Why the neutral is earthed through earthing resistance in case of UT and SUT?

Why the neutral is earthed through earthing resistance in case of UT and SUT? 
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1 Answer

Answer :

This is done to limit the earth fault current.  
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Related questions

Why UT, SUT secondary is rated for 6.9kV where as bus voltage is 6.6kV?

Description : Why UT, SUT secondary is rated for 6.9kV where as bus voltage is 6.6kV? 

Last Answer : The no load secondary 6.9kV voltage level adequately takes into account voltage drop during loaded condition to cater station buses at 6.6kV level. 

Why REF is provided in the LV side of SUT and UT?

Description : Why REF is provided in the LV side of SUT and UT? 

Last Answer : The LV sides of the two transformers are earthed through the resistance. This will limit the flow of current in case of LV earth fault. Hence the differential protection may not act for a LV earth fault. Hence ref protection is provided. 

What is the vector group of GT, UT, SUT?

Description : What is the vector group of GT, UT, SUT?

Last Answer : Yd11 Dy1 Yy0 

During unit operation, can we parallel UT & SUT continuously?

Description : During unit operation, can we parallel UT & SUT continuously?

Last Answer : No, due to switchgear limitation.  

What is E/F current limit for SUT and UT?

Description : What is E/F current limit for SUT and UT?

Last Answer : 400a limited by 10 ohms resistor.  

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

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

Last Answer : Back up for LV winding, LV neutral CT- CDG 12 – resistance earthing – relay set high time delay to discriminate with LV feeder and trip transformer if sustained E/F, also protects neutral earthing resistor.

What is the neutral point earthing and its advantages?

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Last Answer : In substation all the neutrals of rotating machines, transformers, busbars and other equipment are connected to ground. Some of the advantages are: Earth fault protection is based on the method of ... , grounding of neutral helps to reduce the over-voltages which occur on the one healthy phases

Why we do 2 types of earthing on transformer i.e.: body earthing & neutral earthing, what is function. I am going to install a 5oo kva transformer & 380 kva DG set what should the earthing value?

Description : Why we do 2 types of earthing on transformer i.e.: body earthing & neutral earthing, what is function. I am going to install a 5oo kva transformer & 380 kva DG set what should the earthing value?

Last Answer : The two types of earthing are Familiar as Equipment earthing and system earthing. In Equipment earthing: body (non conducting part) of the equipment should be earthed to safeguard the human ... earthing will be further classified into directly earthed, Impedance earthing, resistive (NGRs) earthing.

Why control transformer is earthed?

Description : Why control transformer is earthed?

Last Answer : If it is not earthed grounding of control circuit at two different places can cause bypassing of logics. In case of primary and secondary of the control transformer is getting the main fuse ... 415v will be superimposed in the control circuit during short circuit of primary and secondary winding)

A bird sitting on a high tension electric wire does not get electrocuted because – (1) it has high resistance (2) the body is earthed (3) it does not form a closed path for the flow of current (4) its feet are good insulators

Description : A bird sitting on a high tension electric wire does not get electrocuted because – (1) it has high resistance (2) the body is earthed (3) it does not form a closed path for the flow of current (4) its feet are good insulators

Last Answer : (3) it does not form a closed path for the flow of current Explanation: Electricity travels from a place of high voltage to low voltage, just as water travels from high elevation to low ... When electricity travels through a body in this fashion, electrocution takes place, and the bird can die.

A bird sitting on a high tension electric wire does not get electrocuted because (1) it has high resistance (2) the body is earthed (3) it does not form a closed path for the flow of current (4) its feet are good insulators

Description : A bird sitting on a high tension electric wire does not get electrocuted because (1) it has high resistance (2) the body is earthed (3) it does not form a closed path for the flow of current (4) its feet are good insulators 

Last Answer : it does not form a closed path for the flow of current

What are the protections for SUT?

Description : What are the protections for SUT? 

Last Answer : a) Over current protection for phase and earth fault b) Differential protection c) HV and LV restricted earthfault protection  d) HV side directional back up over current protection for phase ... protection f) Over fluxing protection g) Buchholz and high oil, winding temperature protection. 

Why vector group of SUT is chosen as Yn-Yo-Yo?

Description : Why vector group of SUT is chosen as Yn-Yo-Yo?

Last Answer : To facilitate momentary paralleling of SUT with UT on 6.6kV buses.  

Why twin secondary SUT?

Description : Why twin secondary SUT? 

Last Answer : As per is, the rating single secondary power transformer is limited to 25MVA (6.6 kV) or 40 MVA (11 kV), in order to limit the 3 phase symmetrical fault level with in 26-40 kA (contribution from grid and local machines) 

During unit operation, can we parallel 2 SUT?

Description : During unit operation, can we parallel 2 SUT? 

Last Answer : No, due to switchgear limitation. 

What is the coverage of differential protection for SUT?

Description : What is the coverage of differential protection for SUT?

Last Answer : Covers from 230 kV bushing to 6.6 kV breaker end.  

Why REF is now is used for HV side also in GT/SUT?

Description : Why REF is now is used for HV side also in GT/SUT?

Last Answer : The E/F setting of differential is poor.  

What is different between resistance grounding system and resistance earthing system?

Description : What is different between resistance grounding system and resistance earthing system?

Last Answer : In resistance grounding system the neutral point of the load is connected to the ground to carry the residual current in case of unbalanced conditions. Resistance earthing system is done in an electric equipment in order to protect the equipment in occurrence of fault in the system.

Write down difference between equipment earthing and neutral earthing.

Description : Write down difference between equipment earthing and neutral earthing. 

Last Answer : Sr. No. Equipment earthing Neutral earthing 1 Connection of the non-current carrying metallic parts of the electrical equipment to earth is called as equipment earthing. Connection of the neutral ... 6 It is an equipment earthing. It is a source or system earthing.

State the methods of Neutral Grounding. State difference between Earthing and grounding.

Description : State the methods of Neutral Grounding. State difference between Earthing and grounding. 

Last Answer : Neutral Grounding connections are of three types:  1. Solid earthing 2. Resistance earthing 3. Reactance earthing SR. NO. Earthing Grounding 1 Earthing means connecting the dead part ... earthing provides suitable means for earth fault protecting system.  10

What are the protections for UT?

Description : What are the protections for UT?  

Last Answer : a) Differential protection b) LV restricted earthfault protection c) LV back up earthfault and over current protection d) Buchholz and high oil, winding temperature protection. 

Why main generator/UT is not provided with separate overfluxing protection?

Description : Why main generator/UT is not provided with separate overfluxing protection?

Last Answer : Since GT is provided with overfluxing protection, it is adequate to protect main generator / UT also. Main generator can withstand higher degree of overfluxing. If a generator CB is used, separate overfluxing protection is essential for main generator. 

During unit operation can we have one UT feeding both unit 6.6 kV loads?

Description : During unit operation can we have one UT feeding both unit 6.6 kV loads? 

Last Answer : No, logically prevented.  

Where fault level is more, whether in generator bus duct or UT bus duct? Why?

Description : Where fault level is more, whether in generator bus duct or UT bus duct? Why?

Last Answer : Fault level is more in UT bus duct. Because the fault currents fed by the both generator and GT adds up within UT bus duct in case there is a fault in UT bus duct. 

An electrical appliance is earthed to 1. Protect the appliance against any damage 2. Prevent electric shocks 3. Avoid short-circuiting Which of the above is/are correct? (a) 1 only (b) 2 only (c) 1 and 2 (d) 2 and 3

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Last Answer : Ans:(b)

Can I wear any type of footwear and still be earthed?

Description : Can I wear any type of footwear and still be earthed?

Last Answer : No. Standard plastic/rubber or composite soles do not conduct the Earth's electric energy. Most shoes today are made from those materials. You need leather or hide soles, which used to be ... . Hopefully soon shoe companies will begi shoe companies will begin making n making grounded grounded shoes.

In a semiconductor diode, p-side is earthed and to n-side is applied a potential of -2 volt; the diode shall (a) Conduct (b) Not conduct (c) Conduct partially (d) Break down

Description : In a semiconductor diode, p-side is earthed and to n-side is applied a potential of -2 volt; the diode shall (a) Conduct (b) Not conduct (c) Conduct partially (d) Break down

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State the various types of earthing.

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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?

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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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Last Answer : The voltage generated in the shaft due to the leakage fluxes can circulate current through the shaft. If shaft earthing is not done the leakage current will flow through the bearings to ground and pitting of bearings will result. Hence bearing foundation and pipelines are insulated. 

Why shaft-earthing brush is different from normal brush?

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What should the statutory provision of earthing?

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Home Earthing Of Resistance How much? To be Need ?

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What should be the value of earthing resistance for large power stations?

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From the point of view of safety, the resistance of earthing electrode should be

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