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synchronization and protection of alternators
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INTRODUCTION
We can’t store the power generated from power plant that power would be in the order of (msw), so we should utilize that generated power .for that purpose we have to transmit that power to loads. But we can’t transmit directly (msw) of power to consumer loads. we want one media in between genearation and load i.e substation .substation is a device to step up or step down voltage level if we want to transmit power from generating station to substation conductor are required. So we connect the alternator output conductors to the substation input conductors i.e nothing but bus bars .the process of connecting two alternators or alternator to bus bar is called synchronization .in this project it deals how the synchronization takes place in the msw power station.
In a generating station the generator and transformer are the most expensive equipements and hence it is desirable it employ a protective system to isolate the fault equipement as quickly as possible to keep the healthy section in normal operation and to ensure uninterruptable power supply .The basic electrical quantities those likely to change during abnormal fault conditions are current voltage, phase angle and frequency, protective relays utilizes one or more these quantities to detect.
CHAPTER 2
SYNCHRONISATION
Definition:The operation of connecting an alternator in parallel with another alternator or with common bus bars is known as synchronizing. generally,alternators are used in a power system where they are in parallel with many other alternators. It means that the alternator is connected to a live system of constant voltage and constant frequency. often the electrical system to which the alternator is connected, has already to many alternators and loads connected to it that no matter what power is delivered by the incoming alternator ,the voltage and frequency of system remain the same. In that case ,the alternator is said to be connected to infinite bus-bars
Most of the alternators feed into power systems which are composed of a large number of interconnected alternators.The size of the system is so large that the addition or removal of one alternator does not affect the system voltage and frequency. Such a large system, operation at constant voltage and frequency, is known as an infinite bus bar system.E is the induced emf of alternator and V is the bus bar voltage.when an alternator has just been put in parallel with the bus ,V and E would be equal,alternator current would be zero and alternator power output would be zero. The power input to machine would be just sufficient to supply the losses of the alternator. The machine would be electrically floating, neither generating nor motoring.the increase in power input would tend to accelerate the rotor and E would move ahead of V..the magnitude of E depends on field current. By adjusting the field current, power factor can be adjusted to any value .the excitation controls the reactive power output, while the governor speed setting controls the active power output. The power angle plays an important role in the operation of the machine. when & is made to increase excessively, the machine becomes unstable. When operation alters from generator to motor & changes from positive to negative
2.2 REQUREMENTS:
Frequency:
Before alternators can be paralleled the following conditions must be met:
• The frequency of the machines must be the same;
Ideally, the incoming machine frequency should be within 0.2% of the bus bar frequency, which is indicated by one revolution of the synchroscope every ten seconds. In practice this may be impossible to achieve if the busbar frequency may be fluctuating with load changes. It is usual to synchronize with the incoming machine
• voltage:
The voltages must be the same.
For manual synchronising, the operator should ensure that the incoming voltage is within 5% of the busbar voltage
The alternator already connected to the busbars is called the reference machine, or the
busbar machine.
The alternator being paralleled is called the incoming machine
The diagram above shows a typical arrangement with the busbar machine on the left and
the incoming machine to the right.
2.3 Frequencey control:
• Frequency is directly proportional to the speed of the prime mover (diesel engine). By controlling the engine speed, the frequency can be raised or lowered.
• This is achieved using spring loaded switches on the switchboard that operate an
electric motor mounted on top of the diesel engine governor, as shown in the
diagram below.
Incoming machine frequency:
• It is virtually impossible to get the frequency of the incoming machine exactly the same as the busbar.
• The frequency of the incoming machine should be slightly higher than that of the
busbar frequency. This is to ensure that when the main breaker is closed the
incoming machine will tend to take load, which will hold the breaker on the
board.
• The frequency of the incoming machine should not be lower than the busbar frequency. This is because when the main breaker is closed the incoming machine will tend to resist taking any load, and the breaker may trip out on reverse power.
2.4 Voltage control:
The voltage of the incoming machine should be checked. If the voltage is low then there are several possible causes, that includes:
The voltmeter is not reading correctly;
The automatic voltage regulator (AVR) has a malfunction;
The AVR is not set correctly;
There is a failure with the exciter
2.41 AVR controls
• Besides the prime mover speed control alternators have voltage control (rotor field current control) using the automatic voltage regulators (AVR).
• The effects of adjusting the controls differs depending upon the operating conditions of the generators i.e. single operation or parallel operation.
• For single generator operation the speed control varies the generator speed and hence
the frequency of the stator output voltage:
Frequency,
f = p.n
Where: p = pairs of poles n = speed in revs/sec
• For single generator operation the voltage control varies the strength of rotor magnetic
field and hence the magnitude of the stator output voltage.