Frankfurt (Germany), 6-9 June 2011  Manfred Wurm  EVN Netz GmbH, Austria Wurm – Austria – Session 3 – 0915 EARTH FAULT DISTANCE LOCALIZATION IN INDUCTIVE EARTHED NETWORKS BY MEANS OF DISTANCE PROTECTION RELAYS

Frankfurt (Germany), 6-9 June 2011  Earth fault location in inductive earthed grids: ► detection of the faulty feeder in the substation ► signalling to the system operator  Localization of earth fault position: ► by means of commutations ► personell must find the fault position  wish to get information about fault distance, e.g. Xprim Wurm – Austria – Session 3 – 0915 Cause

Frankfurt (Germany), 6-9 June 2011  usually: natural residual fault current is too less to pick-up a distance protection device  therefore: increasing the fault current by means of an additional ohmic current (« pilot current ») in the neutral of the network Wurm – Austria – Session 3 – 0915 Principle and idea

Frankfurt (Germany), 6-9 June 2011 Wurm – Austria – Session 3 – 0915 Fault calculation: conventional

Frankfurt (Germany), 6-9 June 2011 Wurm – Austria – Session 3 – 0915 Fault calculation: modified

Frankfurt (Germany), 6-9 June 2011  Method A:  Method B: Wurm – Austria – Session 3 – 0915 How to obtain the realistic value of the fault current I F, measured at the busbar?

Frankfurt (Germany), 6-9 June 2011  Three manufacturers Areva (now Schneider) Siemens Sprecher Automation implemented the modified fault distance calculation in their existing relays  1 st step: earth fault testand  2 nd step: field test in a 20-kV-grid of EVN Wurm – Austria – Session 3 – 0915 Reality check

Frankfurt (Germany), 6-9 June 2011  selection: area with difficult atmospheric conditions  substation with 4 outgoing feeders (20 kV), 3 of them are test feeders ► with mixed ratio of OHL and cable ► equipped with one modified distance device of each manufacturer stated above  additionally installation of a fault recorder Wurm – Austria – Session 3 – 0915 Preparation of field test and installation

Frankfurt (Germany), 6-9 June 2011  Size of pilot current: ► R add = 60   max. ≈ 200 A pilot current ► on-time = 0,25 s  Influence of load current: (20 kV: 30 A ≈ 1 MVA) load current and pilot current will add Wurm – Austria – Session 3 – 0915 Further particulars substation normally open DIST O/C, directed recloser 160A / 0,5s 200A / 0,8s 200A / 0,5s 300A / 1,0s 200A / 0,4s 0,05s / 0,8s / 2,5s 400A / 2,0s

Frankfurt (Germany), 6-9 June 2011  Start: January 11 th, 2011  Aim: calculated fault distance should indicate the fault position within one third of the total length of the feeder. Wurm – Austria – Session 3 – 0915 Preparation of field test and installation circuit breaker resistor  Hope: a lot of earth faults until presentation at CIRED 2011

Frankfurt (Germany), 6-9 June 2011 Fault 1: Split of conductor in L2:  X,real = 3,73   X,classic = 1,41   X,improved = 2,98  Wurm – Austria – Session 3 – 0915 Results V 1E V 2E V 3E V NE I R I L 23 A

Frankfurt (Germany), 6-9 June 2011 Fault 2: ??? in L1  X,real = ???  X,classic = 10,09   X,improved = 3,88  Wurm – Austria – Session 3 – 0915 Results V 1E V 2E V 3E V NE I R I L 55 A

Frankfurt (Germany), 6-9 June 2011 Wurm – Austria – Session 3 – 0915 Thank You for Your attention!