TURN KEY PACKAGED ELECTRICAL SYSTEM
A
turn key, packaged electrical system is available for power stations
using diesel / gas ignition generators, including design, supply, technical support services for installation,
commissioning and after sales service. This includes prime power units
either in island mode or connected to the grid at either low voltage
or medium voltage. The power stations are designed for automatic, un-attended
operation with a fully integrated SCADA system for control and monitoring.
GENERATORS
The generators may be diesel engine powered or gas ignition engine powered
with either low voltage or medium voltage alternators. The starting
system may be either compressed air operated or battery powered. Air
start systems require a duty and standby air compressor and a receiver.
Many generators are fitted with an on-board, local, generator start
and fault shutdown system. Alternatively, a custom made system may be
fitted. The local start and fault shutdown system allows local, manual
operation of the generator for maintenance purposes or in the event
of the failure of the automatic controls. The electrical system is fitted
with safety isolation points. The local start and fault shutdown system
is interfaced to a station control panel for automatic operation. The
speed controller, load share unit, automatic voltage regulator and automatic
synchronizer for each generator are generally mounted in the station
control panel. The generators may be installed in an engine hall or
individually installed in an enclosure.
ENCLOSURES
The generator enclosures are usually modular and often incorporate acoustic
attenuation in order to reduce environmental noise. The enclosures are
fitted with cooling fans which run when the engine is running. There
may be electrical accessories such as overhead cranes, lighting, a starting
battery charger, and socket outlets. The enclosure is fitted with a
local distribution board which is used to supply the electrical accessories
and any on-board generator electrics such as anti-condensation heaters.
The electrics in each enclosure are supplied from the low voltage station
auxiliary motor control centre.
FUEL
SYSTEMS
The diesel fuel system generally comprises bulk tanks, transfer pumps,
day tanks, instrumentation and controls. The bulk tanks are usually
tanker filled. A local fuel fill, level control panel is provided for
the tanker operator. Fuel metering is sometimes incorporated. The bulk
tanks and day tanks require level instrumentation and solenoid controls
for valves. The fuel transfer pumps are a dual set, operating in duty
/ standby mode with automatic rotation of the duty pump. Additional
instrumentation may be provided for the day tanks, such as engine supply
fuel temperature / flow, engine return fuel temperature / flow, fuel
consumption rate and consumption total. The fuel system electrics are
extra low voltage 24VDC.
COOLANT
SYSTEMS
The coolant system may be either single or twin circuit. The single
circuit cooling system is generally fitted with an on-board radiator.
The radiator fan may be either engine driven or electric powered. The
twin circuit systems generally have remote radiators with electric powered
fans. The fans may be either fixed speed or variable speed. The variable
speed fans have a feedback control system so that the speed of the fan
is controlled by the temperature of the cooling circuit. The electric
powered fans are supplied from the low voltage station auxiliary motor
control centre.
INSTRUMENT AIR SYSTEMS
Instrument air systems are sometimes required for the operation of valves
in the fuel system. The instrument air system comprises an air compressor
and instrumentation to monitor instrument air pressure. The air compressor
is supplied from the low voltage motor control centre.
STATION
MAIN SWITCHGEAR
The station main switchgear comprises the generator circuit breakers
and the feeder circuit breakers. The main switchgear may be either low
voltage or medium voltage, depending on the voltage of the generators.
If the system is medium voltage, then a step-down transformer is required
for the station auxiliaries and consideration must be given to the type
of neutral - earth connection. The station main switchgear generally
houses the generator electrical protection relays and the current /
voltage transformers for the generator speed control, load sharing and
synchronizing.
LOW
VOLTAGE AUXILIARY MOTOR CONTROL CENTRE
The low voltage, auxiliary motor control centre comprises starters and
distribution boards for the station auxiliaries, including the generator
auxiliaries.
STATION
BATTERIES & CHARGERS
The station batteries and chargers comprise two systems. The first is
the station control battery / charger system, which is usually 24VDC.
The second is the station main switchgear trip / close battery / charger
system, which is required if the station main switchgear is medium voltage.
Redundant battery / charger systems may be used to improve availability.
STATION
CONTROL PANEL
The station control panel comprises the station PLC, the SCADA system,
automatic controls for each generator and the marshalling panel for
field cabling. The station PLC provides control and monitoring of the
power station. Redundant PLCs may be used to improve availability. The
SCADA provides the operator control, status monitoring and reporting.
Remote SCADA control is available. The automatic controls for each generator
include the speed control, load share unit, automatic synchronizer,
automatic voltage regulator, diesel level controls and operator hardwired
controls. The control system is configured with dual levels of control
so that the power station availability is maximised. The normal, unattended
level of control is fully automatic via the PLC. Should the PLC fail,
then the next level of control is semi-automatic control via operator
initiation of hard-wired, automatic processes.
PRE-FABRICATED
SWITCH-ROOMS
Pre-fabricates switch-rooms are used to house the station main switchgear,
the low voltage station auxiliaries motor control centre, the station
batteries and chargers, and the station control panel. The advantage
of using pre-fabricated switch-rooms is that the site erection and testing
work is minimised.
AUTOMATIC
UNATTENDED MODE
Automatic, unattended operation is the normal mode of control. The station
is controlled by the PLC. Generators are sequenced on and off line depending
on the station load. The operator may select and deselect generators
for available operation via the SCADA.
ISLAND MODE
In island mode, the station operates independent of the grid or any
other power station. The station frequency is isochronous and the voltage
has zero droop from no load to full load.
GREY
START MODE
In grey start mode, the station is off-line and grid voltage is on the
main bus of the station main switchgear. The station is started by synchronizing
generators to the grid. The grid is disconnected once the required generation
capacity is on-line. In grey start mode, the generators follow the grid
frequency and voltage as they are synchronized to the grid. Once the
grid is disconnected, the station reverts to isochronous operation with
zero droop voltage.
BLACK
START MODE
In black start mode the station is blacked out and there is no voltage
on the main bus of the station main switchgear. The operator selects
the required number of generators for black start via the SCADA. The
first generator on-line is closed onto a dead bus. The remaining generators
go on-line by synchronizing to the first generator. The station is in
isochronous operation with zero droop voltage.
IMPORT
/ EXPORT MODE
The import / export mode is used if the station is to operate in parallel
with the grid or another power station. An inter-connector circuit breaker
is required in the station main switchgear. The station control panel
requires a master controller to provide the automatic functions of synchronization
to the grid and import / export control. The operator initiates the
functions via the SCADA.
PLC & SCADA SYSTEMS
The PLC provides the control and data acquisition functions for the
station. Redundant PLCs may be provided in order to improve the station
availability. The SCADA system allows operator control and monitoring
either locally or from a remote location.
DOCUMENTATION
Documentation required for the electrical package of a diesel generator
power station project includes:
- Test records and certificates
- Pre-commissioning and commissioning records
- Hand-over documentation, "as installed" drawings
- Operation and maintenance manuals
- Spare parts manuals
The documentation is provided in hard and soft copy.
DESIGN
A complete range of electrical design services is available for diesel
generator power station projects. The services range from cost estimates
and preliminary concepts to detailed electrical schematics and procurement,
according to the needs of the project. Please refer to the section describing
electrical engineering services for more details.
LOAD
TESTING
The load testing of the generators is required to prove that the generators
meet the site rated load capacity. The generators are tested individually
on either a load bank or site load, depending on the site conditions.
FACTORY
ACCEPTANCE TESTING
Factory acceptance testing of the electrical package is an important
milestone. It proves the bulk of the functionality of the main components,
such as the station main switchgear, the low voltage auxiliary motor
control centre, the station control panel and the battery / charger
systems. Not all functionality can be proved because the total package
cannot be interconnected and because generators and other components
may not be available. The factory acceptance testing of each item involves
routine testing as per the relevant standard and functional testing
SUPERVISION
OF SITE ERECTION
The supervision of site erection allows the day-to-day co-ordination
of the electrical installation between the main contractor, the electrical
contractor and the generator contractor. The co-ordination minimises
delays in construction that may otherwise be caused by misinterpretation
of the drawings, unexpected problems which occur on site and by providing
site guidance as to the sequence of work. The supervision of site erection
allows in process testing as portions of the work are completed.
SUPERVISION OF SITE PRE-COMMISSIONING
The supervision of site pre-commissioning allows day-to-day co-ordination
of the pre-commissioning between the main contractor, the owner and
the generator contractor. The co-ordination minimises the delays in
pre-commissioning by providing site guidance and by addressing immediately
any defects which may be identified.
SITE
ACCEPTANCE TESTING
Site acceptance testing is the proving of the installation for hand-over
to the client. The tests are mutually agreed between the client and
the generator contractor at the time of order. The tests generally require
rigorous proving of the functionality of the diesel generator power
station and a proving run under normal operating conditions.
REFURBISHMENT
On occasions, the client may have second hand switchgear which it is
intended to be used in the power station. In such cases, it is necessary
to provide a technical evaluation of the switchgear and supervise the
refurbishment of the switchgear.
TRAINING
In order to provide optimum performance, the electrical portion of the
diesel generator power station requires operators and maintenance personnel
to have a proficient knowledge of the system. Therefore, training is
necessary for the operators and maintenance electricians.
QUALITY
ASSURANCE
Quality assurance is either based on the client's in-house procedures
or is prepared to suit the scope of work required for the project. The
quality assurance is in accordance with IEC standards. The relevant
procedures are prepared and implemented as required.
STANDBY / GRID CONNECTED GENERATOR POWER PLANTS
A turn key, packaged electrical system is available for standby / grid connected generator power plants using diesel / gas ignition generators, including design, supply, installation, commissioning and after sales service. This includes standby power units in island mode or grid connected generators at either low voltage or medium voltage. The power plants are designed for automatic, un-attended operation with a fully integrated SCADA system for control and monitoring.
STANDBY AUTOMATIC MAINS FAILURE CONTROLS
Standby, automatic mains failure controls allow the change-over from grid power to standby generator power and vice versa. The generators may be either single units or multiple units operating in parallel. The generator voltage may be either low voltage or medium voltage. The change-over may be "bump less" i.e. without a break in supply to the load.
GRID CONNECTED POWER PLANTS
Grid connected, diesel generator power plants are either prime power units continuously on-line or power plants which are put on-line for peak lopping. The units follow the grid frequency and voltage. The power plant exports power to the grid.