A blocked rotor test is normally performed on an induction motor to find out the leakage impedance. Apart from it, other parameters such as torque, motor, short-circuit current at normal voltage, and many more could be found from this test. Blocked rotor test is analogous to the short circuit test of transformer.
Why do we perform no load and blocked rotor test on induction motor?
The efficiency of small motors can be determined by directly loading them and by measuring the input and output powers. The power loss will be large if we directly test the load. … Therefore indirect methods are used to determine the efficiency of 3-phase induction motors.
Why blocked rotor test of an induction motor is considered as short circuit test of transformer?
The Blocked Rotor Test of an induction motor is similar to the short circuit test of a transformer. In this test, the shaft of the motor is locked so that it cannot move and the rotor winding is short-circuited. … In the case of the cage motors, the rotor bars are permanently short-circuited.
What is the purpose of no load and blocked rotor test?
Aim of the Experiment:
To obtain the variation of no load power and current and blocked rotor power and current with changes in the applied voltage to the stator. 2. To determine the equivalent circuit parameters of an induction motor.
Why UPF wattmeter is used in blocked rotor test?
Resistive circuits have unity power factor hence UPF wattmeters are used to measure power in these circuits. … As secondary side is short circuited the entire coil will be purely resistive in nature.So the power factor will be unity. So UPF(Unit Power Factor) Wattmeter is used in SHORT CIRCUIT TEST of Transformer.
Why no load test is performed in induction motor?
As the name suggest no load test is performed when rotor rotates with synchronous speed and there is no load torque. … 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.
What is load test of induction motor?
The load test on induction motor is performed to compute its complete performance i.e. torque, slip, efficiency, power factor etc.
How do you test an induction motor rotor?
HIGH CURRENT ROTOR TEST – This test is performed by applying high current through the shaft of the rotor (rotor out of stator) and thermally scanning (infrared or thermoscan) the rotor O.D. searching for shorted laminations. These shorted laminations cause localized hot spots which cause uneven heating of the rotor.
What is the locked rotor current?
Locked rotor current is basically the current drawn by the motor at its rated voltage when its rotor is kept stationary or in other words rotor is not spinning or rotating. So when we start a motor, its rotor is already at rest.
What is no load test of 3 phase induction motor?
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.
What is no load current in motor?
Motor no-load current Calculations:
Motor no-load current is nothing but a measuring the motor current without connecting any mechanical loads in short form “shaft will be driven by hand freely”. Also at no load, the power factor becomes very poor. Since motor draws high reactive current rather than the active current.
Why LPF wattmeter is used in no load test of induction motor?
We use LPF only for no load test because at no load only reactive component of current flows in any machine. In 3 phase induction motor magnitude of reactive component current is more because of air gap. So power factor under no load operation is low and we use LPF wattmeter .
When the rotor of 3 phase induction motor is blocked the slip is?
0.7. 0.3. When the motor is blocked i.e., rotor is at zero speed.
What is Wattmeter Power Factor?
Definition: The instrument that measures the low value of power factor accurately is known as the Low Power Factor Wattmeter (LPFW). The low power factor meter is used for measuring the power of the highly inductive circuit. It is also used in the resistive circuit which has a power factor range from 0.5 to 1.
What is the slip?
Slip is the differentiation between synchronous and asynchronous speed. … The difference between the synchronous speed of the electric motor magnetic field, and the shaft rotating speed is slip – measured in RPM or frequency. Slip increases with increasing load – providing a greater torque.
Why MC is short circuited in wattmeter?
Originally Answered: Why do we short the M & C terminals during a wattmeter connection? Main and Common terminals are shorted in order to make the “load on the current coil” side configuration or you can say to put the potential coil before current coil.