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MV Network Operation and Control

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MV Network Operation and Control

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    1. MV Network Operation and Control

    3. 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. 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. 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. 6 TELECOMMUNICATION SUBSYSTEM Adoption of the existent GSM cellular network; PSTN lines or leased lines can be used.

    7. 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. 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. 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.

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    15. 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. 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. 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.

    18. 18 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.

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    21. 21 TIMES FOR THE SELECTION OF A FAULTY SECTION

    22. 22 RESULTS

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