The copper loss is measured by placing a wattmeter in circuit with the primary when the secondary is short circuited, and when enough pressure is applied to cause full load current to flow.
The wattmeter indicates directly the core loss, which includes a very small loss due to the current in the copper.
If it be desired to separate the load losses from the true I²R loss, the resistances can be measured, and the I²R loss calculated and subtracted from the wattmeter reading.
An ammeter, voltmeter and wattmeter are required to make the tests.
Connect voltmeter and wattmeter as shown in the illustration to the low tension side of the transformer.
The wattmeter reading shows the copper loss at full load.
The core loss is measured by placing a wattmeter in circuit when the transformer is on circuit at no load and normal frequency.
In analogy, the actual power, expended in propelling boat from A to B corresponds to the wattmeter reading in an alternating current power circuit.
In the case of a wattmeter the fixed coils are connected in series with the line, either directly or through a current transformer, while the moving coil is connected in shunt to the line.
In the wattmeter type, the phase relation between the pressure and the current fluxes is such that on a non-inductive load the torque is zero.
The wattmeter connected, as shown, measures the sum of the losses, in the transformer, in the pressure coil of the wattmeter, and in the voltmeter.
If one set of the instruments be removed from the circuit, the reading of the remaining wattmeter will have no meaning.
Therefore, the total power taken by the motor will be three times the wattmeter readings.
The ammeter and the current coil of the wattmeter will then be connected to the middle line of the motor.
With the switches B and D in the position shown, the ammeter and wattmeter series coils are connected in the left hand line.
By this method, just as accurate results can be obtained as with the two wattmeter method.
For this purpose a double pole, double throw switch is sometimes inserted in the circuit of the pressure coil of the wattmeter so that the indications can be reversed without disturbing any of the connections.
With the connections as shown, the sum of the two wattmeter readings gives the total power in the circuit.
The changes in the wattmeter deflections are effected by merely varying the voltage, the value of the current being maintained constant at a value which represents the full current capacity of the meter.
There are several ways of connecting an ammeter, voltmeter and wattmeter in the circuit for the measurement of power.
Three switches, B, C and D, are employed for changing the connection of the ammeter and wattmeter in either one of the two lines.
The figure shows the connection of the wattmeters, without necessary switches, for reading the total energy by two wattmeter method.
It can be easily seen that if the core or copper losses of small transformers are being measured, it is quite necessary to correct the wattmeter readings, for the instrument losses.
We counted the revolutions of the wattmeter and found them to be sixty per minute.
One of the boys connected a wattmeter in the circuit with a hylo lamp and found that the small filament did not pass current enough to move the armature of the wattmeter.
Notice that while the ammeter was like the magneto in having a steel magnet for its field, the wattmeter is like the dynamo in having electro-magnets for both armature and field.
Wattmeter] I will now take you to see the wattmeter which measures all the electric energy used in this building.
If we wish to drive the wattmeteror any other electric motor twice as fast as now, we may choose whether we shall do so by doubling the volts of pressure or by doubling the amperes of quantity.
I next brought the current to the wattmeter through a 16-candle-power lamp and the ammeter, connected in series, showed that half an ampere was passing.
The armature of the wattmeter revolved slowly and it was not long before the boys reported that connections for the current were made by strips of metal sliding on metal plates.
Before the present form of commercial wattmeter was devised electrolytic cells were used to determine what the consumer's bill for electricity should be each month.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "wattmeter" in a variety of sentences. We hope that you will now be able to make sentences using this word.
