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Power Supply Reliability Analysisof Microgrid
considering Switching Operation
Jeju 2011 Symposium on Microgrids
2011. 5. 27
Takao TsujiYokohama National University
Background
“ Microgrid ” with many Distributed Generators
Electric Power Supply Reliability can be improved in microgirdbecause it can operate even in the case of outage in utility grid
Main system
Gas engine Fuel cellPV or WT
Customers
OFF
outage
Power Supply Reliability Analysis
Power Supply Reliability Analysis Method based on“Enumeration method” have been developed
[1] Realistic way of Switching Operation is considered.[2] The required amount of load shedding is calculated
by convolution integral method.
Following probabilistic factors are considered,
・ Fault occurrence・ Probabilistic change of Renewable energy and load
load (low reliability)
load (high reliability) LA
LB
The Concept of Multi Quality Power Supply is introduced.
Components of Microgrid Model
Disconnector
Circuit Breaker
Distribution line
TransformerBus
Gas Engine
Wind Turbine
GE
WT
LoadLoad
Example of Microgrid Model
PCC receives power fromprimary substation using66kV loop distribution line.
double buses
There are four customersincluding DGs (Gas Engineand Renewable energy)
GE outputCase 1: 1000kWCase 2: 1500kWCase 3: 2000kW
“ground fault” or “short circuit fault”
・ It is assumed the circuit breakers which are located nearest to the fault point, are switched off.
・ “Voltage sag” occurs in all customers which have electrical connections with the fault point.
fault point
OFFOFF
OFF
Loadvoltage
sag
Action of Protection Relay
CBs or DCs are switched to minimize the outage area.
OFF
SuppliedSubsystem
NotSuppliedSubsystem
after the timerequired to switch“CB” or “DS”
ON
SuppliedSubsystem
SuppliedSubsystem
withoutincludingany fault
Switching Operation
“Short duration outage” occurs at the loads whose outages are restored by the switching operation
LC LB LB G LC LB LB G
1 2 3 4 5 61 2
OPEN
LC LB LB G LC LB LB G
1 2 3 4 5 61 2
LC LB LB G LC LB LB G
1 2 3 4 5 61 2
LC LB LB G LC LB LB GLC LB LB GLCLC LBLB LBLB GG LC LB LB GLCLC LBLB LBLB GG
1 2 3 4 5 61 2
OPEN
Surplus power istransferred to other customers.
In the case the total capacity for power supply in island subsystem is not sufficient, some loads are shed according to priority based on Power Quality.
Load shedding causes a “Long duration outage”.
Not Supplied
OFF
Not Supplied
OFF(Loadshedding)
Load Shedding (1)
ylyyy
ll yqyqyqyq
21
2211 )()()()(
Probabilistic model of each load
Load Shedding (2)
Probabilistic Load Model in Island Subsystem
zymxg
yqxpzr )()()(
Probabilistic model of RE outputg : GE outputm: total number of REs
Outage probability in the Island Subsystem
exp
ecte
d n
orm
aliz
ed lo
ad
vari
ance
of
load
probabilistic density curve of RE
Probabilistic Model of RE and Load
hourhour
Simulation Results 1
standard deviation of load model is modifiedto five and ten times.
Simulation Results 2
The importance of considering probabilistic load change is shown
Conclusions
A new Reliability Analysis Method of Microgrid based on Enumeration Method Is developed
Switching operation is effectively memorized by “Switching Operation Matrix” and the demand – supply balance of each islanding system is calculated byconvolution integral method
The impact of Scheduled maintenance, other kind offaults, and multiple faults should be considered
The proposed method should be tested in more complicatedlarge scale model and its calculation time must be evaluated
- Future works -