vattenfall peter olsson transient studies

1 | Transient studies | Peter Olsson | 2011.12.06

Transient studiesPresentation

2011-12-06

Confidentiality -2 | Transient studies | Peter Olsson | 2011.12.06

Peter Olsson

Staffanstorps Energi ABElectrician

Lund Technical UniversityElectrical engineering

Vattenfall Eldistribution ABProtection, control room, calculations and analysis and transformers

Vattenfall Research and Development ABSimulation and analysis of power systems


Agenda

Why transient studies

Methods

Some examples


Need for transient studies

Insulation coordination- Resonance- Switching surges- Fault initiating or clearing- Induction between systems- Lightning induced voltages

Power quality- Transformer or reactor energising- Cable or over head line energising- Harmonics

New configurations of grid layout- Extreme values of RLC- Wind power towers and lightning


Method

Mainly PSCAD/EMTDC but also Matlab - SimPowerSystems

Using models - In the PSCAD/EMTDC library- From PSCAD/EMTDC support- Developed by Vattenfall- Developed by suppliers- Developed by Universities

Using theory described in- Literature- Papers- PhD and Master thesis

Simulating frequencies in the range from 50 Hz up to MHz - high frequency models are needed.

Simulation time steps of 10 ns can sometimes be necessary.

PSCAD/EMTDC is a simulation tool for electromagnetic transients.

PSCAD/EMTDC is a flexible tool that gives the user large freedom to implement that of interest.

EMTP Theory book (from 1970-th)Papers


Method

Cable model in PSCAD/EMTDC Mathematical model of

the cable by using the physical parameters

The user defines the physical layout of the conductors.

Only one phase cables can be modelled.

Frequency dependant cable impedance.

Cable models are validated in others work

0.009 [m]

Cable # 1

0.017 [m]0.01735 [m]

0.023 [m]

1 [m]

0.3 [m]

ConductorInsulator 1

SheathInsulator 2

0.003 [m]

Cable # 4

0.3 [m]

0.82 [m]

0.6 [m]


0.009 [m]

Cable # 2

0.017 [m]0.01735 [m]

0.023 [m]

0.948 [m]

0.33 [m]


SheathInsulator 2

0.009 [m]

Cable # 3

0.017 [m]0.01735 [m]

0.023 [m]

1 [m]

0.36 [m]


SheathInsulator 2

0.003 [m]

Cable # 5

0.3 [m]

0.82 [m]

0 [m]



Method

Transformer model in PSCAD/EMTDC

0.001 [uF]

0.001

[uF]

0.001

[uF]

#2umec

#1

Mathematical model of the transformer using electrical design parameters

Saturation is available in the model

Remaining flux is not internally modelled but can be added by an external DC current source

At higher frequencies the transformer capacitances has to be added externally


Examples of transient studies made by Vattenfall

Resonant over voltages during faults

Lightning currents in cable and earthing system


Resonance model and simulation


Resonance

Simulation study made in PSCAD/EMTDC with a 130 kV feeding grid connected to a 30 kV wind power cable grid

Changing the capacitance by adding and removing cables.

Changing the inductance by adding and removing Over Head line

Simulations of wind power grid indicating that high over voltage occurs in the connected underlying 30 kV grid during fault initiation and fault clearing

Cable OH-lines

Cables

~

130/30 kVFeeders

Tower

~130 kV

LSC RSC

R130

C130

L30

R30

C30

Electrical equivalent

130 kV cables

130 kV short circuit impedance

130 kV fault 30 kV cables

130/30 kV transformer


Cable OH-lines

Cables

~

130/30 kVFeeders

Tower

Resonance

Simulation results of fault in 130 kV grid

0.0300 0.0310 0.0320 0.0330 0.0340 0.0350 0.0360 0.0370 0.0380 0.0390 0.0400 ... ...

...

-250

-200

-150

-100

-50

0

50

100

150

200

V

(

k

V

)

Ea130 Eb130 Ec130 E0130

Time ... 0.0300 0.0310 0.0320 0.0330 0.0340 0.0350 0.0360 0.0370 0.0380 0.0390 0.0400 ... ...

...

-150

-100

-50

0

50

100

150

V

(

k

V

)

Ea Eb Ec

30 kV phase to earth voltages130 kV phase to earth voltages

Frequency of the oscillations is ~800 Hz. The rise time of the voltage from zero to the maximum value is about 300 s.

130 kV voltage during the fault

Fault is cleared

130 kV voltage after fault clearance. Oscillating frequency is ~800 Hz

Max voltage is 130 kV, that is about 4.5 p.u.


Resonance

~130 kV

LSC RSC

R130

C130

L30

R30

C30

Impedance from 130 kV towards 30 kV grid.The series LC-circuit have a minimum at the resonant frequency

130 kV impedance without the 30 kV grid connected.The parallel LC-circuit have a maximum at a resonant frequency

1

10

100

1000

10000

100000

1000000

10000000

10 100 1000 10000f(Hz)

I

m

p

e

d

a

n

c

e

(

|

O

h

m

|

)

130 kV: |Z+|(Ohm)30 kV: |Z+|(Ohm)

The impedance at the resonant frequency is: Z=R+j(XL-XC)~R

Only the resistance limits the current, and voltage.

The resistance can be low in these cable networks

The 130/30 kV transformer and 30 kV grid acts like a consuming filter for this frequency.

Grid impedance at different frequencies


ResonanceFrequency components in the 130 kV voltage

~130 kV

LSC RSC

R130

C130

L30

R30

C30

30 kV connected30 kV not connected

A

m

p

l

i

t

u

d

e

(

k

V

)

Frequency (Hn)

Hn=16fn=800 Hz

Frequency component of the oscillating 130 kV voltage after the fault is cleared when the 30 kV grid is disconnected.

Frequency component of the oscillating 130 kV voltage after the fault is cleared when the 30 kV grid is connected.

0.0300 0.0310 0.0320 0.0330 0.0340 0.0350 0.0360 0.0370 0.0380 0.0390 0.0400 ... ...

...

-250

-200

-150

-100

-50

0

50

100

150

200

V

(

k

V

)

Ea130 Eb130 Ec130 E0130


Resonance

Insulation coordination

Mainly three tests are performed to verify the degree of insulation of equipment

- Nominal frequency tests, AC, to verify this frequency voltage withstand level. Test voltage level for 36 kV is 70 kV (IEC)

- Lightning Impulse tests, LI, to verify the withstand level against lightning induced voltages. Rise time of the test voltage is 1.2 s Test voltage level for 36 kV is 145 or 170 kV (IEC)

- Switching Impulse tests, SI, to verify the withstand level against switching induced voltages. Rise time of the test voltage is 250 s Not defined for 36 kV but the level is assumed to

be in the order of 80-85 % of the LI-level.

Frequency of the calculated over voltages in the example is ~800 Hz. The rise time of the voltage from zero to the maximum value is about 300 s. Voltage withstand test at this frequency may therefore be verified by SI test.

SI(36 kV) ~ 0.83*LI(36 kV) = 120/141 kVThis shall be compared with the calculated voltage of 130 kV

This can lead to that higher insulation level for the equipment is needed.


Lightning model and simulation


Lightning

Wind power tower model developed by using a the frequency dependant phase cable model in PSCAD/EMTDC

Conductor

ScreenTower

Insulation

Injected current

Inner conductor, first insulation and second conductor represent a cable within the tower

Second insulation represent the air between the cable and steel tower

Third conductor represent the steel tower

Cable conductorScreen

Earth wire modelled as a distributed parameter line


Lightning

Voltage in the figure is calculated 90 m from A, in C. Blue curve is the voltage in the earth wire and green curve is the induced voltage in the cable screen.

Practical implication: Have large physical distance between parallel different earth systems?

0.100m 0.101m 0.102m 0.103m 0.104m 0.105m 0.106m 0.107m 0.108m 0.109m 0.110m ... ...

...

-200

-100

0

100

200

300

400

V

(

k

V

)

EE6 EE7

30 m 30 m 30 m 100 m 100 m0 m

300 m

A B

C

Conductor

ScreenTower

Insulation

Calculated voltage difference of 400 kV

Parallel earth wire and cable not connected at the same potential


Lightning

The red curve is the voltage in the earth wire and the green/blue curve is the voltage in the cable screen/phase.

The figures shows the calculated voltage at [0 100 1000] meters

The injected current in the screen and the earth wire is 50 kA with 1 s rise time

The soil resistivity is 1000 Ohm*m. At other soil resistivity the damping is different.

It seems like the positive influence of an earth wire is practically gone at a certain distance, determined by the soil resistivity!

0 .0 9 m 0.1 0 m 0 .11 m 0 .1 2m 0 .1 3 m 0.1 4 m 0 .15 m 0 .1 6 m 0.1 7 m 0 .18 m 0 .1 9m 0 .2 0 m ... ...

...

-0 .2 k

0 .0

0 .2 k

0 .4 k

0 .6 k

0 .8 k

1 .0 k

1 .2 k

V

(

k

V

)

EE4 EE3 EEC2

0 .0 9 m 0 .1 0 m 0 .1 1 m 0 .1 2 m 0 .1 3 m 0 .1 4 m 0 .1 5 m 0 .1 6 m 0 .1 7 m 0 .1 8 m 0 .1 9 m 0 .2 0 m . . . . . .

. . .

- 1 0 0

0

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

6 0 0

7 0 0

V

(

k

V

)

EE2 4 EE1 4 EE1 3

0 .0 9 m 0 .1 0 m 0 .1 1 m 0 .1 2 m 0 .1 3 m 0 .1 4 m 0 .1 5 m 0 .1 6 m 0 .1 7 m 0 .1 8 m 0 .1 9 m 0 .2 0 m ... . . .

. . .

-1 0 0

-5 0

0

5 0

1 0 0

1 5 0

V

(

k

V

)

EE3 0 EE3 1 EE3 2

100 m 100 m 100 m 100 m 100 m0 m

100 mAll voltages are the same at 0 m

Different damping gives different amplitude after some distance

10 s


Lightning

The figure is showing the voltage at the beginning of the wire as a function of total wire length, soil resistivity and rise time of the injected lightning current, of 100 kA

0

1

2

3

4

5

6

7

1 10 100 1000 10000

Length (m)

V

o

l

t

a

g

e

(

M

V

)

100 Ohm*m, 1/501000 Ohm*m, 1/5010000 Ohm*m, 1/5010000 Ohm*m, 2 // wires, 1/50100 Ohm*m 8/201000 Ohm*m 8/20100000 Ohm*m 8/20

Conductor

ScreenTower

Insulation

As expected, different soil resistivity gives different efficient length of the wire

Different rise time also gives different efficient length of the wire

Two earth wires are more efficient than increase length


Thank you for your attention

Questions?

vattenfall peter olsson transient studies

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