GE Multilin 745 Instruction Manual

Auto-Configuration745Transformer Management RelaySetpointshttp://www.GEindustrial.com/multilin5ñ6 GE MultilinS2 SYSTEM SETUP !" WINDING 2 ! WINDING 2 NOM Φ-Φ VOLTAGE: ì69.0 kVîS2 SYSTEM SETUP !" WINDING 2 !" WINDING 2 RATED LOAD: ì100 MVAîS2 SYSTEM SETUP !" WINDING 2 !" WINDING 2 PHASE CT PRIMARY: ì1500:1 AîFor a 3-winding transformer, the setpoints under S2 SYSTEM SETUP/WINDING 3 mustalso be set.b) Onload Tap Changerï Onload tap changerï Variable voltage ratioï CT 2 / CT 1 = V1 / V2ï Lower sensitivity on differential elementSolution:ï Tap position monitoring: V2 = Vmin + (n ñ 1)V incrFor example, the onload tap changer changes the Winding 2 voltage, resulting in aneven greater CT mismatch. A perfectly matched Winding 2 CT ratio (based on thetap changer position) is calculated as follows:(EQ 5.2)where n = current tap changer positionV2(min) = Winding 2 minimum voltage (at n = 1)V2(tap) = Winding 2 voltage increment per tapThus, with the tap changer at position 33, the Winding 2 CT ratio must be 1428.6 /1 to be perfectly matched. In this case, the mismatch factor is 1428.6 / 1500 =0.952.The 745 allows monitoring of the tap changer position via the tap position input.With this input, the 745 dynamically adjusts the CT ratio mismatch factor based onthe actual transformer voltage ratio set by the tap changer.Tap changers are operated by means of a motor drive unit mounted on the outsideof the transformer tank. The motor drive is placed in a protective housing containingall devices necessary for operation, including a tap position indication circuit. Thisindication circuit has a terminal for each tap with a fixed resistive increment per tap.A cam from the drive shaft that provides local tap position indication also controls awiper terminal in the indication circuit, as illustrated below.FIGURE 5ñ1: Tap Position InputCT 2 (ideal) CT 1V1V2 min( ) V2 tap( ) n 1–( )+---------------------------------------------------------------× 5001----------- 22061 0.5 n 1–( )+------------------------------------------×= =ZEROPOSITIONTAP 1TAP 2TAP 3TAP 4TAP 6TAP 7TAP 8TAP 9etc.WIPERAT TAP 5RRRR RRRRRZERO POSITIONTERMINAL(to TAP POSITION -)WIPERTERMINAL(to TAP POSITION +)