What is the purpose of back up impedance protection in main generator?

What is the purpose of back up impedance protection in main generator?  
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1 Answer

Answer :

Covers inter-phase faults both externals to the GT and in GT. This also covers partially faults inside generator, time delayed to coordinate with 230 kV-distance protection. 
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Description : What is the basic purpose of class-B protection?

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Description : Purpose of standby E/F protection in SUT/UT? 

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Why the earthing transformer primary voltage is 16.5 kV rated in main generator even though actual voltage during the E/F is root 3 times less?

Description : Why the earthing transformer primary voltage is 16.5 kV rated in main generator even though actual voltage during the E/F is root 3 times less?

Last Answer : The transformer should not saturate during E/F otherwise it will cause ferroresonance with the GT winding capacitance. Dangerous O/V and neutral shifting will occur. During loss of load or field ... saturation. Saturation can also occur due to point on wave of application causing flux doubling. 

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Description : What precautions should be taken while meggering main generator?

Last Answer : All PT’s are racked out. Earthing transformer grounding terminals disconnected. Barring gear shall be kept off. Stator water shall be drained fully and hot air blown through conductors. Generator flexible lines shall be disconnected to isolate GT/UT. 

What are the working principles of generator main protections?

Description : What are the working principles of generator main protections?

Last Answer : GENERATOR START UP PROTECTIONS SUPPLEMENTARY PROTECTION OF GENERATOR The generator is normally expected to run rated speed before excitation power is applied by closing the field breaker. ... position to ensure that the protection is inoperable when the machine is connected to grid.  

How main generator earthing is done?

Description : How main generator earthing is done?

Last Answer : Generator neutral earthing is done through transformer and earth fault current is limited through resistance, which is connected across the secondary of the transformer. Generator 16.5 kV earth fault current is isolated from 220 kV through GT. Only star point of the generator is grounded. 

Write nameplate details of the main generator.

Description : Write nameplate details of the main generator. 

Last Answer : Type THW-235 kW 237700 kVA 264000 Voltage 16500 V Amps 9240 A Power factor 0.9 lag. Field voltage 326 V Field current 2755 A Insulation Class-F Speed 3000 rpm 50 Hz, 3, double star connection. 

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Description : Why cannot we have cables instead of bus duct in main generator? 

Last Answer : Very large number of cables in parallel required problems of sealing the terminations. 

When the hydrogen explosion will take place in main generator?

Description : When the hydrogen explosion will take place in main generator?

Last Answer : When hydrogen concentration in air is more than 4% and less than 74% causes the explosion.