Arc Enemy

© iStockphoto MegaV0lt

It hard­ly ever hap­pens; but if it does, it can end bad­ly: a trans­former fire after a flashover. A new pas­sive pro­tec­tion sys­tem from MR pro­tects oper­a­tors from seri­ous dam­age in such cas­es.


Faults in trans­former wind­ings, bush­ings, and on-load tap-chang­ers, in which large amounts of ener­gy are released, are extreme­ly rare. If they do occur, how­ev­er, high pres­sure is cre­at­ed by an elec­tric arc that vapor­izes the sur­round­ing insu­lat­ing liq­uid. If the process is uncon­trolled, the con­se­quences can be seri­ous. In gen­er­al, trans­former tanks and pro­tec­tion sys­tems, includ­ing those of on-load tap-chang­ers (OLTCs), are pre­pared for this: In the event of a fault, they release pres­sure as con­trolled as pos­si­ble to min­i­mize the impact on the envi­ron­ment.

How­ev­er, there is poten­tial for opti­miza­tion to reduce the risk even fur­ther, espe­cial­ly for the rare events with release of very high ener­gies. For this rea­son, designs and pro­tec­tion sys­tems have been and con­tin­ue to be improved, for exam­ple with robust trans­former tanks. In the event of an arc fault in the trans­former tank, the ener­gy released is dis­si­pat­ed by defor­ma­tion of the tank which has been proven to be the most effec­tive mea­sure against fire after a high-ener­gy arc fault.

The renowned Chi­nese Elec­tric Pow­er Research Insti­tute (CEPRI) has sub­ject­ed the BPS pas­sive-pro­tec­tion sys­tem to tough real-life tests by pro­vok­ing high-ener­gy arc­ing in test trans­form­ers.

Users and grid oper­a­tors can retro­fit their trans­form­ers with rein­forced BPS cov­ers at any time.

MR has devel­oped the BPS –Burst Pre­ven­tion Sys­tem® as a sup­ple­ment for robust trans­former tanks. The over­all result is a trans­former that min­i­mizes the effects of such dam­ag­ing events, which can be of great impor­tance for oper­a­tors of ener­gy infra­struc­ture as well as for indus­tri­al com­pa­nies, and any­where where space is lim­it­ed.

Cover Reinforcement

The engi­neers at MR have scru­ti­nized and rein­forced all rel­e­vant parts of the OLTC, from the cov­er to the gear unit, screw con­nec­tions, flow relay, sight glass, and pres­sure relief valve for direc­tion­al oil drainage. Com­put­er sim­u­la­tions show that the BPS can han­dle dis­tur­bances of up to 10 mega­joules in 80 mil­lisec­onds and 50 bar pres­sure (see the illus­tra­tion below­to see exact­ly how this works).

Five scenarios where the additional passive protection of BPS is particularly worthwhile:

Valuable
components
in the Vicinity

Valuable
components
in the Vicinity

An explo­sion can dam­age near­by com­po­nents and set them on fire. Addi­tion­al pas­sive pro­tec­tion is there­fore par­tic­u­lar­ly rec­om­mend­ed where there is valu­able infra­struc­ture near­by, such as in sub­sta­tions for high-volt­age direct cur­rent (HVDC) trans­mis­sion.

Sensitive
Ecosystems


Sensitive
Ecosystems

For trans­form­ers close to bod­ies of water or in nature reserves, a BPS pre­vents mas­sive envi­ron­men­tal pol­lu­tion and high clean-up costs in the event of oil leaks.

Offshore
Facilities



Offshore
Facilities

Infra­struc­ture that is dif­fi­cult to reach, such as off­shore facil­i­ties, ben­e­fits from the low­er risk because it would be dif­fi­cult and take a long time to fight fires in case of emer­gency at such loca­tions.

Transformers
in Buildings

Transformers
in Buildings

In steel­works and oth­er fac­to­ries, trans­form­ers are often locat­ed inside of build­ings, and an explo­sion here would be a major haz­ard for employ­ees and could even dam­age the build­ing itself.

Urban
Environments


Urban
Environments

The more peo­ple who live near a trans­former, the high­er the risk of some­one being injured or suf­fer­ing smoke inhala­tion in the event of a dis­as­ter. A BPS helps to pre­vent such sit­u­a­tions.

The BPS was val­i­dat­ed not only using numer­ous sim­u­la­tions, but also in a test with a real arc in coop­er­a­tion with the Chi­nese Elec­tric Pow­er Research Insti­tute (CEPRI) where the engi­neers sub­ject­ed a test trans­former equipped with the BPS to the stress of a 5.6 mega­joule arc with­in 50 mil­lisec­onds. The BPS with­stood the sub­se­quent, rapid­ly increas­ing pres­sure of around 40 bar, there­by con­vinc­ing a Chi­nese grid oper­a­tor to retro­fit the first trans­form­ers in the field.

What happens when it happens:

Electric Arc

Elec­tric arcs occur when insu­la­tion sec­tions are over­loaded. While most arc flashovers are harm­less, there are also severe ones with ener­gies of sev­er­al mega­joules. In this exam­ple, we are assum­ing such a high-ener­gy arc.

2.

Pressure Development

The brief, immense heat caus­es the sur­round­ing insu­lat­ing oil to vapor­ize and expand due to the result­ing gas. A pres­sure relief device opens auto­mat­i­cal­ly at the top of the OLTC cov­er and releas­es the oil and pres­sure. In our exam­ple, how­ev­er, this is not enough, and the pres­sure becomes so great that it expands the walls of the OLTC hous­ing.

Reinforced Cover

Normal Cover

Internal Relief

A rein­forced BPS cov­er with­stands the pres­sure which instead breaks open the bot­tom of the OLTC hous­ing and escapes into the trans­former. The flex­i­bil­i­ty of the trans­former tank is such that it absorbs all the ener­gy with­out oil escap­ing uncon­trol­lably. If nec­es­sary, the transformer’s pres­sure relief device releas­es oil into a pan which allows the envi­ron­ment to remain unaf­fect­ed.

Explosion

If the pres­sure increas­es too much or too sud­den­ly, the OLTC cov­er bursts, releas­ing a surge of oil and steam which can ignite and con­t­a­m­i­nate the sur­round­ings.


YOUR CONTACT PERSON

Do you have any ques­tions about the BPS — Burst Pre­ven­tion Sys­tem®?
Mar­tin Guth is here for you:
M.Guth@reinhausen.com


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