Dr.dharshana-Power System Studies Best Practices & International Experiences

April 5, 2017 | Author: boopelectra | Category: N/A

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There are a variety of simulation tools used in power system studies to predict system behaviour. - Load flow - Transient stability - Fault studies - Harmonic analysis - Electromagnetic transient simulations. The fundamental difference between betw een an electromagnetic transient (EMT) type simulation and other types of simulations is in the way w ay the electrical circuit response is mathematically represented. - EMT programs represents the power pow er system response by the respective differential equations. - Other programs represent the power pow er system response by reducing the differential equations to the respective ‘phasor’ form.

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There are a variety of simulation tools used in power system studies to predict system behaviour. - Load flow - Transient stability - Fault studies - Harmonic analysis - Electromagnetic transient simulations. The fundamental difference between betw een an electromagnetic transient (EMT) type simulation and other types of simulations is in the way w ay the electrical circuit response is mathematically represented. - EMT programs represents the power pow er system response by the respective differential equations. - Other programs represent the power pow er system response by reducing the differential equations to the respective ‘phasor’ form.

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All the above features make EMT the most accurate and detailed simulation method available to power system engineers. - It should be noted that such level of details is not required for every analysis. As an example, the load flow solution is essentially a 50 Hz, steady state situation. The power system elements can be represented by the corresponding phasor equations to obtain the correct solution.

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Overvoltage magnitudes and equipment insulation levels -

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Statistical distribution of overvoltage magnitude

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Transmission line ‘flash-over’ rates

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R n e I   r a u c s t   o h r 2 5 M V a r C s p a e p r a p c i   h t   o a r s e /   s t   e p

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TRV is the voltage developed across the breaker poles immediately after current interruption - Fast event - Simulation circuit should consider details of station equipment - Breaker TRV withstand capability limits TRV

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Voltage dips and flicker caused by frequent starting of large motors at industrial plants is a power quality concern for utilities - Model data to match manufactures T-S and I-S curves - Impact of rotating inertia - Power System impedance characteristics near the interconnection point - Representation of load characteristics and the overall impact. Motor starting transients

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Electrical studies: • Switching, and temporary over voltages • Ferro resonance • Harmonic impacts • GIS Very Fast Transients.

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TRV_env _A100

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L2C

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A V

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T TYL2_b

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BT3

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freq F

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E1

   1    E

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-300 400

E2

   2    E

-300 25.0    1    L    Y    T    I

   l   a   n   g    i   s    1   a    B

ITYL1

-20.0 1.00

Ba1

0.0 1.150

1.200

1.250

1.300

1.350

1.400

1.450

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60 40    t   n   e   r   r   u   c    t    l   u   a    F

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2.80

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3.20

3.40

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a n : ra s 50

Isc

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10 0 -10 -20 0.0

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2.0

3.0

4.0

5.0

6.0

7.0

8.0

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T TLine1

I1

RRL

T TLine2

V1

   Q    j   +    P

75 km long second 230 kV transmission line T TLine3

Type1 Timed Fault Logic

RR L

Type2 Timed Fault Logic

Type3 Timed Fault Logic

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k 1 ⋅ r + k 2 r

dr dt

=

k

3

m+ 2

r

⋅i

2

EAF Model V-I Characteristics closely follow field measurements

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1   n   o    i    t   c   e    S    I    P

   L    R

B R K 4 6 _ 1

3

MHSAJAPA B R K 4 6 _ 2

2

4 PI Section

3

Arc furnace facility

PI Section

# 1

6

5 15

PI Section

# 2

14

BRK

MHSAJAPA

PI Section Eln

11 P I   S e c t   i   o n

20

QUEZALTEPEQUE 46kV # 1

5

# 2

10 PI Section

CARGA HORNO

EAF Facility

Network model developed in PSCAD for a recent eaf flicker mitigation study performed by MHRC engineers.

PI Section

12 QUEZALTEPEQUE 23kV

  n   o    i    t   c   e    S    I    P

  n   o    i    t   c   e    S    I    P

17 18

7   n   o    i    t   c   e    S    I    P

P I   S e c t   i   o n

10

PI Section

RRL

9 SITIO NINO 13 - 46kV

MATADEROS

RL

Mataderos Equivalent

13 8 SITIO NINO 23 - 46kV

5 # 1 # 2

12

P I   S e c t   i   o n

  n   o    i    t   c   e    S    I    P

14

20 SITIO NINO 23 - 23kV

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    L     R

The arc furnace absorbs about 25MW and 8.5MVAr from the grid. The voltage at bus 5 drops to 0.98p.u. (45.08kV).

    R

   n    o     i     t    c    e     L

    S     I

    R

    P

MHSAJAPA B

2

B

R

R

K

K

4   6   _ 1

4   6   _ 2

3

4 PISection

3

Arcfurnacefacility

PISection

#   1

6

5 15

PISection

#   2

14

BRK

MHSAJAPA

PISection Eln

11 QUEZALTEPEQUE46kV

P I    S e c t    i    o

#   1

5

n

20

#   2

10 PISection

CARGAHORNO

EAF Facility

The arc furnace also causes flicker with an instantaneous flicker level (I FL) of about 16.6 at the POI.

PISection

12 QUEZALTEPEQUE2 3kV 17

   n    o     i     t    c

   n    o     i     t    c

   e

   e

    S     I

    S     I

    P

    P

18 P

10

I    S e c t    i    o

7

n

   n    o     i     t    c    e

9

PISection

RRL

    S     I     P

SITIO NINO 13 - 46kV

MATADEROS

RL

The simulated voltage waveform at bus this matches field recordings and measured flicker levels. This validates the study model.

Mataderos Equivalent

40

13

Vbus

8 SITIO NINO23- 46kV

30

5 #   1

P

20

I    S #   2

12

e c t    i    o n

10

   n    o     i     t    c    e     S     I     P

    V     k

0 -10

14

-20 20 SITIO NINO23- 23kV

-30 -40

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25 46 [kV] / 0.58 [kV] A V

#1

#2

0.0348 13.14 Ohms - 0.0348 H

4HP

1 4 8 8

3P

1 1 0 . 5 [   m H ]

1 4 8 .7 [   m H ]

4 .1 2

5 .4 4

Varc

1 . 0 e 9 [   o h m ]

Ia

Ib

Ic

Ext.

    0 .     1

Ig

The electrical network of the industrial plant must also be modeled in adequate detail - EAF characteristics are represented by the detailed model available in PSCAD - Filters - SVC and FACTS devices if present - Transformers, lines, cables, other loads - Motor loads with appropriate load characteristic representation to capture their contribution to voltage fluctuations

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STATCOM with special auxiliary control loops targeting flicker mitigation is a viable mitigation method. This principle was used in a recent study for the arc furnace flicker mitigation performed by MHRC.

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i furnace

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G G 1

P = -0.5274 Q = 0.9126 V = 45.86 A ABC V

P = -0.5281 Q = 0.9862 V = 0.4574

2 [MVA] 46 [kV] / 0.48 [kV] #1 #2

SrcLV Is_LV ELV

F   = 4   5   0   [    H z ]

A V

Q

D

2

G G 3

Q

D

2

G G 5

Q

D

2

6   0   0   0

V _dc + 6   0   0   0

Lf

G G 4

Q

D

2

G G 6

Q 2

D

G G 2

Q

D

2

DC

STATCOM model implemented in PSCAD

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iq B iqref

D

+

-

0.395 MaxVq [kV]

Kpq Kpq1

-0.395 MinVq [kV]

Out

Anti-

MaxVq

Rs t Rst

-0.395 MinVd [kV]

A

MinVq

Kpd Kpd1

+

vd

Tid

D

+

vq1 Tid1

F

MaxVd MinVd

vd1

-

vd1

F wL

wL id

0.395 MaxVd [kV]

wind-up

A

Tiq1

Out

Anti-

+

idref D

wind-up Rs t Rst

Tiq

PI

In

-

PI

In

iq

* wLf

* wLf

Refa3 B

Modulation references

Edc X

M

Y

vd1

D

* 0.5 M N

X

M MagInv

N/D

Y

P phase

PhaseInv

M

D Q

A B

X

0

C

P

X Y

Refa

D

P

vq1

+

P

Y

D

-

Refb

B Refa3

   0 .    0

* 57.2958

+

D

+ -

Refc

B Refa3

MagInv

PhaseInv

Theta

* 3

* 3

* 0.16

Angle Resolver

X

M P P Phaseh3

M

Y

Magh3

X

Y    0 .    0

D Q

A B

0

C

Refa3 Refb3 Refc3

Angle Resolver Theta3

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+

   0 .    0

D

-

+

P

-

d PI out

I

B

Ib_ac

id Regulator

idref Err_d * Ifurd_err

A D ++

vd

Ic_ac

* L

Ifurq_err

*

D

+

Vref

+

-

B VmagPU Vpcc

I

C

0

Ifurq

X1

id furnace Ifurd

F FT

vq * -1

A D

+

Calculate d & q components of the furnace current.

X2 Ifurq

Ph2 D (7) Ifurq + dc2 B Ifurq_d c Ifurq_dc

F = 10 [Hz] dc1

iq regulator

vq1 vq1

F

wL id

* 377

* L

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iq furnace

q PI out

I

Err_q

D

Ifurc

D Ifurd Q

P

-

B

P

iq iq

A B

Ifurd_d c

iqref -

0

Ifura Ifurb

Calculate d & q components of the ac-side current. iq B

D +

C

id id

vd1 vd1

wL * 377

D Q

-

F

iq

A B

Ia_ac

Mag2 D (7) + Ph1 Ifurd (7) B Ifurd_dc

Mag1 (7)

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EAF_Facility 40

40

Vbus

30

20

20

10

10

   V    k

0

   V    k

Vbus

30

0 -10

-10

-20

-20

-30

-30

-40

-40 1.0000

Vbus_rms

POI voltage waveform (Zoomed view)

0.9950 0.9900 0.9850    V    k

0.9800 0.9750 0.9700 0.9650 0.9600

t me s)

3.900

3.950

4.000

4.050

4.100

POI voltage waveform (instantaneous and rms)

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Bus 1 Bus 2

#1

#2

P = 24.65 Q = -10.58 V = 118.1 A V

   L    R    R

T TLine_02

T TLine_01

Ia

#1

#2

A

Compressor Motors

45 km line 100 km line

   L    R

345 kv 'Weak system

Ea

System Model and the Synchronous motors driving the compressor load.

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pu

Torque1 1 sT

327.27273 rpm - 22 Pole machine

* -1.0

G 1 + sT

Degrees

Clear

Torque1.dat 1

Average Torque = 0.82 pu (approx) 6 units are pulsating as one Zero Detector

-

+ D

F

The compressor characteristics are stored in a data file.

   0 .    0    6    3

Actual load torque characteristics (torque vs rotor angular position) is stored in a look- up table and fed into the study model to get realistic simulation waveforms, replicating flicker measured in the field.

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  y

  y

  y

  y

98.0 97.0 96.0 95.0 94.0 93.0 92.0 91.0 90.0 0.30 0.20 0.10 0.00 -0.10 -0.20 -0.30 120.0 119.0 118.0 117.0 116.0 115.0 114.0 113.0 30 20 10 0 -10 -20 -30 6.50

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10.00

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176 km Tesla

a 1

147.04 km

b

TLine_11    9    8 .   5 .   9    8    2   1    3    4    9    6   2   - .    A   V   =  =   0    P   Q  =    V

CTT_WD_...

CTT_GR_...

W h i   t   e d e e r

4.81

Hereford

GEN

7.40

E1    ]    H    [ ABC->G    6    1 .    3

TLine_8

a 2

Timed Fault Logic

68 km

Bus 1

Series Caps b a

CTT_ST_T...

68 km CTT_ST_T...

121.6 km

Rieley

52.8 km

76.8 km

102.4 km

Sh_WD_ST

TLine_12 ETT_TS_...

P = 2190 Q = 796.8 V= 1.067

TLine_9

A V

   3    3 . .   8    8    5   6    8    0   6   9    8   3   - .    A   V   =  =   0    P   Q  =    V

99101

Thermal Gen

NAZARETH

67.2 km a1 Silverton

Ea

a2

RRL

ETT_TS_...

a3 7.42 70.2 km

b

ETT_RL_...

250 a SVC Edith Clarke

7.41

100.8 km 121.2 km

Sh_ST_CW

ETT_EC_...

SVC Cottonwood P = 798.5 Q = -369.3 V= 1.055 RRL

A V

   ]    H    [    6    1 .    3

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Response of the system following a fault (cleared in normal time) is shown below for the two scenarios that were studied. In the ‘strong’ connection case, the system seems better damped than in the ‘weak’ connection case. The SVC keeps oscillating between its minimum and maximum Q limits. This is unacceptable control performance. Such issues should be identified at the design stage. Control parameters may be re- tuned to mitigate the issues. SVC_Page : Graphs 1.20

SVC_Page : Graphs

Vpu

1.20 1.00

1.00

0.80    )   u   p    (   y

0.80    )   u   p    (   y

0.60

0.40

0.60 0.40 0.20

0.20

Strong system response

0.00 250

Vpu

Weak system response

0.00

Qsvc

300

200

Qsvc

200

150

100

100    )    R    A    V    M    (   y

   )    R    A    V    M    (   y

50 0 -50

-150

-300 x

-200 0.0

-100 -200

-100

x

0

2.0

4.0

6.0

8.0

10.0

0.0

1.0

2.0

3.0

4.0

5.0

12.0

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A typical LCC - HVDC Scheme Power flow is from the rectifier to the Inverter side 0.5968 [H]

2.5 [ohm]

2.5 [ohm]

0.5968 [H]

Rbus    C    A   r_   e    i    f    i    t   c   e    R

Ibus

2 6 . 0 [   u F ]

A V

A V

Rectifier

Inverter

Rectifier

Rectifier 1.50

AC Voltage

2.00

DC Volts

Rectifier

DC Current

1.50

1.50

0.50    e    g    a    t    o

0.00

    )    u    p     (

-0.50 -1.00

    )    u    p     (

1.00

   e    g    a    t     l

   o     V

0.50

0.50 0.00 -0.50 -1.00 -1.50

-1.50

-2.00

0.00

-2.00 1.660

ACVoltage

1.00

1.00    u    p     (

I   n v e r t   e r _ A C

1.680

1.700

1.720

1.740

1.760

1.780

1.800 ... ... ...

1.660

1.680

1.700

1.720

1.740

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1.760

1.780

1.800

1.660

1.680

1.700

1.720

1.740

1.760

1.780

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1.800

... ... ...

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Power

Id

Rectifier

1

Inverter

+ Vd or Ed

7

5

6

3 4 2

Id

1 Valve group 2 AC Filter 3 Converter transformer 4 DC filter 5 Ground/sea electrode or metallic 6 Receiving ac system 7 Sending ac system

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Introduction The basic building block of a LCC converter – a six pulse Thyristor bridge.  It

is important to note that the thyristors (the switch) can be turned ON with a firing pulse but cannot be forced to turn OFF. The turn off should happen ‘naturally’ when certain ac system conditions are satisfied (more details on this later !)

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12 pulse bridge – The harmonics are reduced compared to the 6 pulse bridge. ��

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12 pulse bridge – Mono pole system

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Bi-pole system, 1- 12 pulse valve group per pole

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147.04 km

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a 1

CTT_WD_...

CTT_GR_...

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b

TLine_11     9     5     8 . .     8     9     2     4     1     3     9     2     6     V   - .     A     0   =  =   =     P     Q     V

h   i    t   e d   e e r

4.81

Hereford

GEN

7.40 a 2

E1     ]     H     [

ABC->G

TLine_8

    6     1 .     3

Timed Fault Logic

68 km

Series Caps b a

CTT_ST_T...

68 km CT T_ST_T...

121.6 km

Rieley

52.8 km 76.8 km

102.4 km

Sh_WD_ST

TLine_12 ETT_TS_...

P= 2190 Q= 796.8 V= 1.067

TLine_9

A RRL V

    3     8     3 . .     8     6     5     8     6     0     9     3     8     V   - .     A     0   =  =   =     P     Q     V

99101 NAZARETH

67.2 km a1 Silverton

Ea

a2

ETT_TS_...

a3 7.42 70.2 km

b

ETT_RL_...

250 a SVC Edith Clarke

7.41

100.8 km 121.2 km

Sh_ST_CW

ETT_EC_...

Cottonwood P = 798.5 Q= -369.3 V= 1.055 RRL

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INVERTER CONTROLS

CO

INVERTER CURRENT CONTROLS

current order for rectifier DC Voltage (compensated)

VDCI

G 1 + sT

D

+

E VDCL

+

D

CORD

Min

MPVS

CORDER

F

voltage compounding

dc voltage measured at inverter

V ol ta g e D e p .C u rr e nt L i m it

   1    *   0 .    0

*

R e ct if ie r C u rr e nt O rd e r

POWER

CMARG

F CMIC

G 1 + sT

D CMIS

-

+

PSCAD implementation of a conventional HVDC inverter controls for thyristor firing pulses.

0.1

Power F CERRI

D

+

-

P

CERRIM

BETAIC

I Current (filtered)

dc current measured at inverter

Angle Order for inverter

Pi B Max

D

INVERTER GAMMA CONTROLS

DGEI

BETAI D

-

+

AOI

E Delta Gamma Error

Alpha Order

F GMES

Min in

GMESS

D

1 Cycle

-

+

B Gamma

Gamma Angle measured 0.2618

P

GERRI

Max

D

+ -0.544

GNLG

I

BETAIG

E

GMIN

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Line Commutated HVDC systems        

Basic concepts Commutation Harmonics Reactive power and filtering Basic HVDC equation Control concepts Impact of AC systems strength Impact of AC System Characteristics

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Ia R=0

Vas

Main : Graphs

   )    V    k    (    e    g    a    t    l    o    V

   )    A    k    (    t    n    e    r    r    u    C

   e    s    l    u    p    g    n    i    r    i    F

10.0 7.5 5.0 2.5 0.0 -2.5 -5.0 -7.5 -10.0 4.0 3.0 2.0 1.0 0.0 -1.0 -2.0 -3.0 -4.0 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00

FP

7.03 kV rms (l-n)

Vas

Ea

T

T FP

0 . 0 0 3 9 3 [   H ]

Load cur

33 MVAR (Max)

Ia_ 4.0

FP1

0.1700

0.1750

0.1800

0.1850

0.1900

0.1950

0.2000

0.2050

0.2100

0.0

[1] 2.30468

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Ia

Ea

1.00

T1 R=0

g1 T

T3

g1 T

  y

E1

g1 T

0.50

g1 T

T4

0.00

T2

200

E1

Ea

150 100 50 0

  y

-50 -100

Firing angle (alpha) = 30 deg

-150 -200 2.0550

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2.0600

2.0650

2.0700

2.0750

2.0800

2.0850

2.0900

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Ia Ea

1.00 g1 T

R=0

g1 T

E1

0.50 g1 T

g1 T

0.00 200

E1

Ea

150

Firing angle (alpha) = 90 deg

100 50

Average dc voltage is zero

  y

0 -50

Half cycle for thyristor to turn OFF

-100 -150 -200 2.0550

��

2.0600

2.0650

2.0700

2.0750

2.0800

2.0850

2.0900

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Inverter:

Ia Ia

1.00

Ea

g1 T

R=0

g1 T

0.50

E1

g1 T

g1 T

0.00 200

Firing angle (alpha) = 135 deg Average dc voltage is now negative

E1

Ea

150 100 50 0 -50

Very small time for thyristor to turn OFF

-100 -150 -200 2.0550

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2.0600

2.0650

2.0700

2.0750

2.0800

2.0850

2.0900

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Ia    1    T    I

Ea

   2    T    I

g1 T

1.00

g1 T

  y 0.05

0.50

E1

1e6

0.00 g1 T

g1 T

200 150 100 50 0 -50 -100 -150 -200

Effect of AC system reactance •Over-lap angle (period)   y

1.20 1.00 0.80 0.60 0.40 0.20 0.00 -0.20

E1

Ea

IT1

IT2

2.0550

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2.0600

2.0650

2.0700

2.0750

2.0800

2.0850

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2.0900

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Vd = 1.35 * Ell * cos( ) − π 3 ∗ Xc * Id Inverter

Vd = 1.35 * Ell * cos( ) − π 3 ∗ Xc * Id

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Dr.dharshana-Power System Studies Best Practices & International Experiences

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