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The document discusses restricted ground fault protection to limit transformer damage from faults close to the neutral. It can provide differential protection for ground faults down to 5% of the transformer winding. Overflux protection for transformers is also discussed, which can result from overvoltage or low system frequency causing excessive heating and potential damage.

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33 views1 page

Untitled

The document discusses restricted ground fault protection to limit transformer damage from faults close to the neutral. It can provide differential protection for ground faults down to 5% of the transformer winding. Overflux protection for transformers is also discussed, which can result from overvoltage or low system frequency causing excessive heating and potential damage.

Uploaded by

kapenzia
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as EHTML, PDF, TXT or read online on Scribd
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4.

3 Sensitive Ground Fault Protection to limit Transformer Damage Differential and overcurrent protection do not provide adequate protection for wye-connected windings with grounded neutrals. Faults close to the neutral produces lesser fault current as shown by the current distribution curve. The restricted ground fault function can be used to provide differential protection for such ground faults, down to faults at 5% of the transformer winding. Restricted ground fault protection can be a low impedance differential function or a high impedance differential function. The low impedance function has the advantage to being able to precisely set the sensitivity to meet the application requirement. This sensitive protection limits the damage to the transformer to allow quicker repair. The restricted ground fault element uses adaptive restraint based on symmetrical components to provide security during external phase faults with significant CT error. This permits the function to maximize sensitivity without any time delay. Available in the 745, T60. 4.4 Overflux Protection Transformer overfluxing can be a result of Overvoltage Low system frequency A transformer is designed to operate at or below a maximum magnetic flux density in the transformer core. Above this design limit the eddy currents in the core and nearby conductive components cause overheating which within a very short time may cause severe damage. The magnetic flux in the core is proportional to the voltage applied to the winding divided by the impedance of the winding. The flux in the core increases with either increasing voltage or decreasing frequency. During startup or shutdown of generator-connected transformers, or following a load rejection, the transformer may experience an excessive ratio of volts to hertz, that is, become overexcited. When a transformer core is overexcited, the core is operating in a nonlinear magnetic region, and creates harmonic components in the exciting current. A significant amount of current at the 5th harmonic is characteristic of overexcitation. Available in the 745, T60, and T35. Ground fault

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