Using in the equation (7),

2
ಗ್ಯ = = (४) - ५] )2>----= (४1 - Vay) ह ஜு

3 Ty = [(೪] - ५.) -(V, - ५५५)? | (8)
But the medium is air hence ‏ع‎ = ६0,
−− ⊺∘−−≔∘↾⇩∨−⋁≻≖∶≳⋁≖−∢⋁≖≁⋁⋯⊃↿∱ ... (9)

The above expression is obtained considering only two quadrants and half needle
hence for all four quadrants the deflecting torque will be doubled.

Ent

ग = (സം அபார -(श, +५,,) (10)

Key Point: The torquc is positive only when 2777 > (177 + ‏۔( پر۷‎ Now ۷ is the potential to
be measured and is eaual to Vis - Vr.

To = त {५२४ ೨ ್ಚಾ + ५41} ಜಾ )1(

If potential of needle V; is very large compared to voltage to be measured then,

7 | Tg ಇ 2V Vy | ೬೬. For heterostatic with V, large

Key Point: Thus in heterostatic connection, the untform scale is obtained.

13.
Wattmeter method- Lloyd Fisher square

This method is used for measurement of iron loss in strip(sheet) material. The strip material to be tested is
assembled as a closed magnetic circuit in the form of a square. Therefore this arrangement is known as a
magnetic square.
Lloyd Fisher square is the most commonly used magnetic square. The strips are usually 0.25m long and 50 to 60
mm wide. Each stack is made up of two types of strips one in the direction of rolling and the other cut
perpendicular to the direction of rolling. The individual strips are insulated from each other.
These strips are built up into four stacks and assembled to form a complete magnetic circuit with the help of
bent corner pieces and clamps. These corner pieces should be of the same material as the strips or atleast
material having similar magnetic properties. The overlapping at the corners should be only a few mm, and a
correction may be applied if necessary to account for the fact that the cross section of the magnetic circuit is
doubled at the overlapping joints. Ref fig.18.20.
A very small no of strips are shown in the fig for sake of clarity. The bundles of strip are placed inside four
similar magnetizing coils of heavy wire connected in series to form primary winding. Each of these coils has,
underneath it, two single layer coils of thin wire having equal no of turns. These secondary coils are connected
in series in groups of four — one on each core to form two separate and similar secondary wdgs.
Advantage:-
If required corrections are made to the measured value, the Lloyd Fisher square is more reliable than Epson
square.
The use of corner pieces makes the Lloyd Fisher square superior for testing of anisotropic materials.
Test Setup:-
Fig18.21 shows the connection diagram for finding total iron loss by wattmeter method. The test specimen is
weighed before assembly and its effective cross section is determined. The primary wdg is connected to a