1. AN UNDER FREQUENCY LOAD SHEDDING
SCHEME FOR
HYBRID AND MULTI AREA POWER SYSTEMS
PRESENTED BY
AJAY PRAKASH SINGH
PSE 152603
EEE NIT WARANGAL
UNDER THE GUIDANCE OF
SREE B. NAGU

2. INTRODUCTION
 What is under frequency load shedding scheme (U.F.L.S)
 Need of U.F.L.S scheme
 Previously used scheme (Adapted U.F.L.S) & related issues
 Problem Statement Of U.F.L.S scheme
 Simulation with Hybrid Power System & its Analysis
 Simulation with Multi Area Power System & its Analysis
 Conclusion

3. NEED OF U.L.F.S SCHEME
U.F.L.S WILL
MAINTAIN
FREQUENCY
WITHIN
PERMISIABLE
LIMIT
IN CASE OF INTER
CONNECTED OR
ISOLATED P.S
IN CASE OF
FAULT
• IN CASE OF SOURCE AND LOAD CONNECTION & DISCONNECTION SYSTEM PAPAMETER
VARIES
• MOREOVER OUTPUT OF DG’S ALSO CHANGE DURING LOAD SHEDDING PROCESS .
• EFFECT IN PERPORMANCE AND RELIABILITY DECREASES
• ISSUES
RESULTS IN

4. HOW TO CONTROL FREQUENCY
• In case of worst possible contingency results in highest initial rate of decay in
frequency.
• Amount of load shed ensures that frequency further do not fall below.
• So we need to determine, number and size of shedding, It is done by hit and
trial method.
• Its not a trivial task it has too be done very precisely and accurately otherwise
results in undesirable damage black outs and serious cost .
• For this few schemes are there-
1. ADAPTIVE U.F.L.S SCHEME
2. NOVEL U.F.L.S SCHEME

5. ADAPTIVE U.F.L.S & ITS ISSUES
• Power deficit is calculated bases on frequency derivative (at the time of disturbance)
• Its advantage is we don’t have determine worst possible contingency
• Calculated amount of load is shed based of power deficit.
• If power deficit is occur due to gen. outage and islanding of power system
• P cal < P actual . …...… … ………………………………
• Amount of load shed do not have a linear relation with power deficit …
• New frequency U.F.L.S technique is based on frequency second derivative
• Calculation of second derivative is very tedious …… …………
• In hybrid P.S power is not constant we require a scheme independent of .
Parameter . .
.
disadvantage

6. U.F.L.S SCHEME
• U.F.L. S scheme uses fre. first derivative , only one parameter that effect power
deficit is H
• In first step estimated H is used, & in next step updated H will be used
• power deficit is Cal by swing equation
• Since this scheme is based on fre first derivative it will account for all the sudden
change of power due to DG’s.
Pd =2Heq f'Hz /t = t0
fN
ADVANTAGE
• Independent of system parameter………………………………………………………………………
• Consider changes in generated power during load shedding …………………………………………...

7. Cal power deficit (Pd)
start
SPECIFY THE LOAD TO BE SHED
If
Fo-Fk/fo
*100
>=T.LS(k)
UPDATE INERTIA & POWER DEFICIT
FOR NEXT STEP
If
F > 0
If
F <
48.4
Shed all the remaining
loads shedding steps
Stop
no
yes
yes
no

8. SIMULATION WITH HYBRID POWER SYSTEM & ITS
ANALYSIS
SCENARIO 1 : ISLANDING
HYBRID POWER SYSTEM
SCENARIO 2 : DECREASE IN SUN
IRRADIANCE DURING L.S

9. SIMULATION WITH HYBRID POWER SYSTEM & ITS
ANALYSIS
SCENARIO 3: INERTIA CONSTANT
VARIATION

10. SIMULATION WITH HYBRID POWER SYSTEM & ITS
ANALYSIS
SCENARIO 4 : IN CASE OF WIND TURBINE OUTAGE

11. SIMULATION WITH MULTI AREA POWER SYSTEM
& ITS ANALYSIS
BLOCK DIAGRAM OF MULTI AREA
P.S
IN CASE OF FAULT ALL FREQUENCY
VARY AND FLUCTUATE BUT Fcoi IS
SMOOTHLY VARRY

12. SIMULATION WITH MULTI AREA POWER SYSTEM &
ITS ANALYSIS
IN CASE OF POWER DEFICIT IN
AREA 1 ,THERE IS STEP CHANGE IN
Fcoi & FI BOTH CAN BE USED TO
ESTIMATE POWER
TO MAINTAIN POWER SYSTEM
STABILITY DERIVATIVE OF Fcoi IS
USED SINCE IN IS NOT VARRYING
FAST
.

13. SIMULATION WITH MULTI AREA POWER SYSTEM
& ITS ANALYSIS
IN CASE OF POWER DEFICIT
FREQUNCY RESPONSE SHOWS
THAT SCHEME IS SUCCESSFUL
EFFECT OF CHANGE IN ‘H’ ON
U.F.L.S SCHEME : ‘H’ IN INCRESE BY
50%
• .

14. SIMULATION WITH MULTI AREA POWER SYSTEM &
ITS ANALYSIS
EFFECT OF CHANGE IN ‘H’ ON
U.F.L.S SCHEME : ‘H’ IN INCRESE
BY 50%
EFFECT OF CHANGE IN SYSTM
PARAMETER ( R,D,Tg,Tt)

15. CONCLUSION
An U.F.L.S scheme for a hybrid distribution system including PV,
FC, DEG, and BESS was proposed.
Under frequency load shedding scheme is successful in
determination of load shed and maintain the frequency within
limit for various scenarios for hybrid and multi area power system.

16. REFRENCES
 U. Rudez and R. Mihalic, “Monitoring the first frequency derivative to
improve adaptive under frequency load-shedding schemes,” IEEE Trans.
Power Syst., vol. 26, no. 2, pp. 839–846, May 2011.
 A. Ketabi and M. H. Fini, “An under frequency load shedding scheme
for islanded microgrids,” Int. J. Elect. Power Energy Syst., vol. 62,
pp. 599–607, Nov. 2014.
 J. J. Ford, H. Bevrani, and G. Ledwich, “Adaptive load shedding and
regional protection,” Int. J. Elect. Power Energy Syst., vol. 31, no. 10,
pp. 611–618, Nov./Dec. 2009.
 U. Rudez and R. Mihalic, “A novel approach to under frequency
load shedding,” Elect. Power Syst. Res., vol. 81, no. 2, pp. 636–643,
Feb. 2011.