Success Story: Oil & Gas

Sonatrach (Algeria)

Electrical network design for the Hassi Messaoud oil field

I. CUSTOMER ENVIRONMENT / PROJECT CONTEXT

Customer profile:

Sonatrach is the Algerian company for research, operation, transport by pipe, transformation and marketing of hydrocarbons and of their by-products. It also intervenes in other sectors such as electrical generation, new and renewable energies and desalination of sea water.

Customer objective and constraints:

The extension to the Hassi Messaoud oil field has in turn led Sonatrach to extend its supply network from 30kV to 220kV.

II. SOLUTION IMPLEMENTATION

Implementation methodology (main phases):

Sonatrach has entrusted the extension of the network and the refurbishment of existing installations to Schneider Electric. This turnkey service includes:

network design
supply and commissioning of: 2 x 220kV GIS substations - 47 x 30kV substations - 12 x LV switchboards - 1 supervision system, combined with PLCs for network monitoring and control.

Duration:

3 months

Solution overview (services, products, systems, architectures...):

The work carried out for this project was largely the same as that generally done for electrical network design.

load flow and voltage profile studies

sizing of equipment (cables, lines, transformers) according to the installed power
calculation of voltage drops over the various links
positioning of power transformer tap changers

short-circuit current calculations

maximum short-circuit current values (device sizing)
minimum short-circuit current values (protection settings)

protection study

choice of protection devices
establishing of settings according to the various operating modes

dynamic stability study

determining maximum fault clearing times for enabling motor reaccelerations
impact of high power (7 MW) motor starting on voltage levels
impact of voltage drops due to the upstream network (220kV)
establishing a load shedding plan

III. RESULTS / ACHIEVEMENT

Customer benefits:

This specfic study is necessary for a such important site.

This electrical network design is essential to ensure proper operation of the Hassi Messaoud oil field.

IV. ADDITIONAL INFORMATION

Other information

Other electrical network studies:

Harmonics: control electrical pollution.
Overvoltages and insulation coordination: guarantee equipment dielectric strength is respected according to expected overvoltage levels (permanent or temporary overvoltages or those due to operating or lightning strikes).
Dependability : guarantee the availability of electric power and the reliability of installations adapted to the application.
Electromagnetic compatibility (EMC): design installations that are fully protected against electromagnetic disturbances.

Solution breakdown

Main services:

Engineering services: Services
Electrical network studies
Power Quality studies

Detail of design services

Calculation of short-circuit currents:
These calculations are achieved using network modelling as defined in IEC 60909. They enable the maximum and minimum short-circuit currents (symmetric and asymmetric) to be determined for phase to phase and phase to earth faults. These calculations are essential for checking:

making and breaking capacity of interrupting devices
electrodynamic withstand of equipment (switchboards, busbars, etc.)
thermal withstand of earthing devices
site earthing characteristics
protection settings

Protection study:
This study enables the type of protection to be determined (over current, directional, differential relays, etc.) by taking into consideration the various technical and economic criteria for the oil process.
Protection settings are defined according to:

short-circuit currents of the different operating modes
transformer switching currents
motor starting or re-energising currents
etc.

Dynamic stability study:

The main objective of a network dynamic study for this type of installation is to estimate the behaviour of high power asynchronous motors should an electrical incident occur.
For example, a phase to phase fault in the installation creates a voltage drop and the slowing of motors of substations close to the faulty feeder. If protection setting times are too long, motor deceleration will be excessive to ensure that all loads can be fully brought up to speed once the fault has been cleared. Pre-determined load shedding will allow priority loads to be rescued.
Furthermore, for this installation, the study enabled network behaviour to be checked should the automatic transfer system (ATS), installed in the main substation, operate. In the event of a fault on one of the 220kV/30kV transformers, the ATS ensures busbar changeover in less than 500ms. The simulation carried out enabled system stability and the re-energising of high power motors to be validated.