1. Coal Mine Connections Lessons from Experience

2. Why are we talking about Coal mine connections Because we had a situation where the customer wanted a service that was out of our standards and therefore caused confusion and eventually a problem. Because we had a situation where the customer wanted a service that was out of our standards and therefore caused confusion and eventually a problem.

3. Here was the plan 1.47 mi LIVINGSTON PODISH 0.13 mi 0.90 mi 0.50 mi SUMMIT JCT. 3.15 mi ELLSWORTH CALVIN JCT. 1.30 mi 0.69 mi WEIR N.O. LITTLE A 25 kV ANDREWS SHAFT RICHARDSON 0.19 mi 4.71 mi 556.5 25 kV 0.01 mi 3/0 AAAC 556.5 3/0 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, 25-4.16 kV PAD-MOUNTED TRANSFORMER PACKAGE WITH 4 kV METERING 1.5 MVA, 25-4.16 kV PAD-MOUNT LFB 54173 LONG FARM BLEEDER TAP LFBT 53773 LSMJ-EPJ (400)

4. 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.

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

7. The situation developed because 1.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 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

8. Metering opened

9. 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

10. 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.

11. So what do coals mines want? There are two types of mines we encounter on our system. There are two types of mines we encounter on our system. Above Ground mines, I like to call them strip mines. Above Ground mines, I like to call them strip mines. Below ground mines such as Quecreek Below ground mines such as Quecreek

12. Above ground mines usually require our standard service, but below ground mines are different. Above ground mines usually require our standard service, but below ground mines are different. Both above ground mining and below ground mining are govern by the State Mining Laws. Each State has their own group that enforces these laws. Both above ground mining and below ground mining are govern by the State Mining Laws. Each State has their own group that enforces these laws. www.dep.state.pa.us/dep/deputate/minres/d ms/guidelines/ www.dep.state.pa.us/dep/deputate/minres/d ms/guidelines/ www.dep.state.pa.us/dep/deputate/minres/d ms/guidelines/ www.dep.state.pa.us/dep/deputate/minres/d ms/guidelines/

13. Below ground mining operations requires special standards from what we are use to Why is below ground so special. Underground mining deals with methane gas and water. Two things that don’t mix well with electric. Why is below ground so special. Underground mining deals with methane gas and water. Two things that don’t mix well with electric. For below ground mining there are two components For below ground mining there are two components a. Electric that goes underground for operating equipment b. An above ground fan that pushes air underground for ventilation

14. Lets look at each component Above ground air fan. Above ground air fan. If that fan goes off line then the mine must be evacuated immediately. Not easy when you are a mile or so into a mine. If that fan goes off line then the mine must be evacuated immediately. Not easy when you are a mile or so into a mine. The operators would like to keep the fan operating until the end of a shift when the mine is emptied. The operators would like to keep the fan operating until the end of a shift when the mine is emptied. If you have a line to ground fault with a solidly grounded neutral the circuit protection will trip the fan immediately. But if the fan were to be served from a delta connection then you can have a line to ground fault and have time to look for the trouble. If you have a line to ground fault with a solidly grounded neutral the circuit protection will trip the fan immediately. But if the fan were to be served from a delta connection then you can have a line to ground fault and have time to look for the trouble.

15. Therefore, most operators would like to serve there fan from a delta system, so a line to ground fault does not cause the fan to shut down and can be corrected not immediately, but in a timely manner. Therefore, most operators would like to serve there fan from a delta system, so a line to ground fault does not cause the fan to shut down and can be corrected not immediately, but in a timely manner. DEP recognizes this and allows either the fan to be served from a solidly grounded wye or from a delta connection. DEP recognizes this and allows either the fan to be served from a solidly grounded wye or from a delta connection. Most of the fans are in the hundreds of horsepower so it requires voltages to operate at 4160 or 2400. Most of the fans are in the hundreds of horsepower so it requires voltages to operate at 4160 or 2400.

16. If the mine has a 4160 volt motor they will want to take voltage at 4160 delta. If the mine has a 4160 volt motor they will want to take voltage at 4160 delta. To give them this delta connection requires us to operate the transformer as an ungrounded wye. To give them this delta connection requires us to operate the transformer as an ungrounded wye. We have transformers that can be connected either 4160 wye or 2400 volts delta. We have transformers that can be connected either 4160 wye or 2400 volts delta. However this delta connection is a non standard for us at 4160 volts, so we have to be careful on how we hook it up and the equipment connected to it. However this delta connection is a non standard for us at 4160 volts, so we have to be careful on how we hook it up and the equipment connected to it.

17. So what does the mines want for the surface fan No ground Metering 3 wire Coal mine owns or DEP wants this connection between ground grids as they require 4 ohms or less AP Transformer Fan and other stuff

18. So what does the mines want for the surface fan No ground Metering 3 wire Coal mine owns or DEP wants this connection between ground grids as they require 4 ohms or less AP Transformer Fan and other stuff 10 foot min If arresters are installed they have to be phase to phase rated

20. So what does the mines want for the surface fan No ground Metering 3 wire contained in the transformer Coal mine owns or AP Transformer Fan and other stuff 10 foot min If arresters are installed they have to be phase to phase rated As a cost savings for both us and the coal mine we are using padmounts They would like us to have a ground ring installed around the padmount with 2 ground rods as a min. If the coal company ever buys the padmount they will have to have a 4 ohms or less resistance.

23. So what does the mines want for the deep mine service No ground Metering 3 wire Coal mine owns or DEP wants this connection between ground grids as they require 4 ohms or less AP Transformer Zig-Zag Transformer if being served Delta and a grounding resistor 10 foot min If arresters are installed they have to be phase to phase rated Grounding resistor to limit fault to 25 amps Ground Bed <4 ohms Zig-zag if delta Neutral ground bed <4 ohms 25ft away, but no more than 100ft from transformer Insulated neutral

24. Transformer connections and voltage The highest voltage allowed is 15kV to serve the coal mine The highest voltage allowed is 15kV to serve the coal mine Delta wye, delta delta, wye delta are permitted provided a grounding resistor and a zig zag on delta connections to provide phase to ground faults limited to 25 amps Delta wye, delta delta, wye delta are permitted provided a grounding resistor and a zig zag on delta connections to provide phase to ground faults limited to 25 amps A Wye Wye is not permitted A Wye Wye is not permitted

25. DEP requires 4 ohms for the ground grid or less instead of 5 ohms as some standards state, because they want to limit the voltage developed to 100 volts at 25 amps through the neutral resister, so that makes the resistance 4 ohms or less. DEP requires 4 ohms for the ground grid or less instead of 5 ohms as some standards state, because they want to limit the voltage developed to 100 volts at 25 amps through the neutral resister, so that makes the resistance 4 ohms or less. The isolated ground grid has to be a minimum of 25 feet away from the power transformer, but no more than 100 ft from the power transformer per the federal mining laws. The isolated ground grid has to be a minimum of 25 feet away from the power transformer, but no more than 100 ft from the power transformer per the federal mining laws.

26. Remember Any time the low side is not solidly grounded Any time the low side is not solidly grounded A. Phase to Phase Arresters must be used A. Phase to Phase Arresters must be used B. 3 wire metering must be used. B. 3 wire metering must be used. When you do not solidly ground the low side, line to ground loads can not be served. So station service must be a phase to phase connected load. When you do not solidly ground the low side, line to ground loads can not be served. So station service must be a phase to phase connected load.

27. What is 5S, 6S, 9S metering 5S or two element metering is for 3 wire systems ie cannot serve line to ground loads 5S or two element metering is for 3 wire systems ie cannot serve line to ground loads 6S or 2 ½ element metering is for 4 wire systems. Not used as a standard any more. 6S or 2 ½ element metering is for 4 wire systems. Not used as a standard any more. 9S or 3 element metering is for 4 wire systems 9S or 3 element metering is for 4 wire systems

28. 3 element, 2 VT’s, 2 CT’s 2 ½ element, 2 VT’s, 3CT’s 3 element, 3 VT’s, 3CT’s VT’s connected to ground

29. So what was the problem Neutral not connected 2 ½ element metering used 2.5 element metering caused neutral to move here Arrester connected line to neutral was not rated for 1.5 p.u. overvoltage there fore boom

30. The situation developed because 1.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 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

31. What can be done in the future to try to prevent these occurrences On all plans specify whether the service is Delta, Wye, or Grounded Wye. Specify the voltage, both phase to phase and phase to neutral where appropriate. Create a single line if it is something outside of our standards. Then if something does fit the plan or changes in the field do not fit the plan, the job should be stopped until it is reviewed by planning and engineering.