Gult-TS1-GTS1 - Sheath Voltage Cal_2016!07!10

Calculations of Induced Sheath Voltage for 115 kV Feeder From GTS1 to EGAT GULF - TASIT 1 Project

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

Power Cable Calculation

115 kV Power Cable

MVA  kV  kA

C  K

CABLE TYPE:

115 kV CU/XLPE/CWS/PE cable, Single Core, copper conductor, wi th co pe r wi re shi el d, 1 x 800 mm2

CONNECTION:

Gulf-Tasit 1 Project to EGAT substation

INSTALLATION PLACE:

Rayong

METHOD OF INSTALLATION: Single core of triangle formation arrangement installed in HDD.

REFERENCES: 1.

ANSI/IEEE, 575-1988, IEEE Guide for Application of Sheath-Bonding Methods for Single-Conductor Cables and the Calculation of Inducted Voltages and Current in Cable Sheaths

2. IEEE 80-2000: IEEE Guide for Safety in AC Substation Grounding 3. IEC 60502-1: Cables for rated voltages of 1 kV ((Um = 1,2 kV) and 3 kV (Um = 3,6 kV)

DATA: a. System Data U  115000

(phase to phase voltage, V)

f  50

(system frequency, Hz)

ω  2  π  f

(angular frequency of system, Hz)

b. Cable Data

Prepared by : Raktham S.

See detaild technical data of power cable in ANNEX 1

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

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Power Cable Calculations Sheath Induced Voltage

np  2

(number of cable in parallel)

Acc  800

(cross-section of conductor, sq.mm) 3

dbcs 

( 74.07  76.15)  10

(outer diameter below metalic copper screen, m)

dbcs  0.0751

2 3

dacs 

( 77.17  79.25)  10

tcws  dacs  dbcs dmm 

(outer diameter above metalic copper screen, m)

dacs  0.0782

2

dbcs  dacs

(thickness of copper screen wire, m)

tcws  0.0031

(mean diameter of metalic copper screen, m)

dmm  0.0767

2

c. Installation

Refer to Plan and Section Drawing in ANNEX 2

c.1 Underground Cable between SD-UG-2(1) to SD-UG-2(3) SM1  12  70  106.25  59.7  168.72  119.75  20  12

SM1  568.42

m.

Select the single point bond at one end by sectionalizing the sheath at MHE3. SM11  12  70  106.25  59.7

SM11  247.95

(cable length from SD-UG-2(1) to MHE3, m)

SM12  168.72  119.75  20  12

SM12  320.47

(cable length from MHE3 t0 SD-UG-2(3) , m)

SM 11

SM 12

A B C Sheath Voltage Limiters

Sheath Voltage Limiters

Sheath Voltage Limiters

Sheath Voltage Limiters

มีLink Box ที่มี SVL 6 ea อยูใ่ นกล่องเดียวกันหรือ ไม่

A B C

SD‐UG‐2(1)

MHE3

SD‐UG‐2(3)

Parallel Ground Continuity Conductor

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

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Power Cable Calculations Sheath Induced Voltage

c.2 Underground Cable between SD-UG-2(5) to SD-UG-2(7) SM2  12  20  148.57  20  12

SM2  212.57

m.

Select the single point bond at one end (SD-UG-2(7))

SM 2

A B C Sheath Voltage Limiters

A B C Sheath Voltage Limiters

SD‐UG‐2(7)

SD‐UG‐2(5) Parallel Ground Continuity Conductor

c.3 Underground Cable between SD-UG-2(9) to EGAT Select the cross-bond of three major sections: sp11  12  20  138.5  189.7

sp11  360.2

(cable length from SD-UG-2(9) to MHE10, m)

sp12  195.3  85.15

sp12  280.45

(cable length from MHE10 to MHE12, m)

sp13  229.9  170.5

sp13  400.4

(cable length from MHE12 to MHE14, m)

sp21  143.99  46.68  166.93

sp21  357.6

(cable length from MHE14 to MHE17, m)

sp22  81.44  ( 140.4  158.8)

sp22  380.64

(cable length from MHE17 to MHE20, m)

sp23  156.9  182.33

sp23  339.23

(cable length from MHE20 to MHE22, m)

sp31  207.35

sp31  207.35

(cable length from MHE22 to MHE23, m)

sp32  206.2

sp32  206.2

(cable length from MHE23 to MHE24, m)

sp33  160.5  55.6  8  4

sp33  228.1

(cable length from MHE24 to EGAT, m)

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

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Power Cable Calculations Sheath Induced Voltage

Total cable length, m SP  sp11  sp12  sp13  sp21  sp22  sp23  sp31  sp32  sp33

SP  2760.17

The longest cable length of the minor section of cross-bonded system, m

 spM  max sp11 sp12 sp13 sp21 sp22 sp23 sp31 sp32 sp33 

 spM   400.4

The shortest cable length of the minor sectionof the cross-bonded system, m

 spm  min sp11 sp12 sp13 sp21 sp22 sp23 sp31 sp32 sp33 

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

 spm  206.2

page 5 of 31

Prepared by : Raktham S.

C

B

A

C

B

A

SD‐UG‐2(9)

Sheath Voltage Limiters

Sheath Voltage Limiters

Minor Section sp11

MHE10

Sheath Voltage Limiters

Sheath Voltage Limiters

Minor Section sp12

1st Major Section

MHE12

Minor Section sp13

MHE14

Sheath Voltage Limiters

Sheath Voltage Limiters

Minor Section sp21

MHE17

Sheath Voltage Limiters

Sheath Voltage Limiters

Minor Section sp22

2nd Major Section

MHE20

Minor Section sp23

MHE22

Sheath Voltage Limiters

Sheath Voltage Limiters

Minor Section sp31

MHE23

Sheath Voltage Limiters

Sheath Voltage Limiters

Minor Section sp32

3rd Major Section

MHE24

Minor Section sp33

EGAT

Gult-Tasit 1 Project Power Cable Calculations Sheath Induced Voltage

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

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Power Cable Calculations Sheath Induced Voltage

c.4 Horizontal drilling duct-HDD Configuration and Cable Arrangment

c.5 Parallel Ground Continuity Conductor - PGCC PGCC is installed for reducing a sheath overvoltage occurred at single point bonded section through providing a return path of fault current. As per IEEE 80-2000, equation (40), on page 43, the require ground conductor size is calculated as follows from the following equation

A  I  c f   



   TCAP   ln K0  Tm   t  α  ρ   K  T   c r r  0 a  1

where Ief

 Ac   Tm  Ta  αr   ρr   K0  tc

is the rms current in kA

Ief  40kA

is the conductor cross section in sq.mm

CV copper conductor

is the maximum allowable temperature in ºC

Tm  250  C

is the maximum ambient temperature in ºC

Ta  40  C

is the thermal coefficient of resistivity at reference temperature (Tr) , from IEEE 80-2000 Table 1 in 1/ºC

αr  0.00393 

is the resistivity of the earthing conductor at reference temperature (Tr) , from IEEE 80-2000 Table 1 in μΩ.cm

ρr  1.72  10

1/a0 or (1/a r ) - Tr , from IEEE 80-2000 Table 1 in ºC

K0  234.5C

is the duration of fault current considering the last line of protection system for the high fault current i.e. operating time of Zone 2 of distance protection from EGAT Substation, in s

1 C

6

 Ω  cm

 tc  0.35s

( TCAP) is the thermal capacity per unit volume from IEEE 80-2000 Table 1 in J/(cm3.ºC)

TCAP  3.42   

Therefore, the minimum size of PGCC is

 Ac   139.574  mm2

J cm

3

   C

The 150 sq.mm. CV copper conductor is selected. The insulated cable is selected to prevent the corrosion.

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 7 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

Calculation for the PGCC resistance: 2

ρ  0.0179 

Ω  mm

copper cable resistivity at 20 C,

m ρ

RPGCC_20 

2

150mm RPGCC_20  0.1193 

Ω

PGCC cable resistance at 20 C

km

 250  234.5  RPGCC_250  RPGCC_20     20  234.5  RPGCC_250  0.2272 

Ω

PGCC cable resistance at 250 C

km

Assign Rg 

RPGCC_250 1000 

(the resistance of ground conductor, ohm/m)

Rg  0.2272  10

(the geometric mean radius of ground conductor, mm)

rg  10.95

Ω

3

km rg  0.75  14.6

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 8 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

CALCULATIONS: For double circuit system (refer to Clause D.2.4 of IEEE 575-2014), the conductor current are; Ia 

1

3

 i

2

assigned to cable 1a

2

Ib  1  i  0 Ic 

1

assigned to cable 1b 3

i

2

assigned to cable 1c

2

For distance between cable, the numbering is assigned to the phase conductor as follows:

S12  0.16

S18 

S23 

S19  2  0.16

2  0.16

10  0.16

S13  0.16

S17  3  0.16

S14  3  0.16

S27 

S25  0.16

S28  3  0.16

S36  3  0.16

S29 

S15  2  0.16

S39  0.16

S35 

5  0.16

S78  0.16

S16 

10  0.16

S79  0.16

S37  2  0.16

S89 

10  0.16

5  0.16

S1_11 

13  0.16

S2_11 

10  0.16

S1_12 

13  0.16

S1_10  3 S38 

2  0.16

5  0.16

S3_11  2  S3_12 

2  0.16

10  0.16

2  0.16

The impedance are 7

Xaa  2  ω  10

7

Xab  2  ω  10

7

Xac  2  ω  10

7

Xbb  2  ω  10

7

Xbc  2  ω  10

7

Xcc  2  ω  10

 

2

 

dmm  S14

 ln

 

1

 

S12  S15

 ln

 

1

 

S13  S16

 ln

1  1       ln S  S   ln S  S    12 18   12 1_11  1   ln 1   ln   S  S  S  S    13 19   13 1_12 

 

2

 

dmm  S25

 ln

 

1

 

S23  S35

 ln

2

 

dmm  S36

Prepared by : Raktham S.

2 2        ln d  S   ln d  S    mm 28   mm 2_11 

1   ln 1   ln   S  S  S  S    23 38   23 3_11 

 

 ln

2 2        ln d  S   ln d  S    mm 17   mm 1_10 

2 2        ln d  S   ln d  S    mm 39   mm 3_12 

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

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Power Cable Calculations Sheath Induced Voltage

The open-circuit voltage on shields/sheaths to neutral are, (V/m) : Ea0  Ia  i  Xaa  Ib  iXab  Ic  i  Xac

Ea0  0.0002

[IEEE 575-2014, Eq. D14, page 41]

Eb0  Ia  i  Xab  Ib  iXbb  Ic  i  Xbc

Eb0  0.0003

[IEEE 575-2014, Eq. D15, page 41]

Ec0  Ia  i  Xac  Ib  iXbc  Ic  i  Xcc

Ec0  0.0003

[IEEE 575-2014, Eq. D16, page 41]

1 In case of normal operation The current flow in the power cable based on 90 MW for one cable is; 3

Ifl 

90  10 0.85 

Ifl  265.7878

3  115  np

load current, in A

The three-sheath voltage gradients for a group of cables in HDD carrying balanced three-phase conductor currents are given by: (sheath voltage on Phase A cable, V/m) Ea  Ifl  Ea0

Ea  0.063

(sheath voltage on Phase B cable , V/m) Eb  Ifl  Eb0

Eb  0.0913

(sheath voltage on Phase C cable, V/m) Ec  Ifl  Ec0

Prepared by : Raktham S.

Ec  0.0913

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 10 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

1. Underground Cable between SD-UG-2(1) to SD-UG-2(3) Tthe metallic screen of power cables are bonded single point bond at one end by sectionalizing the sheath at MHE3. The voltage gradient induced in a cable sheath during the current flow through the conductor are: 20.18

247.95

Sheath Voltage (V)

17.3 14.41 11.53 Ea. ( n) 8.65 5.77 2.88 0 0

94.67

189.33

284

378.67

473.33

568

473.33

568

473.33

568

x( n) Cable Length (m)

The sheath voltage gradient in Phase-A cable 29.25

247.95

Sheath Voltage (V)

25.07 20.89 16.72 Eb. ( n) 12.54 8.36 4.18 0 0

94.67

189.33

284

378.67

x( n) Cable Length (m)

The sheath voltage gradient in Phase-B cable

29.25

247.95

Sheath Voltage (V)

25.07 20.89 16.72 Ec.( n) 12.54 8.36 4.18 0 0

94.67

189.33

284

378.67

x( n) Cable Length (m)

The sheath voltage gradient in Phase-C cable

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 11 of 31

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Power Cable Calculations Sheath Induced Voltage

2. Underground Cable between SD-UG-2(5) to SD-UG-2(7) Tthe metallic screen of power cables are bonded at single one end. The voltage gradient induced in a cable sheath during the current flow through the conductor are: 13.39

Sheath Voltage (V)

11.48 9.56 7.65 Ea. ( n) 5.74 3.83 1.91 0 0

35.33

70.67

106

141.33

176.67

212

176.67

212

176.67

212

x( n) Cable Length (m)

The sheath voltage gradient in Phase-A cable

19.41

Sheath Voltage (V)

16.63 13.86 11.09 Eb. ( n) 8.32 5.54 2.77 0 0

35.33

70.67

106

141.33

x( n) Cable Length (m)

The sheath voltage gradient in Phase-B cable 19.41

Sheath Voltage (V)

16.63 13.86 11.09 Ec.( n) 8.32 5.54 2.77 0 0

35.33

70.67

106

141.33

x( n) Cable Length (m)

The sheath voltage gradient in Phase-C cable

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 12 of 31

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Power Cable Calculations Sheath Induced Voltage

3. Underground Cable between SD-UG-2(9) to EGAT Tthe metallic screen of power cables are cross-bonded. The voltage gradient induced in a cable sheath during the current flow through the conductor are: distance to the end of the 1st major section

sp11  sp12  sp13  1041.05

m

distance to the end of the 2 nd major section sp  sp  sp  sp  sp  sp  2118.52 11 12 13 21 22 23

m

distance to the end of the 3 rd major section

m

Prepared by : Raktham S.

sp11  sp12  sp13  sp21  sp22  sp23  sp31  sp32  sp33  2760.17

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 13 of 31

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Power Cable Calculations Sheath Induced Voltage

26.07

1041.05

2118.52

Sheath Voltage (V)

22.34 18.62 14.9 Ea. ( n) 11.17 7.45 3.72 0 0

460

920

1380

1840

2300

2760

x( n) Cable Length (m)

The sheath voltage gradient in Phase-A cable 38.5

1041.05

2118.52

Sheath Voltage (V)

32.09 25.67 Eb( n) 19.25 12.83 6.42 0 0

230

460

690

920

1150

1380

1610

1840

2070

2300

2530

2760

2300

2530

2760

x( n) Cable Length (m)

The sheath voltage gradient in Phase-B cable 36.47

1041.05

2118.52

Sheath Voltage (V)

30.39 24.31 Ec( n) 18.23 12.16 6.08 0 0

230

460

690

920

1150

1380

1610

1840

2070

x( n) Cable Length (m)

The sheath voltage gradient in Phase-C cable For all cases, the maximum sheath voltage induced during normal operation is 38.5 V which is less than the specified value i.e. 66 V of PEA design criteria.

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 14 of 31

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Power Cable Calculations Sheath Induced Voltage

2 In case of maximum permissible current The current flow in the power cable based on the calculated maximum permissible current of one cable; Refer to the calculation report for permissible current carrying capacity of cable. the calculated maximum permissible current, in A Ifl  421 Maximum power of one cable circuit is, in MVA np 

Ifl



3  115  167.7145

1000

The three-sheath voltage gradients for a group of cables in HDD carrying balanced three-phase conductor currents are given by: (sheath voltage on Phase A cable, V/m) Ea  Ifl  Ea0

Ea  0.0998

(sheath voltage on Phase B cable , V/m) Eb  Ifl  Eb0

Eb  0.1446

(sheath voltage on Phase C cable, V/m) Ec  Ifl  Ec0

Prepared by : Raktham S.

Ec  0.1446

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 15 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

1. Underground Cable between SD-UG-2(1) to SD-UG-2(3) 31.97

247.95

Sheath Voltage (V)

27.4 22.83 18.27 Ea. ( n) 13.7 9.13 4.57 0 0

94.67

189.33

284

378.67

473.33

568

473.33

568

473.33

568

x( n) Cable Length (m)

The sheath voltage gradient in Phase-A cable 46.33

247.95

Sheath Voltage (V)

39.71 33.1 26.48 Eb. ( n) 19.86 13.24 6.62 0 0

94.67

189.33

284

378.67

x( n) Cable Length (m)

The sheath voltage gradient in Phase-B cable

46.33

247.95

Sheath Voltage (V)

39.71 33.1 26.48 Ec.( n) 19.86 13.24 6.62 0 0

94.67

189.33

284

378.67

x( n) Cable Length (m)

The sheath voltage gradient in Phase-C cable

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 16 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

2. Underground Cable between SD-UG-2(5) to SD-UG-2(7) 21.21

Sheath Voltage (V)

18.18 15.15 12.12 Ea. ( n) 9.09 6.06 3.03 0 0

35.33

70.67

106

141.33

176.67

212

176.67

212

176.67

212

x( n) Cable Length (m)

The sheath voltage gradient in Phase-A cable

30.74

Sheath Voltage (V)

26.35 21.96 17.56 Eb. ( n) 13.17 8.78 4.39 0 0

35.33

70.67

106

141.33

x( n) Cable Length (m)

The sheath voltage gradient in Phase-B cable

30.74

Sheath Voltage (V)

26.35 21.96 17.56 Ec.( n) 13.17 8.78 4.39 0 0

35.33

70.67

106

141.33

x( n) Cable Length (m)

The sheath voltage gradient in Phase-C cable

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 17 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

3. Underground Cable between SD-UG-2(9) to EGAT 41.29

1041.05

2118.52

Sheath Voltage (V)

35.39 29.49 23.59 Ea. ( n) 17.7 11.8 5.9 0 0

460

920

1380

1840

2300

2760

x( n) Cable Length (m)

The sheath voltage gradient in Phase-A cable

60.99

1041.05

2118.52

Sheath Voltage (V)

50.82 40.66 Eb( n) 30.49 20.33 10.16 0 0

230

460

690

920

1150

1380

1610

1840

2070

2300

2530

2760

2300

2530

2760

x( n) Cable Length (m)

The sheath voltage gradient in Phase-B cable

57.77

1041.05

2118.52

Sheath Voltage (V)

48.14 38.51 Ec( n) 28.88 19.26 9.63 0 0

230

460

690

920

1150

1380

1610

1840

2070

x( n) Cable Length (m)

The sheath voltage gradient in Phase-C cable For all cases, the maximum sheath voltage induced during maximum permissible current carrying capacity of cable is 60.99 V which is less than the specified value i.e. 66 V of PEA design criteria.

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 18 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

3 In case of MAX. 3-PHASE-FAULT CURRENT I3sc 

40  10

3

designed maximum 3-ph fault current flow through one cable, in A

np

(sheath voltage on Phase A cable, V/m) Ea  I3sc  Ea0

Ea  4.7392

(sheath voltage on Phase B cable , V/m) Eb  I3sc  Eb0

Eb  6.8694

(sheath voltage on Phase C cable, V/m) Ec  I3sc  Ec0

Prepared by : Raktham S.

Ec  6.8694

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 19 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

1. Underground Cable between SD-UG-2(1) to SD-UG-2(3) 1518.53

247.95

Sheath Voltage (V)

1301.6 1084.66 867.73 Ea. ( n) 650.8 433.87 216.93 0 0

94.67

189.33

284

378.67

473.33

568

473.33

568

473.33

568

x( n) Cable Length (m)

The sheath voltage gradient in Phase-A cable

2201.1

247.95

Sheath Voltage (V)

1886.66 1572.22 1257.77 Eb. ( n) 943.33 628.89 314.44 0 0

94.67

189.33

284

378.67

x( n) Cable Length (m)

The sheath voltage gradient in Phase-B cable

2201.1

247.95

Sheath Voltage (V)

1886.66 1572.22 1257.77 Ec.( n) 943.33 628.89 314.44 0 0

94.67

189.33

284

378.67

x( n) Cable Length (m)

The sheath voltage gradient in Phase-C cable

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 20 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

2. Underground Cable between SD-UG-2(5) to SD-UG-2(7) 1007.41

Sheath Voltage (V)

863.49 719.58 575.66 Ea. ( n) 431.75 287.83 143.92 0 0

35.33

70.67

106

141.33

176.67

212

176.67

212

176.67

212

x( n) Cable Length (m)

The sheath voltage gradient in Phase-A cable 1460.24

Sheath Voltage (V)

1251.63 1043.03 834.42 Eb. ( n) 625.82 417.21 208.61 0 0

35.33

70.67

106

141.33

x( n) Cable Length (m)

The sheath voltage gradient in Phase-B cable

1460.24

Sheath Voltage (V)

1251.63 1043.03 834.42 Ec.( n) 625.82 417.21 208.61 0 0

35.33

70.67

106

141.33

x( n) Cable Length (m)

The sheath voltage gradient in Phase-C cable

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 21 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

3. Underground Cable between SD-UG-2(9) to EGAT 1961.54

1041.05

2118.52

Sheath Voltage (V)

1681.32 1401.1 1120.88 Ea. ( n) 840.66 560.44 280.22 0 0

460

920

1380

1840

2300

2760

x( n) Cable Length (m)

The sheath voltage gradient in Phase-A cable 2897.38

1041.05

2118.52

Sheath Voltage (V)

2414.48 1931.59 Eb( n) 1448.69 965.79 482.9 0 0

230

460

690

920

1150

1380

1610

1840

2070

2300

2530

2760

2300

2530

2760

x( n) Cable Length (m)

The sheath voltage gradient in Phase-B cable

2744.27

1041.05

2118.52

Sheath Voltage (V)

2286.89 1829.51 Ec( n) 1372.13 914.76 457.38 0 0

230

460

690

920

1150

1380

1610

1840

2070

x( n) Cable Length (m)

The sheath voltage gradient in Phase-C cable For all cases, the maximum sheath voltage induced during 3-phase short circuit current flow through cable is 2897.4 V

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 22 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

3 In case of MAX. SINGLE LINE-TO-GROUND FAULT CURRENT 3

Ief 

40  10

designed maximum single line to ground fault current, in A

np

1. Underground Cable between SD-UG-2(1) to SD-UG-2(3) Since the cables are bonded at mid span (one end ). The PGCC is installed in vancant conduit of HDD paralleling to the phase conductors as depicted below

Geometric Mean Spacing between cable to PGCC s1g 

2  0.16

(distance from center of phase-A cable (1) to PGCC cable, mm)

s2g  0.16

(distance from center of phase-B cable (2) to PGCC cable, mm)

s3g  0.16

(distance from center of phase-C cable (3) to PGCC cable, mm)

s7g 

(distance from center of phase-A cable (7) to PGCC cable, mm)

5  0.16

s8g  2  0.16

(distance from center of phase-B cable (8) to PGCC cable, mm)

s9g 

(distance from center of phase-C cable (9) to PGCC cable, mm)

2  0.16

For the phase conductor (3-Phase group 1-2-3) When Phase A - to -ground fault (sheath voltage on Phase A cable when Phase-A to ground fault, V/m) Ea  Ief

   2 s 2   s1g  s7g  1g   7      Rg  i  ω  2  10  ln    d  r   ln S  r     mm g   17 g 

[IEEE 575-2014, Eq. E.5, page 40]



Ea

  9.103

(sheath voltage on Phase B cable when Phase-A to ground fault , V/m)



  ln



Eb  Ief  Rg  i  ω  2  10 

7



s 1g  s2g 

s s   ln 1g 8g    S12  rg   S18  rg      

[IEEE 575-2014, Eq. E.6, page 40]



Eb

  11.281

(sheath voltage on Phase C cable when Phase-A to ground fault , V/m)





Ec  Ief  Rg  i  ω  2  10 



  ln

7

s 1g  s3g 

s s   ln 1g 9g    S13  rg   S19  rg      

[IEEE 575-2014, Eq. E.7, page 40]



Ec

  11.1528

The maximum induced sheath voltage is occurred at the un-bonded end of Phase B cable (i.e. Eb) = Eb  SM12  3615.234

Prepared by : Raktham S.

V

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 23 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

When Phase B - to -ground fault (sheath voltage on Phase A cable when Phase-B to ground fault , V/m)



  ln



Ea  Ief  Rg  i  ω  2  10 

7



s 1g  s2g 

s s   ln 2g 7g    S12  rg   S27  rg      

Ea  11.5519

(sheath voltage on Phase B cable when Phase-B to ground fault, V/m) Eb  Ief

   2 s 2   s2g  s8g  2g   7      Rg  i  ω  2  10  ln  ln   d  r   S28  rg     mm g   

Eb  10.3818

(sheath voltage on Phase C cable when Phase-B to ground fault , V/m)



  ln



Ec  Ief  Rg  i  ω  2  10 

7



s 2g  s3g 

s s   ln 2g 9g    S23  rg   S29  rg      



Ec

  12.488

The maximum induced sheath voltage is occurred at the un-bonded end of Phase C cable (i.e. Ec) = Ec  SM12  4002.0365

V

When Phase C - to -ground fault (sheath voltage on Phase A cable when Phase-C to ground fault , V/m)



  ln



Ea  Ief  Rg  i  ω  2  10 

7



s 1g  s3g 

s s   ln 1g 9g    S13  rg   S19  rg      

Ea  11.1528

(sheath voltage on Phase B cable when Phase-C to ground fault , V/m)



  ln



Eb  Ief  Rg  i  ω  2  10 

7



s 3g  s2g 

s s   ln 3g 8g    S23  rg   S28  rg      



Eb

  12.4264

(sheath voltage on Phase C cable when Phase-C to ground fault, V/m) Ec  Ief

   2 s 2   s3g  s9g  3g   7    Rg  i  ω   2  10   ln  ln   d  r   S39  rg     mm g   

Ec  9.541

The maximum induced sheath voltage is occurred at the un-bonded end of Phase C cable (i.e. Ec) = Eb  SM12  3982.2829

V

For the phase conductor (3-Phase group 7-8-9) When Phase A - to -ground fault (sheath voltage on Phase A cable when Phase-A to ground fault, V/m) Ea  Ief

   2 s 2   s1g  s7g  7g   7      Rg  i  ω  2  10  ln  ln   d  r   S17  rg     mm g   



Ea

  8.1256



Eb

  10.2376

(sheath voltage on Phase B cable when Phase-A to ground fault , V/m)





Eb  Ief  Rg  i  ω  2  10 



Prepared by : Raktham S.

  ln

7

s 7g  s2g 

s s   ln 7g 8g    S27  rg   S78  rg      

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 24 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

(sheath voltage on Phase C cable when Phase-A to ground fault , V/m)



  ln



Ec  Ief  Rg  i  ω  2  10 

7



s 7g  s3g 

s s   ln 7g 9g    S37  rg   S79  rg      



Ec

  10.1122

The maximum induced sheath voltage is occurred at the un-bonded end of Phase B cable (i.e. Eb) =

 Eb



 SM12  3280.8513

V

When Phase B - to -ground fault (sheath voltage on Phase A cable when Phase-B to ground fault , V/m)



  ln



Ea  Ief  Rg  i  ω  2  10 

7



s 1g  s8g 

s s   ln 7g 8g    S18  rg   S78  rg      



Ea

  9.9738



Eb

  8.8483



Ec

  10.8838

(sheath voltage on Phase B cable when Phase-B to ground fault, V/m) Eb  Ief

   2 s 2   s2g  s8g  8g   7      Rg  i  ω  2  10  ln    d  r   ln S  r     mm g   28 g 

(sheath voltage on Phase C cable when Phase-B to ground fault , V/m)



  ln



Ec  Ief  Rg  i  ω  2  10 

7



s 8g  s3g 

s s   ln 8g 9g    S38  rg   S89  rg      

The maximum induced sheath voltage is occurred at the un-bonded end of Phase C cable (i.e. Ec) =

 Ec



 SM12  3487.9377

V

When Phase C - to -ground fault (sheath voltage on Phase A cable when Phase-C to ground fault , V/m)



  ln



Ea  Ief  Rg  i  ω  2  10 

7



s 9g  s1g 

s s   ln 9g 7g    S19  rg   S79  rg      



Ea

  10.2376



Eb

  11.281

(sheath voltage on Phase B cable when Phase-C to ground fault , V/m)





Eb  Ief  Rg  i  ω  2  10 



s s   ln 9g 8g    S29  rg   S89  rg      

  ln

7

s 9g  s2g 

(sheath voltage on Phase C cable when Phase-C to ground fault, V/m) Ec  Ief

   2 s 2   s3g  s9g  9g   7      Rg  i  ω  2  10  ln    d  r   ln S  r     mm g   39 g 

Ec  8.7849

The maximum induced sheath voltage is occurred at the un-bonded end of Phase C cable (i.e. Ec) =

 Eb



 SM12  3615.234

Prepared by : Raktham S.

V

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 25 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

2. Underground Cable between SD-UG-2(5) to SD-UG-2(7) The cables are bonded at one end. The PGCC is installed in vancant conduit of HDD paralleling to the phase conductors as depicted below

Since the cable length of this section m

SM2  212.57

is signeficantly shorter than

SM2

<

SM12  320.47

the cable length of item 1 above

SM12

m

Therefore, the calculated induced sheath voltage of this cable section is lower. No calculation is done for this cable section.

3. Underground Cable between SD-UG-2(9) to EGAT As the single major section of cross-bonding cable having the sheath earthed at both ends, the returning current circulates in the path formed by the three sheaths and the ground and divides equally between three sheath circuits Considering the longest minor section, the voltage between sheaths at cross-bonding points can be calculated as follows; For the phase conductor (3-Phase group 1-2-3) For Phase A-Ground Fault (sheath voltage between Phase A and Phase B at the cross bonding point, when fault in phase A cable, V/m



Vab  Ief i  ω  2  10

7

  ln    

2  S12  dmm

S   ln 27    S17    

[IEEE 575-2014, Eq. E.18, page 49]



Vab

  1.8619

(sheath voltage between Phase B and Phase C at the cross bonding point, when fault in phase A cable, V/m) [IEEE 575-2014, Eq. E.19, page 49]

( Vbc  0)



Vbc

0

(sheath voltage between Phase C and Phase A at the cross bonding point, when fault in phase A cable, V/m), [IEEE 575-2014, Eq. E.20, page 49]

( Vca   Vab)



Vca

  1.8619

So, the sheath voltage between Phase A and Phase B at the cross bonding point, when fault in phase A cable



Vab_max  Vab  sp M

Vab_max

  745.4888

V

For Phase B-Ground Fault (sheath voltage between Phase B and Phase C at the cross bonding point, when fault in phase B cable, V/m



Vbc  Ief i  ω  2  10

Prepared by : Raktham S.

7

  ln    

2  S23  dmm

S   ln 38    S28    

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

Vbc  1.8619

page 26 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

(sheath voltage between Phase C and Phase A at the cross bonding point, when fault in phase B cable, V/m) Vca  0

Vca  0

(sheath voltage between Phase C and Phase B at the cross bonding point, when fault in phase B cable, V/m), Vcb   Vbc

Vcb  1.8619

So, the sheath voltage between Phase A and Phase B at the cross bonding point, when fault in phase A cable Vbc_max  Vbc  sp M

Vbc_max  745.4888

V

For Phase C-Ground Fault (sheath voltage between Phase C and Phase A at the cross bonding point, when fault in phase C cable, V/m



Vca  Ief i  ω  2  10

7

  ln    

2  S13  dmm

S   ln 19    S39    

Vca  2.6667

(sheath voltage between Phase A and Phase B at the cross bonding point, when fault in phase c cable, V/m) Vab  0

Vab  0

(sheath voltage between Phase B and Phase C at the cross bonding point, when fault in phase C cable, V/m), Vcb   Vbc

Vbc  1.8619

So, the sheath voltage between Phase A and Phase B at the cross bonding point, when fault in phase A cable Vca_max  Vca  sp M

Vca_max  1067.7445

V

Therefore, the maximum induced voltage due to earth fault is; Vpp_max  max( Vab_max Vbc_max Vca_max )

Vpp_max  1067.7445

V

The calculated max. induced voltage is a voltage across two phase metallic sheath. Each one is connected to ground via Sheath Voltage Limiter (SVL). So, the maximum induced voltage to ground is: Vef 

Vpp_max

Vef  533.8723

2

V

For the phase conductor (3-Phase group 7-8-9) For Phase A-Ground Fault (sheath voltage between Phase A and Phase B at the cross bonding point, when fault in phase A cable, V/m



Vab  Ief i  ω  2  10

7

  ln    

2  S78  dmm

S   ln 18    S17    



Vab

  1.8619

(sheath voltage between Phase B and Phase C at the cross bonding point, when fault in phase A cable, V/m)



( Vbc  0)

Vbc

0

(sheath voltage between Phase C and Phase A at the cross bonding point, when fault in phase A cable, V/m),



( Vca   Vab)

Vca

  1.8619

So, the sheath voltage between Phase A and Phase B at the cross bonding point, when fault in phase A cable Vab_max  Vab  sp M

Prepared by : Raktham S.



Vab_max

  745.4888

V

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 27 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

For Phase B-Ground Fault (sheath voltage between Phase B and Phase C at the cross bonding point, when fault in phase B cable, V/m



Vbc  Ief i  ω  2  10

7

  ln    

2  S89  dmm

S   ln 29    S28    

Vbc  1.8619

(sheath voltage between Phase C and Phase A at the cross bonding point, when fault in phase B cable, V/m) Vca  0

Vca  0

(sheath voltage between Phase C and Phase B at the cross bonding point, when fault in phase B cable, V/m), Vcb   Vbc

Vcb  1.8619

So, the sheath voltage between Phase A and Phase B at the cross bonding point, when fault in phase A cable Vbc_max  Vbc  sp M

Vbc_max  745.4888

V

For Phase C-Ground Fault (sheath voltage between Phase C and Phase A at the cross bonding point, when fault in phase C cable, V/m



Vca  Ief i  ω  2  10

7

  ln    

2  S79  dmm

S   ln 37    S39    

Vca  2.6667

(sheath voltage between Phase A and Phase B at the cross bonding point, when fault in phase c cable, V/m) Vab  0

Vab  0

(sheath voltage between Phase B and Phase C at the cross bonding point, when fault in phase C cable, V/m), Vcb   Vbc

Vbc  1.8619

So, the sheath voltage between Phase A and Phase B at the cross bonding point, when fault in phase A cable Vca_max  Vca  sp M

Vca_max  1067.7445

V

Therefore, the maximum induced voltage due to earth fault is; Vpp_max  max( Vab_max Vbc_max Vca_max )

Vpp_max  1067.7445

V

The calculated max. induced voltage is a voltage across two phase metallic sheath. Each one is connected to ground via Sheath Voltage Limiter (SVL). So, the maximum induced voltage to ground is: Vef 

Vpp_max 2

Vef  533.8723

V

For all cases, the maximum sheath voltage induced during single to ground fault current flow through cable is 4002 V

4. Insulation of Cable Outer Sheath (Jacket) The maximum sheath voltage induced during three phase short circuit current is 4,002 V. In order to determined the insulation level of outer sheath of cable, IEC std 60502-1 could be used. The power frequency withstand voltage of a 2.8 mm PVC sheath thickness for 3.6 kV cable, 800 sq.mm. is 6.5 kV (refer to pages 27 & 49 respectively) The insulation level of PE is superier to PVC. So the insulation level of the 3.5 mm thickness of PE outer sheath for 115 kV power cable is higher than 3.5mm

 6.5kV  8.125  kV

The outer sheath of cable can withstand the maximum induced sheath voltage.

2.8mm

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 28 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

5. Selection of Sheath Voltage Limiter The induced volatge in cable sheaths at the cross-bonding points is high during fault external to the cable circuit. The Sheath Voltage Limiter (SVL) shall be installed to connected between the cable sheath and the earth with separated limiter as per diagram in FIGURE 1. The basic design criterion for selection of cable sheath voltage limiter in case using of non-linear resistance surge arrester, is to keep sheath overvoltage as low as practical. However, the maximum continuous operating voltage (MCOV) of surge arrester shall be high enough to withstand the 50 Hz overvoltages resulting from system faults external to cable circuit [IEEE 575-2014]. The maximum sheath voltage induced from the maximum allowable 3-phase fault current external to the cable circuit is 4002. The IEEE Std C62.22- 1991 recommendation is a minimum margin of protection greater than or equal to 20%. So, the MCOV of the surge arrester shall be not less than = 4002  1.2  4802.4 Select the surge arrester is Ur = 6 kV, 10 kA MCOV = 5.1 kV

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 29 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

ANNEX 1

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 30 of 31

Gult-Tasit 1 Project

Power Cable Calculations Sheath Induced Voltage

ANNEX 2

Prepared by : Raktham S.

Date :10-Jul-16 File: Gult-TS1-GTS1 - Sheath Voltage

page 31 of 31