What is retardation test in DC motor?
What is retardation test in DC motor?
Theory of retardation test: In the retardation test, the dc machine is run as a motor at a speed just above the normal. Then the supply to the armature is cut off while the field is normally excited. The speed is allowed to fall to some value just below normal.
What is direct testing of DC machine?
Direct test method (break over test) In this method of testing the machine is put on full load and whole developed power is wasted by applying the break. Direct test method is used, for small machines. Because of in case of large motors, it is difficult to dissipate the large amount of heat generated at the brake.
What is the purpose of conducting the retardation test?
This is the best and simplest method to find the efficiency of a constant-speed d.c. machine (e.g., shunt generator and motor). In this method, we find the mechanical (friction and windage) and iron losses of the machine.
Which type of losses is calculated by applying retardation test on a DC shunt motor?
Explanation: Retardation test is used for finding the stray losses.
What is retardation?
Retardation is often used to describe problems in human mental development that result in a lack of intelligence or other kinds of physical or learning delays. You can use retardation to describe other kinds of slowness or delays too, including simply a decrease in speed.
What is brake test on DC shunt motor?
In Direct Method, the DC machine is subjected to rated load and the entire output power is wasted. The ratio of output power to the input power gives the Efficiency of DC Machine. For a DC Generator the output power is wasted in resistor. Direct Method of testing when conducted on a motor is also known as Brake Test.
How many tests are there in DC machine?
Basically, the testing of DC machines classified into two types. Namely, direct and indirect tests. The indirect test is further classified into two. They are Swinburne and Hopkinson’s Test.
Why the brake test is called as the direct test?
What is the merits and demerits of Hopkinson’s test?
This test can be done under full-load conditions so that a rise in temperature & commutation can be examined. Iron loss change because of flux distortion is taken into account because of the full-load condition. Efficiency can be determined at dissimilar loads.
What is the purpose of performing retardation test after Swinburne’s test?
6. What is the purpose of performing retardation test after Swinburne’s test? Explanation: While performing Swinburne’s test we get addition of all losses. So, if we want to treat each loss individually, one needs to separate them.
What will happen if field current of generator in Hopkinson’s test is increased?
Explanation: If field current through generator is increased, back emf of generator will increase thus it’ll become greater than back emf of a motor, so to compensate this effect armature current in generator will increase thus, motor armature current will also increase.
What is retardation example?
When the velocity of a body decreases, its acceleration is negative. Negative acceleration is called ‘retardation’ or ‘deceleration’. For example, when a stone is thrown upwards, it is under retardation. Similarly, when a bus approaches a bus-stop, its motion gets retarded.
How are motor speeds determined in a retardation test?
in a retardation test of a drive to determine its moment of inertia the speed of the motor after the supply has been cut off is estimated as N=1000/ (0 97 t)rev/min Motor has a rated speed of 1000rev/min and rotational losses at rated speed of 2 7kw estima
How is torque used in a retardation test?
The method using electrical torque is shown in Fig. 31.12. The double-throw switch S while cutting off the armature from supply, automatically joins it to a non-inductive resistance R as shown. The power drawn by this resistance acts as a retarding torque on the armature, thereby making it slow down comparatively quickly.
How does the running down test work on a machine?
The machine under test is speeded up slightly beyond its normal speed and then supply is cut off from the armature while keeping the field excited. Consequently, the armature slows down and its kinetic energy is used to meet the rotational losses i.e. friction, windage and iron losses.*
How are shunt motors and generators are tested?
This method is applicable to shunt motors and generators and is used for finding stray losses. Then, knowing the armature and shunt Cu losses at a given load current, efficiency can be calculated. The machine under test is speeded up slightly beyond its normal speed and then supply is cut off from the armature while keeping the field excited.