1 60 Hertz Over Voltages For Arrester Applications For Arrester Applications

2 Applying Arresters When Applying Arresters you have to be concerned about 3 items When Applying Arresters you have to be concerned about 3 items 1. Maximum Continuous operating Voltage 2. Maximum 60 Hertz Overvoltage 3. Energy Absorption rating

3 What causes 60 Hertz overvoltages Faults Faults Load Rejection Load Rejection Ferro Resonance Ferro Resonance Charging current in a line Charging current in a line

4 Faults and Grounding A well grounded system will have very little Voltage Rise on the unfaulted phases during a fault A well grounded system will have very little Voltage Rise on the unfaulted phases during a fault As the system becomes less well grounded then the unfaulted phase voltage will rise until it hits the phase to phase value. As the system becomes less well grounded then the unfaulted phase voltage will rise until it hits the phase to phase value.

5 Neutral shifts during clearing of a phase to ground fault Arrester voltage 140kv 197kv 242kv

6 Calculation

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13 Graphical Method

14 Two examples of 60 Hz overvoltages Coal mine grounding 84 Coal mine grounding 84 Coal Mine grounding Majorsville Coal Mine grounding Majorsville

15 Coal mine grounding 84 Here was the plan 1.47 mi LIVINGSTON PODISH 0.13 mi 0.90 mi 0.50 mi SUMMIT JCT mi ELLSWORTH CALVIN JCT mi 0.69 mi WEIR N.O. LITTLE A 25 kV ANDREWS SHAFT RICHARDSON 0.19 mi 4.71 mi kV 0.01 mi 3/0 AAAC /0 ACSR 4/0,1/0 4/0 CU,1/0 CU LONG FARM SHAFT 0.17 mi 3/0 ACSR 0.60 mi 3/0 ACSR 100 ft. 1/0 AL U LONG FARM BLEEDER SUBSTATION U 100 ft. 3/0 ACSR CONSTRUCT 100 FEET OF 1/0 AL, UNDERGROUND 25 kV LINE INSTALL A 25 kV AIR SWITCH AT TAP INSTALL A 1.5 MVA, kV PAD-MOUNTED TRANSFORMER PACKAGE WITH 4 kV METERING 1.5 MVA, kV PAD-MOUNT LFB LONG FARM BLEEDER TAP LFBT LSMJ-EPJ (400)

16 What Happened The transformer was energized with no load and the low side arrester failed. The high side fuse failed and launched upwards and stuck into the roof of the transformer. The transformer was energized with no load and the low side arrester failed. The high side fuse failed and launched upwards and stuck into the roof of the transformer.

17 Blown Arrester Neutral ungrounded 3 CT’s 2 VT’s High Side VT’s Grounded

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19 The situation developed because 1.Planning not aware that coal mine wanted ungrounded service at They were told that this customer want 4160 service nothing was said about ungrounded service 2.Planning issued a plan for 4 wire service 3.Pad mount transformer was shipped with arresters installed, this is not what the T&D manual wants 4.3 element metering specified, but only 2 VT’s showed up 5.It was a rush job so a decision was made to use 2.5 element metering 6.When the transformer was ready to be energized, the Coal company inspector told our people to remove the ground 7.Our crew was confused and called their boss and he checked 8.The metering people said they would have to change the metering 9.Our crew was told to disconnect the metering, they did by opening the low side metering switches 10.They were instructed to remove the ground 11.They were told to go ahead and energize 12.Arrester failed causing a phase to phase fault and failed the high side transformer fuse

20 Metering opened

21 Why did it happen Here is the Schematic of how everything was hooked up when energized. Here is the Schematic of how everything was hooked up when energized. No Ground on Transformer High side on metering VT’s Grounded for 2.5 element metering

22 No Ground on Transformer High side on metering VT’s Grounded for 2.5 element metering This arrester saw a voltage of 1.5p.u. and failed, when it failed it blew stuff all over the place. This stuff caused a phase to phase fault in the transformer, also when the arrester failed, it would fail in the shorted mode, causing line to line voltage across the VT’s putting them into saturation, which would cause a high current to flow through them This transformer used Cooper fuses which was an old design as it did not provide positive latching, using the right hand rule the fuse could have been forced out of the holder and the expelled gas would have launch it upwards into the lid. As it would see maximum fault current at this point.

23 Coal Mine grounding Majorsville Arresters failed when bank was energized. Arresters failed when bank was energized. Resistive grounded Grounded Wye - Grounded Wye Transformer Bank to provide 120/208 service High Pressure Sodium Street Light

24 In Both Cases Grounding was not solid Arresters should have been rated for Phase to Phase Voltage instead of Phase to Ground Arresters should have been rated for Phase to Phase Voltage instead of Phase to Ground

25 Line Charging Current Long open line at 500kV or a piece of underground line Can be modeled as

26 It is a line with a lot of Capacitance Vs Vr jIX I Cap Vr Vs I jX

27 Ferro Resonance Pharaoh Residence- Is where the king of Egypt Sleeps Pharaoh Residence- Is where the king of Egypt Sleeps Actually it is to much to talk about today will do it latter if we have time Actually it is to much to talk about today will do it latter if we have time