DIFFERENCE BETWEEN DRY TYPE AND LIQUID FILLED TRANSFORMERS BASIC AND TUTORIALS

COMPARISON BETWEEN DRY TYPE AND LIQUID FILLED TRANSFORMERS
What Is The Difference Between Dry Type and Liquid Filled Transformers?


The advantages and disadvantages of dry-type transformers versus liquid-filled units depend upon the application. Dry-type transformers can usually be located closer to the load, resulting in cost savings because of shorter cable runs and lower electrical losses.

A liquid-filled transformer, on the other hand, may require special construction features for the room in which it will be placed because of fire safety considerations. This may dictate a location some distance from the load.

In addition, periodic testing must be conducted on the fluid to determine its dielectric strength, water content, dissolved gases, and other parameters.

In some applications, there is no option to the use of liquid-filled transformers; dry-types are limited in size and voltage handling capability. Liquid-filled types are available in almost limitless kVA and voltage ratings.

Also, if requirements call for a transformer to be located outdoors, it may be less expensive to purchase a liquid filled unit. With oil as the liquid, the cost would be lower than for a dry-type of equivalent rating; with low-firepoint fluids, the cost would probably be comparable to a dry-type.

For liquid-filled transformers, the main cooling/insulating mediums used today are mineral oil, high-molecular-weight hydrocarbon, and silicone fluid. If a leak occurs in the transformer tank, fire safety becomes an important issue.

Because of hazards associated with tank rupture and the possible ignition of the dielectric, a thorough analysis covering fire safety and the possible effects on the environment should be carried out well in advance of device installation.

Some materials are covered under the Federal Resource Conservation and Recovery Act and the Clean Water Act, including requirements for:


• Special handling
• Spill reporting
• Disposal procedures
• Record-keeping

These considerations can have an effect on installation costs, long-term operating expenses, and maintenance procedures.

TRANSFORMER FAILURE MODE BASICS AND TUTORIALS

TRANSFORMER FAILURE MODE BASIC INFORMATION
What Is Transformer Failure Mode?


Transformer Failure Modes
The failure of a power transformer is almost always a catastrophic event that will cause the system to fail, and the result will be a messy cleanup job. The two primary enemies of power transformers are transient overvoltages and heat.

Power input to a transformer is not all delivered to the secondary load. Some is expended as copper losses in the primary and secondary windings. These I2R losses are practically independent of voltage; the controlling factor is current flow.

To keep the losses as small as possible, the coils of a power transformer are wound with wire of the largest cross section that space will permit. A medium-power, 3-phase power transformer is shown in Figure 4.29.

A practical transformer also will experience core-related losses, also known as iron losses. Repeated magnetizing and demagnetizing of the core (which occurs naturally in an ac waveform) results in power loss because of the repeated realignment of the magnetic domains.

This factor (hysteresis loss) is proportional to frequency and flux density. Silicon steel alloy is used for the magnetic circuit to minimize hysteresis loss.

The changing magnetic flux also induces circulating currents (eddy currents) in the core material. Eddy current loss is proportional to the square of the frequency and the square of the flux density.

To minimize eddy currents, the core is constructed of laminations or layers of steel that are clamped or bonded together to form a single magnetic mass.