What is the function of the excitation system?
The excitation system creates the electromagnetic field in the rotor. The stator has the armature winding that has the electrical energy induced. The stronger the magnetic field created, the stronger the electrical power produced.
What is excitation (magnetic)?
Excitation (magnetic) The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation.
What is an exciter in a DC excitation system?
1. DC Excitation System. The DC excitation system has two exciters – the main exciter and a pilot exciter. The exciter output is adjusted by an automatic voltage regulator (AVR) for controlling the output terminal voltage of the alternator. The current transformer input to the AVR ensures limiting of the alternator current during a fault.
What is excitation system in synchronous machines?
Definition: The system which is used for providing the necessary field current to the rotor winding of the synchronous machine, such type of system is called an excitation system. In other words, excitation system is defined as the system which is used for the production of the flux by passing current in the field winding.
What is the purpose of excitation?
BASIC FUNCTION 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).
What is the principle of excitation?
In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation.
How does excitation voltage work?
An excitation voltage or current is the amount of electric energy ( D.C ) feed into the field winding of an alternator rotor to produce magnetic flux / field. The output voltage of an alternator depends upon the magnetic field and so the excitation voltage.
How does alternator excitation work?
As the load on the generator is increased, an increase in current flow causes the voltage to drop. The excitation system senses this decrease in voltage and increases the strength of the magnetic field to return the voltage to the desired level.
What is excitation in simple words?
Definition of excitation : excitement especially : the disturbed or altered condition resulting from stimulation of an individual, organ, tissue, or cell.
Why does excitation change real power?
A change in the excitation of an alternator running in parallel with other affects only its KVA output; it does not affect the KW output. A change in the excitation, thus, affects only the power factor of its output.
Does excitation increase voltage?
If we increase excitation that increase excitation current so magnetic flux increase and stator voltage increase. Increased stator voltage increase magnetic flux of all inductive load like motot etc..
What is excitation in power system?
An excitation system is a means to provide regulated DC current to the field windings of a generator, to produce an output voltage to the field. The generator is used to turn mechanical energy from a prime mover into electrical energy for transmission to customers.
What is an excitation signal?
An excitation signal source (generator of the excitation waveform) has inputs for setting the required timing, frequency range, and amplitude. The signal from this generator provides an input excitation for the complex impedance to be measured Ż.
How many volts does it take to excite an alternator?
The exciter wire is used to turn on the voltage regulator. This wire, when unplugged, should have approx. 12.5 volts with the key on. If it does not then the alternator will not work.
Where does the exciter wire go?
Exciter wire is connected to the L terminal of an alternator and is used to turn on the voltage regulator. Excitor wire is needed to generate the voltage required for the alternator to start running. The positive and negative cables are small and connected to the respective terminals of the battery.
What happens if excitation fails in alternator?
If the excitation of the generator fails, suddenly there will be no more magnetically locking between the rotor and rotating magnetic field of the stator.
What is excitation in psychology?
n. the electrical activity elicited in a neuron or muscle cell in response to an external stimulus, specifically the propagation of an action potential.
What is meant by excitation in biology?
One of the responses caused by specific neurotransmitters binding to receptors on a neuron. excitation increases the probability that neurotransmitters will be released by the neuron.
What is excitation theory in chemistry?
Excitation: The process of changing from a ground state to an excited state by energy absorption. In NMR spectroscopy, absorption of a radio wave photon of energy ΔE causes excitation from the ground nuclear spin state (I = +1/2) to the excited nuclear spin state (I = 1-/2).
What is the process of electron excitation?
Electron excitation is the transfer of a bound electron to a more energetic, but still bound state. This can be done by photoexcitation (PE), where the electron absorbs a photon and gains all its energy or by electrical excitation (EE), where the electron receives energy from another, energetic electron.
What is the excitation system?
Excitation System. Definition: The system which is used for providing the necessary field current to the rotor winding of the synchronous machine, such type of system is called an excitation system. In other words, excitation system is defined as the system which is used for the production of the flux by passing current in the field winding.
What is AC excitation?
The AC excitation system consists of an alternator and thyristor rectifier bridge directly connected to the main alternator shaft. The main exciter may either be self-excited or separately excited. The AC excitation system may be broadly classified into two categories which are explained below in details.
What is brushless excitation?
The brushless excitation system consists an alternator, rectifier, main exciter and a permanent magnet generator alternator. The main and the pilot exciter are driven by the main shaft. The main exciter has a stationary field and a rotating armature directly connected, through the silicon rectifiers to the field of the main alternators.
What is the difference between centralised and excitation systems?
The excitation system is the single unit in which the each alternator has its exciter in the form of generator. The centralised excitation system has two or more exciter which feeds the bus-bar. The centralised system is very cheap, but the fault in the system adversely affects the alternators in the power plant.
What is pilot exciter?
The pilot exciter is the shaft driven permanent magnet generator having rotating permanent magnets attached to the shaft and a three phase stationary armature, which feeds the main exciter field through silicon rectifiers, in the field of the main alternator. The pilot exciter is a shaft driven permanent magnetic generator having rotating permanent magnets attached to the shaft and a 3-phase stationary armature, which feeds the main’s exciter through 3-phase full wave phase controlled thyristor bridges.
Why is the field discharge resistor connected to the field winding?
When the field breaker is open, the field discharge resistor is connected across the field winding so as to dissipate the stored energy in the field winding which is highly inductive. The main and the pilot exciters can be driven either by the main shaft or separately driven by the motor.
What is the main requirement of an excitation system?
The main requirement of an excitation system is reliability under all conditions of service, a simplicity of control, ease of maintenance, stability and fast transient response. The amount of excitation required depends on the load current, load power factor and speed of the machine. The more excitation is needed in the system when ...
What is the purpose of the excitation system?
The excitation system creates the electromagnetic field in the rotor. The stator has the armature winding that has the electrical energy induced. The stronger the magnetic field created, the stronger the electrical power produced. The strength of the magnetic field is adjusted by controlling the current to the rotor.
What is exciter control?
The regulator is the source of control and the exciter system is the source of power. The regulator system includes voltage control, current control, power factor control, limiters & protection, power system stabilizer, field flashing control, de-excitation control, and field breaker control. Exciter systems can be rotating or static. Rotating includes brushless and brushed types and static includes compound sources and potential sources.
What is a power bus?
A power bus is required to feed the exciter current to each end of the rotor coil. Field breakers are used to protect both the AC and DC sides of the generator. Power rectifiers convert AC power to DC power. Cooling systems maintain operating temperatures required for reliable operations.
How does a generator convert mechanical energy into electrical energy?
Generators turn mechanical energy into electrical energy by moving electrical conductors in a magnetic field. Excitation creates the electromagnetic field to make this mechanical to electrical conversion occur.
Is an exciter static or rotating?
Exciter systems can be rotating or static. Rotating includes brushless and brushed types and static includes compound sources and potential sources. A generator has a prime mover like a turbine or diesel generator. The excitation system creates the electromagnetic field in the rotor. The stator has the armature winding that has ...
Why is brushless excitation used?
It is typically used for reducing the regular maintenance costs and to reduce the risk of brush-fire. It was developed in the 1950s, as a result of the advances in high-power semiconductor devices.
What happens to the excitation current if the output voltage is high?
This principle is very useful for voltage control: if the output voltage of the system is less than desired, the excitation current can be increased; if the output voltage is high, excitation can be decreased.
What happens if there is no excitation current?
Except for permanent magnet generators, a generator produces output voltage proportional to the magnetic field, which is proportional to the excitation current; if there is no excitation current there is no voltage.
What is field flashing?
Field flashing. If the machine does not have enough residual magnetism to build up to full voltage, usually a provision is made to inject current into the rotor from another source. This may be a battery, a house unit providing direct current, or rectified current from a source of alternating current power.
How do field coils work?
A field coil may be connected in shunt, in series, or in compound with the armature of a D C machine (motor or generator). For a machine using field coils, as is the case in most large generators, the field must be established by a current in order for the generator to produce electricity. Although some of the generator's own output can be used ...
What is the process of generating a magnetic field?
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, ...
Can self excited generators be started without external load?
Starting. Self-excited generators must be started without any external load attached. External load will sink the electrical power from the generator before the capacity to generate electrical power can increase.
What is static excitation?
In Static Excitation System, power for providing field excitation is derived from the Generator output terminals. A transformer know as Excitation Transformer, is connected to the output terminals of Generator to step down the voltage to required voltage level usually 415 V AC. As we need DC supply, therefore Transformer output is connected to a Thyristor Full Bridge Rectifier. Figure below shows simplified block diagram of Static Excitation System.
How to provided Field Excitation during Startup of Generator?
As in Static Excitation System, field excitation power is derived from the Generator output terminals therefore it can only work during the normal and steady operation of Generator. Suppose we are going to start a Generator, in that case it is not possible to have field excitation using static excitation system as there is no Generator output terminal voltage. In such case, excitation power shall be provided using separate source. As shown in figure above, this is normally made available using a Battery Bank. As soon as the Generator reaches its rated speed, its terminal voltage reaches to rated voltage and hence Static Excitation System comes in picture. Thus as soon as Generator reaches its rated speed, Battery Bank is isolated and excitation power is fed by Static Excitation System.
Why does a regulator increase the firing angle?
Therefore, regulator increases the firing angle so that average value of DC current may reduce. Similarly, if the Generator terminal voltage goes below its rated value then field current must be increased. Therefore regulator decreases the firing angle to increase the average value of the field current.
Is there a separate rotating exciter?
As there is no separate rota ting type exci ter, the system is free from friction, windage and commutator loss occurring in the exciter.
How to separate excitation and emission wavelengths?
The separation of excitation and emission wavelengths is achieved by the proper selection of filters to block or pass specific wavelengths of the spectrum as presented in Figure 3. The design of fluorescence illuminators is based on control of excitation light and emission light by readily changeable filter insertions into the light path on the way toward the specimen and then emanating from the specimen. It is important, in view of low emission intensities, that the light source chosen for excitation be of sufficient brightness so that the relatively weak emission light can be maximized, and that fluorochromes of satisfactory absorption and yield be chosen.
How long does it take for electrons to reach a higher energy state?
Upon absorbing a photon of excitation light, usually of short wavelengths, electrons may be raised to a higher energy and vibrational excited state, a process that may only take a quadrillionth of a second (a time period commonly referred to as a femtosecond, 10E-15 seconds).
How does fluorescence occur?
In fluorescence, during an interval of approximately a trillionth of a second (a picosecond or 10E-12 seconds), the excited electrons may lose some vibrational energy to the surrounding environment and return to what is called the lowest excited singlet state. From the lowest excited singlet state, the electrons are then able to "relax" back to the ground state with simultaneous emission of fluorescent light as illustrated in Figure 4 (a). The emitted light is always of longer wavelength than the excitation light (Stokes Law) and continues so long as the excitation illumination bathes the fluorescent specimen. If the exciting radiation is halted, the fluorescence ceases.
How does the emission spectrum change?
As a result, the emission spectrum is shifted to longer wavelengths than the excitation spectrum (wavelength varies inversely to radiation energy). This phenomenon is known as Stokes Law or Stokes shift. The greater the Stokes shift, the easier it is to separate excitation light from emission light. The emission intensity peak is usually lower than the excitation peak, and the emission curve is often a mirror image of the excitation curve, but shifted to longer wavelengths. In order to achieve maximum fluorescence intensity, the fluorochrome is usually excited at the wavelength at the peak of the excitation curve, and the emission detection is selected at the peak wavelength (or other wavelengths chosen by the observer) of the emission curve. The selections of excitation wavelengths and emission wavelengths are controlled by appropriate filters. In determining the spectral response of an optical system, technical corrections are required to take into account such factors as glass transmission and detector sensitivity variables for different wavelengths.
Why is it important to choose a light source for low emission?
It is important, in view of low emission intensities, that the light source chosen for excitation be of sufficient brightness so that the relatively weak emission light can be maximized, and that fluorochromes of satisfactory absorption and yield be chosen .
What is quenching in chemistry?
Often, quenching results from the transfer of energy to other acceptor molecules physically close to the excited fluorophores, a phenomenon known as resonance energy transfer. This particular phenomenon has become the basis for a newer technique of measuring distances far below the lateral resolution of the light microscope.
What is the emission maximum?
The emission maximum is chosen and only emission light at that wavelength is allowed to pass to the detector. Excitation is induced (usually by means of a monochromator) at various excitation wavelengths and the intensity of the emitted fluorescence is measured as a function of wavelength.
What is an excitation transformer?
Excitation transformers are used to ultimately provide power to the field windings. This is done through many stages which include an initial AC stage where the excitation transformers are connected from the secondary side of the main HV transformer to an AC breaker.
What is the principle of mutual induction?
It means due to the current in primary coil, there is voltage induced in the secondary. In order for this to happen. Continue Reading.
What is a single winding?
The single winding is provided with a tap which can be used as the output (for voltage step-down) or as the input (in voltage step-up applications). One end of the winding is a common point for both input and output, and the other end fills the remaining role.
How does an exciter work?
Therefore, when the rotor rotates this exciter produces the power for the electromagnet. Control of the exciter output is done by varying the field current of the exciter. This output from the exiter then controls the magnetic field of the rotor to produce a constant voltage output by the generator. This DC current feeds to the rotor through slip rings.
What is brushless exciter?
Another method is the brushless system. In this system the armature of the exciter is on the rotor shaft itself. The DC output of this armature, after rectification by solid-state devices, goes to the rotor coils. Since the armature and rotor are on the same rotating shaft, this eliminates the need for slip rings. Hence it reduces maintenance and operational requirements and thus improving reliability.
What is the main requirement for electricity generation as per the basic principle?
Brushless Exciter. The main requirement for electricity generation as per the basic principle is a magnetic field. The generator while producing electricity also has to produce this at a constant voltage for the electrical system to work properly.
Is an exciter static or DC?
In modern generators the exciters are static. The DC power for the electromagnet is from the main generator output itself. A number of high power thyristors rectify the AC current to produce a DC current which feeds to the rotor through slip rings.
Why is AC excitation important?
If large dc errors and low-frequency noise are expected, ac excitation is useful. The excitation source is switched on alternate cycles, and the resulting amplitudes are measured and averaged to provide a conversion result. AC excitation thus removes the effects of 1/f noise and dc induced parasitic thermocouple effects in a signal chain. This allows the excitation to be greatly reduced, in turn reducing the errors introduced from self-heating in resistance-based sensors. These benefits usually exceed the disadvantages of somewhat higher implementation cost and the care that must be taken to ensure adequate settling before a measurement is made.
How does a DC excitation sensor work?
With commonly used dc excitation, the excitation current through the sensor must be large enough so that the smallest temperature change to be measured results in a voltage change that exceeds the system noise, offset and drift of the system. The excitation currents required to overcome these errors are typically 1mA or greater. The power dissipated in the RTD causes its temperature to rise, introducing drift errors in the measurement, which reduces system accuracy. For example, using a 1-mA dc excitation source with a 1-kW RTD having a self-heating effect of 0.05°C/mW results in a drift error of 0.5°C.
What are the factors that determine the excitation source?
There are two major factors in selecting an excitation source that will enhance overall system performance. First, resolution: the magnitude of the excitation should be sufficient that the minimum change in the variable being measured produces an output from the transducer that is large enough to overcome the noise and offset in the system. Second, power level: if the sensor is resistive the designer must ensure that the self-heating effects of excitation current flowing through the transducer do not adversely effect the measured results.
What is an input transducer?
Passive sensors, such as thermocouples or photodiodes (in the voltage-output mode) are two-port devices that transform physical energy to electrical energy directly, generating output signals without the need for an excitation source.
What is the field wiring scheme used in designing high resolution data acquisition systems?
In designing high resolution data acquisition systems care must be exercised in selecting the method of excitation, the excitation source for the transducer, and the field wiring scheme used in conveying the low-level analog signal from the transducer to the A/D converter.
How does a RTD circuit work?
In RTD circuits a controlled (usually constant) current is passed through the sensor, a resistor whose resistance increases gradually, repeatably, and approximately linearly with temperature. As its resistance increases, its voltage drop increases and, though small, can be measured without difficulty.
Can transducers be excited?
Active transducers can be excited using a controlled current or voltage. The choice between voltage and current excitation is generally at the discretion of the designer. In data-acquisition systems, it's not uncommon to see constant-voltage excitation used for strain and pressure sensors, while constant current excitation is used to excite resistive sensors such as RTDs or thermistors. In noisy industrial environments, current excitation is generally preferable due to its better noise immunity.
