The Load Characteristics Of Alternator | Practical Example

The Load Characteristics Of Alternator | Practical Example

An alternator is an electrical generator that converts energy to power within the sort of electrical energy. For reasons of price and ease, most alternators use a rotating field with a stationary coil. Therefore the load characteristics of the alternator find out the voltage regulation.

The Load characteristics of alternator:

load characteristics of alternator

The alternator having 3 characteristics, they are given below,

1.output current with speed of the alternator

If the speed of the alternator is decreased then the output current of the alternator also decreased. therefore speed and output current of alternators both are directly proportional.

2. efficiency with the speed of the alternator.

If the speed of the alternator running lower then rated speed then the efficiency of the alternator will be reduced.

3. current drop with increasing alternator temperature.

The output current of the alternator depends on the temperature produced by armature in the alternators. if the temperature increased then the output current of the alternator will be reduced.  because the output current of alternators and temperature of armature both are indirectly proportional.

Other some important characteristics of alternators are:

  1. open circuit characteristics (OSC)
  2. short circuit characteristics (SCC)

Open circuit characteristics:

It’s drawn between the open-circuit voltage and field current If.

Short circuit characteristics:

It’s drawn between the short circuit current and field current If.

the load characteristics of an alternator are given above.

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Experiment-Load characteristics of an alternator

OBJECT :

  1. To find out the voltage regulation characteristics of the alternator with resistive, capacitive and inductive loading.
  2. To observe the effect of unbalanced loads on the output voltage.

 

DISCUSSION :

The output voltage of an alternator builds basically upon the total flux in the air gap. At no load, this flux is established and determined only by the dc field excitation. 

Under load, but, the air gap flux is determined by the ampere-turns of the rotor and the ampere-turns of the stator. The sequence may aid or oppose the MMF (magneto-motive force) of the rotor depending upon the power factor of the load. Leading power factors aid the rotor, and lagging power factors oppose it.

 

Because the stator MMF has such a main effect on the magnetic flux, the voltage regulation of alternators is fully poor, and the dc field current must be continuously adjusted to keep the voltage constant under changeable load conditions.

If a single phase of a three-phase alternator is heavily loaded, its voltage will be reduced due to the IR and IXL drops in the stator winding. This voltage drop can’t be recouped by modifying the dc field currently because the voltages of the other 2 phases will also be changed. Therefore, it is essential that three-phase alternators don’t have loads that are badly unbalanced.

 

INSTRUMENTS AND COMPONENTS :

 

Synchronous Motor/Generator Module                          ———                  EMS  8241

DC Motor/Generator Module                                                ———                 EMS 8211

Resistance Module                                                                    ———                EMS 8311

Capacitance Module                                                                ———                EMS 8331

Inductance Module                                                                  ———                EMS 8321

Power Supply Module (0-120/ 120 Vdc)                           ——-                  EMS  8821

AC Metering Module (250/250/250 V)                                ——–                 EMS  8426

AC Metering Module (2.5A)                                                    ———               EMS  8425

DC Metering Module (2.5A)                                                   ———               EMS  8412

Hand Tachometer                                                                     ———                EMS 8920

Connection Leads                                                                      ———               EMS  8941

Timing Belt                                                                                    ———              EMS 8942

 

PROCEDURE :

Caution: High voltages are present in this Lab Experiment! Don’t make any connections with the power on! The power should be turned off after completing each distinct measurement.

 

1. a) connect the circuit shown in Fig.1, Using your EMS Synchronous Motor/Generator, DC Motor/Generator, Resistance, Power Supply and Metering Modules. Note that, the balanced resistive load is star/wye connected to the three-phase output of the alternator. The alternator rotor is connected to the variable 0-120 Vdc output of the power supply, terminals 7 and N. the dc shunt motor winding is connected to the fixed 120 Vdc output of the power supply, terminals 8 and N.

load characteristics of alternator

2.a)Couple the dc motor/generator to the alternator with the timing belt.
   b) Set the dc motor/generator field rheostat at its full CCW position for minimum resistance.
  c)Set the alternator field rheostat at its full CCW position for maximum resistance.
  d)Adjust each resistance section for the resistance of 300 W.

3.a)Turn on the power supply and, using your tachometer, adjust the dc motor rheostat for a motor speed of 1800 r/min.
    b)If, the synchronous motor has switch S, close it at this time period.                                                                                                                                                                                      
    c) Adjust the dc excitation of the alternator by the output voltage E1 = 208 Vac. Measure and record the full load I 1 , I 2.
    d) Open the 3 resistance load switches for no load on the alternator and measure and record the no-load  E1 and E2. Remember to check the motor speed and readjust to 1800 r/min if essential.
    e) Return, the voltage zero (0)and turn off the power supply.
     f) Calculate, the alternator regulation with resistive loading.

load characteristics of alternator

 

4.a) Using your EMS Inductance Module, replace the resistive load with an inductive load.
b) synthesize each inductance section for a reactance XL of 300.
c) Repeat procedure 3 and record the full-load values of I 1, I2
d) Measure and record the no-load values of E 1, and I2
e) Return the voltage zero(0) and turn off the power supply.
f) Calculate the alternator regulation with inductive loading.
g)With an inductive load, does the stator MMF help or oppose the rotor MMF?

5.a) Using your EMS Capacitance Module, return the inductive load with a capacitive load.
b) Adjust each Capacitance part for a reactance XC of 300
c) Repeat procedure 3 and record the full-load values of I 1, I2
d) Measure and record the no-load values of E 1, and I2
e) Return the voltage zero(0) and turn off the power supply.
f) Calculate the alternator regulation with Capacitive loading.
g) With a Capacitive load, does the stator MMF aid or restrict the rotor MMF

6. a) With a capacitive reactance load of 1200 per phase, turn on the power supply and adjust for a motor speed of 1800 r/min.
    b) Adjust the trouble of the alternator until the output voltage E1 = 208 Vac
   c) Increases the capacitive loading by placing an additional reactance of 600 in parallel with each of the 1200 sections and observe what happens!
   d) Increase the capacitive loading further by placing an additional reactance of 300 across each section and observe what happens.
    e) Return the voltage zero(0) and turn off the power supply.
   f) Described, if you can, the phenomenon you have just respect.

7.a) Connect the circuit shown in Fig 2. Note that only one of the alternator phases has a load.

load characteristics of alternator

   Fig:2

b) Turn on the power supply and adjust the dc motor/generator rheostat for a motor speed of 1800 r/min.
c) Adjust the dc excitation of the alternator by the voltage across the 600 loads E1 = 208.
Vac. Measure and record the 2 other phase voltages E2 and E3
d) Turn off the power supply outside of touching any of the variable controls.
e) Reconnect the three ac voltmeters so they will measure the voltages across each of the
three stator windings.
f) When the Turn on the power supply, Measure and record the voltages across each of the alternators
  windings.
E1 to 4 =……………..Vac E3 to 6 = ……………..Vac
E2 to 5 = ……….……..Vac
g) Return the voltage zero(0) and turn off the power supply.
e) Did the single-phase load generate a large unbalance?

Summary
The Load Characteristics Of Alternator | Practical Example
Article Name
The Load Characteristics Of Alternator | Practical Example
Description
The load characteristics of alternator build basically upon the total flux in the air gap. At no load, the load characteristics of alternator are two,
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Publisher Name
Habib
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5 Comments

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