4_7UT6 low imp REF

(1)

s

Energy Automation

7UT6: Low impedance

Restricted Earth Fault

(2)

No. 1 with

Energy Automation

Internal single pole fault’s close to transformer star point

? ?

w1

w2

(1

f)

w2

f

I

;

R

X

f

3 /

U

f

I

;

L

?

X

FHV FLV 2 F 2 2 LV LV F

?

Example: Autotransformer 500MVA , 400/230kV, u

_k12

= 15.8%

Inductivity L

? winding

2

_{; R}

F

= fault resistance

Short circuited winding part f

I

F HV

[p.u. HV side]

I

_{F LV}

[p.u. LV side]

I

F tot

[p.u. LV side]

I

_F

[p.u.]

400kV 230kV

f

0 1 L2 L3

w2

w1

Trip F 2 Ftot F F 2 Ftot F

I

R

;

Energy

:

W

I

R

t

P

?

(3)

No. 1 with

Limits of the differential protection (1 of 2)

Earth fault current limited by R

_E

to I

_Emax

= 2000A ; R

_E

>> X

_Tr

?

1N 2N Emax 2 1N 2N F K Emax E 2N F

U

3 /

U

I

f

U

3 /

U

f

I

and

I

f

R

3 /

U

f

I

?

* *

?

* nO * K * K * K Elim D nO1 K * K nO2 F * F 2 K F

I/I

0.222 I/I

0.478 0.063I/I

I

1 I

I

0

1 I

:

Correction

Io

0.063I/I

I

1.154 I

I

0

3

1 I

:

n

Eliminatio

-Io

0.055 A

4.82A/87.5

/I

I

;

0.478 400A/837A

/I

I

;

4.82A

132kV

3 13.8kV/

2000A

0.2 I

;

400A

2000A

0.2 I

?

Will the differential protection detect the fault (setting I

_Diff

> = 0.25I/InO , slope 1 = 0.25) ?

(fault location 20% from the star point)

…/1A

20 MVA ; YNd5 Side 1: 132kV Side 2: 13.8kV

2L1

2L2

2L3

1L1

1L2

1L3

100/1A

…/1A

~

R

_E

f

1

0 I

_nO2

= 837A

I

_nO1

= 87.5A

(4)

No. 1 with

Limits of the differential protection (2 of 2)

With the above setting the differential protection (with Io-correction)

would only just fail to pick up!

Short circuited winding part f

I

_F

[p.u. 13.8kV side]

I

D Cor

Io-correction

I

D Elim

Io-elimination

I

_K

[p.u. 132kV side]

I

_F,

I

_D,

I

_K

[p.u.]

Diff. pickup at nom. load

Diff. pickup at no load

REF

Example

In the example at hand, it is therefore advisable to connect a CT with earth

current relay (pick up threshold 200A) in the earth connection of the star-point,

to increase the range of protection coverage to 90%.

This protection however requires a large time delay setting as the earth current

relay in the system must trip faster to maintain selectivity.

(5)

No. 1 with

7UT6: Restricted Earth Fault Protection (General)

The REF measures the Neutral current of the object ( I

_SP

= 3I

₀

’ ) and, depending on the

angle (? f ) between 3I

₀’

_{and the also measured sum of the phase currents}

( 3I

₀

’’ = I

_L1

+ I

_L2

+ I

_L3

), decides for internal or external fault.

The sensitivity of the REF is almost independent from the load of the object.

(The sensitivity of the “Differential Function” especially for high ohm faults will be reduced

by the load due to the slope of its “Tripping Characteristic” ).

The REF can be stetted to 0.1 I/I

_NO

and is therefore more sensitive as the

“Differential Protection” (even without load).

(6)

No. 1 with

7UT6: Tripping Characteristic of REF (1 of 3)

?

???

?

???

?

_?

?

???

?

???

?

_?

?

3Io'

'

3Io'

e

1 3Io'

'

3Io'

e

1 k

1 I

I

3Io'

o'

I

3 I

3Io'

'

3Io'

e

1 3Io'

'

3Io'

e

1 k

o'

I

3 I

1 '

3Io'

e

3Io'

'

3Io'

e

3Io'

k

I

0 )

'

o'

I

(3

reference,

'

o'

I

3 '

o'

I

3 o'

I

3 '

o'

I

3 o'

I

3 k

I

j? j? REF REF REF j? j? REF j? j? REF REF ? ? ? ? ? ?

?

REF REF

for 7UT612 : k ˜ 2

for 7UT613/63 k ˜ 4

2) for extended Trip-Area (90° = ? f = 180°):

I

_REF

> = Setting value (Trip Threshold)

I

_Rest

= Restraint current

I

_REF

= ¦ 3I

₀

’¦

1) for basic Trip-Area (0° = ? f = 90°):

I

_REF

= ¦ 3I

₀

’¦ and must be = I

_REF

>

Characteristic_1)

:

I

_REF

/ I

_REF

> = 1 (no restraining current I

_Rest

effective)

?

_?

?

3Io'

'

3Io'

e

1 3Io'

'

3Io'

e

1 k

1

1 I

I

:

stic_2)

Characteri

j? j? REF REF ? ?

I

_REF

= I

_REF

> + k·I

_Rest

where I

_Rest

= (¦ 3I

₀

’-3I

₀

’’¦ -¦ 3I

₀

’+3I

₀

’’¦ )

I

_Rest

includes the direction

(7)

No. 1 with

7UT6: Tripping Characteristic of REF (2 of 3)

90° = ? f = 0°

Characteristic _1)

180° = ? f > 90°

Characteristic_2)

-0.1

-0.2

-0.3

+0.1

+0.2

+0.3

1

2

3

4

0.0 ?

REF REF

I

' 0 '' 0

3I

Tripping

Blocking

Char. for

?f = 180°

(8)

No. 1 with

7UT6: Tripping Characteristic of REF (3 of 3)

3I

₀

’

I

_Rest

= (¦ 3I

₀

’-3I

₀

’’¦ -¦ 3I

₀

’+3I

₀

’’¦ ) = 0

-3I

₀

’’

+3I

₀

’’

3I

₀

’-3I

₀

’’

3I

₀

’+3I

₀

’’

3I

₀

’’

Figure 4

?f =90°

Figure 5

?f < 90°

3I

₀

’

-3I

₀

’’

+3I

₀

’’

3I

₀

’+3I

₀

’’

3I

₀

’-3I

₀

’’

I

_Rest

3I

₀

’’

I

_Rest

= (¦ 3I

₀

’-3I

₀

’’¦ -¦ 3I

₀

’+3I

₀

’’¦ )

< 0

(neg. values will be set to 0)

? f = 45°

Figure 3

?f > 90°

3I

₀

’

-3I

₀

’’

+3I

₀

’’

3I

₀

’+3I

₀

’’

3I

₀

’-3I

₀

’’

I

_Rest

3I

₀

’’

I

_Rest

= (¦ 3I

₀

’-3I

₀

’’¦ -¦ 3I

₀

’+3I

₀

’’¦ ) > 0

? f = 135°

(9)

No. 1 with

7UT6: REF CT saturation at star point CT (1 of 2)

The star point CT can or even should be weaker designed than the phase Ct’s !

In case of an external fault and saturation on this CT there will be no false trip.

(10)

No. 1 with

(11)

No. 1 with

Comparison of sensitivity between

Differential Protection and REF

200/1A

38.1 MVA ; Vector group: YNd5

Side 2: 11kV Side 1: 110kV

1L1

1L2

1L3

2L1

2L2

2L3

2000/1A

_200/1A

(12)

No. 1 with

Settings

(13)

No. 1 with

(14)

No. 1 with

Fault 1: Internal high ohm Fault L1-E Side 1, without Load (2 of 3)

Idiff ? 0.11 I/InO

Only Ires, no Idiff for L2,L3

(15)

No. 1 with

Fault 1: Internal high ohm Fault L1-E Side 1, without Load (3 of 3)

Trip Area

Block Area

(16)

No. 1 with

(17)

No. 1 with

Fault 2: Internal high ohm Fault L1-E Side 1, with Load (2 of 3)

I

_ref

= actual current, I

_REF

= Setting I

_REF

>,

Ks = 1, IoL = I

₀

’’, IoSt = I

₀

’

(18)

No. 1 with

Fault 2: Internal high ohm Fault L1-E Side 1, with Load (3 of 3)

3I

₀

’’ = 3·6.49mA = 19.47mA, ? 3I

₀

’/ 3I

₀

’’ = 19.47/140 = 0.139

InO = 200A ? 1000mA, I

= 140mA, I

> = 0.1 ? I

/I

> = 1.4

(19)

No. 1 with

7UT6: REF settings

1.0 _?

_I

_InO

InO

I

_Ref

3.5

1313A slope = 0.1

I

_Ref

>

0

0.5

1.5

2.0

2.5

3.0

0

0.2

0.1

0.3 Increasing the pickup value

nominal

load

? I = ¦ I

_L1

¦ + ¦ I

_L2

¦ + ¦ I

_L3

¦ + ¦ I

_SP

¦

(to be handled with care) !!!

proposed value

(20)

No. 1 with

Setting the direction of the Star point CT

Transformer-winding

L1

L2

L3

7UT612

Q7

Q8

0230 Earthing Electrode versus Terminal Q7

7UT612

Q7

Q8

0230 Earthing Electrode versus Terminal Q7

7UT612

Q7

Q8

_{0230 Earthing Electrode versus Terminal Q8}

7UT612

Q7

Q8

_{0230 Earthing Electrode versus Terminal Q8}

Secondary earthing of Star point CT has no influence on the direction

Setting for “CT-Strpnt in Direct. Of Object”

(21)

No. 1 with Energy Automation

7UT6: versions

No

1 7UT612

Version 4.0

Yes

No

REF for

Autotransformer

2

1 Number of

Low impedance REF

7UT613/63.

Version 4.6

(Jan. 2006)

7UT613/63.

(22)

No. 1 with

Application

Device Configuration

0105 Protected Object 3 phase Transformer

0112 Differential Protection Enabled

0113 REF Protection Enabled

Power System Data 1

CT-Numbers

0211 No. of connected Meas. Loc. 2

0212 No. of assigned Meas. Loc. 2

0213 No. of sides 2

CT-Assign

0222 Assignment at 2 assig.

Meas.Loc./2 sides S1:M1, S2:M2

0251 Auxiliary CT IX1 is used as Side 1 earth

0252 Auxiliary CT IX2 is used as Side 2 earth

Transf. ….

0313 Starpoint of Side 1 is Solid Earthed

0314 Transf. Winding Connection Side 1 Y (Wye) ….

0323 Starpoint of Side 2 is Solid Earthed (!!)

0324 Transf. Winding Connection Side 2 D (Delta)

0325 Vector Group Numeral of Side 2 11

Funct.

0413 REF assigned to Side 2

0420 DMT/IDMT Phase assigned to Side 1

Setting Group A

Differential Protection-Settings Group A

1211A Diff-Prot. with meas. Earth Curr. S1 Yes (Io- correct. Side 1)

1212A Diff-Prot. with meas. Earth Curr. S2 No

X2 X1

Y

?

7UT613

M1 M2 Main protect. object S1 S2 Starpoint-bilder Sides:

S1 High voltage side (HV) S2 Low voltage side (LV)

Measuring locations 3-phase , assigned

M1 assigned to the main protected object (side 1) M2 assigned to the main protected object (side 2) Auxiliary measuring locations 1-phase

X1 assigned to the main protected object (side 1) X2 assigned to the main protected object (side 2) X3 not assigned to the main protected object