Why is no load test of DC shunt generator conducted?
In this experiment we aim to conduct a No-Load test on a DC Generator to determine its open circuit characteristics followed by a Load test on a DC shunt Generator to determine its external load characteristics. The DC Generator as we know can be either separately excited or self excited in shunt.
What is no load characteristics of DC shunt generator?
No-load Characteristics : No-load or open circuit characteristics of a shunt generator are obtained by plotting ammeter reading (field current) i.e. Ish, versus voltmeter reading E (generated voltage). Under the no-load condition, the generator is said to be open-circuited and rotating at a constant speed.
What is the purpose of doing load test on DC shunt motor?
AIM: To conduct load test on DC shunt motor and to determine the efficiency using mechanical loading arrangement. To Draw the following characteristics curves.
What is no load voltage of DC shunt generator?
The straight line is also known as the field- resistance line. The shunt generator continues to build up voltage until the point of intersection of the field-resistance line and the magnetic saturation curve. This voltage is known as the no-load voltage.
How do you do a no-load test?
The voltmeter measures the standard-rated supply voltage and an ammeter measures the no-load current. Since the motor is running at no-load, total power is equal to the constant iron loss, friction and winding losses of the motor. Pconstant = Pi = P1 + P2 = Sum of the two wattmeter readings.
What is the working principle of a DC shunt generator?
The DC shunt generator working principle is similar to a normal generator like electromagnetic induction. In this generator, the connection of field winding can be shunt toward the armature. Once input is provided through the prime mover, then the conductor can be turned within the permanent magnetic field.
What are the load characteristics of DC shunt generator?
AC curve is showing the external characteristic of the shunt wound DC generators. It is showing the variation of terminal voltage with the load current. Ohmic drop due to armature resistance gives lesser terminal voltage the generated voltage. That is why the curve lies below the internal characteristic curve.
When a DC shunt motor running on no load the input power is equal to?
zero
Because the motor is running at no-load condition, the net output is zero. This means the input power is supplying only the losses, including: mechanical losses, including both friction and windage losses.
What is the procedure of performing the load test on DC shunt motor?
Load is varied gradually and for each load, voltmeter and ammeter readings are noted. 5. Then the generator is unloaded and the field rheostat of DC shunt generator is brought to maximum position and the field rheostat of DC shunt motor to minimum position, DPST switch is opened.
What is the effect of increase in the load on the performance of DC shunt motor?
As the load increases, to maintain the voltage at a constant value, current decreases, due to which the strength of magnetic field produced by the Internal winding of DC motor decreases. This results in a decreased interaction of the two magnetic fields and thus decrease in speed of motor.
When a DC shunt motor running on no load the input power is?
Because the motor is running at no-load condition, the net output is zero. This means the input power is supplying only the losses, including: mechanical losses, including both friction and windage losses.
What is the purpose of the no load test?
No Load Test is an indirect method used for determining the efficiency and also to determine the circuit parameters of the equivalent circuit of the three-phase induction motors. The open-circuit test is performed on the transformer. The no-load test is the same as the open-circuit test performed on the transformer.
Why do we use no load test?
This test gives the information regarding no-load losses such as core loss, friction loss and windage loss. Rotor copper loss at no load is very less that its value is negligible. Small current is required to produce adequate torque. This test is also well-known as running light test.
What is the application of DC shunt generator?
Applications of shunt generator: Used for general lighting. Used to charge the battery because they can be made to give constant output voltage. Used for giving the excitation to the alternators.
What are the general characteristics of shunt generator?
A shunt generator is a type of dc generator in which the field winding is connected in parallel with the armature winding so that the terminal voltage of the generator is applied across it. The shunt field winding has many turns of fine wire having high resistance.
What do you mean by no load saturation characteristics?
Open circuit characteristic is also known as a magnetic characteristic or no-load saturation characteristic. This characteristic shows the relation between generated emf at no load (E0) and the field current (If) at a given fixed speed.
When a DC motor runs on no load?
When the motor is connected across the supply mains without load, it draws small current from the supply mains. This current will flow through the series field and armature, the speed tends to increase so that back emf may approach the applied voltage in magnitude.
What is load test on DC motor?
Load Test. The load testing of DC machine is needed to determine the rating of a machine. When we run a machine, then some energy is lost in the machine, which converts into the heat and cause temperature rise.
What happens when a DC shunt generator is used at no-load?
At no-load conditions, the generator’s terminal voltage will be stable which is signified through the MC horizontal dotted line. Once the dc shunt generator is loaded, then flux for each pole can be decreased because of the armature reaction. Thus, e.m.f. can be produced on load is low as compared to the e.m.f. produced at no load.
How do you identify a shunt generator?
The external characteristic of a shunt generator can be obtained by conducting a load test on it in a manner similar to that described for a separately excited generator. The connections are made as shown in Fig. 1 (a).
What is “no load voltage” in a DC generator?
If a DC generator is run (its shaft rotated) at rated speed by a prime mover and no load is connected to its terminals then the voltage measured at its terminals is called as “No Load Voltage”. When load is connected, load current flows and terminal voltage falls slightly (due to internal impedance or resistance) below no load voltage.
What is critical resistance in a shunt generator?
If the shunt generator has to build up its field with the load circuit closed, the load resistance should not be below a certain minimum value called critical resistance for the load. Otherwise, it will fail to excite.