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.