Transformer Reactive Component

the readings have been taken on no load and in one hour .so this can be taken as 3kw and 40kva.KVA*pf should give kw.even assuming on no load pf is as low as 0.3 the kw should be 12.Check the manufacturers test certificates for no load losses then u can find out .the meter is not reading correctly.recalibrate and try

The readings make sense as far as being mostly reactive. Since you are monitoring the transformer during a "no-load" state, the majority of current flow should be magnetizing current, which by its nature would explain the reactive power.

Lendog is correct. When dealing with power in AC circuits, there are three vector components to be considered: VARS (or KVARS = kilo Volt Amps Reactive), VA (or KVA = kilo Volt Amps), and W (or KW = kilo Watts). In a standard vector diagram, VARS or KVARS are drawn on the vertical or IMAGINARY axis, W or KW are drawn on the horizontal or REAL axis, and VA or KVA are the resultant vector sum, appearing at an angle THETA measured counterclockwise from the horizontal or REAL axis. THETA is called the Power Factor Angle, and Cosine(THETA) is called the Power Factor.

From the vector diagram that results,

Cos(THETA) = Power Factor = KW/KVA = 3/40 = 0.075

And Theta = ArcCos(0.075) = 85.6987 degrees = almost straight up = Almost all Imaginary or Reactive power, with very little real power being dissipated.

The primary current magnitude is given by VA/V = 40,000/11,000 = 3.6363 amps.

This is what a good transformer's primary winding displays with no secondary winding load. An ideal transformer would display a power factor of 0.0 and a THETA of 90.0 degrees under such conditions. Your transformer is pretty good, but not ideal.

The 3 KW power loss is due to the 3.6363 amperes of transformer excitation or magnetizing current flowing in the primary winding. This causes a power loss in the resistance of the primary winding, and a hysteresis plus eddy current loss in the transformers magnetic core.

Under full resistive load conditions, assuming worse case conditions, I would expect your transformer to have a power factor of at least 0.9, representing a real power output of 0.9 x 400KVA = 360 KW. The transformer's resistive power loss would increase because the real component of the input current would increase, but the imaginary component would remain relatively unchanged (unless you overloaded and saturated the magnetic core which would probably destroy the transformer or at least trip the overload current limiters.)

In any event, very roughly, the input power loss might rise to 3.6KW, which is one percent of 360KW. A one percent loss in a transformer is usually acceptable.

DEar sir

Since this is No load readings that is power fator of the transformer is very less = PF =0.043 . the transformer is drawing more magnetising current . no load loss is more . it is not normal

KWH = √3 v i cosØ

cosØ = KWH / √3 v i = 0.043 in this case .

It depends Upon the Impedence of the Transformer & design details

Regards

I. Dhanaraj Lazarus