Distribution Automation Solutions – An approach to increase availability in distribution networks

A major requirement on electricity supplysystems is high supply reliability for thecustomer – which is mainly determinedby the distribution networks. Supply reliabilityis influenced by various technical andorganizational factors, and typically quantifiedusing criteria such as SAIDI and SAIFI.

Ingeneral, customer expectations on supplyreliability are steadily increasing – in some casesexplicit power quality criteria are even includedin negotiated contracts between customersand utilities. Moreover, in liberalized markets,regulators typically require the utilities to reporton the reliability performance, or define explicitperformance targets – that are even penalized
in case of violations in several countries.

Given this background, the power qualityperformance of distribution networks is comingmore and more into focus of system operators.Today’s distribution networks typically featurea rather low degree of automation only. Theimplementation of distribution automation isa highly capable and powerful approach toincrease supply reliability performance. Eventhe automation of a smaller share of ringmain units in a system only can already realizesignificant improvements. Intelligent agents insubstations and on the feeder devices alloweffective monitoring and local decision makingwithout human intervention.

The automation allows detecting and fasterreacting on specific circumstances in thenetwork. The system itself is monitored by
centralized systems such as a Regional ControlSystem. The Regional Controller authorizes localautomation and provides additional supervisoryinformation, in order to handle networksituations, which are out of the range of thelocal automation system and can interact withthe central SCADA.

Scalable distribution automation solutionsare starting with the monitoring of distributionsubstations through RTUs and the use of shortcircuit indicators, mainly this configuration isused in ring main units for cable networks.Over headline networks can also be automatedby using peer-to peer interaction betweenreclosers and sectionalizers on the feeders evenwith in combination with Regional ControlSystem. The two concepts can provide secureand reliable access to disconnectors, circuitbreakers and reclosers for monitoring purposesand provide control over these devices.

Concept 1: Self Healing Implementationwith a centralized Regional Controller onSubstation level with decentralized IEDs

Protection relays monitor and protectdistribution feeders from the substationand control feeder switches. Additionaldisconnectors or circuit breakers at thesecondary substations can be controlled viaRTUs or protection relays. Standard ANSIprotection functions for distribution feedersare included in the device to handle criticalfault satiations by tripping circuit breakers atthe in feed and sending the information to aso Regional Controller. Currents, voltages andstatus information from primary equipmentof the distribution network are sent to theRegional Controller to analyze and take furtheraction.

The Regional Controller is a layer betweenthe central SCADA system and the intelligentdevices in the field, like IEDs on the
disconnectors and circuit breakers. The IEDssent the status of the distribution network tothe regional controller to analyze and takefurther action. The regional controller is setupto handle standard switching for fault detectionvia fault indicators and will also handlefurther actions for fault isolation and servicerestoration.

Concept 2: Self Healing Implementationwith decentralized IEDs with peer to peerinteraction

The system is designed to work usingindependent automated devices and the selfhealing logic resides in individual IED located
in the feeder sections. The IEDs located ateach secondary substation are associated witha circuit breaker or disconnector and includecurrent and voltage sensors to provide thenecessary input data used to determine logicalsequences. This information is then madeavailable to each of the other IEDs, startingover the communications channel locatedwithin that particular loop and then back to thesubstation.

Modern communication systems use open standards rather than proprietary technology,especially the IEC 61850 standard supportthis decentralized application. IEC 61850provides the required logic and flexibility for therealization of self healing functionality.

Peer-to-peer functionality via IEC 61850generic-object-oriented substation event(GOOSE) messages provides not only binary
data, but analog values as well. Each devicecontains extensive programmable logic torealize the automation functionalities – usinginput data such as voltage, current, timecurrentcharacteristic curves or load. The IEDsthen handle the self healing functionality andattempt to clear and isolate faults, and to theninitiate the supply restoration logic.

Such advanced distribution automationconcepts – up to the self healing functionalityoffered by autonomously operating breakers– can be realized using technologies andequipment that is readily available today.In distribution networks, advanced and“smart” distribution automation solutions canprovide substantial technical and commercialadvantages to network operators – being muchmore cost-effective compared to solutionsbased on primary technology only.

Siemens ENEAS (Efficient Network and EnergyAutomation Systems) -Solutions for distribution automation
www.siemens.com/eneas