What happens when synchronous generator is over excited?

What happens when synchronous generator is over excited?

CASE 3: If the field current is more than the normal field current, motor is said to be over excited. This excess field current produces excess flux (flux set up by DC supply rotor winding – resultant air gap flux) which must be neutralized by the armature winding. This is called V curve of synchronous motor.

What is under excitation of synchronous generator?

Abstract. Excitation system of synchronous generator can help to an effective voltage control and power system stability support. Under-excitation limiter prevents the decrease of generator field current to the values lower than the stability margin or the thermal limit of end side of the stator core.

What will be the power factor of a synchronous motor if the field is under Excited?

Answer : If the field of synchronous motor is under excited, power factor will be lagging.

How can a synchronous generator be made to have a leading power factor?

Once the synchronous motor is synchronized, the field poles on the rotor are in line with the rotating magnetic poles of the stator. To increase the line voltage, the motor will supply ac magnetizing current to all “magnets” on the system to increase their magnetic flux. This is leading power factor.

What is excitation EMF?

The process of generating a magnetic field by means of an electric current is called excitation. Field coils yield the most flexible form of magnetic flux regulation and de-regulation, but at the expense of a flow of electric current.

Why synchronous motors are not self starting?

Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator. Once the rotor nears the synchronous speed, the field winding is excited, and the motor pulls into synchronization.

Which synchronous motor will be smallest in size?

Which synchronous motor will be smallest in size ? (D) 10 HP, 375 rpm. Explanation: Q15.

Why do we use damper winding?

The main purpose of using Damper winding in synchronous Machine is to provide starting torque and eliminate damping or hunting. The damper winding is used in Synchronous Motor to provide starting torque and the damper winding is used in the synchronous alternator to eliminate damping or hunting.

How do you adjust the power factor of a generator?

You can improve power factor by adding power factor correction capacitors to your plant distribution system. When apparent power (kVA) is greater than working power (kW), the utility must supply the excess reactive current plus the working current . Power capacitors act as reactive current generators .

When does a synchronous motor have a lagging power factor?

If the field excitation is such that back EMF E b is less than the applied voltage V, then the motor is said to be under-excited. An under excited synchronous motor has a lagging power factor. If DC field excitation of a synchronous motor is such that back EMF E b is greater than applied voltage V, then the motor is said to be over-excited.

Why does a generator become over excited when synchronizing?

Double check me on this: When synchronizing the generator, increasing the field current will increase the flux density, which increases the voltage induced in the stator. When the generator is paralleled with the utility, you have an infinite bus and cannot adjust stator voltage so the generator becomes over-excited.

How does the excitation of a generator affect the load?

Some do not have a shaft extension. As the excitation is increased, the machine exports VARs to offset load VARs. Some synchronous motor applications use an oversized motor and over excite the motor to supply VARs to the system.

What does it mean when a synchronous motor is under excited?

Depending on the level of excitation, the synchronous motor is capable of operating in one of the following four conditions: In this case, induced back EMF E b is equal to the applied voltage V. If the field excitation is such that back EMF E b is less than the applied voltage V, then the motor is said to be under-excited.