(1, 2, 3) 025 Test, connect transformers

What symbol in a circuit signifies a transformer?

What can transformers do?

Transform voltage into current (step down), transform current into voltage (step up), and provide isolation (isolating transformer)

How do isolating transformers work?

No physically conductive path between ground and appliance, no electrocution

How does transformer work?

AC run through cable produces changing electromagnetic field if wound into coil (primary coil), EMF mutually inducts an iron or iron-based core which then mutually inducts another coil (secondary coil)

What is high- and low- tension windings?

high-tension has more turns than low-tension

What is the formula relationship between voltage, current and turns?

N1/N2 = V1/V2 = I2/I1

Name these cores?

Toroid, Shell, Core

Name these winding formats?

Sandwich, Side-by-side, Concentric

What is an autotransformer?

Instead of two coils wrapped around opposite ends of a looped core, the two coils are wrapped around each other and the straight core. The secondary is tapped at certain turns in order to provide more dynamic voltage control.

What is a current transformer?

Transformer placed around cable with low amount of secondary turns, amps provide current reading in main cable

What are some benefits/negatives between autotransformers and double wound transformers?

Autotransformer secondaries are more likely to affect primary in fault and theres no electrical insulation between primary and secondary, but double wound transformers are larger + less efficient for the same rating with worse voltage regulation

What is the types of losses in a transformer?

MAGNETIC LEAKAGE: EMF not going through second winding, useless leakage flux. WINDING RESISTANCE: Conductor has resistance, heat loss within transformer

What are transformer cores made of?

laminated high-grade silicon steel or amorphous steel

Why are transformer cores laminated?

Reduces hysteresis loss (energy needed to magnetise core at 50Hz)

How does a shell type transformer work?

Both primary and secondary coils wound together on middle branch, flux travels efficiently as it goes down the middle branch and up both side branches equally

What is no-load current made up of?

Magnetising current (lags voltage 90 degrees) and iron current (provides energy to overcome hysteresis + eddy current losses). Equal to phasor sum of magnetising and iron loss current.

What is the EMF equation in a transformer?

Vi=4.44*f*N*Φm, where Vi = induced emf (v), f = supply frequency (Hz), Φ = core flux (Wb), N = winding turns amount, 4.44 = sine wave constant

Mutual inductance in a transformer happens when…?

primary’s changing current induces voltage in the secondary

What is reluctance?

Measure of opposition to flow of magnetic flux. Basically magnetic resistance.

What are the single-phase and three-phase formulas for VA? (apparent power)

S=V2*I2 for single phase and S=√3*VL*IL for three phase, where both current and voltage measure secondary winding