Transformer Protection - Siemens
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Transformer Protection
Page 188
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer: Function principle and equivalent circuits
I1
w1
w2
I2
Φ
U1
Xσ1
R1 U2
U1
Φ σ1 Φ σ2
I1
I ⋅ w + I ⋅ w = I µ ⋅ w1 1 1 2 2
Page 189
2007-08
RTK
I µ << I1, 2 '
Xµ
R2 '
I2'
U 2'
Equivalent electric circuit
Equivalent electromagnetic circuit
At load and short-circuit:
Iµ
Xσ 2'
U1
Author: G. Ziegler
X TK
I1 = I 2 '
I1⋅ w1 = I 2 ⋅ w2
U 2'
X TK = X σ 1 + X σ 2 ' RTK = R1 + R2 '
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Typical Transformer data
Rated power
Ratio
MVA
Page 190
kV/kV
Short-circuit voltage % UN
No-load magnetizing current % In
850
850/21
17
0.2
600
400/230
18.5
0.25
300
400/120
19
0.1
300
230/120
24
0.1
40
110/11
17
0.1
16
30/10.5
8.0
0.2
6.3
30/10.5
7.5
0.2
0.63
10/0.4
4.0
0.15
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer Inrush current
IRush
Flux
φ
φ φRem
Inrush-current of a single phase transformer
U
Im
t
Source: Sonnemann, et al.: Magnetizing Inrush phenomena in transformer banks, AIEE Trans., 77, P. III, 1958, pp. 884-892
Page 191
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Inrush currents of a Y-∆-transformer Neutral of Y-winding earthed ΦT
IR
ΦS ΦR
IS
I mT
ID
IC
I mR Oscillogram:
IR
5 1 I R = ⋅ I mR − ⋅ I mC 6 6
IR
IS
1 1 IS = − ⋅ ImR − ⋅ ImT 6 6
IS
IT
5 1 IT = ⋅ ImT − ⋅ ImR 6 6
IT
Source: Sonnemann et al. : Magnetizing Inrush phenomena in transformer banks, AIEE Trans., 77, P. III, 1958, pp. 884-892
Page 192
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Inrush current : Content of 2nd und 3rd harmonic I m(ν ) I m(1)
%
100 B
80
B
360O 60
I m ( 2) 40
I m(3) 20
I m(1)
I m(1) 90O
17,5%
180O
270O
360O Width of base B
240O
Page 193
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Inrush currents of a three-phase transformer recorded with relay 7UT51
Page 194
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer Inrush current: Amplitude and time constant
ˆI Rush
12
ˆI N
10
Rated power in MVA
time constant in seconds
8
0,5....1,0
0,16....0,2
6
1,0
0,2 .....1,2
>10
4
10
1,2 ....720
2
5
10
50
100
500
Rated transformer power in MVA
Page 195
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Sympathetic Inrush Wave form:
Transient currents:
I1
I
I1
I2
I2
IT IT I1
IT T1
G resistance
I2
Transformer being closed
G Transformer already closed
T2
Page 196
2007-08
Author: G. Ziegler
Current circulating between transformers
RS
IT
t
XS
I1
I2 T1
T2
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer overfluxing
Deduction of wave form
B 1,5
Harmonic content % 100 80
Im
×104 Gauß
U
1,0
I150/I50
60
I250/I50
40
I350/I50
I50/InTr
20 0
0,5
5
Page 197
10
15 A Im
2007-08
0
20 ms
10
100
120
140
% 160 U/Un
t
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Vector group adaptation with matching CTs Current distribution with external ph-ph fault
IR
I1
R
3
Ir r
1
IS
I2
IT
I3
S
T
Is It
s
G
t
3 /1 87T
Page 198
2007-08
87T
87T
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Vector group adaptation with matching CTs Current distribution with external ph-E fault IR
R
Yd1
IS
S
IT
I1
Ir
I2
Is s It
I3
T
r
G
t
tm IT=3
87T
87T
87T
Ir = 3
Tg
R0 S0 T0
30O
tm
sm
Sm
Rm Page 199
= 3
tg
3 /1
Tm
It
Rg 2007-08
Sg
rg
30O sg
rm Author: G. Ziegler
tg
rm
rg
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Traditional I0-elimination with matching CTs Current distribution in case of an internal earth fault
L1 L1 L2 L2
G
L3
L3
!
∆Ι
∆Ι
∆Ι
• Sensitivity only 2/3 IF! •Non-selective fault indication!
Page 200
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Traditional I0-correction with matching CTs Current distribution with external ph-E fault
a A b B
G
c
C
3/1
87T 87T
Page 201
2007-08
87T
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Traditional I0-correction with matching CTs Current distribution with internal ph-E fault
a A b B
G
c C
3/1
87T
Page 202
2007-08
87T
87T
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer differential protection, connection
L1
IA1
IB1
UA
L2
IA2
IB2
UB
(110 kV)
L3
IA3
IB3
(20 kV)
Digital protection contains: Adaptation to
7UT6
∆I
∆I
∆I
• Ratio UA / UB • Vector group
Software replica of matching transformers
Page 203
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Digital transformer protection Adaptation of currents for comparison (1) CT 1
JR-sec JS-sec JT-sec
JR-prim
Js-prim
JT-prim
Jt-prim
N o r m
I IS = N − Prim − CT 1 ⋅ I N − Transf - W1 IT
Page 204
Jr-prim
JS-prim
IR IS IT
I N −Transf − W1 =
IR
W2
W1
IR* ComI0parison elim. IS* ∆I IT* SN
Ir* Is* It*
I0elim.
Ir Is It
N o r m
I N −Transf − W2 =
3 ⋅ U N-1
J R −sec
J R −sec
J S −sec = kCT −1 ⋅ JT −sec
J S −sec
2007-08
Ir** Vector Is** group It** adapt.
JT −sec
Author: G. Ziegler
Ir
J r − sec
CT 2
Jr-sec Js-sec Jt-sec SN 3 ⋅ U N -2
I I s = N − Prim −CT 2 ⋅ J s −sec = k CT − 2 ⋅ I N −Transf -W2 It J t −sec
J r − sec J s − sec J t −sec
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Digital transformer protection Adaptation of currents for comparison (2) CT 1
I0 =
Js-prim
JT-prim
Jt-prim
IR IS IT
IR* Com_ I0parison elim. IS* ∆I IT*
1 ⋅ (I R + IS + IT ) 3
I R * = I R − I0 IS* = IS − I0 IT * = IT − I0
Page 205
Jr-prim
JS-prim
N o r m
JR-sec JS-sec JT-sec
W2
W1
JR-prim
Ir** Vector Is** group It** adapt.
Ir* Is* It*
I0elim.
Ir Is It
N o r m
Example Yd5: I∆−R
IR *
Ir **
I∆−S = I S * + I s ** IT * I t * * I ∆ −T
2007-08
I r ** −1 0 1 Ir * 1 I s ** = 1 −1 0 ⋅ I s * 3 It ** 0 1 − 1 It *
Author: G. Ziegler
CT 2
Jr-sec Js-sec Jt-sec
1 I0 = ⋅ (I r + Is + I t ) 3
I r * = I r − I0 Is * = Is − I0
I t * = I t − I0
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Adaptation of currents for comparison Relay input data Input data: •n times 30O
vector group number (only for 2nd and 3rd winding, 1st winding is reference)
Winding 1 (reference) is normally: •High voltage side
•UN (kV)
Rated winding voltage
•SN (MVA)
rated winding power
•INW (A)
Primary rated CT current
•Line or BB
direction of CT neutral
•Elimination / Correction / without
I0-treatment
•Side XX
Assignment input for REF
•INW S (A)
Primary rated current of neutral CT
•Neutral CT
Earth side connection to relay: Q7 or Q8?
Page 206
2007-08
Author: G. Ziegler
At windings with tap changer:
U max ⋅ U min UN = 2⋅ U max + U min
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Digital transformer protection Current adaptation, Example (1) SN = 100 MVA UN1= 20 kV 3000/5 A
Yd5
W2
UN2= 110 kV W1
600/1 A 2.400 A
7621 A
1A 5A
Page 207
2007-08
∆I
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Digital transformer protection Current adaptation, Example (2) 20-kV-side
I N − Trafo − W2 =
100MVA 3 ⋅ 20kV
110-kV-side
= 2887A
1 ⋅13200 3 = 4,4 3 A 3000 3000 I Norm = ⋅ 4,4 3 = 4,57 3 A 2887 J r,s, t -sek =
I0-elimination: − 1 0 1 4,57 3 − 4,57 / 3 I r ** 1 1 − 1 0 ⋅ − 4,57 3 = 2 ⋅ 4,57 / 3 I s ** = 3 0 1 −1 0 It * * − 4,57 / 3
I N − Trafo − W1 =
J R,S,T -sek = I Norm =
100MVA 3 ⋅110kV
= 525A
1 ⋅ 2400 = 4,0 A 600
600 ⋅ 4 = 4,57A 525
Vector group adaptation: Yd5 Ir * 2 −1 −1 0 4,57 3 1 Is * = ⋅ − 1 2 − 1 ⋅ − 4,57 = − 2 ⋅ 4,57 3 3 It * −1 −1 2 0 4,57 3
4,57 3 − 4,57 3 I A − R = I R * +I r * * = =0 I A − S = I S * + I s * * = − 2 ⋅ 4,57 3 + 2 ⋅ 4,57 3 = 0 I A −T = IT * +I t * * = 4,57 3 − 4,57 3 =0 Page 208
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7UT6 Operating characteristic
5
B
I IF F =
7UT6
7 6
I DIFF >>
ST A
8
ID
IDiff/ In
I2
I1
9
IDIFF = |I1+ I2| Tripping area
IStab = |I1| + |I2|
4
e p o Sl
3
2
Stable operation
2
I DIFF >
Page 209
0 0
2007-08
Additional stabilisation for high Is.c.
1 Slope
1
1
2
3
4
5
6
Author: G. Ziegler
7
8
9
10
11
Istab / In
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
I0-elimination / correction: Summary
Î I0- elimination necessary at all windings with earthed neutral or with grounding transformer in the protection range Earth fault sensitivity reduced to 2/3 ! Incorrect fault type indication! Î I0- correction provides full earth current sensitivity and correct phase selective fault type indication, however requires CT in the neutral-to-earth connection of the transformer. Î As an alternative, earth differential protection can be used to enhance earth fault sensitivity.
Page 210
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer winding to earth fault Solid earthed neutral
IF per unit 10 8
UR h⋅UR
IF
6
Infeed side
4
IF
IK
2
IK 0
20
40
60
80
100
Short-circuited winding part h in %
Source: P.M. Anderson: Power System Protection, McGraw-Hill and IEEE Press (Book)
Page 211
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer winding to earth fault Resistance or reactance earthed neutral
UR h⋅UR Infeed side
% 100
I IF
I Max IF
IK
50
IK
RE 0
h ⋅U R IF = RE U 2n h ⋅ w2 IK = ⋅ IF = h ⋅ ⋅ IF w1 U1n ⋅ 3
20
40 100 60 80 Short-circuited winding part h in %
1 U 2n U R 2 IK = h ⋅ ⋅ ⋅ 3 U1n RE
Source: P.M. Anderson: Power System Protection, McGraw-Hill and IEEE Press (Book)
Page 212
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer winding to earth fault Earth fault in the delta winding
IK
R
IK
0%
5
20%
x In
Grid
4 33,3%
3
50%
2
100%
1
20
40
60
80
100
Location of the earth fault h in %
Page 213
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer winding short-circuit
100
IK
10
IF , IK x In 80
8
60
6
IP x In
IF 4
40
IK 20
2
IF 0
5
10
15
20
25
Short-circuited winding part h in % Source: Protective Relays, Application Guide, GEC Alstom T&D, 1995
Page 214
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Restricted earth fault protection of relay 7UT6
I0* = IN I0** = I R + I S + IT = 3I0 I restr = I − I − I + I * 0
** 0
* 0
IR IS
** 0
IT
Basic operating area: IOp = I0*
(
)
for − 900 ≤ ϕ I 0* / I 0** ≤ +900 if IOp ≥ Iset Extended operating area: IOp = I 0* − k0 ·I restr
(
I>
IN ∆ IE I0*
I0**
)
for + 900 ≤ ϕ I 0* / I 0** ≤ +2700 if IOP ≥ Irestr Page 215
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Restricted earth fault protection of 7UT6 Operating characteristic (2)
K0
ϕ Limit
1.0
130
1.4
120
k0 =2
I*0 I 0-set
ϕ Limit=110O 4
2.0
110
4.0
100
3
∞
90
2
I*0* I*0
=
ΣI Ph =1 IN
1
Internal fault
External fault 180O
130O 120O 110O
100O
(
90O
80O
ϕ I*0*/I*0
Page 216
2007-08
)
Author: G. Ziegler
70O
60O
50O
0O
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Restricted earth fault protection of 7UT6 Polar characteristic
K0= 4 100
K0= 2 120
2
80 60
1.2
I0 * ϕ (I 0 */I 0 **) ⋅e 40 I0 * *
0.8
20
1.6 140
K0= 1.4
160
K0= 1
Blocking
0.4
180
ϕ
0
Tripping +1
0
200
340
220
320 240
300 260
Page 217
2007-08
280
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Restricted earth fault protection 87N (7UT6) Application aspects
Increased sensitivity with earth faults near winding neutral
Preferably used in case of resistance or reactance neutral earthing Sensitive to turns short-circuit I0 / IN amplitude and angle comparison 2nd harmonic stabilised Can protect a separate shunt reactor or neutral earthing transformer in addition to the two winding transformer differential protection Not applicable with autotransformers! (as only one stabilising input at transformer terminal side, -- high impedance principle to be used in this case.
Page 218
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer HI-earth fault protection
IR
Ir
IS
Is
IT
It
ZE ∆IE>
Page 219
2007-08
IN
Author: G. Ziegler
∆IE>
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
HI differential protection of an autotransformer
Ir
IR
Is
IS
It
IT
87
Page 220
2007-08
87
87
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
HI earth fault protection of an autotransformer
Ir
IR
Is
IS
It
IT
IN ∆I>
Page 221
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer tank protection 64T: Principle
IE>
Insulated
Page 222
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer protection, Relay design
Transformer Protection with Siemens SIPROTEC 7UT6
7UT612
Page 223
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Digital transformer protection relay 7UT613: Current inputs and integrated protective functions YN
yn0
d5
R S T
ϑ> (2)
Page 224
2007-08
ϑ> (1)
I>>, I>t
Author: G. Ziegler
∆ITE
∆IT
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Relay 7UT6: Application examples
∆ ∆I ∆I
Three winding transformer
Two winding transformer
Shunt Reactor
G
∆I
2007-08
Transformer bank (1-1/2-LS)
∆I
∆I
Generator / Motor Page 225
∆I
∆I
Busbars Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7UT6 Operating characteristic
B
8
I
ST A
IF F =
7UT61
7
IDIFF = |I1+ I2|
6
IStab = |I1| + |I2|
5
Tripping area
4 3
pe o l s
2
I DIFF > (1603) 0
0
1
2007-08
2
2
ot o (f
1 slope ) (1606
1
Page 226
I DIFF >> (1604)
ID
IDiff/ In
I2
I1
9
in o p
t=
1
7, 0 6
e p o sl
=
1
8 60
)
Restraining area
of 1606 slope = 1/2 e) = (1618 ) n li r e rd o b t f (le pick-up limit
Add-on restraint for high ISC 3
4
5
6
Author: G. Ziegler
7
8
9
10
11
Istab / In
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Advantages of digital transformer differential protection
High stability against c.t. saturation provided by integrated saturation detector and add-on stabilisation High stabile against inrush currents due to advanced filter technology (Fourier analysis) and optional cross-blocking function High stability against over-excitation ( 5th harmonic blocking) Short tripping time - typically 1.5 cycles High set ∆I fast tripping < 1 cycle Sensitive earth differential protection against interturn faults and earth faults near winding neutral Integral ratio and vector group adaptation (no external auxiliary CTs required) Integral thermal overload protection External start of fault recording (e.g. by gas pressure relays)
Page 227
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7UT6 Integrated protection functions 87T
Transformer differential protection ∆I> Rush-stabilised (2nd harmonic) Stabilised against overfluxing (5th harmonic)
49-1 49-2
∆I>> high set element, non-stabilised
Thermal overload protection
50/51 50HS
Time overcurrent protection (IT or DT) Earth current differential protection (7UT613)
87N
Tank protection (7UT613) 64T
Page 228
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Application examples
Page 229
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Protection of a two winding transformer
7SJ600 7UT512 50
51 W1
52
87T
Bu
W1 (OS)
49
W2 (US) W2
52
Page 230
2007-08
52
Author: G. Ziegler
51
52
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Protection of a three winding transformer 7SJ600 50
51
52
7UT513 W1 49-1
Bu 87T
W1 W2
W3
W2 49-2
W3
51
52
Load
Page 231
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Restricted earth fault protection for a two winding transformer
7SJ600 7UT513 50
51 W1 49-1
52 Bu
W1 (OS)
87T W2 (US) ZE 51 87TE
52
Page 232
2007-08
52
Author: G. Ziegler
W2
52
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Protection of an autotransformer
52
7SJ600 51BF
51N
50 51
7UT513 87 TL Load
52
87 TH
7VH600
49 52
3Y
51 59 7RW600
Bu
50 BF
50 51 50 BF
7SJ600
7SJ600 51 N
Page 233
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Protection of a large transformer bank
52
52
7SA6 50 BF
49
21
7UT513 87 TL
87 TH
7VH6 (3)
49
3
Load
52 52
51 59N 7RW6
50 BF 7SJ6
Page 234
2007-08
7SA6 51N
21
49
51 BF
7SJ6
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Differential protection of generation units
52
52
52
52
∆IT
∆IT
∆IT
∆IT
G
G G
∆IG
52
∆IG
G
Page 235
2007-08
Author: G. Ziegler
∆IG
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Differential protection of generation units (2)
52
∆IT 52 *) ∆IT
G
∆IG *) same ratio as generator CTs
52 Auxiliaries
Page 236
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Thermal protection of transformers
ΘCu
ΘOil Rth2
Rth1
Legend: PCu: Winding losses (I2·R) PFe: Core and tank losses
C1 PCu
C2 PFe ΘAmb
Lifetime of insulation depends on the winding Hot-spot temperature.
Rth1: Thermal resistance Copper-Oil Rth2: Thermal resistance Oil-Air (cooling medium) C1:
Winding thermal capacity
C2:
Thermal capacity of Oil, Core and tank
ΘCu:
Winding copper temperature
ΘOil:
Oil temperature
ΘAmb.: Ambient temperature
6 OC higher temperature increases the aging of the insulation by the factor 2!
Page 237
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7SA6: Temperature monitoring
RS485 Interface
Oil Temp.
Two thermo-devices can be connected to the serial service interface Monitoring of up to 12 measuring points (6 per thermo-device) One input is reserved for hot spot monitoring (measurement of oil temperature) Thermistors: Pt100, Ni100 or Ni120
The the upper oil temperature is directly measured by the use of thermoelement. The hot spot temperature is calculated by the relay using the thermal model Cu-Oil: 2
dΘ Cu 1 ⎛I⎞ 1 ⋅ (Θ Cu − Θ Oil ) = ⋅⎜ ⎟ − dt τ Th τ Th ⎝ Ir ⎠ Page 238
2007-08
Author: G. Ziegler
I = actual transformer current Ir = rated transformer current τth =time constant of the winding Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7UT6: Temperature monitoring with hot spot calculation (1) Example: Natural cooling
Θ h = Θ O + H gr ⋅ k Y
Θh= hot spot temperature Θh= oil temperature Hgr=hot-spot-to-oil temperature gradient k= load factor I/In Y= winding exponent
Oil Temp.
Aging rate:
V=
HV LV
Aging at Θ h = 2(Θ h −98)/6 Aging at 98°C
98O is reference for the aging of Cellulose insulation
Mean value of aging during a fixed time interval: T
2 1 L= ⋅ ∫ V ⋅ dt T2 − T1 T1
Page 239
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7UT6: Temperature monitoring with hot spot calculation (2) Example: Natural cooling
Θ h = Θ o + H gr ⋅ k Y ≈ 73 + 23 ⋅1.151.6 = 102°C
(L)
V = 2(Θ h −98)/6 = 2(102−98)/6 ≈ 1.6
k, V, L
108°C 98°C
102°C 73°C
Θh Hot spot temp.
[°C]
Θh Θo
1.6
Θo oil temp. (from thermodevice)
k (I/In)
V (relative aging) L (mean value of V)
1.15
t
Page 240
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Page 188
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer: Function principle and equivalent circuits
I1
w1
w2
I2
Φ
U1
Xσ1
R1 U2
U1
Φ σ1 Φ σ2
I1
I ⋅ w + I ⋅ w = I µ ⋅ w1 1 1 2 2
Page 189
2007-08
RTK
I µ << I1, 2 '
Xµ
R2 '
I2'
U 2'
Equivalent electric circuit
Equivalent electromagnetic circuit
At load and short-circuit:
Iµ
Xσ 2'
U1
Author: G. Ziegler
X TK
I1 = I 2 '
I1⋅ w1 = I 2 ⋅ w2
U 2'
X TK = X σ 1 + X σ 2 ' RTK = R1 + R2 '
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Typical Transformer data
Rated power
Ratio
MVA
Page 190
kV/kV
Short-circuit voltage % UN
No-load magnetizing current % In
850
850/21
17
0.2
600
400/230
18.5
0.25
300
400/120
19
0.1
300
230/120
24
0.1
40
110/11
17
0.1
16
30/10.5
8.0
0.2
6.3
30/10.5
7.5
0.2
0.63
10/0.4
4.0
0.15
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer Inrush current
IRush
Flux
φ
φ φRem
Inrush-current of a single phase transformer
U
Im
t
Source: Sonnemann, et al.: Magnetizing Inrush phenomena in transformer banks, AIEE Trans., 77, P. III, 1958, pp. 884-892
Page 191
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Inrush currents of a Y-∆-transformer Neutral of Y-winding earthed ΦT
IR
ΦS ΦR
IS
I mT
ID
IC
I mR Oscillogram:
IR
5 1 I R = ⋅ I mR − ⋅ I mC 6 6
IR
IS
1 1 IS = − ⋅ ImR − ⋅ ImT 6 6
IS
IT
5 1 IT = ⋅ ImT − ⋅ ImR 6 6
IT
Source: Sonnemann et al. : Magnetizing Inrush phenomena in transformer banks, AIEE Trans., 77, P. III, 1958, pp. 884-892
Page 192
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Inrush current : Content of 2nd und 3rd harmonic I m(ν ) I m(1)
%
100 B
80
B
360O 60
I m ( 2) 40
I m(3) 20
I m(1)
I m(1) 90O
17,5%
180O
270O
360O Width of base B
240O
Page 193
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Inrush currents of a three-phase transformer recorded with relay 7UT51
Page 194
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer Inrush current: Amplitude and time constant
ˆI Rush
12
ˆI N
10
Rated power in MVA
time constant in seconds
8
0,5....1,0
0,16....0,2
6
1,0
0,2 .....1,2
>10
4
10
1,2 ....720
2
5
10
50
100
500
Rated transformer power in MVA
Page 195
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Sympathetic Inrush Wave form:
Transient currents:
I1
I
I1
I2
I2
IT IT I1
IT T1
G resistance
I2
Transformer being closed
G Transformer already closed
T2
Page 196
2007-08
Author: G. Ziegler
Current circulating between transformers
RS
IT
t
XS
I1
I2 T1
T2
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer overfluxing
Deduction of wave form
B 1,5
Harmonic content % 100 80
Im
×104 Gauß
U
1,0
I150/I50
60
I250/I50
40
I350/I50
I50/InTr
20 0
0,5
5
Page 197
10
15 A Im
2007-08
0
20 ms
10
100
120
140
% 160 U/Un
t
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Vector group adaptation with matching CTs Current distribution with external ph-ph fault
IR
I1
R
3
Ir r
1
IS
I2
IT
I3
S
T
Is It
s
G
t
3 /1 87T
Page 198
2007-08
87T
87T
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Vector group adaptation with matching CTs Current distribution with external ph-E fault IR
R
Yd1
IS
S
IT
I1
Ir
I2
Is s It
I3
T
r
G
t
tm IT=3
87T
87T
87T
Ir = 3
Tg
R0 S0 T0
30O
tm
sm
Sm
Rm Page 199
= 3
tg
3 /1
Tm
It
Rg 2007-08
Sg
rg
30O sg
rm Author: G. Ziegler
tg
rm
rg
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Traditional I0-elimination with matching CTs Current distribution in case of an internal earth fault
L1 L1 L2 L2
G
L3
L3
!
∆Ι
∆Ι
∆Ι
• Sensitivity only 2/3 IF! •Non-selective fault indication!
Page 200
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Traditional I0-correction with matching CTs Current distribution with external ph-E fault
a A b B
G
c
C
3/1
87T 87T
Page 201
2007-08
87T
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Traditional I0-correction with matching CTs Current distribution with internal ph-E fault
a A b B
G
c C
3/1
87T
Page 202
2007-08
87T
87T
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer differential protection, connection
L1
IA1
IB1
UA
L2
IA2
IB2
UB
(110 kV)
L3
IA3
IB3
(20 kV)
Digital protection contains: Adaptation to
7UT6
∆I
∆I
∆I
• Ratio UA / UB • Vector group
Software replica of matching transformers
Page 203
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Digital transformer protection Adaptation of currents for comparison (1) CT 1
JR-sec JS-sec JT-sec
JR-prim
Js-prim
JT-prim
Jt-prim
N o r m
I IS = N − Prim − CT 1 ⋅ I N − Transf - W1 IT
Page 204
Jr-prim
JS-prim
IR IS IT
I N −Transf − W1 =
IR
W2
W1
IR* ComI0parison elim. IS* ∆I IT* SN
Ir* Is* It*
I0elim.
Ir Is It
N o r m
I N −Transf − W2 =
3 ⋅ U N-1
J R −sec
J R −sec
J S −sec = kCT −1 ⋅ JT −sec
J S −sec
2007-08
Ir** Vector Is** group It** adapt.
JT −sec
Author: G. Ziegler
Ir
J r − sec
CT 2
Jr-sec Js-sec Jt-sec SN 3 ⋅ U N -2
I I s = N − Prim −CT 2 ⋅ J s −sec = k CT − 2 ⋅ I N −Transf -W2 It J t −sec
J r − sec J s − sec J t −sec
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Digital transformer protection Adaptation of currents for comparison (2) CT 1
I0 =
Js-prim
JT-prim
Jt-prim
IR IS IT
IR* Com_ I0parison elim. IS* ∆I IT*
1 ⋅ (I R + IS + IT ) 3
I R * = I R − I0 IS* = IS − I0 IT * = IT − I0
Page 205
Jr-prim
JS-prim
N o r m
JR-sec JS-sec JT-sec
W2
W1
JR-prim
Ir** Vector Is** group It** adapt.
Ir* Is* It*
I0elim.
Ir Is It
N o r m
Example Yd5: I∆−R
IR *
Ir **
I∆−S = I S * + I s ** IT * I t * * I ∆ −T
2007-08
I r ** −1 0 1 Ir * 1 I s ** = 1 −1 0 ⋅ I s * 3 It ** 0 1 − 1 It *
Author: G. Ziegler
CT 2
Jr-sec Js-sec Jt-sec
1 I0 = ⋅ (I r + Is + I t ) 3
I r * = I r − I0 Is * = Is − I0
I t * = I t − I0
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Adaptation of currents for comparison Relay input data Input data: •n times 30O
vector group number (only for 2nd and 3rd winding, 1st winding is reference)
Winding 1 (reference) is normally: •High voltage side
•UN (kV)
Rated winding voltage
•SN (MVA)
rated winding power
•INW (A)
Primary rated CT current
•Line or BB
direction of CT neutral
•Elimination / Correction / without
I0-treatment
•Side XX
Assignment input for REF
•INW S (A)
Primary rated current of neutral CT
•Neutral CT
Earth side connection to relay: Q7 or Q8?
Page 206
2007-08
Author: G. Ziegler
At windings with tap changer:
U max ⋅ U min UN = 2⋅ U max + U min
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Digital transformer protection Current adaptation, Example (1) SN = 100 MVA UN1= 20 kV 3000/5 A
Yd5
W2
UN2= 110 kV W1
600/1 A 2.400 A
7621 A
1A 5A
Page 207
2007-08
∆I
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Digital transformer protection Current adaptation, Example (2) 20-kV-side
I N − Trafo − W2 =
100MVA 3 ⋅ 20kV
110-kV-side
= 2887A
1 ⋅13200 3 = 4,4 3 A 3000 3000 I Norm = ⋅ 4,4 3 = 4,57 3 A 2887 J r,s, t -sek =
I0-elimination: − 1 0 1 4,57 3 − 4,57 / 3 I r ** 1 1 − 1 0 ⋅ − 4,57 3 = 2 ⋅ 4,57 / 3 I s ** = 3 0 1 −1 0 It * * − 4,57 / 3
I N − Trafo − W1 =
J R,S,T -sek = I Norm =
100MVA 3 ⋅110kV
= 525A
1 ⋅ 2400 = 4,0 A 600
600 ⋅ 4 = 4,57A 525
Vector group adaptation: Yd5 Ir * 2 −1 −1 0 4,57 3 1 Is * = ⋅ − 1 2 − 1 ⋅ − 4,57 = − 2 ⋅ 4,57 3 3 It * −1 −1 2 0 4,57 3
4,57 3 − 4,57 3 I A − R = I R * +I r * * = =0 I A − S = I S * + I s * * = − 2 ⋅ 4,57 3 + 2 ⋅ 4,57 3 = 0 I A −T = IT * +I t * * = 4,57 3 − 4,57 3 =0 Page 208
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7UT6 Operating characteristic
5
B
I IF F =
7UT6
7 6
I DIFF >>
ST A
8
ID
IDiff/ In
I2
I1
9
IDIFF = |I1+ I2| Tripping area
IStab = |I1| + |I2|
4
e p o Sl
3
2
Stable operation
2
I DIFF >
Page 209
0 0
2007-08
Additional stabilisation for high Is.c.
1 Slope
1
1
2
3
4
5
6
Author: G. Ziegler
7
8
9
10
11
Istab / In
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
I0-elimination / correction: Summary
Î I0- elimination necessary at all windings with earthed neutral or with grounding transformer in the protection range Earth fault sensitivity reduced to 2/3 ! Incorrect fault type indication! Î I0- correction provides full earth current sensitivity and correct phase selective fault type indication, however requires CT in the neutral-to-earth connection of the transformer. Î As an alternative, earth differential protection can be used to enhance earth fault sensitivity.
Page 210
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer winding to earth fault Solid earthed neutral
IF per unit 10 8
UR h⋅UR
IF
6
Infeed side
4
IF
IK
2
IK 0
20
40
60
80
100
Short-circuited winding part h in %
Source: P.M. Anderson: Power System Protection, McGraw-Hill and IEEE Press (Book)
Page 211
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer winding to earth fault Resistance or reactance earthed neutral
UR h⋅UR Infeed side
% 100
I IF
I Max IF
IK
50
IK
RE 0
h ⋅U R IF = RE U 2n h ⋅ w2 IK = ⋅ IF = h ⋅ ⋅ IF w1 U1n ⋅ 3
20
40 100 60 80 Short-circuited winding part h in %
1 U 2n U R 2 IK = h ⋅ ⋅ ⋅ 3 U1n RE
Source: P.M. Anderson: Power System Protection, McGraw-Hill and IEEE Press (Book)
Page 212
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer winding to earth fault Earth fault in the delta winding
IK
R
IK
0%
5
20%
x In
Grid
4 33,3%
3
50%
2
100%
1
20
40
60
80
100
Location of the earth fault h in %
Page 213
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer winding short-circuit
100
IK
10
IF , IK x In 80
8
60
6
IP x In
IF 4
40
IK 20
2
IF 0
5
10
15
20
25
Short-circuited winding part h in % Source: Protective Relays, Application Guide, GEC Alstom T&D, 1995
Page 214
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Restricted earth fault protection of relay 7UT6
I0* = IN I0** = I R + I S + IT = 3I0 I restr = I − I − I + I * 0
** 0
* 0
IR IS
** 0
IT
Basic operating area: IOp = I0*
(
)
for − 900 ≤ ϕ I 0* / I 0** ≤ +900 if IOp ≥ Iset Extended operating area: IOp = I 0* − k0 ·I restr
(
I>
IN ∆ IE I0*
I0**
)
for + 900 ≤ ϕ I 0* / I 0** ≤ +2700 if IOP ≥ Irestr Page 215
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Restricted earth fault protection of 7UT6 Operating characteristic (2)
K0
ϕ Limit
1.0
130
1.4
120
k0 =2
I*0 I 0-set
ϕ Limit=110O 4
2.0
110
4.0
100
3
∞
90
2
I*0* I*0
=
ΣI Ph =1 IN
1
Internal fault
External fault 180O
130O 120O 110O
100O
(
90O
80O
ϕ I*0*/I*0
Page 216
2007-08
)
Author: G. Ziegler
70O
60O
50O
0O
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Restricted earth fault protection of 7UT6 Polar characteristic
K0= 4 100
K0= 2 120
2
80 60
1.2
I0 * ϕ (I 0 */I 0 **) ⋅e 40 I0 * *
0.8
20
1.6 140
K0= 1.4
160
K0= 1
Blocking
0.4
180
ϕ
0
Tripping +1
0
200
340
220
320 240
300 260
Page 217
2007-08
280
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Restricted earth fault protection 87N (7UT6) Application aspects
Increased sensitivity with earth faults near winding neutral
Preferably used in case of resistance or reactance neutral earthing Sensitive to turns short-circuit I0 / IN amplitude and angle comparison 2nd harmonic stabilised Can protect a separate shunt reactor or neutral earthing transformer in addition to the two winding transformer differential protection Not applicable with autotransformers! (as only one stabilising input at transformer terminal side, -- high impedance principle to be used in this case.
Page 218
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer HI-earth fault protection
IR
Ir
IS
Is
IT
It
ZE ∆IE>
Page 219
2007-08
IN
Author: G. Ziegler
∆IE>
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
HI differential protection of an autotransformer
Ir
IR
Is
IS
It
IT
87
Page 220
2007-08
87
87
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
HI earth fault protection of an autotransformer
Ir
IR
Is
IS
It
IT
IN ∆I>
Page 221
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer tank protection 64T: Principle
IE>
Insulated
Page 222
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Transformer protection, Relay design
Transformer Protection with Siemens SIPROTEC 7UT6
7UT612
Page 223
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Digital transformer protection relay 7UT613: Current inputs and integrated protective functions YN
yn0
d5
R S T
ϑ> (2)
Page 224
2007-08
ϑ> (1)
I>>, I>t
Author: G. Ziegler
∆ITE
∆IT
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Relay 7UT6: Application examples
∆ ∆I ∆I
Three winding transformer
Two winding transformer
Shunt Reactor
G
∆I
2007-08
Transformer bank (1-1/2-LS)
∆I
∆I
Generator / Motor Page 225
∆I
∆I
Busbars Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7UT6 Operating characteristic
B
8
I
ST A
IF F =
7UT61
7
IDIFF = |I1+ I2|
6
IStab = |I1| + |I2|
5
Tripping area
4 3
pe o l s
2
I DIFF > (1603) 0
0
1
2007-08
2
2
ot o (f
1 slope ) (1606
1
Page 226
I DIFF >> (1604)
ID
IDiff/ In
I2
I1
9
in o p
t=
1
7, 0 6
e p o sl
=
1
8 60
)
Restraining area
of 1606 slope = 1/2 e) = (1618 ) n li r e rd o b t f (le pick-up limit
Add-on restraint for high ISC 3
4
5
6
Author: G. Ziegler
7
8
9
10
11
Istab / In
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Advantages of digital transformer differential protection
High stability against c.t. saturation provided by integrated saturation detector and add-on stabilisation High stabile against inrush currents due to advanced filter technology (Fourier analysis) and optional cross-blocking function High stability against over-excitation ( 5th harmonic blocking) Short tripping time - typically 1.5 cycles High set ∆I fast tripping < 1 cycle Sensitive earth differential protection against interturn faults and earth faults near winding neutral Integral ratio and vector group adaptation (no external auxiliary CTs required) Integral thermal overload protection External start of fault recording (e.g. by gas pressure relays)
Page 227
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7UT6 Integrated protection functions 87T
Transformer differential protection ∆I> Rush-stabilised (2nd harmonic) Stabilised against overfluxing (5th harmonic)
49-1 49-2
∆I>> high set element, non-stabilised
Thermal overload protection
50/51 50HS
Time overcurrent protection (IT or DT) Earth current differential protection (7UT613)
87N
Tank protection (7UT613) 64T
Page 228
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Application examples
Page 229
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Protection of a two winding transformer
7SJ600 7UT512 50
51 W1
52
87T
Bu
W1 (OS)
49
W2 (US) W2
52
Page 230
2007-08
52
Author: G. Ziegler
51
52
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Protection of a three winding transformer 7SJ600 50
51
52
7UT513 W1 49-1
Bu 87T
W1 W2
W3
W2 49-2
W3
51
52
Load
Page 231
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Restricted earth fault protection for a two winding transformer
7SJ600 7UT513 50
51 W1 49-1
52 Bu
W1 (OS)
87T W2 (US) ZE 51 87TE
52
Page 232
2007-08
52
Author: G. Ziegler
W2
52
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Protection of an autotransformer
52
7SJ600 51BF
51N
50 51
7UT513 87 TL Load
52
87 TH
7VH600
49 52
3Y
51 59 7RW600
Bu
50 BF
50 51 50 BF
7SJ600
7SJ600 51 N
Page 233
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Protection of a large transformer bank
52
52
7SA6 50 BF
49
21
7UT513 87 TL
87 TH
7VH6 (3)
49
3
Load
52 52
51 59N 7RW6
50 BF 7SJ6
Page 234
2007-08
7SA6 51N
21
49
51 BF
7SJ6
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Differential protection of generation units
52
52
52
52
∆IT
∆IT
∆IT
∆IT
G
G G
∆IG
52
∆IG
G
Page 235
2007-08
Author: G. Ziegler
∆IG
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Differential protection of generation units (2)
52
∆IT 52 *) ∆IT
G
∆IG *) same ratio as generator CTs
52 Auxiliaries
Page 236
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
Thermal protection of transformers
ΘCu
ΘOil Rth2
Rth1
Legend: PCu: Winding losses (I2·R) PFe: Core and tank losses
C1 PCu
C2 PFe ΘAmb
Lifetime of insulation depends on the winding Hot-spot temperature.
Rth1: Thermal resistance Copper-Oil Rth2: Thermal resistance Oil-Air (cooling medium) C1:
Winding thermal capacity
C2:
Thermal capacity of Oil, Core and tank
ΘCu:
Winding copper temperature
ΘOil:
Oil temperature
ΘAmb.: Ambient temperature
6 OC higher temperature increases the aging of the insulation by the factor 2!
Page 237
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7SA6: Temperature monitoring
RS485 Interface
Oil Temp.
Two thermo-devices can be connected to the serial service interface Monitoring of up to 12 measuring points (6 per thermo-device) One input is reserved for hot spot monitoring (measurement of oil temperature) Thermistors: Pt100, Ni100 or Ni120
The the upper oil temperature is directly measured by the use of thermoelement. The hot spot temperature is calculated by the relay using the thermal model Cu-Oil: 2
dΘ Cu 1 ⎛I⎞ 1 ⋅ (Θ Cu − Θ Oil ) = ⋅⎜ ⎟ − dt τ Th τ Th ⎝ Ir ⎠ Page 238
2007-08
Author: G. Ziegler
I = actual transformer current Ir = rated transformer current τth =time constant of the winding Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7UT6: Temperature monitoring with hot spot calculation (1) Example: Natural cooling
Θ h = Θ O + H gr ⋅ k Y
Θh= hot spot temperature Θh= oil temperature Hgr=hot-spot-to-oil temperature gradient k= load factor I/In Y= winding exponent
Oil Temp.
Aging rate:
V=
HV LV
Aging at Θ h = 2(Θ h −98)/6 Aging at 98°C
98O is reference for the aging of Cellulose insulation
Mean value of aging during a fixed time interval: T
2 1 L= ⋅ ∫ V ⋅ dt T2 − T1 T1
Page 239
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
7UT6: Temperature monitoring with hot spot calculation (2) Example: Natural cooling
Θ h = Θ o + H gr ⋅ k Y ≈ 73 + 23 ⋅1.151.6 = 102°C
(L)
V = 2(Θ h −98)/6 = 2(102−98)/6 ≈ 1.6
k, V, L
108°C 98°C
102°C 73°C
Θh Hot spot temp.
[°C]
Θh Θo
1.6
Θo oil temp. (from thermodevice)
k (I/In)
V (relative aging) L (mean value of V)
1.15
t
Page 240
2007-08
Author: G. Ziegler
Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI
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