An Alternative Approach to Improving SAIDI and … Alternative Approach to Improving SAIDI and SAIFI Indicators Philippe Deschamps - Schneider Electric Industries - France Jean-Christophe

An Alternative Approach to Improving SAIDI and SAIFI Indicators

Philippe Deschamps - Schneider Electric Industries - France Jean-Christophe Orsini - Schneider Electric Industries - France Kaare Seest Rasmussen - DONG Energy - Denmark

C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009

Summary

Abstract ......................................................................................................p 1

Introduction .................................................................................................p 2

DONG Energy's network .............................................................................p 3

The concept of a SACSe substation ............................................................p 4

SACSe control unit architecture ...................................................................p 7

F200C: Possible further enhancement .........................................................p 8

Conclusion ..................................................................................................p 9

C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 Paper 0635 | 1



Abstract

Under the pressure of regulating authorities, utilities are being challenged to

improve their SAIDI and SAIFI indicators. Usually, to reach this goal, more

intelligence is put inside DMS, increasing at the same time the amount

of data to be processed and the importance of communication in the

network. An alternative way, discussed in this paper, consists of using local

automation, allowing faster reactions, and therefore a drastic reduction of the

number of customers affected by permanent faults, without requiring heavy

communication infrastructure. In addition, this paper introduces a further

enhancement allowing a faster power restoration for the remaining affected

customers.




Introduction

Challenged by the Danish authorities, DONG Energy has for a long time

experimented with several methods to optimize network management and

particularly increase power availability. An important step was reached when

it was decided to reduce the maximum time to reenergize a faulty location to

less than a minute to avoid the outage to be counted as a long one, that is

degrading the SAIDI and SAIFI indexes.




Fig.1 - Typical feeder (neighbouring feeders in white)

DONG Energy's network

DONG Energy is a major DNO in Denmark, however this experience involves only one part of its

network.

The 10 kV grid in DONG Energy North, is a 100

per cent underground radial network, with a high

degree of access to neighbouring feeders for

backup, as shown in Fig. 1.

The grid is mainly urban and consists of

approximately 7000 substations on 600 feeders.

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The goal is to put in one strategic MV/LV

substation, a line circuit breaker intended to split

the feeder into 2 segments in order to minimize

the number of customers affected by a fault, if it

happens on the downstream side. Time selectivity

is used to prevent primary substation CB from

tripping simultaneously. In some cases, there

could be up to two line CBs on the feeder: in such

a case they would use the same setting and trip

simultaneously.

The second concept is a step further. In case

of a phase-to-phase fault upstream in the same

substation, it allows the faulty segment to be

automatically isolated and the healthy ones to be

automatically resupplied. This process is based on

local automation, allowing a fast reaction, and not

needing any human intervention or communication

infrastructure. The solution was developed in

collaboration with Schneider Electric, which offers

a wide range of products for network automation.

These substations are equipped with a four-

function switchgear (Fig. 3):

• 1 fuse switch or circuit breaker for the

transformer protection. It can be forgotten since it

has no role in the concept.

• 2 circuit breakers and 1 switch distributed

among the incoming, the outgoing, and the

backup lines. There are two circuit breakers among

the three to be sure that there will be at least one in

the circuit in all network configuration cases.

First of all, let’s clarify the management of

phase-to-phase and phase-to-earth faults in the

DONG Energy network:

• phase-to-phase faults: these cause the

tripping of a breaker and therefore an outage

which explains how SACSe limits the number of

customers affected

• phase-to-earth faults: the network is

Petersen-coil grounded, allowing temporary

operation with single earth fault. However, SACSe

provides an earth-fault localization information

because a second earth fault would cause a

tripping.

SACSe means "Sectionalizing And Changeover

System enhanced". The concept of SACSe

described below is the latest evolution of the

network, which has already seen significant

improvement over the last 10 years.

A first step was taken by deploying circuit breakers

in the network [1].

First of all, in a given feeder, one or two substations

are selected to support the automation. They are

chosen because of their location: they divide the

feeder into two or three segments, each supplying

roughly the same number of customers. They are

also chosen because of the ease of upgrading

them. The principle of layout in the network of

these substations is described in the ref [2].

Second, a backup line coming from the neighbour

feeder is connected to these strategic MV/LV

substations to allow a backup supply if required

(Fig. 2).

The concept of a SACSe substation

SACSe - Main principle

Fig. 2 - Principle of a SACSe substation layout in DONGEnergy’s network

Fig. 3 - Typical make-up of a switchgear in a SACSe MV/LVsubstation

MV/LV subSACSe MV/LV sub

Backup line

MV/LVtransformerIncoming/outgoing/backup

HV/MV subFeeder 1

Feeder 2

Feeder n




If a fault occurs downstream, the breaker opens

instantaneously, isolating the downstream

segment(s). The status of the switchgear is then

sent to the SCADA. If a fault occurs upstream, the

switchgear acts as an auto changeover (ACO):

the circuit breaker will not trip, but the lack of

voltage releases the auto changeover process,

ordering the incoming to open and the backup

to close, which supplies the healthy downstream

segment. This is the general principle. Two cases

are shown in Fig. 4. Since the breaker in the HV/

MV substation is delayed and those in the SACSe

are not, the breaker in the HV/MV sub will only trip

when the fault is in the first segment

(Fig. 4 - case 1).

In a particular case (2 SACSe on the same feeder),

a fault downstream in the second SACSe results

in both SACSe circuit breakers tripping. In order

to resupply the segment between the two SACSe

circuit breakers, the downstream one will act as a

Reverse Auto Changeover (RACO): based on the

CB tripping information, it will keep the incoming

closed, and order the backup to close, therefore

resupplying the upstream segment

(Fig. 5).

In all cases, the time required to reconfigure is less

than 20 seconds, saving automatically up to 2/3 of

the customers normally affected by such a fault.

In addition, several logic processes are embedded

in the automation in order to avoid any improper

action in certain cases:

• once the ACO/RACO has operated, it is blocked

until there is some human interaction from the

control center to prevent further action in a non-

standard network configuration

• a logic process is in action to avoid any ACO

and/or RACO action if the network is subject to

a global outage, from the transport for instance.

This event is detected by monitoring the voltage

presence on the backup line. If an absence of

voltage is observed on both incoming and backup

lines, then no action is taken

• in case of a frequency drop, a recovery process

exists in the HV/MV substation and it, it reacts by

switching off some feeders. So in this case, the

ACO/RACO is inhibited to allow the load-shedding

process to be prioritized.

Fig. 4 - ACO - principle of fault restoration

Fig. 5 - ACO - principle of fault restoration

Trip+

reservebackup

Trip

Case 1 Case 2

Open+

backup

Trip

Open+

backup

Trip




Infrastructure

Earth fault

Basically, the system does not require any means

of communication to react properly and fulfil its

purpose. In fact this is even an advantage in terms

of security and reliability. But of course, it is linked

with the SCADA to report the outage on the faulty

segment, in order to restore the power. In addition,

it reports its status to the operating staff, as Danish

regulations require the operator

As explained above, SACSe also integrates

directional fault passage indicators (FPIs). These

FPIs allow the staff to locate the fault in the field

more accurately and faster, and therefore prevent a

tripping due to a second fault.

to know the real status of all switches and

breakers in the network all times. By these

means, other information available in the MV/LV

substation can also be transmitted. In this case,

and thanks to good coverage of the area by GSM

infrastructure, GPRS has been chosen to transfer

data in a very economical way.

All these features are embedded in a single box

provided by Schneider Electric, which is described

below.




of robustness required by such an application,

openness in terms of communication protocols,

and a ready-to-use product to minimize the

settings on-site during the installation. All these

products are integrated in a single box (Fig. 7)

in a way to make it easy to integrate into DONG

Energy's existing installed base. No assembling is

needed on-site, just the mounting of one box, and

the connection of the sensors and the commands

in the switchgear.

In terms of size, the system is made to be

mounted directly on the wall of the substation. The

dimensions allow it to be used even in a compact

substation with reduced volume available.

Interfaces are designed to make installation

simple and minimize the risk of mistakes by using

prefabricated cables and connectors to link the

unit with sensors.

The box is equipped with a transparent window

on the front door, allowing all indicators of the

status of the system to be read locally. If needed,

operating staff have access to the local operation

by opening the front door. Fig. 7 - SACSecontrol unit

Fig. 6 - General architecture of the SACSe system

SACSe control unit architecture

Functional description

Design

The unit integrates the following functions (Fig. 6):

• phase-to-phase fault protection ensured by two

protection relays, for the incoming/outgoing and

backup breakers

• phase-to-earth fault detection ensured by two

directional fault passage indicators on the same

functions

• voltage presence on incoming, outgoing, and

backup cables

• automation ensuring the ACO/RACO logic

• communication with the SCADA on the status of

the substation

• power supply with batteries to supply the unit

under all conditions.

In addition, LV and MV measurement features have

been included in the unit to provide a much better

knowledge of the substation and the network load.

SACSe is designed as an industrial solution

integrating existing or slightly modified products

from the Schneider Electric Easergy offer:

• relays from the SEPAM range

• FPI for earth protection is based on the Flair

range

• automation is based on the Easergy T200 which

includes peripheral functions such as backup/main

power supply and modem.

All these products were designed specifically

for the network automation environment. As a

consequence, they comply with the specificities

of this application: harsh environment withstand

(temperature, EMC, electrical insulation -10 kV on

mains, dust, humidity, etc.), allowing the high level

ACORACOlogic

I

I

U

U I

Com

Phaseprotection

Eartdetection

Powersupply




Thanks to the unit presented above, the SAIDI

index is drastically reduced, but ultimate quality

requires some additional instrumentation of the

network:

• In case of a phase fault, only half (if 1 SACSe) or

one third (of 2 SACSe) of the feeder customers are

affected by an outage more than one minute.

However, the half or third of customers in the faulty

segment still need to get power back as soon as

possible.

• In case of an earth fault, the SACSe control

unit can indicate whether the fault is upstream or

downstream the SACSe substation. But a more

accurate localization is required in order to allow

faulty cable isolation without power interruption

for any customer.

Of course, for obvious cost and complexity

reasons, more than two SACSe substations on

a feeder are not possible. Increasing the number

of SACSe substations is therefore not a way to

achieve ultimate quality.

This means a device allowing accurate localization

of both phase faults and earth faults is needed

in the other substations, both upstream and

downstream from the SACSe.

Accurate localization would ideally mean knowing

which cable between the two substations is faulty.

Schneider Electric has recently launched a new

communicating fault passage indicator, the

Flair 200C, combining in a single cost-effective

product the phase-to-phase and phase-to-earth

fault detection and the GPRS communication

functions. This would suit the above purpose

particularly well. It should be noted that this new

Flair 200C embeds a new algorithm for detection

of phase-to-earth faults on compensated networks

not requiring voltage sensing. This allows the

commissioning of such devices to be drastically

simplified, especially for retrofit in existing

substations, and it reduces the global cost.

Additionally, the Flair 200C can optionally provide

measurements, further increasing the knowledge

of network load.

F200C: Possible further enhancement




References[1] Peter Vinter, Henrik Vikelgaard, 2005, "A novel approach to distribution grid automation at NESA A/S", CIRED Conference 18th international conference on electricity distribution. Session 3.

[2] Kåre Seest Rasmussen, 2009, "A real case of self healing distribution network", CIRED Conference 20th international conference on electricity distribution. Session 3.

Conclusion

Increasing pressure on SAIDI/SAIFI improvement

usually requires more performance from DMS,

and at the same time the management of

more and more information. A complementary

solution involves the use of local automation

able to perform simple actions quickly. By this

means, when a fault occurs, a rough but fast

reconfiguration is done while the operation is

simplified.

The implementation of this requires a dedicated

device to prevent complex commissioning from

spoiling the solution, and therefore the Return On

Investment.

09-2011998-5592

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An Alternative Approach to Improving SAIDI and … Alternative Approach to Improving SAIDI and SAIFI Indicators Philippe Deschamps - Schneider Electric Industries - France Jean-Christophe