utility design method to eliminate voltage collapse presented by jason taylor

Utility Design Method to Utility Design Method to Eliminate Voltage CollapseEliminate Voltage Collapse

Presented by

Jason Taylor

Motivation

• Interest in utility system design and planning

• Potential “Hot Spot” of activity

• Utility systems were originally designed to be overly conservative. With the onset of deregulation, companies are looking for ways to optimize cost and still improve power quality

• Current method for analyzing the potential voltage collapse situations is lengthy, shorting the options for corrections

Method Design

• Developed using industry standard software

• Easy to follow procedure

• Prompt results that are conservative in nature

• A non-customer specific application

Voltage Collapse

• Voltage collapse is the uncontrollable drop in system voltage following a large disturbance

• Two basic ways to incite voltage collapse

– Sharp rise in system load

– Major outage

Theory

VE

QXE

X P XE Q 2 4

2 2 2

2 4

V E jX I

S P jQ V I *

I

Increase in Load

• As load increases the operating point moves further along the nose curve until it passes the nose

• This results in voltage collapse

Change in System

• Large disturbances in the system can change the properties of the system, leading to voltage collapse

Pre-disturbance

Post-disturbance

Run load flowsimulation

Model systemparameters

Is impedance within

limits

Run dynamicsimulation

Is voltage within

limits

Develop correction scheme

Within safety margin

No

No

Yes

Yes

Analysis Method

Utility System Model

• Utility System can be represented by the Thevenin equivalent

• Changes in the line impedance (Zline) will determine the potential for voltage collapse

• Changes in Zline are be caused by:

– Unintentional line outages

– Utility line switching for system maintenance+

-

Vs

Zline=R + jX

ServicePoint

+

-


Customer System Representation

• IEEE standard one-line diagram for a refinery from IEEE color books

• Actual configuration consists of

– 38 busses

– 16 transformers

– 45 branches

– 20 loads modeled as 50% motor load

Utility Service

Generator 1 Generator 2

M

M MMM

Bus 3

Bus 69

Bus 28

Bus 4

Bus 27

M


Optimal Operation

• Implemented load flow simulation using industry standard software (PSS/E)

• Both generators in operation

• No impedance nose point developed


Generator 1 Offline

• Nose curve generated

• Impedance nose point located at:

0.0750 + j0.600 pu


Generator 2 Offline

• Changes is system result in different shaped nose curve

• Impedance nose point located at: 0.0450 + j0.360 pu


Utility Service Only

• Results in the smallest nose curve point

• Impedance nose point located at: 0.0057 + j0.0456 pu


Impedance Nose Point

• Decide which case is applicable with given model and the predicted customer operations

• Conservative values decrease possibility of collapse but may result in an increase in the cost of counteractive measures

• If predicted line impedances are not within determined limits then dynamic simulation may be necessary to determine voltage limits

Generator 1 Generator 2Nose Point Impedance

ON ON NONE

OFF ON 0.060+j0.480

ON OFF 0.045+j0.360

OFF OFF 0.0057+j0.0456

Worst Case ?

Is impedance within

limits

Dynamic Simulation

• Simulate using PSS/E and defined dynamic load characteristics

• Dynamic simulation will provide the voltage response as a function of time for the system

• Validation of method by dynamic simulation:

– Are the method’s predicted impedance results conservative

– The effects of different load models


Method Validation

• Impedance is increased in increments until voltage collapse occurs

• In this case the load flow nose point does not result in voltage collapse

• Voltage collapse occurs at the next increment of the impedance

• In this case the load flow results are conservative


Voltage at load flow impedance

Voltage one Increment higher

Method Validation

• The load flow values for a 90% motor load simulation will not be applicable

• User must be aware of the properties of the modeled system to judge accuracy of load flow solution

Zline 20% motor

load

50% motor load

90% motor load

0.01 + j0.080.872 0.852 0.745

0.02 + j0.160.862 0.824 Collapse

0.03 + j0.24 0.853 0.793 X

0.04 + j0.32 0.824 0.764 X

0.05 + j0.40 0.787 Collapse X

0.06 + j0.48 0.752 X X

0.07 + j 0.56 Collapse X X

Load flow predictedCollapse point



Is impedance within

limits


Is voltage within

limits


Within safety margin

No

No

Yes

Yes

Validated Analysis Method

Voltage Limits

• Are the determined voltage values within the determined dynamic limits?

• Is there enough margin left for inaccuracy of the line impedance measurements?

• If not then a correction scheme will need to be implemented

Is voltage within

limits

Correction Scheme

• Corrections to improve the impedance or protection of the system vary in cost and effectiveness

• Examples of utility corrections are:

– Tree Trimming

– Protection equipment

– Redundant Lines

• Customers can install other load configurations that correct voltage collapse potential


Cost Optimization

• A potential customer wishes to locate a large industrial plant in utility service area using a 1000 hp motor

• Using the designed method, the user can determine the potential for collapse

– If system is within limits than no corrections needed

– If outside of limits then dynamic simulation is necessary

• Dynamic study results show a potential for a voltage collapse situation

• Utility side solution:

– Construct 10 mile redundant 115 kV line

– Total cost: $1.5 Million

• Customer side solution:

– Install 2 500 hp motors in the place of the 1000 hp motor with an utility provided incentive

– Total cost: $100,000


Method Benefits

• Foresee the effects of utility system operations

• Provide strong system at minimal cost when attracting and planning for future customers

• Provide a screening method to remove cases from study that have no potential for collapse

• Quick analysis can allow for corrections before a system is implemented

Future Design Possibilities

• Voltage collapse occurs at buses 4 and 34

• Plot the equipment time voltage curve to determine equipment dropout

• This can be applied to method by accounting for changes in power as loads are removed

Conclusion

• The designed method allows for conservative screening of non-potential voltage collapse situations

• The user then can concentrate efforts in analyzing the situations that lead to collapse

• By removing unnecessary analysis corrections can be made before the system is in place

References

[1] H.O. Wang, E.H. Abed, R.A. Adomaitis, A.M.A. Hamdan “Control of Nonlinear Phenomena at the Inception of Voltage Collapse” Institute for Systems Research, University of Maryland, March 1993. [2] T.V. Cutsem, C. Vournas, Voltage Stability of Electric Power Systems, Kluwer Academic Publishers, Boston, 1998. [3] Y. Mansour, Voltage Stability of Power Systems: Concepts, Analytical Tools, and Industry Experience, IEEE Press, New York, 1990. [4] H.G. Kwatny, A.K. Parrija, L.Y. Bahar “ Static Bifurcation in Electrical Power Networks: Loss of Steady-State Stability and Voltage Collapse” IEEE Trans., Circuits Systems, 1986. [5] B.D. Hasssard, N.D. Kazarinoff, Y.H. Wan “Theory and Applications of Hopf Bifurcation” Cambridge University Press, Cambridge, 1981. [6] A Seidman, H.W. Beaty., H. Mahrous, Handbook of Electric Power Calculations, McGraw Hill , New York ,1997. [7] R.C. Dungan, M.F. McGranaghan, H.W. Beaty, Electric Power System Quality, McGraw Hill, New York, 1996. [8] J.D. Glover, M. Sarma, Power System Analysis and Design, PWS Publishing Co., Boston1994. [9] C.L. DeMarco, A.R. Bergen, “A security Measure for Random Load Disturbances in Nonlinear Power System Modals”, IEEE Transactions on Circuits and Systems, vol. CAS-34, no. 12, December 1987. [10] T.V. Cutsem, C.D. Vournas “Voltage Stability Analysis in Transient and Mid-term Time Scale”, IEEE Transactions on Circuits and Systems, vol. 11, no. 1, February 1996. [11] H.D. Chang, “Chaos in Simple Power System” IEEE Transactions on Circuits and Systems, vol. 8, no. 4, November 1993. [12] D.J. Hil, “Nonlinear Dynamic Load Models with Recovery for Voltage Stability Studies”, IEEE Transactions on Power Systems, vol. 8, no. 1, February 1993.

utility design method to eliminate voltage collapse presented by jason taylor

Documents