WHY TRANSFORMERS EXPLODE

THE PHENOMENON

During a transformer short-circuit, the electrical arc vaporizes oil and creates a Dynamic Pressure Peak which travels at the speed of 1,200 meters per second (4,000 feet per second). This phenomenon occurs within a few milliseconds. Because of reflections in the tank the pressure peak will generate pressure waves. The integration of all of the waves pressure peaks creates static pressure. Then, the pressure becomes equal throughout the entire transformer tank within 50 to 100 milliseconds after the electrical arc, and causes the transformer tank to rupture.

LACK OF INTERNATIONAL TRANSFORMER STANDARDS AND REGULATIONS

Transformers can only withstand a small overpressure and are not designed as pressure vessels according to ASME Codes and Controls. Consequently, transformers have proven to be very dangerous. Because transformer standards describe electrical requirements but do not cover mechanical design.

TRANSFORMER ELECTRICAL AND MECHANICAL PROTECTION LIMITS

Pressure Relief Valve inadequacy: Pressure Relief Valves are suitable for slow pressure rise whereas pressure gradients developed during low impedance faults

are extremely fast. Transformers that have exploded were usually equipped with Pressure Relief Valves.

Buchholz and Rapid Pressure Relay inefficiency: transformer electrical protections are not designed to react to sharp pressure gradients. During the 62 TRANSFORMER PROTECTOR tests, the Buchholz always failed to detect any gas and oil movement or pressure variation.

Electrical Breaker opening time: the best breaker technology trips in 50 milliseconds, far too late to prevent the explosion because most of the gases are generated within milliseconds after short-circuit. Consequently, the tank pressure keeps increasing even after the breaker has opened.

CAN PROPER MAINTENANCE GUARANTEE A TRANSFORMER WILL NOT EXPLODE?As transformers are typically the most expensive and vital piece of equipment located in power plants and substations, they require a comprehensive maintenance plan to ensure their proper functioning and longevity. These maintenance procedures are usually detailed in lengthy manuals which can easily reach several hundred pages. Furthermore, these maintenance standards are multiplied in highly regulated industries, such as Nuclear Power Plants.Following these meticulous maintenance guidelines can reduce the occurrence and possibility of a transformer explosion, however, it does not nullify this risk. In fact, numerous explosions have occurred on extremely well-maintained transformers. For example, let’s look at the transformer fire that the James FitzPatrick Nuclear Power Plant  experienced in November of 2012. Upon investigation, it was confirmed that this incident was caused by an internal fault, regardless of proper testing and maintenance. A FitzPatrick Plant spokesperson stated that*:“All test results and monitoring data prior to the transformer failure indicated it was operating appropriately. There was nothing observed that would indicate the transformer would fail.”Just a few other examples of incidents occurring at Nuclear Power Plants in the US include: Bay City in Texas, Limerick in Pennsylvania , Indian Point in New York , and Brunswick in North Carolina . These cases confirm that even following the high maintenance standards of Nuclear facilities, transformer explosions cannot be prevented.

*Source: Syracuse.com, “Nuclear experts work to figure out why a transformer caught fire at the James FitzPatrick Nuclear Power Plant” .

WHY CAN’T OIL AND GAS ANALYSIS PREVENT TRANSFORMER EXPLOSIONS?Most transformers are equipped with an On-Line Dissolved Gas Analyzer to measure the concentration of gases such as hydrogen, acetylene, ethylene, methane, carbon monoxide, etc. This equipment is used as a preventive action for slow moving changes in the dielectric properties of the oil due to humidity, moisture and particles from the winding insulation degradation. On-Line DGA’s are ideal for checking the long-term evolution of transformer corposant from oil to paper, etc.However, transformer short-circuits occur without warning every day, producing catastrophic explosions and fires. Most of these incidents occur on  transformers that are equipped or monitored by DGA’s, proving that oil and gas analysis can’t prevent an explosion. The response time of the sensors used for analyzing the oil and gas can vary from 10 to 40 minutes. Since a transformer explodes within milliseconds of a short circuit, it is simply not possible to receive the On-Line DGA results and decide whether to trip the transformer before an explosion occurs.Furthermore, when most transformer explosions occur, the oil and gas analysis results are normal, even perfect. An example of this is the transformer explosion which happened at the James FitzPatrick Nuclear Power Plant. It was reported* that:

“All test results and monitoring data prior to the transformer failure indicated it was operating appropriately. There was nothing observed that would indicate the transformer would fail.”Basically, a short circuit can occur at any time and the best way to prevent the transformer tank from explosion is to equip it with a TRANSFORMER PROTECTOR (TP). During the first milliseconds of the short circuit, the first Mega Joule creates a volume of 2.3m3 of explosives gases inside the transformer tank. At the same time, a dynamic pressure peak travels inside the tank at the speed of sound inside the oil, 4,000 ft/sec (1200 m/sec). The dynamic pressure peak activates the TRANSFORMER PROTECTOR (TP) within milliseconds and creates an opening for the oil and gas to be evacuated before static pressure increases.

*Source: Syracuse.com, “Nuclear experts work to figure out why a transformer caught fire at the James FitzPatrick Nuclear Power Plant” 

HOW TRANSFORMER PROTECTOR WORKS

TRANSFORMER PROTECTOR OPERATION

As shown in the video diagram above:

The TRANSFORMER PROTECTOR activates within milliseconds depressurizing the transformer main tank.

Once the depressurization is complete, to avoid the bazooka effect from killing maintenance technicians during tank opening, the transformer is then injected with inert gas to evacuate the remaining explosive gases.

After the explosive gases have been cleared, the transformer is then safe and ready for repair.

The TRANSFORMER PROTECTOR is the only proven solution to transformer explosion and fire. 20 years of extensive high-level mechanical research and tests were necessary to design the TRANSFORMER PROTECTOR.

The TRANSFORMER PROTECTOR is a transformer explosion and fire prevention system suitable for any type of oil-immersed transformer and including surrounding equipment such as the On Load Tap Changer (OLTC), Oil Cable Box (OCB), and Oil Bushing Cable Box (OBCB).

TRANSFORMER PROTECTOR COMPONENTS

Watch the slideshow below to learn more about some of the components of the TRANSFORMER PROTECTOR.

CONFIGURATIONS

Standard

The Pictures below show some examples of standard configurations for new transformers.

TP3A VDS SOGST TPA6B VDS SOGST

TPA VDS SOGST TP VDS SOGST

2TP3A6B VDS SOGST Small-TP

Non-Standard

The Pictures below show some examples of non-standard configurations used for retro-fitting.

TP-HDS-EOGST TPA-HDS-SOGST

TPA3B-HDS-WOGST

CLIENT INSTALLATIONSSince 2005, the TRANSFORMER PROTECTOR has been included in the technical specifications of 171 companies in 65 countries. It currently protects thousands of transformers manufactured by 175 different transformer manufacturers and has also achieved the following:

Thousands of TPs sold worldwide CEPEL, Brazil, one of the world’s top High Voltage laboratories has performed 34

successful live tests on three different large transformers

Electricity De France (EDF), High Voltage Laboratory has performed 28 successful live tests

on a small transformer

Power-Gen Europe – Best Paper Award 2008

The NFPA recommends Fast Depressurization Systems for all Power Plant and Substation transformers the following Civil Codes which the TRANSFORMER PROTECTOR (TP) complies with:

NFPA 850   (Recommended Practice for Fire Protection for Electric Generating Plants and

High Voltage Direct Current Converter Stations)

NFPA 851   (Recommended Practice for Fire Protection for Hydroelectric Generating Plants)

Client installation examples:

United States

Great Britain

Mexico

Brazil

Panama

Philippines

FINANCIAL BENEFIT

A GROWING CONCERN FOR CORPORATE RISK MANAGERS AND INSURANCE COMPANIES

Transformers are considered by Corporate Risk Managers and Insurers as the most critical equipment inside plants because of the large quantity of oil in contact with high voltage elements.

DAMAGE COST OF TRANSFORMER EXPLOSION AND FIRE

The cost to replace a transformer unit is several million dollars (USD) and the cost of the outage in the tens of millions (USD) with potential to reach hundreds of millions (USD). Transformer explosions and fire result in: lost income, purchase of high-priced replacement power, replacement of transformers and surrounding equipment, polluting the environment and negative public relations, etc.

The damage caused depends on the transformer location:

Power plant incidents result in very high loss of revenue and can lead to company bankruptcies if not insured. For insurers, the projected cost reference can approach USD 500,000 per MVA.

Transmission substation incidents can result in the complete blackout of a region or a country. Several well-known cases have been recorded recently (USA, UK, Italy, Spain, etc.).

Distribution transformer explosions in urban areas can have disastrous financial consequences in related pollution and litigation costs.

PURCHASING THE TRANSFORMER PROTECTORThe TRANSFORMER PROTECTOR comes with a liability insurance policy with coverage up to 20 million USD (2013) per occurrence should an incident occur.Equipping your transformers with the TRANSFORMER PROTECTOR: Decreases the risk to surrounding equipment and buildings.

Enables the quick internal repair of the transformer and sharply reduces plant outages.

Leaves the environment unharmed.

RESEARCH & TESTSSince 1999, our Research Department has released 59 scientific articles about transformer short-circuit calculations, tests, mathematical models, simulations and TRANSFORMER

PROTECTOR efficiency to avoid transformer tank explosions and oil fires (list available upon request).In order to study the energetic transfer phenomenon that occurs during a short circuit in transformers 2 experimental test campaigns were carried out; the first by Electricité de France in 2002 and the second by the Brazilian high voltage laboratory CEPEL, in 2004 on large scale transformers.These 62 experimental tests consisted in creating low impedance faults in oil filled transformers equipped with the TRANSFORMER PROTECTOR. The tests showed that the arc first creates a huge volume of gas that is quickly pressurized, generating one high pressure peak that propagates through the oil. This First Dynamic Pressure Peak activates the TP within milliseconds preventing the transformer from exploding.In addition to the experiments, a compressible two-phase flow numerical simulation tool has been developed. The experimental results have been used to validate the simulation model. Adding to this model a dynamic structural analysis package has been coupled to create a fluid structure interaction. These simulations definitively show the efficiency of theTRANSFORMER PROTECTOR to prevent explosion and fire.

The arc used in the simulation, located at the base of the right bushing, has parameters given in the table below and total energy of 7.19 MJ.

Current(Peak Voltage (Peak) Frequency Duratio Total Energy

) n

2,000 A 80,000 V 50.0 Hz 0.110 s 7.1986 MJ

CONSERVATOR SHUTTERWhen a transformer is under normal operation, the CONSERVATOR SHUTTER is open, enabling oil volume expansion or retraction from the conservator.

As soon as the CONSERVATOR SHUTTER detects an abnormal high oil flow, it quickly and effectively isolates the conservator. If this activation is caused by a transformer tank explosion, the CONSERVATOR SHUTTER prevents oil from the conservator, from pouring onto the transformer tank or ground surrounding the transformer.

IN ADDITION, THE CONSERVATOR SHUTTER:

Is used by electric utilities located in earthquake and hurricane risk areas where movement causes pipe ruptures or leaks

 

AVAILABLE TYPES

TL 24 Type – for 2-inch piping (DN 50)TL 34 Type – for 3-inch piping (SN 80)

PRINCIPLES

1. The Conservator Shutter, a flow sensitive device, is as essential to transformer safety as a Buchholz relay.

2. While the transformer is operating normally, the Shutter is open. When the Buchholz detects the presence of gases, the Shutter quickly isolates the conservator tank, as soon as it detects abnormal oil flow.

3. When a short-circuit occurs, the resulting pressure increase forces the transformer cover off and the oil catches fire. The conservator oil causes oil overflow which burns the main tank. The resultant oil flow between the conservator and tank closes the Shutter.

4. The Shutter is equipped with an integrated magnetic switch. When the Shutter closes, the magnetic contact sends an alarm signal to the control room.