Table of Contents
- 1 What is the effect of loss of excitation in synchronous machines?
- 2 What is the impact when DC exciter of synchronous motor is over excite and under excite?
- 3 What do you mean by loss of excitation?
- 4 How do you test for loss of excitation?
- 5 What is the purpose of DC excitation?
- 6 Why is excitation DC?
What is the effect of loss of excitation in synchronous machines?
The following subsequent decrease of the power curve as result of loss of excitation will cause that generator will no longer be able to transmit the electric power corresponding to the mechanical power of turbine.
What is the impact when DC exciter of synchronous motor is over excite and under excite?
If DC field excitation of a synchronous motor is such that back EMF Eb is greater than applied voltage V, then the motor is said to be over-excited. An over-excited synchronous motor draws leading current. Therefore, if the field of the synchronous motor is overexcited then its power factor will be leading.
What are the effects of loss of excitation?
When a generator loses its excitation, the rotor current gradually decreases and the field voltage decays by the field time constant as well. In this case, the generator operates as an induction generator and draws reactive power from the power system instead of generating reactive power.
Why do we use DC voltage source for synchronous motor excitation?
In the alternator, as the rotor conductor changes its position as the rotor rotating so constant flux is to be produced in the rotor winding and it is possible only when the DC supply is given to the rotor winding. As we need constant flux that is why DC is used instead of AC for excitation of Synchronous Alternator.
What do you mean by loss of excitation?
Generator loss of excitation fault means that the excitation current provided by the excitation system suddenly disappears completely or partially. The causes of generator loss of magnetism fault are: generator rotor winding fault, excitation system fault, automatic demagnetization switch trip and circuit fault.
How do you test for loss of excitation?
An impedance-based Loss-of-Field relay has proven to be the most reliable and selective method to detect loss of excitation (a different way to say loss-of-field) conditions because the measured generator impedance will drop during loss-of-field conditions, as shown in Figure 15-4.
What is the effect of increase in excitation of a synchronous motor?
As the excitation is increased, the power factor improves till it becomes unity at normal excitation. Under such conditions, the current drawn from the supply is minimum. If the excitation is further increased (i.e., over excitation), the motor power factor becomes leading. Note.
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.
What is the purpose of DC excitation?
The basic function of an excitation system is to provide a continuous (DC) current to the field winding of a synchronous machine. This is achieved through the use of closed-loop control (or feedback control).
Why is excitation DC?
Why only D.C is used for Excitation in Alternators? Excitation voltage or current is supplied to the field windings of a rotor to produce a static magnetic field. If we use alternating current instead of direct current; we will get a fluctuating magnetic field.
Which relay is used for loss of excitation?
Type 40 is an offset mho impedance relay. The Type 40 is an offset mho impedance relay used for loss of excitation protection of a generator operating in parallel with other system generators.