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Hyundai Heavy Industries

HN2559 Rowan Drillship 1

P025038

Report
Earth Fault Analysis
HV Power System

External doc. no.

Based on Project HN2559 Rowan Drillship 1

Prep. PAMA / Olav Fønstelien 12/15/2011 Customer Hyundai Heavy Industries
Appr. PAMA / Frank Zhou 12/15/2011 Proj. no. P025038
Doc. Ref.
Doc. kind Report des. des.
Title Earth Fault Analysis
HV Power System Resp. dept PAMA Status Approved
Doc. no. Lang. Rev. ind. Page
1
ABB AS 3AJM002064-031 en A No. of p.
9
FILE: 3AJM002064-031_A_EF Cal.doc; SAVEDATE: 08/02/2012 15:40; TEMPLATE: Techn_Doc_Deliv_P_MPE.dot A; SKELETON: 3BNP100013D0019 en -
Contents

Contents .......................................................................................................................... 2
1. Introduction .............................................................................................................. 3
1.1 Objectives .................................................................................................... 3
1.2 Design criteria .............................................................................................. 3
1.3 Network configuration ................................................................................... 3
2. Conclusion ............................................................................................................... 3
3. System Description ................................................................................................. 4
3.1 System principle sketch ................................................................................ 4
3.2 Formulas ...................................................................................................... 4
3.3 System Design ............................................................................................. 5
4. Related documents .................................................................................................. 5

Doc. kind Report Project HN2559 Rowan Drillship 1

Title Earth Fault Analysis Customer Hyundai Heavy Industries
HV Power System Proj. no. P025038
Doc. no. Lang. Rev. ind. Page
2
ABB AS 3AJM002064-031 en A No. of p.
9
1. Introduction

1.1 Objectives
The purpose of this study is to verify the capacity of the designed high resistant earthing
system with respect to IEC regulations. Correct design of the earthing system is of major
importance in order to avoid over-voltages due to intermittent oscillating arcing earth fault
(EF), which may cause insulation damage and critical fault situations.
The earthing system is also of essential interest with regards to trip of circuit breakers by
earth fault relays.

1.2 Design criteria

IEC 61892-2 requires that the resistive component of the total earth fault current must be
equal to or larger than the total capacitive current component if an earth fault occurs in
one of the phases of the high-voltage network.
I R0 ≥ I C0tot (1)

According to IEC, the release set point shall be equal or less than 1/3 of the total resistive
earth fault current.
I R0
I set ≤ (2)
3

1.3 Network configuration

In power systems with high resistant earthing system on switchboard busbar the
maximum capacitive earth fault current compared to the resistive component occurs
when:
• All generators are connected
• All bus-ties are closed
• All feeders (transformers and motors) are connected

The contributions from transformers are omitted due to the fact that the capacitive current
contribution is very small compared to generators, motors and cables.

2. Conclusion
Based on the calculations (ref. appendix 1), the design is as follows:
• Total capacitive current: I C0tot = 16.4 A

• Maximum capacitive current for one switchboard section: I C0 / syst = 3.7 A

• Chosen resistive component pr. switchboard section: I R0 / syst = 7.7 A
• Chosen resistive component for system : I R0 = I R0 / syst × 6 = 46.2 A

Doc. kind Report Project HN2559 Rowan Drillship 1

Title Earth Fault Analysis Customer Hyundai Heavy Industries
HV Power System Proj. no. P025038
Doc. no. Lang. Rev. ind. Page
3
ABB AS 3AJM002064-031 en A No. of p.
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 • Maximum relay setting value: I set = 14 A
The requirements in equation (1) and (2) are fulfilled and the earthing system is correctly
designed.

3. System Description

3.1 System principle sketch

3.2 Formulas
To determine the total capacitive current contribution ( I C0 ) from the components, the
following formulas are applied:

Cables : I C0 = 3 × I C j = 3 × U n × ω × l × C j (3)
3 × U n × ω × C0
Machines : I C0 = (4)
2

Cj [F] : Phase-earth capacitance for cables (per phase)

C0 [F] : Capacitance for the whole winding (per phase)
l [m] : Cable length
ω [Hz] : 2πf
Un [V] : Phase-phase voltage

Doc. kind Report Project HN2559 Rowan Drillship 1

Title Earth Fault Analysis Customer Hyundai Heavy Industries
HV Power System Proj. no. P025038
Doc. no. Lang. Rev. ind. Page
4
ABB AS 3AJM002064-031 en A No. of p.
9
3.3 System Design
A high resistant earthing system consisting of an YNopend transformer with primary star
solid earthed and a resistor connected in the open delta winding is connected on each
high voltage switchboard busbar. If bus-ties are connected, the systems operates in
parallel, otherwise each system works separately.
In case of failure of one earthing system on one of the main SWBDs PORT, CENT or
STBD, the other earthing system on the SWBD is big enough to carry the whole SWBD
alone.
The earth fault protection philosophy is further described in document Protection Device
Co-ordination Study [2].

4. Related documents

Document Number Document Title

[1] 3AJM002068-034 Input Data Power System Analysis
[2] 3AJM002068-032 Protection Device Coordination Study

Doc. kind Report Project HN2559 Rowan Drillship 1

Title Earth Fault Analysis Customer Hyundai Heavy Industries
HV Power System Proj. no. P025038
Doc. no. Lang. Rev. ind. Page
5
ABB AS 3AJM002064-031 en A No. of p.
9
Appendix 1 Calculation pages
Calculation of component contribution:
Cap.
Capacitance No. of
Current
C0 units
Ico
[µF/ph] - [A]
PORT B Generator 0.087 1 0.31
PORT A Generator 0.087 1 0.31
CENT B Generator 0.087 1 0.31
CENT A Generator 0.087 1 0.31
STBD B Generator 0.087 1 0.31
STBD A Generator 0.087 1 0.31

Calculation of cable contribution:

Cap.
Cable No. of
From To Length current
size cables
Ico
2
[mm ] [m] [A]
PORT 11kV SWBD Hammer Mill Unit 3x95 1 150 0.33
PORT 11kV SWBD Pre-Mag 3x35 1 30 0.05
PORT 11kV SWBD TR480V AFT PORT 2 3x95 1 9 0.02
PORT 11kV SWBD BT M STBD 3x150 7 33 0.60
PORT 11kV SWBD TR480V FWD PORT 3x95 1 166 0.36
PORT 11kV SWBD TR480V DRILL PORT 3x95 1 114 0.25
PORT 11kV SWBD TH4 3x120 2 89 0.42
PORT 11kV SWBD G4 3x150 3 27 0.21
PORT 11kV SWBD ET 3x35 1 12 0.02
PORT B 2.26
PORT 11kV SWBD ET 3x35 1 12 0.02
PORT 11kV SWBD G2 3x150 3 32 0.25
PORT 11kV SWBD TR690V DRILL PORT 3x70 2 139 0.55
PORT 11kV SWBD TR480V AFT PORT 1 3x95 1 8 0.02
PORT 11kV SWBD TH1 3x120 2 183 0.87
PORT 11kV SWBD Pre-Mag 3x35 1 30 0.05
PORT A 1.75
CENT 11kV SWBD Pre-Mag 3x35 1 30 0.05
CENT 11kV SWBD TR480V AFT CENT 2 3x95 1 9 0.02
CENT 11kV SWBD BT M PORT 3x150 7 18 0.33
CENT 11kV SWBD TR690V DRILL PORT 3x70 2 127 0.50
CENT 11kV SWBD TR480V DRILL PORT 3x95 1 100 0.22
CENT 11kV SWBD TH5 3x120 2 124 0.59

Doc. kind Report Project HN2559 Rowan Drillship 1

Title Earth Fault Analysis Customer Hyundai Heavy Industries
HV Power System Proj. no. P025038
Doc. no. Lang. Rev. ind. Page
6
ABB AS 3AJM002064-031 en A No. of p.
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From To Cable No. of Length Cap.
CENT 11kV SWBD G6 i
3x150 bl
3 143 1.11 t
CENT 11kV SWBD ET 3x35 1 12 0.02
CENTER B 2.83
CENT 11kV SWBD ET 3x35 1 12 0.02
CENT 11kV SWBD G5 3x150 3 140 1.09
CENT 11kV SWBD TR480V DRILL STBD 3x95 1 127 0.28
CENT 11kV SWBD TR690V DRILL STBD 3x70 2 151 0.59
CENT 11kV SWBD TR480V AFT CENT 1 3x95 1 8 0.02
CENT 11kV SWBD TH2 3x120 2 244 1.16
CENT 11kV SWBD Pre-Mag 3x35 1 30 0.05
CENTER A 3.21
STBD 11kV SWBD Pre-Mag 3x35 1 30 0.05
STBD 11kV SWBD TR480V AFT STBD 2 3x95 1 7 0.02
STBD 11kV SWBD BT M CENT 3x150 7 30 0.54
STBD 11kV SWBD TR690V DRILL STBD 3x70 2 129 0.51
STBD 11kV SWBD TH6 3x120 2 124 0.59
STBD 11kV SWBD G3 3x150 3 29 0.23
STBD 11kV SWBD ET 3x35 1 9 0.01
STBD B 1.94
STBD 11kV SWBD ET 3x35 1 9 0.01
STBD 11kV SWBD G1 3x150 3 27 0.21
STBD 11kV SWBD TR480V FWD STBD 3x95 1 172 0.38
STBD 11kV SWBD TR480V DRILL STBD 3x95 1 105 0.23
STBD 11kV SWBD TR480V AFT STBD 1 3x95 1 8 0.02
STBD 11kV SWBD TH3 3x120 2 185 0.88
STBD 11kV SWBD Pre-Mag 3x35 1 30 0.05
STBD A 1.78

* Data for the length of the power cables are missing for these feeders.

Doc. kind Report Project HN2559 Rowan Drillship 1

Title Earth Fault Analysis Customer Hyundai Heavy Industries
HV Power System Proj. no. P025038
Doc. no. Lang. Rev. ind. Page
7
ABB AS 3AJM002064-031 en A No. of p.
9
Total capacitive current in system:
Capacitive current
Component Cable Total
Ico [A] Ico [A] Ico [A]
MAIN SWBD PORT B 0.31 2.26 2.58
MAIN SWBD PORT A 0.31 1.75 2.06
MAIN SWBD CENT B 0.31 2.83 3.15
MAIN SWBD CENT A 0.31 3.21 3.52
MAIN SWBD STBD B 0.31 1.94 2.26
MAIN SWBD STBD A 0.31 1.78 2.09
15.65

Chosen total resistive current acc. to

Iro/tot = 46.2 A (Iro tot  Ico tot)
design criteria

No. of earthing systems N = 6

Total resistive current per system Iro/syst = 7.7 A (Iro/tot/N)
Total resistive current per system per
Iro/ph = 2.57 A (Iro/syst/3)
phase
Chosen fuse size = 10 A

Transformer calculation:

Calculated rating Scalc = 48.9 kVA (√3 x Un x Iro/ph)

Chosen rating ST = 50 kVA
Secondary phase to earth voltage U ph sec = 220 V
Secondary phase to earth voltage during
U ph sec fault = 381 V (U ph sec x √3)
earth fault
Secondary voltage during earth fault U sec fault = 660 V (UL1 + UL2)
Secondary current Isec = 74.1 A

Resistor calculation:

R = 9 Ω (U sec fault / Isec)

Doc. kind Report Project HN2559 Rowan Drillship 1

Title Earth Fault Analysis Customer Hyundai Heavy Industries
HV Power System Proj. no. P025038
Doc. no. Lang. Rev. ind. Page
8
ABB AS 3AJM002064-031 en A No. of p.
9
REVISION

Page (P) Date

Rev. ind. Description
Chapt. (C) Dept./Init.
12/15/2011
- For approval
PAMA/OFON
2012-08-02
A All Cable data updated to latest
PAMA/FRKZ

Doc. kind Report Project HN2559 Rowan Drillship 1

Title Earth Fault Analysis Customer Hyundai Heavy Industries
HV Power System Proj. no. P025038
Doc. no. Lang. Rev. ind. Page
9
ABB AS 3AJM002064-031 en A No. of p.
9