What are the differences between power transformer and distribution transformer?

Power transformer Distribution transformer
Power transmitted High low
Voltage Step up or Step down Step Down
Size Large small
Application Transmission lines and generating stations To transmit the power to end user.
Load fluctuations Less (constantly operated) High (as the loads will be disconnected and connected)
Tap changer Off-load tap changer On-load tap changer to encounter the load fluctuations
Losses Heat losses are high because of high rated current Heat losses are low because of low rated currents
Place Indoor (Generally) Outdoor (near end user)

Advantages of iron core transformer?

  • The magnetic reluctance of iron is less so that it allows more flux through it.
  • Efficiency is high compared to air core
  •  Heat losses are less.
  • It is used for low frequencies (<10KHz).

 Advantages of air core transformer?

  • It is used for the high frequencies (>10KHz).
  • Core saturation problem is not there in air core.
  • Simple in construction.
  •  Size is less because of no iron.
  • Cost is less.
  • Magnetization losses are less in air core compared to iron core.

What is isolation transformer?

Isolation transformer is a static machine used to isolate the two circuits and provides a magnetic coupling between two circuits. It avoids the coupling losses and provides better safety to the both the circuits from the fault in other circuit. As the name specifies it provides only isolation, so the primary and secondary windings turns are same to ensure that there is no change in signal quantities like voltage and current.

What is transformer tap changer?

A tap changer is a device used to change the primary or secondary voltage of the transformer by changing the turn’s ratio without remodeling the transformer. The primary function of the transformer is it removes or connects some portion of the winding either load side or source side. The importance of tap changer is maintaining the load side voltage constant irrespective of load variations. There are two types of tap changer one is off-load changer and on-load tap changer.  

What is off-loading tap changer?

Off-load tap changer works on the principle “Break before Make” which breaks the current flow and makes the new tap connection. So this tap changer works when there is no current flow in the transformer windings i.e. it cannot work even when the transformer is energized because it can break the magnetizing current. It is nowadays called as De-energizing tap changer instead of No-load or Off-load tap changer.

What is on-load tap changer?

 On-load tap changer is device which operates and changes the tap connection even when the transformer is supplying the load. This works on the principle of “Make before Break” which makes the new circuit before breaking the old tap circuit. It is very important invention that it can keep the transformer load voltage irrespective of load varying during operation itself.

What is the difference between isolating and shielding transformer?

Isolating transformer: This transformer is used to provide isolation between primary and secondary to protect the winding from the faults.

Shielding transformer: In high power applications the isolation transformers are provided with shielding plates between primary and secondary to reduce the high frequency noise in the transformer. When high frequency surge pulse is introduced in system, the capacitor near primary winding creates a short circuit path and diverts this pulse to the ground.

Shielding Transformer

Shielding Transformer

What is the difference between instrument and protection transformer?

Instrument transformer is used to measure the signal parameters (voltage and current) to indicate in the meters (voltage and current) where as protection transformer measuring signal is used for relay operation for protection of transformer.

Instrument transformer can be operated at near core saturation limit as the meter indicates up to rated values but the protection transformer should be available for 50 % higher than rated current so these should be operated below the core saturation.

The accuracy should be high for Instrument transformers where as in protection it can be somewhat less.

What is the impact if the 60 Hz transformer is operated at 50 Hz transformer?

The 50 Hz transformer can be operated at 60Hz for some cases but 60 Hz transformer cannot be operated for 50Hz. Because as the frequency decreases the flux increase for a constant voltage.

Fi = volateg/flux

The increase in flux leads to core saturation.

What happens if the input voltage of the transformer is higher than name plate?

The transformer cannot be operated more than 10% higher than the rated voltage because if the primary is high therefore secondary also increases which leads to increase in power rating of a transformer. This increases the heat losses and may damage the transformer. The second one is that if the voltage is increased beyond the rated value at rated frequency then the flux will increased in the transformer

Flux = Voltage/frequency

The increase in flux leads to core saturation and heating affect and degrades the transformer performance.

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