What are the reasons for over voltage on transformer secondary?

What are the reasons for over voltage on transformer secondary?

Abstract – When an unloaded power transformer is switched on via a relatively long cable, sometimes ex- treme high voltages appear at the secondary side of the transformer. These overvoltages are caused by a resonant phenomenon that occurs when the resonant frequencies of the transformer and the cable match.

What is the effect of impedance of transformer?

The lower the impedance, the lower the voltage required to produce full load current. Lower imped- ance transformers allow higher fault currents to flow at a particular voltage. Measuring impedance in units of percentage greatly simplifies the calculation of currents and voltages in a power system.

Why do we use Delta Star in transformer?

Delta-Star Connection of Transformer The main use of this connection is to step up the voltage i.e. at the begining of high tension transmission system. It can be noted that there is a phase shift of 30° between primary line voltage and secondary line voltage as leading.

What causes voltage change in transformer?

This changing magnetic field (and associated magnetic flux) will pass through to the secondary coil inducing a voltage across the secondary coil, thereby effectively coupling the AC input from the primary to secondary component of the transformer.

What are possible reasons for overcharging of the transformer?

A transformer can fail for a variety of reasons, but the most common causes include lightning strikes, overloading, wear and corrosion, power surges and moisture. Regardless of the cause, the result can be remarkable. Transformers contain mineral oil keeping the transformer cool.

What causes impedance in a transformer?

Why is impedance given in a percentage? The percentage impedance of a transformer (Z\%) is the voltage drop on full load due to the winding resistance and leakage reactance expressed as a percentage of the rated voltage.

Why is Wye better than Delta?

An advantage of the Delta connection is higher reliability. If one of the three primary windings fails, the secondary will still produce full voltage on all three phases. An advantage of the Wye connection is that it can provide multiple voltages without the need for additional transformers.

What happens when it is star connected or delta connected?

If the delta connected motor is connected in star, the voltage across the stator winding get reduced to 1/√3 (58\%) of the voltage when the stator is connected in the delta. The torque delivering capacity of the motor is proportional to the square of the stator voltage.

What is the reflected impedance of a transformer?

The reflected impedance is a function of the turns ratio of the transformer. Notice that the ratio of the primary impedance to the secondary impedance is the square of the turns ratio, or 100:1. In other words, a 10:1 turns ratio will give an impedance ratio of 100:1.

What is transtransformer percent impedance?

Transformer percent impedance is a measured value stamped on the nameplate and is actually a voltage measurement.

What is the impedance ratio of a 25-1 turns ratio transformer?

With our 25:1 turns ratio transformer in figure 2, the impedance ratio is the turns ratio squared or, 25 X 25 = 625:1. So if the transformer is working into an 8 ohm load, the impedance that will be reflected to the primary will be the impedance ratio (625) multiplied by the load impedance (8 ohms), equal 5,000 ohms.

How do you calculate the number of turns in a transformer?

The primary turns number should be enough, so the primary winding of the transformer has reactance (it is a coil) four times the output impedance of the source at the lowest frequency of operation. The secondary turns number is equal to the number of turns on the primary, divided by the square root of the impedance ratio.