Why CTs are connected in star on T/F delta connected winding side & in delta on T/F star connected winding side for T/F differential protection?

Sandeep Nautiyal

 Profile Answers by Sandeep Nautiyal Questions by Sandeep Nautiyal

• Jun 5th, 2009

This to compensate the phase shift

bejoyengineer

 Profile Answers by bejoyengineer Questions by bejoyengineer

• Mar 1st, 2009

The differential relay will not activate when we energize the transformer as the relay will activate only if there is a difference in the flow of current and that to if it exceeds the setting values.

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Why does wattmeter's reading go negative?

bittu123

 Profile Answers by bittu123 Questions by bittu123

• Nov 9th, 2011

Suppose, phase difference between V and I is "A"(angle). and wattmeter reads +ve. Now if phase difference became (A+180), wattmeter will read -ve of same magnitude.

It simply means, direction of power flow gets changed just because of changing in direction of either current or voltage

SURAJTHEGREAT

 Profile Answers by SURAJTHEGREAT Questions by SURAJTHEGREAT

• Mar 3rd, 2009

If you have seen the wattmeter ratings, it will be (300V,10A,UPF) (Voltage, Current, Power Factor) That is wattmeter needs voltage and current to measure power.  So a wattmeter consists of t...

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What do you mean by skin effect?

sindhejs

 Profile Answers by sindhejs Questions by sindhejs

• Feb 16th, 2009

Tendency to concentrate the electrons towards the outer surface of the conductor is the Skin effect. It can be avoided by small dimension cables instead of large dimension.

vinod25988

 Profile Answers by vinod25988 Questions by vinod25988

• Dec 1st, 2008

As the answers given are correct. It is a loss if the diameter of the conductor is large.So skin effect have to be prevented

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Why is alternating current used for transmission?

bonanova

 Profile Answers by bonanova Questions by bonanova

• Mar 6th, 2009

To reduce I-squared x R loss, transmission is done at voltages much higher than what is usable by consumers.  Transformers can easily raise AC voltage for transmission and then lower it for consumption.  The same cannot be done for DC power.

Nwannaa

 Profile Answers by Nwannaa Questions by Nwannaa

• Jan 22nd, 2009

Alternating current is used for transmission because it is easier to transmit AC over high distance at high Voltage levels.It is also more flexible to handle AC at different levels of transformation t...

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Why does Table Fan rotates Clockwise while Ceiling Fan rotates anti-clockwise? Any technical reason?

Nitin Banegaon

• Oct 29th, 2015

Normally, any motors rotates in anticlockwise direction as seen from non driving end. So in ceiling fan blades are attached to non driving end. So it seems to rotate in anticlockwise. While in table f...

shaik abrar

 Profile Answers by shaik abrar Questions by shaik abrar

• Jan 17th, 2010

When we provide supply to the stator of ceiling fan emf is generated. The set up of rotor and stator in ceiling fan is such that due to flux emf generated is in clockwise direction. As ...

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Why capacitors are not used in 3 phase induction motors?

mohann2008

 Profile Answers by mohann2008 Questions by mohann2008

• Apr 11th, 2009

In three phase induction motors, capacitors are not needed, because when the current passes through? three wires, three magnetic fields will be produced. Due to the interaction between those magnetic fields, RMF will be produced automatically without the help of capacitors.

naresh20047038

 Profile Answers by naresh20047038 Questions by naresh20047038

• Mar 20th, 2009

In 3 phase Induction motors rotating magnetic field will be created which in turn interacts with the rotor conductors resulting in rotation of rotor, so there is no need of capacitors for starting pur...

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How can we find u1,v1,w1 and u2,v2,w2 in three phase motor when operating in delta as we have on identification on motor lead which comes out from winding.

siddharth

• Jan 27th, 2015

P=VI,
V=I/R,
cu.losses=I*I*R

bineet

• Jan 4th, 2015

How to check the Windings of a 3-Phase AC motor The rotor of a squirrel-cage motor There are several different AC motor types, each one with different operating and mechanical characteristics. The mo...

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Does lightening contain voltage or current, Explain.

shrinirmal

 Profile Answers by shrinirmal Questions by shrinirmal

• May 1st, 2009

An electrical discharge between cloud and earth, between the charge centre of the same cloud is known as LIGHTENING,A direct or indirect lightening stroke on a transmission line produces steep-fronted voltage wave on line, the voltage of this wave may be rise?from zero to peak value.

gdhana2006

 Profile Answers by gdhana2006 Questions by gdhana2006

• Apr 25th, 2009

You just imagine a heavy source accumulated in the form of clouds at the sky. You just think the very nearest contact point of earth potential to the cloud. Eg Tower, Lighting arrester etc. Once ...

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How is UPF Wattmeter different from LPF Wattmeter?

Siva

• Apr 21st, 2017

LPF Watt meters are specially designed to measure the power at low power factor (inductive circuits).

UPF type Watt meters are not so accurate in measuring power at low factor (resistive circuits).

sharath

• Oct 28th, 2011

LPF watt meter is used for measuring power in highly inductive circuits & UPF watt meter is used for measure power in resistance circuit in which the power factor ranges from 0.5 to unity.

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Considering the short circuit fault, which switchgear is preferable, SFU OR MCCB? Which operates faster?
which one is popular in Indian Market and why? 2) Define SCPD. What is type2 co-odination?

3) Why the contactor rating is higher for the fuseless selection than for fuse selection? whether the ratinf of SFU or MCCB remains the same in both the cases?

4) If...

veena_gyanchandani

 Profile Answers by veena_gyanchandani Questions by veena_gyanchandani

• Feb 24th, 2010

2) SCPD - Short Ckt. Protection Device.eg - SFU.Type 2 coordination says that there should be no danger to personnel as well as no damage to the controller for downstream faults.Light contact welding ...

veena_gyanchandani

 Profile Answers by veena_gyanchandani Questions by veena_gyanchandani

• Feb 24th, 2010

During short ckt. faults, the most reliable switchgear is SFU. It is fastest to operate and takes only few miliseconds. The operator just has to replace the fuse.MCCB is good for overload protection.

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Why tapings of Transformer is always provided on HT side? why not on LT side?

ravs42

 Profile Answers by ravs42 Questions by ravs42

• Aug 21st, 2010

It is because of two reasons1.high voltage regulation.Large range of voltage can be obtained.2.less current value on the HV side,as a result,no sparking problem.

Raman Jain

 Profile Answers by Raman Jain Questions by Raman Jain

• Dec 3rd, 2009

Tapings in transformers are provided at HV side . The reasons are : 1. Less current has to be handled .2. As the LV windind is wounded first i.e near the core and HT winding is wounded on the top of the LV winding. So it is easier to provide Taps on HV side.

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Why 2-phase induction motors are NOT used in industries even though they have rotating magnetic field.

abhinav Kumar

• Sep 6th, 2015

Two phase motor essentially use in domestic use like water pump set ... It gives high torque and low efficiency. The phase diff 180 or 90 make the two phases with the help of capacitor.

anilsabaji

• Mar 11th, 2012

2 Phase motors have low efficiency and low power factor. There are higher chances of stalling.

MOST IMPORTANT: 2 phase load will create imbalance in the power system and high current and bulky too. Why should we use it when we have more efficient 3 phase induction motors

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Why armature control is used, not the field control for DC motors?What is the drawbacks in field control method?

chiragmistry

• Mar 14th, 2014

In case of the dc motor the armature control mathod is used blow the based the motor is run below the based speed Because,above based speed motor react as generator.

AHORDZI ERIC

• Nov 20th, 2013

What is ammeture reation

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Will u please give the formula, for selection of cable sizing (both Copper and Aluminium) depend upon the electrical loads...

ENGR.MUHAMMAD YOUNAS KHAN

• Mar 24th, 2014

CABLE SIZING FORMULA:-2 *L * I/(K*Vd) ...............FOR SINGLE PHASE LEGEND:- I :- LOAD CURRENT =160 AMPS L :- LENGTH OF THE CABLE = 200 METERS K :- CONDUCTIVITY OF COPPER = 58 AND CONDUCTIVITY OF...

mahmoudp1

 Profile Answers by mahmoudp1 Questions by mahmoudp1

• May 3rd, 2012

It depends on a lot of factors like current density for mm^2 temperature is the cable on cable trays or buried or inclosed in PVC is that a 3 phase cable multicore or what and also depends on the voltage but in general making a current density 2 A/mm^2 for copper for simple applications is good.

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1)What is the latest generation of circuit breakers called?

2)What are the special cables required for explosion proof wiring?

3)What are the different types of soft starters for large motors?

4)What is the similarity and what is the difference between relays and PLC?

priyobrato

• Dec 7th, 2014

Relay can be used as potential free dry contact,with less switching speed cause its a electro mechanical device .PLC has better switching speed.BOTH are controlling device.

Chakry

• Nov 30th, 2014

The cables used in Inflammable and explosive situations should be Mineral insulated Copper sheathed complying with BS 6207.

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Why isolation tranformer used in mcc panel?

Niaz

• Jul 14th, 2013

Isolation transformer at MCC are usually Y-Delta connected, so a fault on low voltage Y side would not travel towards high voltage delta circuit, so providing isolation to HV side

Raman Jain

 Profile Answers by Raman Jain Questions by Raman Jain

• Dec 3rd, 2012

To reduce the fault level.

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what happens when we apply ac voltage to a DC motor (nothing but if any DC motor)?

atul sudhakar

• May 2nd, 2014

Depends if it is dc shunt motor it will not work but if its a dc series motor it might

Shuvendu Das

• Nov 8th, 2013

Excess heat would be produced due to hysteresis and eddy current loss

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pralhad

• Jan 25th, 2015

At the time of British rules the standard equipments designed in India are for 50hz so the power is also generated at 50 hhz...and now its impossible to create new equipment which will run on other frequency

jyotsna

• Jan 15th, 2015

Because all the equipement based on 50hz frequecy na our country economical condition is not good and when we required more than 50hz frequecncy then all the equipment are failed

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We are using neutral in Star Circuit and same in Delta Circuit is not used. What is the reason? Explain in brief.

Maheshkanna

• Nov 9th, 2015

Neutral is used to close a circuit but delta circuit is already closed so the neutral connection not used in delta circuit.

bala

• Oct 23rd, 2015

Normally delta connection is arrived by connecting two terminals of successive phase in a closed path and there is no common point of reference. But in case of star network one terminal is common to all phase thus creating a neutral.

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What happens if load increases when the generation is constant?

Mayilsamy Kasipandi

• Jul 11th, 2017

Load increases when power is constant - Result voltage drop depending upon the load

Ravi

• Mar 7th, 2017

The excess load draws more current from source. since the the power is constant in source side, voltage on load side drops and losses are more and power factor reduced.

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