Lab 2: Separation of Eddy Current and Hysteresis Losses
Objectives
To separate the eddycurrent and hysteresis losses at various frequencies and flux densities using the Epstein Core Loss Testing equipment.
Equipment
 One power quality meter and banana cables from the stockroom..
 One digital multimeter from the stockroom.
 One Epstein piece of test equipment. (It is mounted on a 3 ft × 3 ft slide equipped square platform stored in a cabinet and weighs 22 lbs.)
 Three phase Variac.
 One switch Box from cabinet.
References
 Hurley, W.G, Transformers and Inductors for Power Electronics , Wiley, John & Sons, Incorporated, 2013.
 Vincent Del Toro, Basic Electric Machines , pp. 3438, Prentice Hall, 1990.
 Philip Beckley, Electrical Steels for Rotating Machines, pp. 113121, The Institution of Engineering and Technology, London, United Kingdom, 2002.
Background
Designers of electrical machines must know the magnetic characteristics of the material they use in order to predict the performance of their ﬁnished products. In this experiment core losses resulting from eddy currents and hysteresis in steel sheets will be measured. The Epstein test frame is a special onetoone transformer having provisions for inserting the sample where it serves as a core. The testing procedure is specified by the American Society for Testing Materials (ASTM).
Description of the Apparatus
The windings are on four sections hollow square tube, each 1.57 × 1.57 inches square and about 17.25 inches long. Each section is wound with 150 turns of No. 18 wire. These turns are wound parallel to each other and in the same plane so that the primary and secondary turns lie alternately adjacent to each other in order to improve their magnetic coupling. The core material used is Armco 6M (USS Transformer 66).
The four sections are arranged to form a square. Primary turns on all sections are connected in series. The secondary turns are also connected in series.
The sample to be tested consists of 10 kg (22 lbs) of strips 3 cm wide and 59 cm long. One half of the sample is cut with the grain and the other half is cut across the grain. Four equal bundles are made of the specimen and each bundle is tightly taped and placed in a section of the winding. The four ends are then butted together in the form of a square with a piece of 0.004 inch thick paper in each joint, and all joints made as tight as possible.
Because of the tight coupling between the primary and secondary coils, the voltage induced in them by the AC magnetic flux is the same. Since the primary winding carries the current which establishes the magnetic flux in the core, the voltage applied to the primary winding includes the ohmic voltage drop due to the resistance of that winding. The secondary winding, on the other hand, is opencircuited; hence, its terminal voltage is equal to the induced voltage. The latter is given by
Substituting the values for N_{s} , m, l and p, we get.
In order to separate the eddycurrent loss (P_{e} ) and hysteresis losses (Ph ) when only total power loss (W ) is measured, the following calculations must be performed.
where K_{h} and K_{e} are constants related to
the material of the transformer core and its volume.
In (2.13) we see that if (W/f ) is plotted
against f for
fixed B_{m}, a
straight line is obtained whose slope is and yaxis
intercept The hysteresis power loss for that value
of B_{m} is then obtained by multiplying the yintercept by the
frequency. The corresponding eddycurrent loss is the slope multiplied by the frequency squared. The procedure is repeated for each
value of B_{m}.
To obtain the value of K_{h}, the logarithmic values of obtained above are plotted against log B_{m}.The slope of the resulting straight line is n and its yintercept is log K_{h}. Thus K_{h} and n can be obtained. Similarly, by plotting log against log B_{m} as a straight line of slope 2, log K_{e} can be obtained and, hence, K_{e}.
An alternatordc motor set is used as a variable frequency AC voltage supply.
The frequency can be changed by varying the motor speed. The magnitude of voltage can be altered by varying the alternator field current.
Note: Only the instructor can change the frequency and the maximum AC voltage. The students can then obtain fractions of the supplied voltage by turning the threephase variac.
Prelab
 Complete table 2.1 using formula 2.10 Remember that the V_{s} in 2.10 refers to the root mean square (RMS) of the secondary voltage. The DMM reads the average value of the secondary voltage and converts it to an approximate RMS value by multiplying by 1.11 which assumes a pure sinusoidal voltage. (V_{RMS} = V_{AV(s)} * 1.11)
 Connect the meters into the circuit of figure 2.1 to measure the total power lost (W) of the Epstein test frame and primary current (I_{P}). Show connections with a Low Power Factor (LPF) Wattmeter and with Power Quality Meter (Fluke 43B).
 Read the reference sections 10.1 through 10.5. Explain which of the precautions at the end of section 10.5 you think we might have the most difficulty with.
Eddy Current and Hysteresis Losses
 Connect the circuit as shown in figure 2.1.
Note: Use only the primary and secondary connections outside the coil, ignore the connections inside.
 Connect the power quality meter to monitor only core losses by connecting to the primary current and to the secondary voltage (one side of the DPDT switch ).
 Connect the power supply from the bench panel to the variac and connect the OUTPUT of the variac to the circuit.
 Wait for the instructor to adjust the frequency and maximum output voltage available for your panel.
 Adjust the variac to obtain voltages E_{s} as calculated in table 2.1. For each applied voltage, measure and record V_{s} and W in table 2.2.
 Perform the previous steps for frequencies of 30, 40, 50 and 60 hertz.
T able 2.1: E_{s} = 1 .73 f B_{m}  
B m 
f = 30 Hz 
f = 40 Hz 
f = 50 Hz 
f = 60 Hz 
0.4 




Report
 Plot a graph of kg core loss (W/10), against the frequency f at different ﬂux densities B_{m} on the same graph.
 Separate the EddyCurrent P_{e} and hysteresis P_{h} losses at different flux densities B_{m} and frequencies f . Complete table 2.3.
 Plot graphs for P_{e} and P_{h} against the frequencies for different flux densities on the same graph.
Discussion Questions
 Discuss how eddycurrent losses and hysteresis losses can be reduced in a transformer core.
 Plot the log of the values against the log of B_{m}. Determine K_{n} and n.
 Plot the log of the values against the log of B_{m} (slope should be approximately 2) Determine the values of K_{e} from the intercept (log K_{e})
 Explain why the wattmeter voltage coil must be connected across the secondary winding terminals.
Table 2.2: Core Loss Data.  

f = 30 Hz 
f = 40 Hz 
f = 50 Hz 
f = 60 Hz 

B_{m} 
E_{s} 
W 
E_{s} 
W 
E_{s} 
W 
E_{s} 
W 
0.4  
0.6  
0.8  
1.0  
1.2 
Table 2.3: Data Sheet for EddyCurrent and Hysteresis Losses.  

f = 30 Hz 
f = 40 Hz 
f = 50 Hz 
f = 60 Hz 

B_{m} 
P_{e} 
P_{h} 
P_{e} 
P_{h} 
P_{e} 
P_{h} 
P_{e} 
P_{h} 
0.4 0.6 0.8 1.0 1.2 







