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60 Hertz Over Voltages

60 Hertz Over Voltages. For Arrester Applications. Applying Arresters. When Applying Arresters you have to be concerned about 3 items Maximum Continuous operating Voltage Maximum 60 Hertz Overvoltage Energy Absorption rating. What causes 60 Hertz overvoltages. Faults Load Rejection

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60 Hertz Over Voltages

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  1. 60 Hertz Over Voltages For Arrester Applications

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

  3. What causes 60 Hertz overvoltages • Faults • Load Rejection • Ferro Resonance • 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 • As the system becomes less well grounded then the unfaulted phase voltage will rise until it hits the phase to phase value.

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

  6. Calculation

  7. Graphical Method

  8. Two examples of 60 Hz overvoltages • Coal mine grounding 84 • Coal Mine grounding Majorsville

  9. 0.01 mi 3/0 AAAC Coal mine grounding 84 Here was the plan WEIR N.O. CALVIN A LIVINGSTON JCT. 0.69 mi 3/0 ACSR 1.30 mi 3/0 ACSR 0.13 mi LSMJ-EPJ (400) RICHARDSON ELLSWORTH 4/0,1/0 0.50 mi 0.19 mi 1.47 mi 556.5 LITTLE ANDREWS 0.90 mi SUMMIT 25 kV 3/0 ACSR 3/0 ACSR SHAFT JCT. 4.71 mi 556.5 0.60 mi 3/0 ACSR 0.17 mi 3/0 ACSR 25 kV CONSTRUCT 100 FEET OF 1/0 AL, UNDERGROUND 25 kV LINE INSTALL A 25 kV AIR SWITCH AT TAP INSTALL A 1.5 MVA, 25-4.16 kV PAD-MOUNTED TRANSFORMER PACKAGE WITH 4 kV METERING 3.15 mi PODISH 4/0 CU,1/0 CU U LONG FARM BLEEDER TAP 100 ft. 3/0 ACSR 1/0 AL 100 ft. LONG FARM SHAFT U LFBT 53773 1.5 MVA, 25-4.16 kV PAD-MOUNT LONG FARM BLEEDER SUBSTATION LFB 54173

  10. 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.

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

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

  13. Metering opened

  14. Why did it happen • 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

  15. 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 No Ground on Transformer 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. High side on metering VT’s Grounded for 2.5 element metering

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

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

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

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

  20. Ferro Resonance • 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

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