Relay Coordination

(1)

Koordinasi Arus Lebih

Pada Jaringan Radial

Dr. Ir. Redy Mardiana

Laboratorium Teknik Tegangan dan Arus Tinggi Sekolah Teknik Elektro dan Informatika

Institut Teknologi Bandung

Radial System

• R

₁

provides primary protection to line 1

• R

₂

provides primary protection to line 2 & remote

backup for line 1

• Farthest relay from the source is set first

• Relays located on source side of the line

– Trip direction towards the line

(2)

Dr.Ir. Redy Mardiana - STEI ITB

Time-Current

Characteristic of

overcurrent relay

PSM = Pickup Setting Multiplier (know also as Plug Setting Multiplier)

Primary current (fault current) Primary seting current (pickup) = F PU PSM I I =

Pickup can be changed using Tap I_PU=I_TAP

Inverse Characteristic

Adjustable Setting of Inverse Relay

• Time Dial Setting (TDS) also

known as Time Multiplier Setting

(TMS)

– To set relay operating time

• Pickup Current which relate to

Pickup Setting Multiplier (PSM)

(also known as Plug Multiplier

Setting)

– To set pickup current for relay to

(3)

Time Multiplier Setting (TMS)

m

T

TDS

T

=

T = the required time of operation

T_m= the time obtained from the relay characteristic curve at TDS = 1.0

Example: If the time obtained from relay characteristic curve (TDS=1.0) is 4.0 , while the required time to operate the relay is 0.4s , then TDS is set to 0.4/4.0 = 0,1.

Pickup Setting Multiplier (PSM)

Primary Current (Fault Current)

Primary setting current (pickup)

Primary Current (Fault Current)

Relay current setting CT Ratio

F PU

I

PSM

I

=

×

Example: If fault current I_F is 3000A and primary pickup current is 200A, then PSM = 3000/200=15. If the installed CT has a ratio of 400/5 then the relay current setting is 200 x 5/400 = 2.5A. (or the relay tap = 2.5A)

3000

15

200 2.5 (400 / 5)

PSM

=

×

* Pickup current sometimes refers to relay current setting if it is seen from secondary side of CT

(4)

To determine Pickup and Time Dial

setting of Time Overcurrent R

₁

• Determine minimum fault current

(I

_F-MIN

) and full load current (I

_FL

)

• Determine primary pickup I

_PU

I

_FL

< I

_PU

< I

_F-MIN

• Determine relay current setting

(= I

_PU

/CTR)

– Relay current setting also

known as pickup current at

secondary side

• TDS is set at the lowest value

(e.g. 0.5)

– No coordination is necessary

for R

₁ 3 3 3

1.3

3 ;

2

3

0.33 1.3 2 2

F MIN FL PU F MIN FL PU

I

<

=

<

=

× ×

Handbook recommendation, the effect of arc resistance has been considered

Coordination for all

currents is done at

maximum multiple of

pickup. It is achieved at

I

_F-MAX

1. Calculate I

_PU

2. Calculate I

_F-MAX

3. Calculate PSM

4. Set TDS at 0.5 (the

lowest)

5. Determine time from

curves (=t

_OP-R1

)

To determine Pickup and Time Dial

(5)

t

_OP-R2

' t

_OP-R1

+ t

_CTI

– t_CTIis the coordinating time interval (known as time margin) – t_B1is the CB time to operate – t_OTis the over-travel time – t_SFis safety factor

1. Choose t

_CTI

and calculate t

_OP-R2

2. Calculate I

_PU

3. Calculate I

_F-MAX

(at closest to

R

₁

)

4. Calculate PSM

5. Determine TDS time from

curves

To determine Pickup and Time Dial

setting of Time Overcurrent R

₂

Coordinating Time Interval (CTI)

The CTI Consists of:

1. CB fault-interruption or fault-clearing time, typically 2–8 cycles

(0.033–0.133 sec).

2. Relay overtravel time: The energy stored in the electromechanical

induction disk or solid-state circuitry will continue operation after

the initiating energy is removed. Typically, this is not more than

0.03–0.06 sec for electromechanical units; less, but not zero, for

solid-state units.

3. Safety factor (safety margin) for errors or difference s in

equipment-operating time, fault current magnitudes , CT ratios, and so on.

The CTI values frequently used in relay coordination range

between 0.2 and 0.5 sec, depending on the degree of confidence

or the conservatism of the protection engineer—0.3 sec, is the

frequently used CTI value.

(6)

Selection of Time Characteristic

• Inverse

– used when IF is dependent on generation – not fault location • Very Inverse

– used when I_Fis dependent on fault location

– used when I_Findependent of normal changes in generating capacity

• Extremely Inverse

– used when I_Fis dependent on fault location

– used when I_Findependent of normal changes in generating capacity

– Ease coordinates with fuses and reclosers

Relay Characteristics Equations

• Inverse Time

• Very Inverse Time

• Extremely Inverse Time

• IDMT (Inverse Definite

Minimum Time)

(

)

10

3 log

T

TDS

PSM

=

×

0.02

0.14

1 T

TDS

PSM

=

×

13.6

1 T

TDS

PSM

=

×

2

80

1 T

TDS

PSM

=

×

(7)

Persamaan Karakteristik Rele

(8)

Combination Inverse and Instantaneous

• Upstream relay has longer t

_OP

than downstream relay

• Very undesirable – for the fault closes to the source, I

_F

will be very large but the relay operating time is longer.

This will damages the equipment (the source)

• Combine inverse and instantaneous overcurrent relay to

reduce fault clearing time

Reduction of Operating Times With

Instantaneous Overcurrent Relays

• The most significant reduction in operating time

is on line section 4

• Instantaneous relay provides primary protection

mainly for close-in faults

(9)

Instantaneous Overcurrent Relays (IOC)

• Use to reduce fault clearing times

• Provide no backup protection

• IOC relay must NEVER operate for faults beyond line

section end

• Setting Pickup for IOC:

3

(at F1)

1.25

1.5

PU MAX

I

k I

k

= ×

F1 is the closest to R1

RELE ARUS LEBIH

Pengaman Hubung Singkat

Relai dialiri oleh Arus Fasa, Tetapi Juga Dialiri

oleh Arus Beban, maka I

_set

> I

_beban

Cara 1

R S T

Cara 2

R S T

(10)

RELE ARUS LEBIH

Pengaman Hubung Singkat 1 Fasa Ketanah

Arus gangguan (1 fasa ketanah) < (arus beban max.), karena :

- Gangguan lewat tahanan gangguan

- Pentanahan Netral Lewat Impedansi

Oleh sebab itu relai gangguan tanah tidak dipasang di arus

fasa tetapi mengambil arus residu dari arus ke tiga fasa.

Cara 1

R S T OC OC GF

Cara 2

R S T OC OC OC GF

*Setting pickup ground fault relay jauh lebih rendah dari overcurrent.

Residual Earth Fault Relays

• There are two types:

– Residual Current Relay (also known as zero

sequence current relay)

– Residual Voltage Relay (also known as zero

sequence voltage relay)

• Residual current and voltage only exists

when a fault current flows to earth,

• Need to coordinate with similar relays

downstream.

(11)

Residual Earth Fault Relays

Residual Current Relay

• Commonly used for :

– Solidly grounding system – Low resistance grounding

system.

• Current flowing on relay is

quite high due to solidly or

low resistance groundings.

• Rarely used for high

resistance grounding system.

• Fault current is higher

compared to ungrounded or

high resistance grounding

systems.

a) Single ground relay

b) Combine ground and 3

phase relays

c)

Combine ground and 2

phase relays

Residual earth fault

(EF) connection:

Configuration (c) consists of two phases since these will detect any interphase fault; the connections to the earth-fault relay are unaffected by this

consideration.

The typical settings for earth-fault relays are 30%-40% of the full-load current or minimum earth-fault current on the part of the system being protected.