MV Network Operation and Control Barcelona 12-15 May 2003 Eugenio Di Marino Italy Session 3 Alpha 1 Block 1

MV Network Operation and Control

Barcelona 12-15 May 2003

Eugenio Di Marino Italy Session 3 Alpha 1 Block 1

ENEL DISTRIBUZIONE MV NETWORK:

• primary (HV/MV) substations: 1,650all remotely controlled;

• secondary (MV/LV) substation: 270,00018 % of them remotely controlled

• total length of MV lines: 332,000 km(37% cable and 63% overhead)



3

MEDIUM TERM PROGRAM TO IMPROVE THE QUALITY OF SUPPLY:

• remote control of MV/LV substations;

• introduction of a new grounding system in medium voltage (MV) networks;

• automation of fault detection, isolation and service restoration procedures on MV network.



4

REMOTE CONTROL OF MV/LV SUBSTATIONS

80,000 secondary substations by the year 2004

• motorised switch disconnectors;

• low cost/high performance Remote Terminal Units;

• telecom modules based on GSM system;

• 29 Control Centres for the all territory.



5

RTUS FOR MV/LV SUBSTATIONS

• Operate the switch disconnectors;• localize the fault;• restore supply automatically. • RTUs are fully programmable through a PC;• application program and all the main important parameters

are downloadable from the control centre.



6

TELECOMMUNICATION SUBSYSTEM

• Adoption of the existent GSM cellular network;

• PSTN lines or leased lines can be used.



7

CONTROL CENTRES• Based on powerful servers for operation and network

configuration;• multiserial interface boards and ISDN modems implement the

connections with RTUs.• spontaneous call originates directly from the peripheral when a

severe alarm generates in the substation; • the operator in order to acquire alarms, measurements or to send

commands on switches can launch a request of connection;• each alarm or command or change in status of the switches is

displayed and recorded.



8

MEDIUM VOLTAGE NEUTRAL EARTHING SYSTEM

• The Italian choice, in the past, has been to operate the MV networks with isolated neutral in almost all the cases;

• At the end of the 90s Enel Distribuzione experimented the connection of neutral to earth through impedance in some of its MV networks;

• In 2000, the very interesting operation results brought Enel Distribuzione management to spread the application of the connection on MV neutral to earth through impedance.

• Goal is 2800 MV bars with neutral connected to earth trough impedance by 2007



9

COEXISTENCE OF NETWORKS WITH PETERSEN COILS WITH NEIGHBOURING ONES HAVING THE NEUTRAL POINT ISOLATED

• a new generation of protections (called NCI) has been developed;

• protection against earth faults independently from neutral operation: isolated or compensated;

• this feature is obtained by adding several programmable thresholds and angular sectors of intervention active at the same time.



10

VoVo

Re

Im

Ios: zero sequence current on sound feeders (NI and NC)

Iof: zero sequence current on faulted feeder (NC)

Iof: zero sequence current on faulted feeder (NI)

Vo: zero sequence voltage (NI and NC)

Ios

Iof

Iof

Fig. 1: Feeder protection relays intervention sectors for isolated (NI) and compensated (NC) networks



mode of connection to ground of MV neutral 15 kV 20 kVResistance 0-45 0-60

Fixed coil impedance 45-150 60-200Automatic Tunable coil impedance 75-225 100-300

Automatic Tunable coil + fixed coil impedance >225 >300

range of application(phase to ground current with

insulated MV neutral)[A]

MV neutral connection to ground choice criterion



IsolatedCompensated

Jan-Sep 2001Jan-Sep 2002Variation

Phase to ground2380301-87%

Total 43401875-57%


Total 18781122-40%


Total 1063717-33%

Operation performance (interruptions) comparison betweenMV networks operated with neutral connected to ground throughimpedance or insulated making reference to equivalent time periods.

Long (>180 s)

MV neutral operation

Period

Transient (<1 s)

Short (<180 s)



MV networkswith cable %greater thanmean value

All

MVnetwoks

MV networkswith cable %lower thanmean value

Number 316332length [km] 259973484749cable %62%38%24%

Phase to ground-88%-87%-87%Total -56%-57%-57%Phase to ground-65%-53%-48%

Total -49%-40%-36%Phase to ground-17%-28%-32%Total -37%-33%-30%

Operation performance (interruptions variation) comparisonbetween MV networks operated with neutral connected to groundthrough impedance or insulated making reference to equivalent time periods as a function of cable percentage.

MV Networks

Transient (<1 s)

Short (<180 s)

Long (>180 s)



CHANGE OF MV NEUTRAL EARTHING SYSTEM FROM ISOLATED TO COMPENSATED BY MEANS OF PETERSEN COIL

• The number of transient interruptions are strongly (by 57%) reduced as well as short ones (by 40%);

• significant reduction of long interruptions (by 33%);• The control systems used for MV network with compensated

neutral allow a better network monitoring increasing the number of “low” signals available to focus on preventive maintenance.



15

BASIC CONCEPTS OF MV AUTOMATION

• Based on a group of automatons resident in the RTU memory;

• automatons operate fault detection and selection through simple actions and delays triggered locally by two signals: Voltage and Fault;

• The recloser unit, installed inside the line protection panel, masters the timing sequence of the operations.



16

FAULT DETECTORS (RGDAT)

• This device detects earth faults and short circuit and has: directional sensitivity; remote changing of the working direction;

high sensitivity in both grounding configuration of the MV network (isolated/compensated neutral).



17

DESCRIPTION OF FRG AND FNC AUTOMATION TECHNIQUES

• FRG and FNC are two different methods of automatic fault location, isolation and service restoration on the healthy sections located upstream from the faulty ones.

• The operator in the Control Centre can:

select the appropriate procedure depending on the type of the line and the status of the neutral;

– receive the spontaneous call from RTUs in order be alerted and complete the procedure, re-supplying the healthy sections of the line located downstream from the faulty section.



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FRG TECHNIQUE

• Rules performed by each automated switch:

1. the switch is opened if there is a lack of voltage on the Voltage Detector (VD) lasting more that a certain time and the Fault Detector (FD) has been activated by the fault current;

2. the switch is closed when the VD detects the voltage restoration due to the reclosing of the circuit breaker or the switch located upstream;

3. the switch is opened and locked in the open position when, executing the closing operation according to the rule n.2, there was a lack of voltage (VD) and at the same time the activation of FD, both within a time window starting from the closed position of the switch.



FNC TECHNIQUE

• The adopted logic is different depending on the type of fault so as

detected by RGDAT: for short-circuits (overcurrent detector) the logic act as in the

FRG procedure; for earth faults:

the switch is opened and locked, after a programmed delay; the delay programmed for each automated switch is

calculated according to the position of the substation along

the feeder so as to open the farthest switch from the Primary

substation among those having detected the fault.



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: MOTORISED/AUTOMATISED SWITCH DISCONNECTORS

(SS1)

CB (A) 1

2

FAULT LOCATION 1

FAULT LOCATION 2

FAULT LOCATION 3

(SSB)

TYPICAL ENEL MV FEEDER

CUSTOMERS: 5.5% total amountINTERRUPTIONS: 7.7% total amount

CUSTOMERS: 33% total amountINTERRUPTIONS: 27% total amount



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TIMES FOR THE SELECTION OF A FAULTY SECTION

MANUAL (2 TEAMS)

SIMPLE TELECONTROL

AUTOMATISATION

1) Opening of CB (A) 0 0 02) First reclosure CB (A) (0,4-1 s) with negative effect 1 1 13) Second reclosure CB (A) (30 s) with negative effect 30 30 304) Opening of switch disconnector 1 in SS1 2400 270 405) Opening of switch disconnector 2 in SS1 2700 400 407) Closing of CB (A) 2410 280 1508) Closing of switch disconnector 1 in SS1 2820 520 1609) Closing of switch disconnector 2 in SS1 2940 640 170

11) Opening of CB (A) 2940 640 170

12) (Definitive) opening of switch disconnector 2 in SS1 2950 650 18013) Closing of CB (A) 2970 670 270

With manual operation (traditional) 94,5% of customers are supplied in 50 minutesWith simple telecontrol operation 94,5% of customers are supplied in 11 minutesWith automatised operation 94,5% of customers are supplied in 6 minutes

38,336,67

Differences [min]

FAULT LOCATION 1OPERATING TIMES (sec)



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RESULTS



020406080

100120140160180200

Minutes

1998 1999 2000 2001 2002

Cumulative duration outages

Documents

MV Network Operation and Control Barcelona 12-15 May 2003 Eugenio Di Marino Italy Session 3 Alpha 1 Block 1