Post on 06-Feb-2023
Page 188 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Transformer Protection
Page 189 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Transformer: Function principle and equivalent circuits
12211 wIwIwI ⋅=⋅+⋅ µ
At load and short-circuit: '2,1II <<µ2211 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
I1w2 I2
σ1Φ σ2Φ
TKR TKX
Page 190 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Rated power
MVA
850
600
300
300
40
16
6.3
0.63
Ratio
kV/kV
850/21
400/230
400/120
230/120
110/11
30/10.5
30/10.5
10/0.4
No-load magnetizing current % In
0.2
0.25
0.1
0.1
0.1
0.2
0.2
0.15
Short-circuit voltage % UN
17
18.5
19
24
17
8.0
7.5
4.0
Typical Transformer data
Page 191 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Transformer Inrush current
Source: Sonnemann, et al.: Magnetizing Inrush phenomena in transformer banks, AIEE Trans., 77, P. III, 1958, pp. 884-892
Inrush-current of a single phase transformer
Fluxφ φ
IRush
U
tIm
φRem
Page 192 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
mTI
mRI
RI
SI
mCmRR III ⋅−⋅=61
65
mTImRISI ⋅−⋅−=61
61
mRmTT III ⋅−⋅=61
65
RΦ
TI
Oscillogram:
Inrush currents of a Y-∆-transformerNeutral of Y-winding earthed
DIRI
SI
CI
Source: Sonnemann et al. : Magnetizing Inrush phenomena in transformer banks, AIEE Trans., 77, P. III, 1958, pp. 884-892
SΦ
TΦ
RI
SI
TI
Page 193 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
20
40
60
80
100
90O 180O 270O 360O
17,5%
)1(
)(
m
m
II ν
)1(
)2(
m
m
II
)1(
)3(
m
m
II
240O
B B
360O
Width of base B
Inrush current : Content of 2nd und 3rd harmonic
%
Page 194 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Inrush currents of a three-phase transformerrecorded with relay 7UT51
Page 195 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
N
Rush
I
I
Rated transformer power in MVA
Transformer Inrush current:Amplitude and time constant
Rated power time constant in MVA in seconds
0,5....1,0 0,16....0,2
1,0 10 0,2 .....1,2
>10 1,2 ....720
5 10 50 100 500
6
10
2
4
8
12
Page 196 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Sympathetic Inrush
Wave form: Transient currents:
1I
2I
Current circulating between transformers
TI t
I
G
SR SX
1I 2ITI
Transformer being closed
T1
T2
Transformer already closed
G
1I
2I
TI
resistance
2I
1I
TI
T1 T2
Page 197 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Transformer overfluxing
Deduction of wave form Harmonic content
U/Un
0,5
1,5
1,0
BUGauß410×
15105 AIm
Im
t0 10 20 ms
100 120 140 160%
20
4060
80100
0
I150/I50
I250/I50
I350/I50
I50/InTr
%
Page 198 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
IRIr
Vector group adaptation with matching CTsCurrent distribution with external ph-ph fault
87T87T 87T
1/3
IS
IT
I1
I2
I3
R
S
r
s
t
Is
It
13
G
T
Page 199 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
1/387T87T 87T
Sg
Tg R0 S0 T0
Rm
Tm
Sm Rg
sm
IT=3
30O30O
rm
tm tgsg
rg
3=tI
tm
tg
rg
rm
3=rI
IR
IS
IT
I1
I2
I3
R
S
T
r
s
t
Ir
Is
ItG
Yd1
Vector group adaptation with matching CTsCurrent distribution with external ph-E fault
Page 200 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
L1
L2
L3
L1
L2
L3
G
∆Ι∆Ι ∆Ι
Traditional I0-elimination with matching CTsCurrent distribution in case of an internal earth fault
• Sensitivity only 2/3 IF!
•Non-selective fault indication!
!
Page 201 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Traditional I0-correction with matching CTsCurrent distribution with external ph-E fault
A
B
C
a
b
c
G
87T87T 87T
3/1
Page 202 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
A
B
C
a
b
c
G
87T87T 87T
3/1
Traditional I0-correction with matching CTsCurrent distribution with internal ph-E fault
Page 203 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Digital protectioncontains:
Adaptation to
• Ratio UA / UB
• Vector group
IB1
IB2
IB3L3
IA1
IA2
IA3
∆I ∆I∆I
L2
L1
UA
(110 kV)
UB
(20 kV)
7UT6
Transformer differential protection, connection
Software replica of matching transformers
Page 204 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
I0-elim.
Com-parison
∆I
IRISIT
Ir**Is**It**
IR*IS*IT*
Ir*Is*It*
Vectorgroupadapt.
Norm
Norm
JR-secJS-secJT-sec
Jr-prim
Js-prim
Jt-prim
JR-prim
JS-prim
JT-prim
Jr-secJs-secJt-sec
CT 1 CT 2W1 W2
I0-elim.
IrIsIt
1-NU3NS
W1TransfN⋅
=−−I2-NU3
NSW2TransfN
⋅=−−I
secsecsecRJ
1secsecsecRJ
W1-TransfNI1 CTPrimNI
TISIRI
−−−
⋅−=
−−−
⋅−
−−=
TJSJCTk
TJSJ
sect
secs2CT
sect
secsJJk
JJ
−
−
−
−
−
−
−
−
−− ⋅=⋅=secrsecr
W2-TransfN
2 CTPrimN
t
s
r JJ
II
III
Digital transformer protectionAdaptation of currents for comparison (1)
Page 205 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
I0-elim.
Com_parison
∆I
IRISIT
Ir**Is**It**
IR*IS*IT*
Ir*Is*It*
Vectorgroup adapt.
Norm
Norm
JR-secJS-secJT-sec
Jr-prim
Js-prim
Jt-prim
JR-prim
JS-prim
JT-prim
Jr-secJs-secJt-sec
CT 1 CT 2W1 W2
I0-elim.
IrIsIt
( )TISIRI31
0I ++⋅=
0ITI*TI0ISI*SI0IRI*RI
−=−=
−=
( )tIsIrI31
0I ++⋅=
0ItI*tI0II*sI0IrI*rI
−=
−=
−=
s***
110011101
31
******
tIsIrI
tIsIrI
⋅−
−−
=
Example Yd5:
******
***
tIsIrI
TISIRI
TISIRI
+=
−∆−∆−∆
Digital transformer protectionAdaptation of currents for comparison (2)
Page 206 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Input data:•n times 30O vector group number
(only for 2nd and 3rd winding, 1st winding is reference)
•UN (kV) Rated winding voltage
•SN (MVA) rated winding power
•INW (A) Primary rated CT current
•Line or BB direction of CT neutral
•Elimination / I0-treatmentCorrection / without
•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?
minmax
minmaxN UU
UU2U+⋅
⋅=
At windings with tap changer:
Winding 1 (reference) is normally:
•High voltage side
Adaptation of currents for comparison Relay input data
Page 207 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Yd5
SN = 100 MVAUN2= 110 kVUN1= 20 kV
600/1 A3000/5 A
2.400 A7621 A
∆I
W2 W1
1 A
5 A
Digital transformer protectionCurrent adaptation, Example (1)
Page 208 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
525A110kV3
100MVAW1TrafoNI =
⋅=−−
4,57A4525600
NormI
A 4,024006001
sek-TS,R,J
=⋅=
=⋅=
357,4357,42
357,4
04,570
211121112
31
*tI*sI*rI
⋅−=−⋅−−
−−−−
⋅=
2887A20kV3
100MVAW2TrafoNI =
⋅=−−
A34,5734,428873000
NormI
A 34,43132003000
1sek-tr,s,J
=⋅=
=⋅=
3/57,43/57,42
3/57,4
0357,4
357,4
110011101
31
******
−⋅
−=−⋅
−−
−=
tIsIrI
000
34,5734,5734,57234,572
34,5734,57
**tI*TI**sI*SI**rI*RI
TAISAIRAI
===
−⋅+⋅−
−
=+=+=+
=−
=−
=−
110-kV-side20-kV-side
I0-elimination: Vector group adaptation: Yd5
Digital transformer protectionCurrent adaptation, Example (2)
Page 209 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
7UT6 Operating characteristic
1
2
3
4
1 2 3 4 5 6 7 8 9 10 11
Stable operation
Slope 1
Slope 2
I DIFF >>
5
6
7
8
Istab / In
I DIFF
= I STAB
00
9I1 I2
IDIFF = |I1+ I2|
IStab = |I1| + |I2|
7UT6
Additional stabilisation for high Is.c.
IDiff/ In
I DIFF >
Tripping area
Page 210 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
I0- elimination necessary at all windings with earthed neutral or with grounding transformer in the protection rangeEarth fault sensitivity reduced to 2/3 ! Incorrect fault type indication!
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.
As an alternative, earth differential protection can be used to enhance earth fault sensitivity.
I0-elimination / correction: Summary
Page 211 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Source: P.M. Anderson: Power System Protection, McGraw-Hill and IEEE Press (Book)
Transformer winding to earth faultSolid earthed neutral
h⋅UR
UR
IFIK
Infeed side
IF
IK
200 40 60 80 100
2
4
6
8
10
IFper unit
Short-circuited winding part h in %
Page 212 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
E
RF R
UhI ⋅=
Fn
nFK I
UUhI
wwhI ⋅
⋅⋅=⋅
⋅=
31
2
1
2ERRU
nUnUhKI ⋅⋅⋅=
12
312
Source: P.M. Anderson: Power System Protection, McGraw-Hill and IEEE Press (Book)
h⋅UR
RE
UR
IFIK
Infeed side
Short-circuited winding part h in %
MaxII
50
020 40 60 80 100
100%
IF
IK
Transformer winding to earth faultResistance or reactance earthed neutral
Page 213 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Location of the earth fault h in %20 40 60 80 100
Grid
Transformer winding to earth faultEarth fault in the delta winding
1
2
3
4
5 20%0%
R
33,3%
50%
100%
x In
IKIK
Page 214 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
IPx In
IF , IKx 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
05 10 15 20 25
2
4
6
8
10
IF
IK
Page 215 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
I>
∆ IEI0* I0**
IN
IRISIT
Restricted earth fault protection of relay 7UT6
Extended operating area:
Basic operating area:
NI
IsetOpIif ≥
Op II *0=
restr IIIII **0
*0
**0
*0 +−−=
TSR IIIII 0**
0 3=++==
for ( ) 0**0
*0
0 90/90 +≤≤− IIϕ
for ( ) 0**0
*0
0 270/90 +≤≤+ IIϕ
I *0
IrestrOPIif ≥
restrOp IkII 0*0 −= ·
Page 216 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Restricted earth fault protection of 7UT6Operating characteristic (2)
k0 =2ϕ Limit=110O
( )*0
**0 /IIϕ
180O 120O 110O 100O 90O 80O 70O 60O 50O
External fault
130O
K0 ϕ Limit
1.0 130
1.4 120
2.0 110
4.0 100
∞ 90
1II
*0
**0 =
Σ=
N
PhII
4
3
2
1
set-0
*0
I I
0O
Internal fault
Page 217 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
0
20
40
60
80100
120
140
160
180
200
220
240
260 280
300
320
340
2
1.6
1.2
0.8
0.4
0
*)*/I*(Ie**0I
*0I 00ϕ⋅
+1
BlockingTripping
K0= 4K0= 2
K0= 1.4
K0= 1
ϕ
Restricted earth fault protection of 7UT6Polar characteristic
Page 218 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Restricted earth fault protection 87N (7UT6)Application aspects
Increased sensitivity with earth faults near winding neutralPreferably used in case of resistance or reactance neutral earthingSensitive to turns short-circuitI0 / IN amplitude and angle comparison2nd harmonic stabilisedCan protect a separate shunt reactor or neutral earthing transformer in addition to the two winding transformer differential protectionNot applicable with autotransformers! (as only one stabilising input at transformer terminal side, -- high impedance principle to be used in this case.
Page 219 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
∆IE>IN
IrIsIt
∆IE>
IR
IS
IT
ZE
Transformer HI-earth fault protection
Page 220 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
IrIsIt
87
IRISIT
87 87
HI differential protection of an autotransformer
Page 221 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
IN
IrIsIt
∆I>
IRISIT
HI earth fault protection of an autotransformer
Page 222 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Transformer tank protection 64T: Principle
Insulated
IE>
Page 223 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Transformer Protectionwith
Siemens SIPROTEC7UT6
7UT612
Transformer protection, Relay design
Page 224 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
YN yn0 d5RST
ϑ>(2)
I>>,I>t
ϑ>(1) ∆ITE ∆IT
Digital transformer protection relay 7UT613:Current inputs and integrated protective functions
Page 225 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Relay 7UT6: Application examples
Two winding transformer
Three winding transformer
Busbars
G ∆I
Generator / Motor
∆I
Shunt Reactor
∆I
∆I ∆I
∆I
Transformer bank (1-1/2-LS)
∆
∆I
Page 226 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
1
2
3
4
1 2 3 4 5 6 7 8 9 10 11
Restraining area
slope = 1/2 of 1606
pick-up limit (left border line) = (1618 )
slope 1
(1606)
slope 2
(foot p
oint= 1607, s
lope = 1608 )
I DIFF >> (1604)
5
6
7
8
Istab / In
I DIFF
= I STAB
00
9I1 I2
IDIFF = |I1+ I2|
IStab = |I1| + |I2|
Tripping area
7UT61
Add-on restraint for high ISC
IDiff/ In
I DIFF >(1603)
7UT6Operating characteristic
Page 227 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
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 228 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Transformer differential protection∆I> Rush-stabilised (2nd harmonic)Stabilised against overfluxing (5th harmonic)∆I>> high set element, non-stabilised
Thermal overload protection
Time overcurrent protection (IT or DT)
Earth current differential protection (7UT613)
Tank protection (7UT613)
49-149-2
50/5150HS
87T
87N
64T
7UT6Integrated protection functions
Page 229 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Application examples
Page 230 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Protection of a two winding transformer
7SJ600
W2 (US)
W1 (OS)
49
87T
51
50 51
52 52
52
52
7UT512
Bu
W2
W1
Page 231 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Protection of a three winding transformer
7UT513
52
52
W1
W3
49-1
87T
49-2
51
7SJ600
50 51
W3W2
W1
Load
Bu
W2
Page 232 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
W1
W2
7SJ600
W2 (US)
W1 (OS)
49-1
87T
50 51
52 52
52
52
51
87TE
7UT513
Restricted earth fault protectionfor a two winding transformer
ZE
Bu
Page 233 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Protection of an autotransformer
3YLoad
52
52
4987TL
51
87TH
505151BF
7VH600 7UT513
597SJ600
7SJ6007RW600
50BF
51N
7SJ600
5051
51N
50BF
52
Bu
Page 234 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
Protection of a large transformer bank
3Load 52
4987TL
51
49
87TH
7SA6
7VH6 (3)7UT513
59N
7SJ67SJ67RW6
50BF
50BF4921
52
51BF21
7SA6
51N
52 52
Page 235 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
52
52
G ∆IG
∆IT
52
G ∆IG
∆IT
52
G ∆IG
∆IT
52
G
∆IT
Differential protection of generation units
Page 236 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
52
52
G ∆IG
∆IT
52
∆IT
*)
*) same ratio as generator CTs
Auxiliaries
Differential protection of generation units (2)
Page 237 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
ΘCu ΘOil
C1 C2
Rth1 Rth2
PCu PFe
ΘAmb
Legend:PCu: Winding losses (I2·R)
PFe: Core and tank losses
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
Thermal protection of transformers
Lifetime of insulation depends on the
winding Hot-spot temperature.
6 OC higher temperature increases the aging of the insulation by the factor 2!
Page 238 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
7SA6: Temperature monitoring
Two thermo-devices can be connected to the serial service interfaceMonitoring 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
RS485 Interface
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:
Oil -Temp.
( )OilCuTh
2
Th
Cu 1IrI1
dtd
Θ−Θ⋅τ
−⎟⎠⎞
⎜⎝⎛⋅
τ=
Θ I = actual transformer currentIr = rated transformer currentτth =time constant of the winding
Page 239 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
7UT6: Temperature monitoring with hot spot calculation (1)Example: Natural cooling
HVLV
Oil -Temp.
YgrOh kHΘΘ ⋅+= Θh= hot spot temperature
Θh= oil temperature
Hgr=hot-spot-to-oil temperature gradient
k= load factor I/In
Y= winding exponent
98)/6(Θ2C98at AginghΘat AgingV h −=°
=
∫ ⋅⋅−
=2
1
T
T12
dtVTT
1L
Aging rate:
Mean value of aging during a fixed time interval:
98O is reference for the aging of Cellulose insulation
Page 240 2007-08Copyright © Siemens AG 2007. All rights reserved.
PTD SE PTIAuthor: G. Ziegler
1.622V 98)/6(10298)/6(Θh ≈== −−
C1021.152373kHΘΘ 1.6Ygroh °=⋅+≈⋅+=
ΘhΘo
t
[°C]98°C
Θh Hot spot temp.
1.6
102°C
1.15
73°C
k (I/In)
108°Ck,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