aliran-daya.pdf

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ANALISIS SISTEM TENAGA

Analisis Aliran Daya

Dr. Muhammad Nurdin

Ir. Nanang Hariyanto, MSc

Departemen Teknik Elektro ITB



Introduction (1)

The basic load flow question is: Given the load powerconsumption at all buses of a known electric powersystem configuration and the power production ateach generator, find the power flow in each line and

transformer of the interconnecting network and thevoltage magnitude and phase angle at each bus

Analyzing the solution of this problem for numerousconditions helps ensure that the power system isdesigned to satisfy its performance criteria whileinducing the most favorable investment and operationcosts.



Introduction (2)

By using load flow studies we will be able todetermine:

• Component or circuit loadings

• Steady-state bus voltages

•

Reactive power flows• Transformer tap settings

• System losses

• Generator exciter/regulator voltage set points

•

Performance under emergency conditions. As the load distribution, and possibly the network, will vary

considerably during different time periods, it may be necessaryto obtain load flow solutions representing different systemconditions such as peak load, average load, or light load.



Introduction (3) These solutions at different loading condition will be used to

determine:• Optimum operating modes for normal conditions, such as the proper

setting of voltage control devices

• How the system will respond to abnormal conditions, such as outagesof lines or transformers.

• The basis form for determining the condition when new equipmentadditions are needed.

• The basis form for determining the effectiveness of new alternatives tosolve present deficiencies.

•

The basis form for determining to meet future system requirements. The load flow model is also the basis for several other types of

study such as short-circuit, stability, motor starting andharmonics studies. The load flow model supplies the networkdata and an initial steady-state condition for these studies.



System Representation (1)

A simplified visual means of representing thecomplete system is essential to understanding the

operation of the system under its various possible

operating modes => single-line diagram

The single-line diagram consists of a drawing

identifying buses and interconnecting lines. Loads,

generators, transformers, reactors, capacitors, etc.,

are all shown in their respective places in the system




System Data: Most load flow programs perform their

calculations using a per unit representation of the

system, while still some programs work with volts,

amperes, and ohms.

Bus Data: The data includes: bus number, bus

name, bus type, load, shunt, per unit voltage and

angle, and bus base kV. There three bus types, they

are: Load bus (P-Q bus), Generator bus (P-V bus),and Swing bus (Slack bus)




Generator Data:

• Real power output in MW.

• Maximum reactive power output in MVAR, that is the

machine maximum reactive limit.

• Minimum reactive power output in MVAR, that is themachine minimum reactive limit.

• Scheduled voltage in per unit

•

Generator in-service/out-of-service code, or generatoroperated continuously, operated intermittently, or

operated as spare.




Line Data:• Resistance

• Reactance

• Charging susceptance (shunt capacitance)

• Line ratings

• Line in-service/out-of-service code

• Line-connected shunts




Transformer Data:

• Tap setting in per unit

• Tap angle in degrees

• Maximum tap position• Minimum tap position

• Scheduled voltage range with tap step size



Load Flow Solution Methods

Problem simulations [ ] [ ] [ ]V Y I ⋅=

( )*

*

i

iii

V

jQP I +=

[ ] [ ]V Y

V

jQP⋅=⎥

⎦

⎤⎢

⎣

⎡ −*



Iterative Solution Algorithms

The primary parameters are: Active power into the transmission network

Reactive power into the transmission network

Magnitude of bus voltage (voltage to ground)

Angle of bus voltage referred to a common reference



Load Flow Bus Specifications

Bus Type P Q V

δ Comments

Load √ √ Usual Load Representation

√ √

whenQ-<Qq<Q

+

Generator or SynchronousCondenser (P = 0) with var Limits

Generator or Synchronouscondenser

√ √whenQg< Q

-

or Qg> Q

+

Q- = Minimum var Limit

Q+ = Maximum var Limit

V is held as long as Qg is withinlimit.

Swing √ √ Swing bus must adjust net power to hold voltage constant

(essential for solution).



Comparison of Load Flow Solution

Techniques (1)

.The Gauss-Seidel method is generally tolerant of power

system operating conditions involving poor voltage distributionand difficulties with generator reactive power allocation, butdoes not converge well in situations where real power transfersare close to the limits of the system.

.The Newton-Raphson method is generally tolerant of powersystem situations in which there are difficulties in transferringreal power, but is likely to failure if there are difficulties in theallocation of generator reactive power output or if the solution

has a particularly low voltage magnitude profile..The Gauss-Seidel method is quite tolerant of poor startingvoltage estimates but converges slowly as the voltage estimategets close to the true solution.



Load Flow Analysis (1) predefined set of criteria that the system must

meet, which includes:• Voltage criteria, which are usually divided into an

acceptable voltage range for normal conditions and awider range of acceptable voltage under outage

conditions.• Flows on lines and transformers must be within defined

thermal ratings, while the thermal criteria for lines andtransformers may also have such a division that allowingfor a temporary overload capability due to the thermaltime constant of the equipment of additional forcedcooling capabilities of transformers.

• Generator reactive outputs must be within the limitsdefined by the generator capability curves



Load Flow Analysis (2)

To solve low-voltage problems, possiblechanges include:

• Change in transformer tap positions

• Increase in generator schedule voltage

• Addition of shunt capacitors

• System reconfiguration to shift load to less

heavily loaded lines

• Disconnection of shunt reactors

• Addition of lines or transformers



Load Flow Analysis (3)

The system must be examined to checkoperation under abnormal conditions

(contingency analysis). These

conditions include:• Loss of a transmission line of cable

•

Loss of a transformer• Loss of generator

• Abnormal supply conditions



Conclusion (1)

The load flow analysis is used to designa system that has a good voltage profile

and acceptable line loadings during

normal operation and that will continueto operate acceptably when one or

more lines become inoperative due toline damage, lightning stroke, failure of

transformers, etc.



Conclusion (2)

A study of reactive power flows on thebranches can lead to reduce line losses and

improved voltage distribution. Reduction in

kVA demand due to power factor correctioncan lead to lower utility bills for an industrial

plant. The size and placement of power factor

correction capacitors and setting of generatorscheduled voltages and transformer tap

positions can be studied with load flows.



Conclusion (3)

Knowledge of branch flows supplies theprotection engineer with requirements

for proper relay settings. The load flow

studies can also provide data forautomatic load and demand control, if

needed.



Conclusion (4) The load flow is also used to check the effects of

future load growth and the effectiveness of planned

additions. These studies are performed in the same

way as studies of the present system. The future

loads are determined and entered into the model.Base case conditions are studied and additions

made, if necessary, to get the system to meet the

performance criteria. Then outage conditions arestudied and again system changes may be required.



Hands-on Experience

Laboratory works on

Load Flow Studieswith

ETAP Power Station

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