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Page 1

Page 188 2007-08

PTD SE PTIAuthor: G. Ziegler

Transformer Protection

Page 2

Page 189 2007-08

PTD SE PTIAuthor: G. Ziegler

Transformer: Function principle and equivalent circuits

12211 wIwIwI ⋅=⋅+⋅ µ

At load and short-circuit: '2,1II <<µ
2211 wIwI ⋅=⋅

'21 σσ XXTKX +='2U1U '21 II = '21 RRTKR +=

Equivalent electromagnetic circuit

1R
'2R1σX '2σX

µX1U µI1I '2I '2U

Equivalent electric circuit

Φ

w1

U1 U2

I1
w2

I2

σ1Φ σ2Φ

TKR TKX

Page 26

Page 213 2007-08

PTD SE PTIAuthor: G. Ziegler

Location of the earth fault h in %
20 40 60 80 100

Grid

Transformer winding to earth fault
Earth fault in the delta winding

1

2

3

4

5 20%
0%

R

33,3%

50%

100%

x In

IK
IK

Page 27

Page 214 2007-08

PTD SE PTIAuthor: G. Ziegler

IP
x In

IF , IK
x In

Short-circuited winding part h in %

IF

IK

Transformer winding short-circuit

Source: Protective Relays, Application Guide, GEC Alstom T&D, 1995

100

80

60

40

20

0
5 10 15 20 25

2

4

6

8

10

IF

IK

Page 52

Page 239 2007-08

PTD SE PTIAuthor: G. Ziegler

7UT6: Temperature monitoring with hot spot calculation (1)
Example: Natural cooling

HV
LV

Oil -
Temp.

Y
grOh kHΘΘ ⋅+=

Θh= hot spot temperature

Θh= oil temperature

k= load factor I/In

Y= winding exponent

98)/6(Θ2
C98at Aging
hΘat AgingV h −=
°

=

∫ ⋅⋅−=
2

1

T

T12

dtV
TT

1
L

Aging rate:

Mean value of aging during a fixed time interval:

98O is reference for
the aging of
Cellulose insulation

Page 53

Page 240 2007-08

PTD SE PTIAuthor: G. Ziegler

1.622V 98)/6(10298)/6(Θh ≈== −−
C1021.152373kHΘΘ 1.6Ygroh °=⋅+≈⋅+=

Θh
Θo

t

[°C]
98°C

Θh Hot spot
temp.

1.6

102°C

1.15

73°C

k (I/In)

108°C
k,
V,
L

V (relative
aging)
L (mean
value of V)

Θo oil temp.
(from thermo-
device)

(L)

7UT6: Temperature monitoring with hot spot calculation (2)
Example: Natural cooling