Answer / k.prakashchandra

Isolate all phase windings at both ends and measure IR of
each phase to body and between windings

Answer / subash

A. Purpose and Theory

The IR test measures the resistance of the electrical
insulation between the copper conductors and the core of
the stator or the rotor. Ideally this resistance is
infinite, since after all, the purpose of the insulation is
to block current flow between the copper and the core. In
practice, the IR is not infinitely high. Usually, the lower
the insulation resistance, the more likely it is that there
is a problem with the insulation.

PI is a variation of the IR test. PI is the ratio of the IR
measured after voltage has been applied for 10 minutes
(R10) to the IR measured after one minute (R1), i.e.:

PI = R10/R1

A low PI indicates that a winding may be contaminated with
oil, dirt, insects, etc. or soaked with water. In the test,
a relatively high DC voltage is applied between the winding
copper and the stator or rotor core (usually via the
machine frame). The current flowing in the circuit is then
measured

Answer / nithin

Insulation resistance of alternator is checked using a megger and before measuring it the connections to the protective devices like CT,PT and also the connection to the AVR to be disconnected. Then the star connection of the winding to be disconnected ,then we can check IR value

i am completed my degree(B.E EEE) 2014 anychance to get electrical licence plz help me

0 Answers   JLL,

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in transformers for ex. 100mva and 400kv the secondary current is about 420 amps but for selection of bushing the capacity of selected bushing is 2000A why there is such big difference ?

2 Answers   ABB,

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What are the protective devices in a DC/AC motor starter?

1 Answers   CTS,

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can u please mail me the syllabus for GET exam for damodar valley corporation?

0 Answers  

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What is E.M.F ?

6 Answers  

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A commercial Building is designed with 14th floor levels with indoor substation of three phase transformer with rated capacity of 1000 Kva.The transformer delivered 65% of its rated capacity at 0.67 power factor lagging.Because of low power factor, the power customer was penalized and certain cost was charged accordingly based on every point percentage lower than 85%.This situation may repeatedly happen on the succeding energy bills of power customer.The power customer is desired to improve its historical power factor of 0.67 lagging and no further penalty be impose by the local power company on the next bill. Q: Identify the appropriate solution you want to offer to Client?.Justify SCIENTIFICALLY and MATHEMATICALLY the principles behind the solution.

0 Answers  

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hw to calculate flc of motor ? data are:3-phase,50Hz,30kw

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a power supply to be constructed from voltage cells is required to provide Max. 20A Current with a terminal voltage of 6v.Several voltage cells are available each of which has terminal voltage of 1.5V & each of which can supply a max current of 5A .the no of cells required will be ??

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what is the formula for computing cable tray size & capacity

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what is ideal transformer?

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1)What will happen when 240 VDC supply is connected to 240VAC supply(DC supply +ve is connected to phase of AC supply & DC supply is to neutral of AC supply). 2)Also what will happen when 240 VDC supply is connected to 240 VAC supply in reverse polarity as of Sr. No 1.

2 Answers  

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what happens when a power transformer neutral earthing broken???

11 Answers   MacLellan,

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