OLTC - On Load Tap Changer 2

[Linspire]

Dear all,

I would like to seek opinion how you guys review the submission approval for transformer accessories transformer - OLTC.

As far as I know, substation here, they prefered MR Germany - OLTC.

 

[prc]

When you review OLTC documents, look for the following:
-Rated voltage, rated current and rated step voltage match with the maximum values of transformer during in service or testing at factory
- Guaranteed number of operations before overhaul
- Type test report in line with relevant IEC
- Minimum protection provided - bursting plate, surge relay, out of step relay

 

[ScottyUK]

Reinhausen make very good tapchangers. Most of my experience has been on their large high voltage types with separate diverter switches. The Reinhausen design proved very reliable, so much so that I am struggling to think of any problems on the power components. We had a couple of minor problems with the drive mechanism, but I suspect better maintenance could have avoided those difficulties.

 

[Linspire]

prc,

I would like to seek clarification on regards your suggested few points;

i) Guaranteed number of operations before overhaul, overhaul means maintenance as I suppose ?
ii) Bursting plate,surge relay, out of step relay, what is that ? kind new terms for me.

ScottyUK,

Your utilities prefer Reinhausen yeah.
Diverter switches is referring the tap-changer switcher right ?

 

[ScottyUK]

The diverter switch is the load-making / load-breaking switch element of the tapchanger. The oil in the diverter tank is (relatively) dirty and contaminated by arc breakdown products, and is in a separate compartment from the core and windings.

You should look at the maintainability of the design: top-mounted tapchangers are common but you will need to provide a lifting frame or gantry to remove it for maintenance. A high voltage OLTC is a substantial size but is also a fairly delicate piece of precision engineering - removing it and replacing it in the tank is not a trivial task.

Make sure that you determine whether the OLTC manufacturer, or perhaps the transformer OEM, have suitably trained and experienced personnel available in your location. You might consider integrating a long-term service agreement with the manufacturer as part of the bidding process.

 

[prc]

Once upon a time almost all leading transformer manufacturers were making OLTC.Then the mergers started due to economies of scale.In 1960's and 70's UK had atleast 4-5 well known tap changer makers, but today none.(Scotty can correct me)Today there are two popular designs available around the world -MR and ABB,both reputed and reliable.There are many smaller manufacturers in China &India with limited markets.

Number of operations meant arcing contact life after which contacts to be changed.Bursting plate=pressure relief device fitted to arcing chamber, surge relay= relay mounted between the diverter chamber and its oil conservator to detect excess surges from faulty diverter switch.

 

[Linspire]

ScottyUK,

You mention lifting frame / gantry, do you mean provide on the transformer or OLTC itself ?
Well, honestly, I havent see any high voltage power transformers myself.

Do you agree what prc stated in his reply on "Once upon a time almost all leading transformer manufacturers were making OLTC.Then the mergers started due to economies of scale.In 1960's and 70's UK had atleast 4-5 well known tap changer makers, but today none.(Scotty can correct me)Today there are two popular designs available around the world -MR and ABB,both reputed and reliable.There are many smaller manufacturers in China &India with limited markets." ?

prc,

Minimum protection means the OLTC design specifications suppose to have these kind protection for itself.

 

[ScottyUK]

I've seen A-frames, scaffolding and cranes of various sizes used for the purpose. I haven't yet seen a permanent lifting beam or jib used although there is no reason why it couldn't be done if a suitable structure was available to mount it on. An OLTC isn't especially heavy in comparison to the rest of the transformer. The main considerations when removing one are avoiding contamination of the tank and avoiding damage to the tapchanger itself.

prc knows the transformer industry rather well.

Reinhausen and ABB are both well-respected manufacturers and are often specified by name in client specifications. The old British manufacturers like Ferranti, English Electric / AEI / GEC, Fullers, Hawker-Siddeley and ATL are all gone. I think Brush are still in the business or were until recently: I have an idea that Brush merged with the old ATL company and Hawker-Siddeley under FKI's ownership but I might be wrong about that.

 

[dpc]

In the US, I believe Waukesha manufactures their own LTC, but pretty much everyone else has gone to Reinhausen.

 

[Linspire]

ScottyUK,

Appreciate for your sharing input.


prc,

I'm wating for prc reply on regard minimum protection. Does it give minimum protection for power transformer or for OLTC itself ?

 

[inpran]

Linspire,
OLTC will have its own surge relay and pressure relief device. Transformer will have a separate pressure relief device. So the protection will be two separate and independent entities.

 

[prc]

Yes. inpran is correct.

 

[bacon4life]

In order to sample oil from each of the LTC tanks, it may require several liters per tank to flush the pipes leading from the tank to the sample valve. Make sure you have a large LTC conservator or an easy way to add oil. We also had a problem with the transformer manufacturer incorrectly wiring the Reinhausen provided relays as alarm contacts instead of tripping contacts. If you want relays to both alarm and trip, be sure to include that in the specification.

 

[prc]

Trust you are referring to the surge relay provided for OLTC protection.As the name indicates it has only surge contacts and no gas(ie alarm)contacts.When tap changer operates there will be flow of gases to conservator and may actuate gas contacts.Hence this relay is provided with only one pair of contacts which will get actuated in case of a serious fault inside the arcing chamber and consequent oil surge in to conservator.Some users wire it for alarm, others for trip.

 

[bacon4life]

PRC is right that tripping on surge and/or pressure relief are controversial due to concerns of either seismic activation or maintenance activities causing inadvertent activation.

In the operating manual for the Reinhausen Vacutap VR OLTC, the instructions have a warning at the beginning of the manual that states "Connect the protective relay in such a way to ensure that the transformer is immediately disconnected when the protective relay is tripped." The standard RS 2001 surge relay includes just a single tripping contact, with multi contact versions available upon request. The relay resets once the flow stops, so either a seal-in relay or an alarm contact is needed to identify which phase trips.