Grounding transformers

In summary, a grounding transformer (wye-delta) only allows a small magnetizing current to flow in the wye side under balanced non-fault operation. During single phase to ground fault, the zero sequence currents require a return path, provided by the wye-delta grounding transformer. Without the delta secondary connection, the grounding transformer would only draw useless magnetizing current.
  • #1
KraakeCrest
18
2
Hi

Got some questions regarding grounding transformers (wye-delta), or maybe I should write, I need someone to tell me if my understanding is correct.

First, under no fault operation:
Only a small current will flow in the wye side of the grounding transformer, aka magnetizing current. Because, if the system is balanced, no other current will flow in the wye side, because amp-turns must be balanced (except magnetizing current), and since using KVL around the delta loop yields 0 there are no place for any currents in wye to be "amp-turn balanced". Conclusion: Only a small current is flowing in the wye primary side of the grounding transformer during balanced non-fault operation.During single phase to ground fault:
Because of the single phase to ground fault, zero sequence currents arise. For them to flow they require a return path via neutral or ground back to the source, which is provided by the wye-delta grounding transformer. So for zero sequence current to flow as shown in the picture below, the amp-turns on the wye side of the grounding transformer must be balanced by something. And this something is the delta secondary connection, using KVL around the loop with zero sequence induced voltages, yields something different from zero, and hence currents can flow in the closed loop and amp-turns are balanced.

Without this delta secondary and only a wye primary the grounding transformer would not add anything useful and only draw useless magnetizing current, right?

WYE-DELTA
upload_2017-10-3_16-28-21.png
 
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  • #2
Your understanding is correct.
 

What is a grounding transformer?

A grounding transformer is a type of transformer that is used to provide a low-impedance path for fault currents in electrical systems. It is connected between the neutral point of a power system and the ground, and is designed to limit the voltage rise in the event of a ground fault.

Why are grounding transformers used?

Grounding transformers are used to provide safety and protection in electrical systems. They help to limit the voltage rise in case of a ground fault, which can otherwise cause damage to equipment and pose a safety hazard to individuals.

How does a grounding transformer work?

A grounding transformer works by providing a low-impedance path for fault currents to flow to the ground. This helps to limit the voltage rise in the system and protect equipment and individuals from potential harm.

What are the different types of grounding transformers?

There are two main types of grounding transformers: solidly grounded and impedance grounded. Solidly grounded transformers have a connection between the neutral point and the ground with no impedance, while impedance grounded transformers have a connection with some resistance or reactance, limiting the fault current.

What are the benefits of using a grounding transformer?

Using a grounding transformer has several benefits, including improved safety, protection of equipment from damage, and reduced risk of power outages caused by ground faults. They also help to improve the overall reliability and stability of the electrical system.

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