What is the purpose of a grounding transformer?

What is the purpose of a grounding transformer?

Grounding transformers are used to provide a ground path to either an ungrounded “Y” or delta connected system. Large multi-turbine wind farms often require Grounding transformers for fault protection on ungrounded lines.

How do you size a zig-zag transformer?

zig-zag transformer is sized for 3 < X0/X1 <10. That is to say that the short-circuit current phase to ground should be equal to or less than the three-phase short circuit.

What is a zig-zag grounding transformer?

The Zigzag grounding transformer is a commonly used option. It is a three-phase, dry-type, air- cooled auto-transformer with no secondary winding. Each phase has two identical windings, which are wound in opposite directions to give the high impedance to normal phase currents.

How do you size a neutral grounding resistor?

The main challenge in designing an HRG system is determining the proper ohmic value for the neutral-grounding resistor. The primary rule is that the NGR should be sized so that ground-fault current is equal to or slightly greater than the system charging current.

How do you calculate NGR?

Once the current rating is determined, the Resistance or Ohmic Value of the resistor is calculated by dividing the Line to Neutral Voltage by the Current Rating. i.e. for a 4.16 kV System Neutral Grounding Resistor rated at 400 A. The line to Neutral Voltage will be 4.16 kV /√(3) = 2400 V.

What happens if you don’t ground a transformer?

There is no return circuit to earth and therefore nothing can flow through you to earth and back to the transformer to cause a shock. One may therefore safely touch EITHER output lead and not receive a shock as there is no earth reference. However touching BOTH output leads simultaneously will give one a shock.

How are transformers grounded?

If a neutral-to-case bond is made at both the transformer and at the secondary panelboard, neutral current will flow through metal raceways (and on the grounding and bonding path) on its return to the power supply. In this case it permits the use of a wye connected transformer to establish a neutral grounded point.

What is ground Wye?

Solidly-grounded Wye System The solidly-grounded system is the most common system arrangement, and one of the most versatile. The most commonly-used configuration is the solidly-grounded wye, because it will support single-phase phase-to neutral loads.

What is a corner grounded Delta?

Corner-Grounded Delta System A system in which the transformer secondary is delta-connected with one corner of the delta solidly grounded. Ungrounded System A system without an intentional connection to ground, except through potential indicating or measuring devices.

Why neutral is grounded in transformers?

Connecting to ground at the transformer (or at the incoming connection point, depending on local regulations) ties the return conductor to ground and effectively “neutralises” it. Because it presents a low risk of significant voltage on it the neutral lines are normally unfused.

How do you select NGR?

The following factor should be considered before selecting the NGR resistance value.

1. The fault current should be kept in mind while deciding on the NGR value.
2. The system capacitance should be taken care, the NGR should discharge the capacitor during the earth fault.
3. System voltage should be considered.

What is the size of a grounding conductor?

The NEC-minimum conductor size for a ground ring is 2 AWG, but sizes as large as 500 kcmil are more frequently used. The larger the conductor and the longer the conductor, the more surface area is in contact with the earth, and the lower the resistance to earth.

What is the size of a grounding electrode?

A plate electrode that exposes no less than 2 square feet (0.186 m2) of surface to exterior soil shall be considered as a grounding electrode. Electrodes of iron or steel plates shall be at least 1⁄4 inch (6.4mm) in thickness. Electrodes of nonferrous metal shall be at least 0.06 inch (1.5mm) in thickness.

What is ground transformer?

Grounding Transformer. The grounding transformer is used to provide a path to an ungrounded system or when the system neutral is not available for some reason, for example, when a system is delta connected. It provides a low impedance path to the neutral and also limits the transient overvoltage when the ground faults occur in the system.