Visit to a 1100kV Stubstation and Transmission Line in Japan

In November of 2009, the IEC Arrester Committee (IEC-TC37-MT4) and the Cigre Arrester Working Group A3.25 met in Kawasaki Japan to discuss several arrester standards and arresters issues. The Japanese IEC National Committee was an incredible host for the meetings. A very interesting highlight of the meeting arranged by our host was a visit to Tokyo Electric’s (TEPCO) 1100kV GIS test substation and UHV transmission line. The sheer size of both of these structures is a bit intimidating. When considering lightning and switching mitigation we certainly will need to do some things we have never done before to meet the requirements. Arrester energy dissipation, switching surge level, corona control, new concept grading rings and more will all have to be better evaluated.

In the GIS substation, Toshiba, Mitsubishi, and NGK all have 1100kV GIS arresters.

TEPCO 1100kV GIS Substation

A 1100kV GIS arrester

The behamouth 1100kV transmission line and tower

Base of the 1100kV transmisison line

Low Inductance Arrester Leads

An Alternative to Shorter Lead Lengths

Lead length can sometimes be an issue with arresters in that they inherently possess inductance. This inductance can cause a problem by developing a relatively high voltage along its length during a fast rising surge through the lead. If the arrester lead is in parallel with the protected insulation, this high lead voltage is also experienced by the protected insulation. Since the whole purpose of the arrester is to reduce the stress on insulation, it is counterproductive to have long leads that result in even more undesirable stress than needed. See Arrester Facts 001 on Arrester Lead length for much more on this subject.

Until a few days ago, I had not thought it possible to have a low inductance lead, and that we just needed to live with the inherent inductance of arrester leads and keep the lengths as short as possible. However while running tests this past week using a Marx generator, the shape of the impulse was modified using inductance free resistors. Now I have been using this type of resistor for 30 years and never thought that the method used to achieve low inductance resistors could also be used to achieve low inductance arrester leads. A quick Google search showed me that low inductance cable is used in other disciplines, such as the audio world. As it turns out, for high frequency music to sound good on speakers located many feet from the source amplifier, they require low inductance cable. If it can be done for such mundane tasks as making music sound better, then why not create low inductance arrester leads to improve surge protection. And yes, the method of achieving this low inductance cable for audio applications is exactly the same as it is for achieving low inductance resistors for surge generators.

The method is known as bifilar winding. The physics behind it is simple. If two inductors are wound in opposite direction and placed in the immediate vicinity of each other, they will cancel out each others electro-magnetic field. A bifilar wound resistor is created by winding resistive wire on a core using two conductors in parallel and winding them in opposite direction. An example of this method is shown for audio cables at this site

In this figure, two sets of counter-clockwise wound wires are shown.

  In this figure, the two pairs of counter-clockwise wires are wound together in a clockwise direction thus creating a non-inductive cable.

Typically arrester leads are considered to be about .3uH/ft to .4uH/ft. Using a winding method as shown above a .05uH/ft can be achieved.

Arrester Condition Assessment

Just finished writing an article for the INMR Quarterly Journal on Insulators, Arresters and Bushings. The topic was a State of the Art of Arrester Condition Monitoring. As always as one writes an article on a subject that requires some research, you climb your learning curve a few more steps. This was the case for me this time. As I looked through the various leakage current monitors available on the market, the AMC produced by Siemens stands out in the crowd.

- - - - - - - - - - - The Marx Generator - - - - - - - - - - - - - - - A critical tool for Arrester Testing - - - -

In 2009 I had the opportunity to visit Hermsdorf Germany. While there I learned that this city was the place where Erwin Otto Marx invented his now famous Marx Generator. Anyone who has ever impulsed an arrester will probably recognize the name. The folks in Hermsdorf are quite proud of the fact that Marx invented the generator there and they should be. Their present city hall is in the building where Marx performed his experiments on the generator. As you can see from the photo below they even have an electrical insulator mounted on the building.

For more informaton on the Marx Generator check Wikipedia.  It is interesting to note that in the Wiki entry a different city is given credit for the location where Marx worked.   I think after personal discussion with Hermsdorf residents they would not like this Wiki error.

How to Improve ArresterWorks.com

ArresterWorks.com has been on the net for 2.5 years now and is visited by several thousand unique visitors each month. However until I started this forum, there has not been a convenient way to provide me feedback on how to improve the site.

If you have any ideas on how I can improve ArresterWorks.com, I would be very pleased to hear from you as a comment here or an email to Jwoodworth@arresterworks.com

Many thanks for using ArresterWorks.com and this forum. Between all of us we can make surge protection a more rational and easier to understand topic.

Jonathan Woodworth

Surge Counter as TOV Detector

----- Email from a an Arrester User ------
Jonathan
My project has a 230 KV line which may develop a TOV of @350 KV in the event of multiple failure of protecting equipment and in that event, to prevent transformer of 230/6.9 KV to see this high TOV, it is being proposed to provide a scheme which has surge arrestor and counter contact to be used as input to protection relay with time delay to differentiate lightening surge and TOV ( i guess) to trip transformer breaker.

My question-
1) Have you come across such scheme ever?
2) To your opinion, is this scheme good enough to protect transformer against line TOV.
3) Your opinion other than above questions.

Regards
P.S., Systems Engineer

Greetings PS
I believe there is a fundamental misconception in this scheme.
Surge counters do not sense TOV conditions. A TOV is not considered a surge as far as I understand it. The Surge counters I have worked with are usually sensitive only down to a few hundred amps. TOV conditions may force 5-20 amps through an arrester but that’s all.

If they did sense this low current, this may be a nice scheme.

I believe the only real solution is to use a voltage sensor of some type to trigger the protection scheme.

Good Luck
Jon

Riser Pole Arresters for Transmission Line Applications

------ Email from an ArresterFacts reader ---

Dear Sir:

We need to select an arrester for a short underground 115 kV cable system. In your paper "ArresterFacts 015" you mentioned The Transmission System Riser Pole arresters.
Can you receommend a supplier of this type of arrester?
Please send your comments,

Best Reggards
NRS

My Response

Greetings NSR,
Thank you for using ArresterWorks.com, I hope you are enjoying it.
Regarding 115kV riser pole arresters, there is no such arrester by that name in the high voltage range like there is in the medium voltage range. Standard station class or Class 2 in your case, arresters would be used. If you wish to have the best possible protection, then you can increase the arrester class to 3 or 4. The increase in class reduces the residual voltage.

When you install them, remember to keep the arrester and line terminal as close together as possible, and make sure you connect the shield of the terminal to the bottom of the arrester.

Hubbell, ABB, Siemens, Cooper, Joslyn, Tyco and most of the suppliers listed on my front page, supply these arresters since they are standard station type arresters.

Regards JJW