will still interrupt in about the

same timeframe, about 1-2 ms, since they are in se-

ries through the closed PSEs. Phase C may not in-

terrupt. The upstream 51G-1 or 51G-2 will not see

ground current within its pick up range.

Upon UFES operation, all three fuses should be re-

placed, since the phase C fuse may be damaged by

microsecond internal arcing, along with the three

PSEs. The UFES to ground bonding jumper can be

small thermally, approximately #2 AWG, since it only

has to carry current for 5 ms.

—

Low resistance/grounded MV

systems

UFES

MV “E” RATED FUSE

MV BUS

OIL or DT

XFMR

LV EQUIPMENT

MV SWITCH

(normally closed)

REA

10A

BONDING JUMPER

UFES: 3 PSEs

(CLOSED)

MV “E” RATED FUSES

MV BUS (3 PHASE)

OIL or DT

XFMR

LV EQUIPMENT

(3 PHASE)

MV SWITCH

(normally closed)

REA

BONDING

JUMPER

GROUND

FAULT

PATH

HIGH RESISTANCE

TECHNICAL AND APPLICATION GUIDE 9

If the MV system is high resistance neutral

grounded (Figure 5) the application of the Ar-

cLimiter solution needs to change. These types of

systems are typically applied in older industrial

plants, feeding a process. A single line to ground

fault does not cause major damage and the MV

switchgear breakers usually do not have ground

fault protection. Indications of a ground fault are

usually detected via installed voltmeters. The oper-

ating process continues as a plant benefit.

The UFES closes all three phases to ground simulta-

neously. At this point, the LV AF is essentially over.

Depending upon UFES closing time and phase se-

quence, phase A and B CLF melt in 1 ms (MV voltage

system recovery starts) with full CLF interruption

by 1.5-2 ms (SCC dependent). When phases A and B

CLF clear, the entire phase C current (now very lim-

ited) appears as a zero sequence current.

The only path for fault current is through the phase

C CLF to UFES phase C PSE to transformer’s neu-

tral, but is now very limited by the source neutral

return path’s resistance (Figure 6).

—

High resistance/grounded MV

systems

If the MV system is high resistance neutral grounded, the application of

the ArcLimiter solution needs to change.

—

05 MV system is

high resistance

neutral grounded

—

06 Path for fault current

is through the phase C

CLF to UFES phase C PSE

to transformer’s neutral,

but is now very limited

by the source neutral

return path’s resistance

—

10 ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES

Typically, in industrial plants, the maximum high im-

pedence ground fault current flow value is limited

to 10 A. Phase C could remain energized to the

transformer primary for an extended time and,

since most of the plant’s SUS are delta-wye, all

three transformer phases have the same equally ap-

plied potential. Since there is no potential differ-

ence between the delta windings, there is no cur-

rent flow, therefore, there is no induction to

generate secondary potential. With no supporting

secondary potential, the LV AF collapses in micro-

seconds.

However, having a sustained bolted line-to-ground

phase C 10 A fault will activate the plant’s ground

fault alarm system. Maintenance would be chasing

the wrong problem. To prevent this nuisance alarm,

the MV SWITCH should be installed (or retrofitted)

with a shunt trip activated by one of the QRU1’s trip

out contacts.

Two of the CLFs will still interrupt in about the same

timeframe, about 1-2 ms, Phase C CLF may not in-

terrupt. This prevents the false ground fault alarms.

Upon UFES operation, all three fuses should be re-

placed, since the phase C fuse may be damaged by

microsecond internal arcing, along with the three

PSEs. The UFES to ground bonding jumper can be

small, approximately #2 AWG, thermally, since it

only has to carry current for 5 ms.

—

High resistance/grounded MV

systems

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