Blocked Rotor Test of Induction Motor

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This Block rotor test of Induction motor test is analogues to the short circuit test on transformer. This test gives information about copper loss of motor. The circuit diagram for this test is shown in Fig. 1.

Blocked rotor test of Induction motor

Fig. 1: Blocked rotor test of Induction motor

The rotor is held stationary or rotor is blocked i.e. it is not allowed to rotate. The stator supply voltage is gradually increased till motor carries rated or full load current. The corresponding readings are noted down. The voltage required to circulate rated current is very less (merely 5 to 8% of rated value) so main flux is considerably less because flux is proportional to voltage. Hence the iron loss occurring is very less and can be neglected safely. The stator and hence rotor carries rated current so copper loss occurs. Since no useful output is extracted from motor (rotor is blocked), the entire power input is equal to copper losses. So wattmeter reading represents copper losses.

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What is Transformer Protection? Theory, Protection Relays & Types

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The transformer is heart of power system. Power transformer is a major equipment in power system. It requires highly reliable protective devices. The protective scheme depends on size of transformer. The rating of transformers used in transmission and distribution systems range from few kVA to several hundred MVA. For small transformers, simple fuse is sufficient for protection. For medium capacity transformers over current relays are used. For large transformers differential protection scheme is used.

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What is Earthing Switch? Working, Symbol, Installation & Function

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Earthing Switch is connected between the line conductor and the earth. Normally, it is open when isolation work of opening is over the earthing switch is closed. Due to this closing, whatever the voltage is trapped on the line is discharged to the earth and working becomes safe. (Though the line is disconnected by isolators there is some voltage on the line to which capacitance between line and earth is charged). Normally. the earthing switch is mounted on the frame of isolator. The symbol of earthing switch is shown in Fig. 1.

Earthing Switch

Fig. 1: Earthing Switch

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What is Reactance Relay? Theory, Diagram, Torque Equation & Characteristics

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Reactance relay is over current relay with directional restraint. The current polarizing flux goes from upper polarizing coil magnet to lower electromagnet through cylinder and iron core. So due to this flux current is induced in the cylinder whose direction is perpendicular to the plane of this paper. And it flows up and down at the sides of cylinder which are opposite of the other two poles (i.e. operating coil magnet pole and restraining coil magnet pole).

Reactance Relay

Fig. 1: Reactance relay

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What is MHO Relay? Theory, Diagram, Torque Equation & Characteristics

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The impedance relay is not normally used because of need of a separate directional unit. So mho type relays are normally used. Working is similar to impedance relay. It is made directional by providing polarising winding so torque produced is polarizing flux times fluxes from (opposed) I and V poles as shown in Fig. 1.

MHO Relay

Fig. 1: MHO Relay.

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What is Semiconductor Fuse? Working, Diagram & Selection

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Semiconductor Fuse is a power device required to be protected against large currents. The semiconductor fuse is the fast-acting fuse that is normally used to protect the semiconductor devices. The physical appearance of a semiconductor fuse is as shown in Fig. 1.

Working of Semiconductor Fuse

Fig. 1: Semiconductor fuse.

As the fault current increases, the fuse connected in series with the device is open circuited to protect the device.  The nature of fuse current is shown in Fig. 2.

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