Load test on DC series motors.

Experiment No.: – 06

Aim of the Experiment: –

Load test on DC series motors.

Apparatus Required: –

Sl. No.NameSpecificationQuantity
1DC series motor with spring balance load2 BHP, 110V, 18A, 1440 rpm1 no.
2TachometerDigital type1 no.
3Ammeter(0-20) A, PMMC1 no.
4Voltmeter(0-150) V, PMMC1 no.
5Connecting wiresPVC insulated copperAs per required.
Table No. 6.1

Circuit Diagram: –

Theory: –

The load test on a DC series motor is performed to analyze its performance characteristics under varying load conditions. It provides valuable information about the motor’s torque-speed characteristics, speed regulation, efficiency, and ability to handle different loads. Here is the theory behind the load test on a DC series motor:

Torque-Speed Characteristics: The torque-speed characteristic of a DC series motor shows the relationship between the motor’s torque output and its speed of rotation. As the load on the motor increases, the torque required to overcome the load also increases. The motor responds by decreasing its speed to maintain the balance between the torque produced and the torque required by the load. The torque-speed characteristic curve is typically a downward-sloping curve, indicating that the motor’s speed decreases as the load torque increases.

Torque Calculation: Torque is the rotational force generated by the motor. It is proportional to the current flowing through the armature windings. The torque can be calculated using the formula:

\[\color\red{Torque\; (T)\; = \;Kt I_a}\] \[\color\red{T\;=\; (W_2-W_1)\times{r}\times{9.81}}\] \[\color\green{Where:}\] \[ \color\orange{T\;}\color\green{is\; Torque\;}\color\green{ Nm}\] \[ \color\orange{ Kt}\;\color\green{is\;Torque\; constant\; of\; the\; motor}\] \[ \color\orange{ I_a}\;\color\green{\; Armature \;current\; (A)}\] \[ \color\orange{W_1;\;and \;W_2}\color\green{\;are\; loads\; in\; kg}\] \[ \color\orange{r}\color\green{\; is\; the\; effective\; radius\; of\; the\; pulley}\]

Power Calculation: Power is the rate at which work is done. In the case of a motor, it represents the output power generated by the motor. The power output of the motor can be calculated using the formula:

\[\color\red{Power\; (P)\; = \;\dfrac{2π N T}{ 60}}\] \[\color\green{Where:}\] \[\color\orange{ P}\;\color\green{ Power\; output\;in\;watts}\] \[\color\orange{ N}\;\color\green{ Speed\; of\; the\; motor\;in\;RPM}\] \[\color\orange{ T}\;\color\green{ Torque\; in\; Nm}\]

Efficiency Calculation: Efficiency is an important parameter that indicates how effectively the motor converts electrical energy into mechanical energy. It is calculated using the formula:

\[\color\red{\%\;Efficiency\; }=\;\color\green{\dfrac{Power\; output}{Power\; input}\times{100}}\] \[\color\magenta{Where:}\] \[\color\orange{ Power\; output\;=}\] \[\color\gray{\; Power\; delivered\; to\; the\; load}\] \[\color\orange{ Power\; input\;=}\] \[\color\gray{\;Electrical\; power\; input\; to\; the \;motor}\]

By varying the load and calculating the power and efficiency at different load settings, we can observe how the motor performs under different operating conditions.

Procedure: –

  1. Connect all the apparatus as per circuit diagram.
  2. Start motor with the help of starter and take the readings from measuring instruments in no load condition at rated speed.
  3. Gradually increase the load on the pully and take the corresponding readings as per observation table.
  4. During the experiment pour water in the groove of the pulley to keep it cool.

Observation Table: –

 Radius of the pully(r) in meter =…………

Sl. No.Input Voltage (V) in Volts.Armature Current (I) in Amps.Speed (N) in RPMW1 in KgW2 in KgW=(W2-W1) in KgTorque (T) in N-mOutput Power (Po) in wattsInput Power (Pi) in watts% Efficiency 
1          
2          
3          
4          
5          
6          
Table No. 6.2

Calculation:

\[\color\red{W\;=\;(W_2-W_1)\;}\color\green{ in\; Kg}\] \[\color\red{T\;= \;(W_2-W_1) \times{r}\times{9.81} \;}\color\green{in\;Nm}\] \[\color\red{P_i\; = \;\dfrac{2π N T}{ 60} \;}\color\green{watt.}\] \[\color\red{P_0 \;= \;V\times{I} \;}\color\green{watt.}\] \[\color\red{\%\; Efficiency\;= \;\dfrac{P_0}{P_i}\times{ 100}}\] \[\color\red{BHP\;= \;\dfrac{P_i}{746}}\]

Draw curve between

  1. BHP vs Torque
  2. Speed vs Torque
  3. BHP vs Speed
  4. BHP vs Efficiency

Conclusion: –

                    To be written by student.

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