Non-Dir. Overcurrent APPS ALSTOM

7/26/2019 Non-Dir. Overcurrent APPS ALSTOM

1/65

GRID

Technical Institute

This document is the exclusive property of Alstom Grid and shall not betransmitted by any means, copied, reproduced or modified without the prior

written consent of Alstom Grid Technical Institute. All rights reserved.

Non-Direct ion al Overcurrent

and Earth Fault Protec t ion


2/65

> Non-Directional Overcurrent and Earth Fault Protection2

Overcurrent Protect ion: Purpose of Protect ion

Detect abnormal conditions

Isolate faulty part of the system

Speed

Fast operation to minimise damage and danger

Discrimination

Isolate only the faulty section

Dependability / reliability

Security / stability

Cost of protection / against cost of potential hazards


3/65


Overcu rrent Protect ion Co-ord inat ion

F3

2

1

Co-ordinate protection so that relay nearest to fault

operates first

Minimise system disruption due to the fault


4/65


Fuses


5/65


Overcu rrent Protect ion Fuses

Simple

Can provide very fast fault clearance


6/65


Overcu rrent Protect ion Fuses - disadvantages

Problematic co-ordination

IFAapprox 2 x IFB

Limited sensitivity to earth faults

Single phasing

Fixed characteristic

Need replacing following fault clearance

Fuse A Fuse B


7/65> Non-Directional Overcurrent and Earth Fault Protection7

Tr ipp ing Methods



Overcu rrent Protect ion Direct Act ing AC Trip

AC series trip

common for electromechanical O/C relays

51

IF

Trip Coil



Overcu rrent Protect ion Direct Act ing AC Trip

Capacitor discharge trip

used with static relays where no secure DC supply is

available

IF'

SensitiveTrip

Coil

51

+

-

IF



Overcu rrent Protect ion DC Shun t Trip

Requires secure DC auxiliary

No trip if DC fails

IF'

DCBATTERY

SHUNTTRIP COIL

51

IF



No Volt Trip Coil: Relay Un-Operated

Used for fail-safe tripping on motor feeders

No Volt

ReleaseTrip Coil

51

V



No Volt Trip Coil: Relay Operated

Used for fail-safe tripping on motor feeders

No Volt

ReleaseTrip Coil

51

V

IF

IF'



Overcurrent Protect ion



Overcu rrent Protect ion Principles

Operating Speed

Instantaneous

Time delayed

DiscriminationCurrent setting

Time setting

Current and time

Cost

Generally cheapest form of protection relay



Overcu rrent Protect ion Ins tantaneous Relays

Current settings chosen so that relay closest to fault

operates

Problem

Relies on there being a difference in fault level between the

two relay locations

Cannot discriminate if IF1= IF2

IF1IF250

B

50

A

IF2 IF1



Overcur rent Protect ion Definite (Independent)

Time Relays

TOP

TIME

IS Applied Current

(Relay Current Setting)



Overcur rent Protect ion Definite (Independent)

Time Relays

Operating time is independent of current

Relay closest to fault has shortest operating time

Problem

Longest operating time is at the source where fault level is

highest

51

0.9 sec 0.5 sec

5151

0.9 sec 0.5 sec

51



Overcu rrent Pro tect ion IDMT

TIME

Applied Current(Relay Current Setting)

IS

Inverse Definite Minimum Time characteristic



Overcu rrent Protect ion Disc Type O/C Relays

Current setting via plug bridge

Time multiplier setting via disc

movement

Single characteristic

Consider 2 ph & EF or 3 ph plus

additional EF relay



Overcu rrent Protect ion Stat ic Relay

Electronic, multi characteristic

Fine settings, wide range

Integral instantaneous elements



Overcu rrent Protect ion Numerical Relay

Multiple characteristics and stages Current settings in primary or secondary values

Additional protection elements

Current

Time

I

>1

I>2

I>3

I>4



Co-ordinat ion


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Overcu rrent Protect ion Co-ordinat ion Princ iple

Relay closest to fault

must operate first

Other relays must have

adequate additional

operating time to

prevent them operating

Current setting chosen

to allow FLC

Consider worst caseconditions, operating

modes and current

flows

T

IS1IS2 MaximumFaultLevel

I

R2R1

IF1


24/65


Overcu rrent Protect ion Co-ordinat ion Example

C AB

0.01

0.1

1

10

Operatingtime(s)

Current (A) FLB FLC FLD

ED

C

B

DE C AB

0.01

0.1

1

10

Operatingtime(s)

Current (A) FLB FLC FLD

ED

C

B

DE


25/65


Overcu rrent Protect ion IEC Character ist ics

SI t = 0.14

(I0.02-1)

VI t = 13.5

(I2-1)

EI t = 80

(I2-1)

LTI t = 120(I- 1)

Current (Multiples of Is)

0.1

1

10

100

1000

1

1000

O

p

a

n

T

m

e

s

VI

EI

SI

LTI


26/65


Overcur rent Protect ion Operat ing Time Sett ing -

Terms Used

Relay operating times can be

calculated using relay

characteristic charts

Published characteristics are

drawn against a multiple of

current setting or Plug SettingMultiplier

Therefore characteristics can be

used for any application

regardless of actual relay

current setting

e.g at 10x setting (or PSM of 10)

SI curve op time is 3sCurrent (Multiples of Is)

0.1

1

10

100

1000

1

1000

O

p

a

n

T

m

e

s


27/65


Overcu rrent Protect ion Current Sett ing

Set just above full load currentallow 10% tolerance

Allow relay to reset if fault is cleared by downstream

device

consider pickup/drop off ratio (reset ratio)

relay must fully reset with full load current flowing

PU/DO for static/numerical = 95%

PU/DO for EM relay = 90%

e.g for numerical relay, Is = 1.1 x IFL/0.95


28/65


Overcu rrent Protect ion Current Sett ing

Current grading

ensure that if upstream relay has started downstream relay has

also started

Set upstream device current setting greater than downstream relay

e.g. IsR1 = 1.1 x IsR2

R1 R2 IF1


29/65


Overcu rrent Protect ion Grading Margin

Operating time difference between two devices to ensure

that downstream device will clear fault before upstream

device trips

Must include

breaker opening time

allowance for errors

relay overshoot time

safety margin

GRADING

MARGIN

O t P t t i G di M i


30/65


Overcu rrent Protect ion Grading Margin -

between relays

Traditional

breaker op time - 0.1

relay overshoot - 0.05

allow. For errors - 0.15

safety margin - 0.1

Total 0.4s

Calculate using formula

R2R1



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between relays

Formula

t = (2Er + Ect) t/100 + tcb + to + ts

Er = relay timing error

Ect = CT measurement error

t = op time of downstream relay

tcb = CB interupting time

to = relay overshoot time

ts = safety margin

Op time of Downstream Relay t = 0.5s

0.375s margin for EM relay, oil CB

0.24s margin for static relay, vacuum CB



32/65



relay w ith fuse

Grading Margin = 0.4Tf + 0.15s over whole characteristic

Assume fuse minimum operating time = 0.01s

Use EI or VI curve to grade with fuse

Current setting of relay should be 3-4 x rating of fuse to

ensure co-ordination

O erc rrent Protect ion Grading Margin


33/65



relay w i th upstream fuse

1.175Tr + 0.1 + 0.1 = 0.6Tf

or

Tf= 2Tr + 0.33s

Allowance for CTand relay error

CB Safety margin Allowance forfuse error (fast)

Tf

Tr

IFMAX

Overcu rrent Protect ion Time Mult ip l ier Setting


34/65


Overcu rrent Protect ion Time Mult ip l ier Setting

Used to adjust the

operating time of an

inverse characteristic

Not a time setting but a

multiplier

Calculate TMS to give

desired operating time

in accordance with the

grading margin

Current (Multiples of Is)

0.1

1

10

100

1

1000

O

p

a

n

T

m

e

s

Overcur rent Protect ion


35/65



Time Mult ip l ier Sett ing - Calculat ion

Calculate relay operating time required, Treq

consider grading margin

fault level

Calculate op time of inverse characteristic with

TMS = 1, T1

TMS = Treq/T1

Overcu rrent Protect ion Co ord inat ion Procedu re


36/65


Overcu rrent Protect ion Co-ord inat ion - Procedu re

Calculate required operating current

Calculate required grading margin

Calculate required operating time Select characteristic

Calculate required TMS

Draw characteristic, check grading over whole

curve

Grading curves should be drawn to a common

voltage base to aid comparison

Overcu rrent Protect ion Co ordinat ion Example


37/65



Grade relay B with relay A

Co-ordinate at max fault level seen by both

relays = 1400A

Assume grading margin of 0.4s

Is = 5 Amp; TMS = 0.05, SI

IFMAX= 1400 Amp

B A

200/5 100/5

Is = 5 Amp



38/65



Relay B is set to 200A primary, 5A secondary

Relay A set to 100A If (1400A) = PSM of 14

relay A OP time = t = 0.14 x TMS = 0.14 x 0.05 = 0.13(I0.02-1) (140.02-1)

Relay B Op time = 0.13 + grading margin = 0.13 + 0.4 = 0.53s

Relay A uses SI curve so relay B should also use SI curve

Is = 5 Amp; TMS = 0.05, SI

IFMAX= 1400 Amp

B A

200/5 100/5

Is = 5 Amp



39/65



Relay B Op time = 0.13 + grading margin = 0.13 + 0.4 = 0.53s

Relay A uses SI curve so relay B should also use SI curve

Relay B set to 200A If (1400A) = PSM of 7

relay B OP time TMS = 1 = 0.14 x TMS = 0.14 = 3.52s

(I0.02

-1) (70.02

-1) Required TMS = Required Op time = 0.53 = 0.15

Op time TMS=1 3.52

Set relay B to 200A, TMS = 0.15, SI

Is = 5 Amp; TMS = 0.05, SI

I

FMAX= 1400 Amp

B A

200/5 100/5

Is = 5 Amp



40/65



LV Protect ion Co -ord inat ion

Relay 1

Relay 2

Relay 3

Relay 4

Fuse

1

2

3

4

F

350MVA

4

3 3

2

F

11kV

MCGG CB

ACB CTZ61 (Open)TZ61

ACB

MCCB

27MVA

20MVA

oad

Fuse

2 x 1.5MVA

11kV/433V

5.1

K

1



41/65


O e cu e o ec o


1000S

100S

10S

1.0S

0.1S

0.01S

0. 1kA 10kA 1000kA

TX damage

Very

inverse



42/65



Relay 1

Relay 2

Relay 3

Relay 4

Fuse

1

2

3

4

F

350MVA

4

3 3

2

1

F

11kV

KCGG 142 CB

ACB (Open)CEG 142

ACB

MCCB

27MVA

20MVA

oad

Fuse

2 x 1.5MVA

11kV/433V

5.1

K



43/65



1000S

100S

10S

1.0S

0.1S

0.01S

0. 1kA

10kA

1000kA

TX damage

Long time

inverse


44/65


Block ing Schemes


45/65

> Non-Directional Overcurrent and Earth Fault Protection45 Manufacturers Technical Update Oct 2010 -

System Grading

Downstream protection must grade with the utility incomer at the maximum

fault level 11kV Supply

Load

LoadLoad

Metering CB(Utility)

0.7s

0.4s

1.0s

0.1s

??s

??s

??s

1.0s

1.0s

(2)Compromised

Grading

0.7s

0.7s

0.4s

0.4s

0.1s

(1)First

Attempt

Bl ki S h P i i l (2)


46/65


Blocking Schemes - Principles (2)

Incomer

IF2

IF

Blocking schemes eliminates grading time and will trip the CB after 100ms has elapsed, schemewill remove blocking signal should the CB fail to trip

Ideal application for GOOSE messaging over IEC61850

BLOCK for IF1


47/65


IEC61850 Architecture

Agile with

IEC61850


48/65


Delta/Star Trans fo rmers



49/65


Trans former Protection - 2-1-1 Fault Current

A phase-phase fault

on one side of

transformer produces

2-1-1 distribution on

other side

Use an overcurrent

element in each

phase (cover the 2x

phase)

2

& EF relays canbe used provided

fault current > 4x

setting

Iline

0.866If3

Turns Ratio=3 :1

Idelta



50/65



Istar= E-/2Xt = 3 E-n/2Xt

Istar= 0.866 E

-n/Xt

Istar= 0.866 If3

Idelta= Istar/3 = If3/2

Iline= If3

Iline

0.866 If3

TurnsRatio =3 :1

Idelta



51/65



Grade HV relaywith respect to

2-1-1 for -

fault

Not only at max

fault level

51

HV

/51

LV

If386.6%If3


52/65


Use of High Sets



53/65


Ins tantaneous Protect ion

Fast clearance of faults

ensure good operation factor, If>> Is (5 x ?)

Current setting must be co-ordinated to prevent

overtripping

Used to provide fast tripping on HV side of transformers

Used on feeders with Auto Reclose, prevents transient

faults becoming permanent

AR ensures healthy feeders are re-energised

Consider operation due to DC offset - transient overreach



54/65


Ins tantaneous OC on Trans form er Feeders

Set HV inst 130% IfLV

Stable for inrush

No operation for LV fault

Fast operation for HV fault

Reduces op times

required of upstream

relays

CURRENT

HV2 LVHV1

HV2

LVTIME HV1

IF(LV) IF(HV)

1.3IF(LV)

Overcu rrent Protect ion:


55/65


Trans ient Overreach

Ability to ignore DC offset

Low overreach allows los Inst setting to be used

high operation factor

Immunity to LV transformer faults



56/65


Trans ient Overreach

Overreach = (I1I2)/I2

Typical values

numerical relay = < 5%

Simple EM relay = >60%

Low overreach allows low

settinghigh operationfactor

High transient overreach

necessitates high settings

poor sensitivity, slow

I1

I1 = steady state rms pickup I2 = rms pickup with fully offset signal

I

2


ff


57/65


Part ial Differential Protect ion

Zoned busbarprotection usingovercurrent relays

Bus section relay notrequiredreducedgrading stages

Time delayed trippingfor busbar fault

67

51

67

51

51

51


I t l k d OC P t t i


58/65


Inter locked OC Protect ion

Problem due to location ofCTs

Feeder circuit fault seenoutside feeder zone butinside busbar zone

Fault remains fed fromremote end will be cleared byremote time delayedprotection

Speed up fault clearance withlocal Interlocked OC relayshort time delay enabled by

BB protection trip

Circuit

Protection

Busbar

Protection


59/65


Earth fau l t Protect ion


E th F lt P t t i


60/65


Earth Fault Protect ion

Earth fault current may be limited

Sensitivity and speed requirements may not be met by

overcurrent relays

Use dedicated EF protection relays

Connect to measure residual (zero sequence) current

Can be set to values less than full load current

Co-ordinate as for OC elements

May not be possible to provide co-ordination with fuses


E th F lt R l C t i 3 Wi S t


61/65


Earth Fault Relay Connect ion - 3 Wire System

Combined with OC relays Economise using 2x OC

relays

E/F OC OC OC E/F OC OC

Overcur rent Protect ionE th F lt R l C t i 4 Wi S t


62/65


Earth Fault Relay Connect ion - 4 Wire System

EF relay setting must begreater than normal

neutral current

Independent of neutralcurrent but must use 3 OC

relays for phase to neutral

faults

E/F OC OC OC E/F OC OC OC

Overcur rent Protect ionE th F lt R l C t S tt i


63/65


Earth Fault Relays Cur rent Sett ing

Solid earth

30% Ifull loadadequate

Resistance earth

setting w.r.t earth fault level

special considerations for

impedance earthing -

directional?

Overcur rent Protect ionSens it i e Earth Fa lt Rela s


64/65


Sens it ive Earth Fau lt Relays

Settings down to

0.2% possible

Isolated/high

impedance earth networks

For low settings cannot use residual connection, use

dedicated CT

Advisable to use core balance CT

CT ratio related to earth fault current not line current

Relays tuned to system frequency to reject 3rd harmonic

B

C

E/F

A

Overcur rent Protect ionCore Balance CT Connect ions


65/65

Core Balance CT Connect ions

Need to take care with core

balance CT and armoured

cables

Sheath acts as earth returnpath

Must account for earth

current path in connections

- insulate cable gland

NO OPERATION OPERATION

CABLE

BOX

CABLE GLAND

CABLE GLAND/SHEATHEARTH CONNECTION

E/F

INSULATION

Documents

Non-Dir. Overcurrent APPS ALSTOM