Transformer Lecture Notes

Vocabulary-style flashcards covering transformer principles, construction, types, parameters, tests, and fittings based on the lecture transcript.

Transformer

A static device that transfers electric power from one voltage level to another voltage level while keeping frequency constant, operating on the principle of electromagnetic induction.

Laminated Core

A part of the transformer constructed of silicon sheet steel laminations assembled to provide a continuous magnetic path with a minimum air gap.

Primary Winding

The winding of a transformer that is connected to the supply mains.

Secondary Winding

The winding of a transformer from which the output voltage is taken.

Core type transformer

A type of transformer construction where the iron core is surrounded by the windings.

Shell type transformer

A type of transformer construction where the windings are surrounded by the iron core.

Distribution Transformer

Transformers up to a size of about $200\,KVA$ used to step down distribution voltage to standard service voltage, operating $24$ hours a day.

Power Transformer

Transformers with ratings above $260\,KVA$ used at generating stations and substations for stepping up or stepping down voltage, disconnected during light load periods.

Ideal Transformer

A transformer consisting of two purely inductive coils on a loss-free core, with negligible winding resistance, no magnetic leakage, and constant permeability.

Transformation Ratio ($K$)

The ratio defined as $K = \frac{E_2}{E_1} = \frac{T_2}{T_1}$. A transformer is step up if $K > 1$ and step down if $K < 1$.

No load current ($I_0$)

A very small current that lags the applied voltage by an angle of about $80^{\circ}$ to $85^{\circ}$, with a power factor of about $0.1$ to $0.2$ lag.

Loss component ($I_c$)

The component of no load current in phase with the applied voltage, calculated as $I_c = I_0 \cos(\phi_0)$; it represents core losses.

Magnetizing component ($I_{\mu}$)

The component of no load current in phase with the flux or in quadrature with the applied voltage, calculated as $I_{\mu} = I_0 \sin(\phi_0)$, and is greater than $I_c$.

Regulation of Transformer

The ratio of the change in secondary terminal voltage from no load ($E_2$) to full load ($V_2$) relative to the secondary rated voltage ($E_2$), expressed as a percentage.

Copper losses

Variable losses that occur in the transformer windings due to resistance and are proportional to the square of the load current.

Iron losses

Constant losses occurring in the core, subdivided into hysteresis and eddy-current losses; they depend on supply voltage and frequency but are independent of load current.

Efficiency

Defined as $\frac{\text{output power}}{\text{output power + total losses}}$. It is maximum when variable copper losses equal constant iron losses.

All day efficiency

The ratio of Kwh output per $24$ hours to the sum of Kwh output and Kwh wasted as losses in $24$ hours; it is always less than commercial efficiency.

Open Circuit (O.C.) Test

A test conducted on the LV side at rated voltage to estimate iron losses, the magnetizing branch of the equivalent circuit, and no load power factor.

Short Circuit (S.C.) Test

A test conducted on the HV side by shorting the LV side to estimate full load copper losses, series elements of the equivalent circuit, and voltage regulation.

Sumpner's Test

Also called a Back to Back test, it is used to estimate efficiency, regulation, and temperature rise when two similar transformers are available.

Auto Transformer

A transformer that transfers power both conductively and inductively; the power transferred inductively is $(1-K)$ times input and conductively is $K$ times input.

Scott connection

A method (Tee-Tee) used for the conversion of three-phase supply to two-phase supply or vice versa.

Magnetostriction

The property of magnetic material causing small changes in linear dimensions, which is a main cause of transformer noise.

Conservator

A tank connected to the transformer that takes care of the expansion and contraction of the oil.

Breather

A device containing silica gel that arrests moisture from incoming air to prevent oil contamination.

Buchholz Relay

A gas-operated device connected between the transformer tank and the conservator that operates when a fault occurs inside the transformer.