Download - 06 AET - Genset Sizing
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Genset Sizing
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Required Information
Duty rating to be applied
Frequency (50Hz/60Hz)
Nominal Voltage
Climatic Conditions
Voltage and Frequency dip requirement
Load parameters
Mandatory load steps or sequence of load step, if they exist
Number of genset in parallel
Sizing software(Power-Suite)
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Motor Load
AC electric motors represent inductive loads withlagging power factors
Different types of motors have different starting
characteristics.
Starting characteristics may drive the need for a
larger or smaller generator.
Starting an electric motor can create voltage dips in
excess of 40% if the genset is not properly sized.
Cummins Confidential
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Inductive Load: kW vs. KVars
Inductive loads need two kinds of power to function properly:
– Active power (kW) – actually performs the work
– Reactive power (kvar) – maintains the electromagnetic fields
Engines Produce kW--Fuel Rate Controls
Alternators Make kVAR--Excitation Controls
kW Dem anded b y Load
kVa r Dem anded b y Lo ad
kW = engine
k V A
R =
a l t e r n
a t o rppa r en t pow e r
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Voltage Response at Constant Speed
Voltage
requency
Generator Transient Response to StepLoads
Alternator Must Support kVA:
– Limit Initial Dip
– Recover to Acceptable Voltage(Motor Torque Proportional to
Voltage2
)
Engine Must Support kW (Similarto Voltage Response)
Dynamic Response Combination ofFrequency and Voltage
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We are going to create a project with PowerSuite with thefollowing criterias:
50Hz
400V
Min rated capacity 30%
18% Voltage Dip, 5% Frequency Dip
25C
150m
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Electrical Motors
UPS
Lighting
Regenerative loads
Miscellaneous load
Differents types of loads
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Apply Alternative Starting Methods on HighInertia Loads With Caution
Motor Torque Proportional to
Appl ied (Vol tage)2 Okay for low inertia applications.
Watch out with high loads!
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Typical 3 Ø Induction MotorCharacteristics
Direct On-Line (DOL) Start
High Locked Rotor Currentand KVA
Torque Shown for 100%
Rated Voltage (sol id red line) Starting (instantaneous) PF
0.2 to 0.4 for 3 Ø Motors
Higher StartingRequirements for HighEfficiency 3Ø and for 1Ø
Treat Synchronous MotorsLike Induction Motors
P E
R C E N T T O R Q U E , P O W
E R , C U R R E N T
PERCENT MOTOR RATED SPEED
20 40 60 80 100
100 0.2
1.0
P O W E R F A C T O R ( L
A G G I N G )
600
Current
Power Factor
Load Torque
Motor Torque
Power
0
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Let’s enter the following load with direct on line starting
method in Powersuite:
Motor Running Power (Electrical) = 300kWe, 350kVA
Starting kVA = 6 x 350kVA = 2100kVA
Starting kW = 2100kVA x 0.3 p.f. = 630kW
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Star-delta Starting…
Reduced Starting Impact
Watch out for the transition(kVA)
Potential start failure ifalternator cannot sustainvoltage in transit ion.
Typical kVA demand of motor…
Typical kW demand of motor…
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Transit ion on Reduced Voltage Starters
Same as DOLTrue Reduced
Voltage
Transition
too Early
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We will now enter the following load with star/delta startingmethod in PowerSuite:
Motor Running Power (Electrical) = 300kWe, 350kVA
Starting kVA = 3 x 350kVA = 1050kVA
Starting kW = 1050kVA x 0.3 p.f. = 315kW
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Auto TransformerThis method uses transformer action to reduce the voltage applied to the motor
and current seen by the supply. An improved torque/amp ratio is achieved and
starting current is typically 3 x FLC, depending on the voltage tapping selected.Normally the voltage is applied to the motor in voltage steps through the T/F
taps being selected through contactors. Typical tappings are 50%, 70%,
followed by full voltage being applied to the motor . The major disadvantages
are size & cost. Mechanical snatch at switch on is not controllable and may
cause problems. Once tappings have
been selected, it may be necessary tochange them according to changes in
load parameters.
Advantages
• Simple operation
Disadvantages
• Poor controllability
• Bulky
• Very Expensive
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Soft Starters Limit the starting current by limiting the amount of
starting torque. Current distortion has to be considered for the non
linear loads.
Advantages: Less mechanical stress, reduced startcurrent, improved control of acceleration and
deceleration
Disadvantages:
Size & Cost
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Uninterruptible Power Supply
UPS can produce high levels of
current distortion.
Excessive generator voltage
distortion
Increased Power SystemComponent losses and heating
Harmonics can be reduced by
filters on the UPS.
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(Or 18 Pulse)
Cummins Confidential
Phase Controlled Rectif iers: Voltage andCurrent Distortion
3 1
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Let’s enter the following UPS Load in PowerSuite
Rated Output= 200kVA
Rectifier= 12 Pulses
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Lighting Loads
Fluorescent & Discharge
Both are non-linear loads which may need to be
considered when sizing your generator
Incandescent
Defined as a general load for sizing purposes
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Let’s enter the following light ing load in PowerSuite
Light Type : Fluorescent
Running KVA = 50kVA
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Regenerative Load
Reverse power needs to be considered.
http://upload.wikimedia.org/wikipedia/commons/5/55/Gondola_car_20060409.jpg
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Regenerative Load
Stage 1:-
Genset Supplies Site Loads
Stage 2:-
Lift Motor Produces
Reverse Power 200kW
100kW Load Bank Removes
Risk of Reverse Power
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Miscellaneous Loads
If the load is so specific that you can not find its kind in PowerSuite,you can create your own kind of load
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Let’s enter the following load in PowerSuite
Running & Starting = 100 kW
Running Power factor= 0.95
Starting Power factor= 0.50
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We are going to size the genset with a single load step and the load weentered:
(In case a single genset is not enough to start the loads with the criteriasit is possible to add more gensets)
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Size of genset optimization
Step Starting Sequence
Step Loading the Generator
• Apply Load in Increments
• Apply Large Motor Loads First
• Limit Voltage and Frequency dip
• Ultimately reduce genset size
Let’s now optimise the genset size
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Questions?
27
Thank You