1. CHARLES ISIADINSO
BALANCE OF PLANT (BoP)
Apart from the turbine, generator, and generator step-up
transformer, the balance of plant system controls the entire of
plant. It is a complex system designed to manage regulate the rest
of the plant to ensure reliable and efficient power. The BoP system
controls and monitors complimentary devices, values, gauges, fuel
levels and pumps, electronically using a number of different
systems, including SCADA (Supervisory Control And Data
Acquisition). It works by measuring current running condition (e.g.
rate of fuel injection into the combustion cans), comparing the
values with pre-set reference values and altering the system in
charge (e.g. fuel valve and pump system) to ensure it matches the
referenceexactly (or within pre-set tolerance levels).
There are two parts of balance of plant system, the Electrical
Balance of Plant (EBoP) and Mechanical Balance of Plant (MBoP).
The electrical balance of plant system is made up of High Voltage
(or Primary) Systems
1. TRANSFORMERS:used to step-up (or down) voltage.

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2. GAS / AIR INSULATED HIGH VOLTAGE SWITCHGEAR:
switchgear is a collection of electrical devices (e.g. fuses,
disconnect switches etc.) used for switching, protecting,
control, monitoring and measurement of electrical
equipment such as transformers, large motor pumps, fans
etc. The switchgear is also used to isolate these components
whenever the need arises. They can be insulated with either a
specific type of gas or surrounding air.
3. DISCONNECT SWITCHES: are used to completely de-
energize electrical equipment for maintenance and repairs.
These are usually opened after interrupting current by a
suitable device (e.g. a circuit breaker).
4. CIRCUIT BREAKERS: are used to interrupt high voltage
current safely and quickly in the event of an electrical fault
or for maintenance.
5. INSTRUMENT TRANSFORMERS: are used to transform
high current and voltage to lower, more manageable values.
6. SURGE ARRESTER: are electrical devices used to divert
lighting, which could cause damage, safely away from the
other systems, and
Low/Medium Voltage Systems:
1. MEDIUM/LOW VOLTAGE SWITCHGEAR: are used for low
to medium voltage electricity. It works the same way as the
high voltage switchgear.
2. BUS BARS: are used to transport generated electricity from
the generator, to the generator step-up transformer.
3. DRIVES & MOTORS: Drives are used to ensure safe, effective
running of DC and AC motors. The drives ensure smooth
start, precise speed and torque control and efficient process

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control. Motors are used to drive various components (e.g.
fuel pumps) across the plant.
4. MOTOR CONTROL CENTER (MCC): is an assembly of
enclosed sections mainly containing control units for motors
around the plant.
5. VARIABLE SPEED (OR FREQUENCY) DRIVES: are used to
vary the running speeds of motors when there is need for
speed adjustment.
6. AUXILIARY TRANSFORMER: supplies low voltage
electricity to AC systems (e.g. lighting, heating etc.).
7. MV/LV CIRCUIT BREAKERS: are used to interrupt medium
to low voltage current safely and quickly in the event of an
electrical fault or for maintenance.
8. STATIC FREQUENCY CONVERTER: is used to change the
frequency of AC current from one to another. It works by
passing the input AC power through a sine-wave rectifier
(which makes the negative half of the AC current positive),
then to a DC link (which connects the rectifier to the
inverter) and final through an AC sine-wave inverter (which
converts the DC current back into an AC current, but with a
different frequency).
Sine-wave rectifier input to output

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Sine-wave inverter input to output
9. EXCITATION EQUIPMENT: is used to provide variable DC
current to the generator’s rotor windings.
Components of the MBoP system, on the other hand, depend
largely on the type of plant (i.e. the MBoP for a Nuclear power
plant is different from that of a Hydro or CCGT power plant). We
are looking at a CCGT power plant and its MBoP is made up of:
1. COOLING WATER SYSTEM: cools condensed spent steam
from the steam turbine so it can be fed back to the HRSG. It
is also used the cool the lube oil systems, flame detectors,

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turbine supports, liquid fuel shaft pump and atomizing air
systems.
2. DRAINAGE SYSTEM: used to remove unwanted water from
the different systems.
3. BLOW DOWN SYSTEM: occasionally removes water from
the boiler racks to avoid the build up of impurities.
4. EMERGENCY DIESEL: Emergency diesel is used to run the
emergency generator used if there is loss of power to the
plant. The emergency generator is used to run utilities (e.g.
lighting, heating and air conditioning etc.).
5. FIRE PROTECTION SYSTEM: is used to monitor the turbine,
especially the combustion cans, to ensure low concentration
of the combustive agent. The system not only detects fires
automatically, but also trips the system and extinguishes the
fire quickly and effectively.
6. HEATING, VENTILATION, AIR CONDITIONING
SYSTEMS: These systems are used to remove hot air and heat
the enclosures during downtime. The system also protects
potentially dangerous systems (e.g. gas turbine, gas valves,
load gear, etc.) from gas leaks as they cause to fires or
explosions.
7. OIL TREATMENT SYSTEM: ensures clean oil is supplied
where it is needed. In use oil is flushed out of components,
like gas-insulated transformers, as fresh oil is pumped in. The
difference in density between the used oil (as a result of dirt
and other impurities) and new oil makes it easy to flush used
oil out the bottom of each unit, and pump new oil in through
the top. Used oil is then sent through the oil treatment
system to recover as much oil as possible, to reduce wastage,
and the dirt from the spent oil is discarded.

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8. RAW, POTABLE, AND DEMINERALIZED WATER
SYSTEMS: are responsible for providing water for the power
plant. Raw water is pumped, usually from a natural source
(e.g. a river) into reservoirs. This water is then converted to
portable water for consumption and demineralized water.
Demineralized (or de-ionized) water is water with most
mineral ions removed. Water has to be demineralized to
ensure water fed to the HRSG for boiling, is free from
impurities and boils as close to 100o
as possible, this reduces
heat used during boiling.
9. FUEL FORWARDING SKID: is used to provide the gas
turbine’s combustion cans with fuel that is at the optimal
pressure and temperature. The unit usually includes an
electric heater (for fuel heating and/or cooling), pressure
control valve (for pressure control) and a flow meter (to
measure the fuel flow).
10.BACK UP POWER: there are occasions where the plant losses
power. To avoid serious damage being caused to the plant
equipment, there are a few power loss prevention and control
system employed.
a. UNINTERRUPTIBLE POWER SUPPLY (UPS): is
usually located between the power source and the load
and is used to provide power in the event of power
interruptions. The UPS also protects the supply
network from surges and other electrical problems.
The UPS gives plant operators time to react to sudden
power outages.
b. EMERGENCY GENERATOR: is used to provide power
to the plant for lighting, heating and other basic tasks
in the event of a power outage. The emergency
generator does not power the gas and steam turbines or
generator.

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c. BACK-UP GENERATOR: is used the start the gas
turbine in the event of a black start. In the event where
there is no power to start, as soon as the turbine is
running at full power, the back-up generator is tripped.
11.GAS CONDITIONING SKID: is used to treat gas before it
enters the gas turbine. This treatment process removes liquid
droplets and solid particles from the gas ensuring only gas is
injected into the gas turbine. The skid also adjusts gas
temperature and pressure to injection requirements.
12.OIL-WATER SEPARATOR: is used to separate oil and other
solids from water. The system uses gravity to perform the
separation, wastewater (including oil and particles) is
pumped into a large tank, since oil is denser than water, it
floats and the solid particles, which are denser than water,
sink. Oil is skimmed off the top of the water, via an oil
skimmer, while the water is drained, and the solid particles
settle at the bottom of the tank. See figure below.
13.STORAGE TANKS & VESSELS: are metal units of varying
strengths and sizes used as reservoirs for water, oil and fuel
(e.g. diesel). Gas is usually not stored in large volumes, rather
it is supplied directly from the source, the gas storage facility
is used to hold gas before it enters the gas conditioning skid.

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14.SEWAGE TREATMENT SYSTEM: is used to ensure waste
discharged from the plant is treated. The system separates
dirt and waste from water via a system of filters, aeration
chambers and sediment tanks. After separation, microbes
from the atmosphere are introduced to breakdown
biodegradable materials. The microbes digest sludge to
produce methane, carbon dioxide and traces of other gases.
15.COMPRESSED AIR SYSTEM: is used to provide valves,
pumps and other equipment high-pressureair for operation.
REFERENCE:
1. Amitava, Paul. "Balance of Plant - Standard Technical
Specification." Scribd. Amitava Paul, 08 Feb. 2011. Web.
[Accessed20 June 2014].
2. Swapanbasu. "Balance of Plant - Introduction." Scribd.
Swapanbasu, 23 Sept. 2010. Web. [Accessed20 June 2014].
3. "Standby Generator." Wikipedia. Wikimedia Foundation, 07
May 2014. Web. [Accessed08 July 2014].
4. "Emergency Power System." Wikipedia. Wikimedia
Foundation, 07 May 2014. Web. [Accessed08 July 2014].
5. "Fact Sheet." Chemical & Engineering News 47.10 (1969):
101A. Web.
6. "Voith | Balance of Plant Mechanical Systems." Voith |
Balance of Plant Mechanical Systems. N.p., n.d. Web.
[Accessed08 July 2014].
7. "Electrical Balance of Plant :: Power Delivery Projects :: GE
Digital Energy." Electrical Balance of Plant :: Power Delivery

9. CHARLES ISIADINSO
Projects :: GE Digital Energy. N.p., n.d. Web. [Accessed 08 July
2014].
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