Jonathan Woodworth ArresterWorks

Todays Presentation

• Quick review of the EGLA Concept

• Answer Frequently Asked Questions about the EGLA

• Details on critical aspects of the EGLA design

The EGLA Concept

The EGLA is an improved surge arrester design that can be used to achieve “Lightning Proof”

distribution and transmission lines

How it Works Sequence of Events in EGLA Surge

Protection

1. Surge Travels down the line to the Insulator

2. Voltage builds up across the EGLA Gap and across the Insulator

3. Since the EGLA Gap is smaller than the Insulator strike distance the EGLA Gap flashes over

4. The Varistors in the SVU immediately conduct and transfers the surge charge to ground

5. Once the charge is depleted and the current is reduced to milliamps, the gap interrupts and all current flow ends…..

The Surge Event is over, there is no fault current and no breaker operation……

How it Works

• The Gap functions as the On Switch controlled by the gap distance

• The Varistors function as the Off Switch by limiting the current to a level that the gap will not sustain an arc

Frequently Asked Questions • Why is it an improvement over the non-gapped line arrester (NGLA)?

• How is it any different than the Gapped Arresters of the Past?

• Isn’t it the same as a safety gap around an insulator?

• Doesn’t the weather affect the performance?

• How can you tell if it has failed?

• Doesn’t the gap have to be precisely set?

• What system voltages can they be used on?

• Do they have enough Energy Handling Capability?

• Do they need a down Ground?

Frequently Asked Questions Why is it an improvement over the non-gapped line arrester (NGLA)?

The improved performance comes from

1. No Leakage current or losses (internal or external)

2. No possibility of a long term outage.

3. No aging of the dielectric due to voltage stress

4. Less Material (25% fewer Varistors)

5. Fewer lead management issues

Frequently Asked Questions How is it any different than the Gapped Arresters of the Past?

No follow current through the arrester on EGLA like there was on Gapped Silicon Carbide Arresters

Frequently Asked Questions How is it any different than the Gapped Arresters of the Past?

No Damage on the EGLA Gap as there was on SiC gapped arresters

Frequently Asked Questions Isn’t it the same as a horn gap around an insulator?

Absolutely not, a horned gap just keeps the inevitable lightning induced arc away from the insulator. A horn gap flashover always leads to a fault on the circuit and a breaker operation.

The EGLA does keep the arc away from the insulator, but never leads to a fault or breaker operation due to it current limiting varistor stack.

Frequently Asked Questions Doesn’t the weather affect the performance?

Fortunately for this product, air is the insulating medium of the gap. Air pressure will change the flashover point a percent or two, but humidity has no major affect on the flashover point. Neither does rain or snow.

Frequently Asked Questions

How can you tell if it has failed?

Until recently there was no failure indicator but one has been introduced that not only indicates, but restores the original system BIL.

It is available for distribution and transmission line arresters.

Operates on Fault current like a standard disconnector US Patent 8,711,538

Frequently Asked Questions Doesn’t the gap have to be precisely set?

For a gap that is set for lightning and switching surges, the spacing can be as much as +/- 25% without affecting performance.

To be covered in detail in the design review

Frequently Asked Questions Do they need a down ground?

Technically they do not need a down ground since their only function is to channel the lightning or switching surge current around the insulator.

As long as the insulator does not flashover it doesn’t matter where the arc goes after it leaves the EGLA. It may need a short negative electrode instead of a down ground.

Design Review

Important Design Criteria to Consider

1. Gap Spacing Max, Min, Incorrect, Altitude

2. Overload Considerations Impulse, TOV

3. Electrode Mechanical Strength, Current Carrying, Finish

4. Energy Ratings Less than 200kV, >200kV

5. Wildlife Protection

6. Voltage Ratings

Gap Spacing Considerations 1. Max Spacing is function of Insulator BIL

The gap should never be greater than 85% of the insulator BIL

2. Minimum spacing is a function of Maximum expected Power Frequency Voltage

Minimum gap should be capable of withstanding 168% of max Line to ground voltage.

3. Altitude

Typical Gap Spacing and Tolerance

Example of how to set gap on a distribution system

Electrode

Fundamental Requirements

• Mechanical strength

• Non-aging finish

• Shape conducive to the system voltage and the potential swinging of the arrester or phase conductor.

• Conductivity adequate for surges but not power frequency current

• Acceptable failure mode

• Wind withstand

Energy Ratings

Distribution Systems

• Heavy Duty Arrester Rating or in some cases a Normal Duty Rating

Transmission Systems

• For systems <230kV : Distribution Heavy duty unless fault current is >20kA.

• For Systems >230kV: Intermediate or Station Class. Charge Transfer Rating of 2C may be necessary.

Wildlife Protection Not necessary since the arrester is all at the same voltage.

If the animal gets in the gap, only leakage current flows no fault will occur.

Voltage Ratings Per C62.11 that doesn’t address it well, the voltage ratings would be the same as standard arresters. MCOV is the maximum continuous operating voltage of the device.

Test Standards

IEEE C62.11 Makes no reference to this type of arrester. But it is on the agenda for upcoming meeting.

IEC 60099-8 Published in 2008 Covers the a similar arrester but is for an EGLA for lighting only.

Summary

• The EGLA is an arrester design that can be a big part of line reliability if adopted.

• The EGLA offers several performance improvements for line protection.

• The EGLA can be used on all system voltages.

Questions