Download Cable System Modelling

DIgSILENT Pacific User Conference 2007
DETAILED MODELLING OF HV
SINGLE CORE CABLE SYSTEMS
USING POWERFACTORY
…..to determine armour and screen
current magnitudes under varying
conditions of installation
Peter Willis, DIgSILENT Pacific
Perth Office
DIgSILENT Pacific PowerFactory Training
1
SYSTEM MODELLING
Cable Systems – Frequency domain model
• Traditionally represented by equivalent PI
representation for Z1 and Z0 impedances.
• Impedance data is typically taken from
manufacturers’ catalogues
DIgSILENT Pacific PowerFactory Training
2
1
CABLE SYSTEM MODELLING – Multi-Core Cables
For multi-core cables,
manufacturer data is used.
Here we see a non-SWA
OLEX cable.
DIgSILENT Pacific PowerFactory Training
3
CABLE SYSTEM MODELLING – Multi-Core Cables
..and here we see the same
OLEX cable with SWA.
DIgSILENT Pacific PowerFactory Training
4
2
CABLE SYSTEM MODELLING – Single-Core Cables
For single core cables systems,
the overall impedance is based
on
assumptions
on
the
installation and connection of
screens.
DIgSILENT Pacific PowerFactory Training
5
CABLE SYSTEM MODELLING – Single-Core Cables
For single core cables systems, the overall impedance
must be calculated from the geometric arrangement of
the conductors, as is the requirement for overhead lines.
These complexity of these calculations are also
compounded by the multiple insulation and conducting
layers of single core cable profiles, however the new
PowerFactory cable system tools encapsulates this.
DIgSILENT Pacific PowerFactory Training
6
3
CABLE SYSTEM MODELLING – Single-Core Cables
Unlike multi-core cables, the individual phase screens
are not in electrical contact along the cable length, so
there can be substantial induced currents flowing when
screens are bonded together and earthed at the cable
terminations.
If the screens are not bonded at both ends, induced
currents do not flow however screen voltages become
elevated.
All this requires engineering assessment, hence new
tools were developed (first supported in Version 13.1) to
model single phase cable systems.
DIgSILENT Pacific PowerFactory Training
7
CABLE SYSTEM MODELLING – New PowerFactory Objects
There are three new PowerFactory objects in the model:
TypCab
Single Phase cable profile
TypCabsys
Geometric arrangement of cables
making up the circuits in a cable
system
ElmCabsys
The link between cable system type
and the line elements in the active
network
Overhead line equivalents:
TypCon
Arial Conductor Type
TypTow
Tower geometry Type
ElmTow
Tower Element
DIgSILENT Pacific PowerFactory Training
8
4
CABLE SYSTEM MODELLING – TypCab
DIgSILENT Pacific PowerFactory Training
9
CABLE SYSTEM MODELLING – TypCabsys
DIgSILENT Pacific PowerFactory Training
10
5
CABLE SYSTEM MODELLING – ElmCabsys
DIgSILENT Pacific PowerFactory Training
11
CABLE SYSTEM MODELLING – ElmCabsys (EMT Tab)
DIgSILENT Pacific PowerFactory Training
12
6
GRAPHICS
DIgSILENT Pacific PowerFactory Training
13
GRAPHICS
DIgSILENT Pacific PowerFactory Training
14
7
WHY DO IT ???
Why do we need this tool?
• Customers asked for this
• Screen and armour currents need to be
quantified so connections & equipment can be
correctly dimensioned.
• Where screens or armours are lifted, the
standing voltage can be determined under
load and fault conditions.
• Screen-cross bonding distances can be
examined
• Effect of cascading failures can be examined
DIgSILENT Pacific PowerFactory Training
15
CASE STUDY – Real Failure
Example of how the ‘Cabsys’ model was used to
quantify screen currents following screen joint
failure in 6.6kV generator incomer and how the
geometric orientation of cable grouping in the field
affects current imbalance across all conducting
layers.
DIgSILENT Pacific PowerFactory Training
16
8
CASE STUDY
Oil & Gas Installation
- VESDA System detected fault but damage was
already done
- Generator outage
- Very significant $AUD in production losses
DIgSILENT Pacific PowerFactory Training
17
SINGLE CORE CABLE SYSTEMS
3 Main Areas of Concern
- Orientation & configuration
multiple cable runs, rotating phases within trefoil groups..
- Circulating currents
armour and screen bonding and earthing, termination kits..
- Eddy Currents
steel pipes, transit boxes, gland plates..
DIgSILENT Pacific PowerFactory Training
18
9
SCREEN CURRENTS – Cable Damage due to Hot Joints
DIgSILENT Pacific PowerFactory Training
19
SCREEN CURRENTS – Cable Damage due to Hot Joints (cont)
DIgSILENT Pacific PowerFactory Training
20
10
Cable Profile
DIgSILENT Pacific PowerFactory Training
21
Joint Instructions
DIgSILENT Pacific PowerFactory Training
22
11
Constant Force Springs
DIgSILENT Pacific PowerFactory Training
23
Final outer layer of joint
DIgSILENT Pacific PowerFactory Training
24
12
What should have been done
DIgSILENT Pacific PowerFactory Training
25
Thermography – Effect of screen connection
Screens Connected
DIgSILENT Pacific PowerFactory Training
Screens Lifted on end
26
13
Thermography – Effect of screen connection
PowerFactory Study cases:
• Effect of parallel circuits
• Lack of transposition
• Phase positions in trefoil
groups
• Effect of high resistance
joints leading to cascading
failure
• Lifting screens and isolating
armour-clamping glands
Screens Connected
DIgSILENT Pacific PowerFactory Training
27
Repaired Joints
DIgSILENT Pacific PowerFactory Training
28
14
SUMMARY
Modelling Cable Systems• A tool that has a time and a place
• Can also be used to offline to valid Z1/Z0 in conventional models.
• Has associated line objects for each conducting path (sheath, armour,
conductor) of each circuit.
Going forward…..
• Easier to visualise with composite branch line graphic (V14 feature)
• Has some application for EPR calculation, whereby ground
impedance is modelled from external tool (CDEGS).
Feedback welcome…always
DIgSILENT Pacific PowerFactory Training
29
15