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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

60 Hertz Over Voltages

For Arrester Applications

applying arresters
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
What causes 60 Hertz overvoltages
  • Faults
  • Load Rejection
  • Ferro Resonance
  • Charging current in a line
faults and grounding
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.
slide5

197kv

242kv

Arrester voltage

140kv

Neutral shifts during

clearing of a phase to

ground fault

two examples of 60 hz overvoltages
Two examples of 60 Hz overvoltages
  • Coal mine grounding 84
  • Coal Mine grounding Majorsville
coal mine grounding 84

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

slide16

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.
slide17

Blown Arrester

High Side VT’s Grounded

2 VT’s

3 CT’s

Neutral ungrounded

slide19

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
slide21

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

slide22

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

coal mine grounding majorsville
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

in both cases grounding was not solid
In Both Cases Grounding was not solid
  • Arresters should have been rated for Phase to Phase Voltage instead of Phase to Ground
line charging current
Line Charging Current

Long open line at 500kV or a piece of underground line

Can be modeled as

ferro resonance
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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