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 -