ABSTRACT remain constant and varies in a

ABSTRACT

Automatic
synchronization is widely used to connect more than one alternators or an
alternator with busbar. The main task of a synchronizer is to capture the
voltage, frequency and phase sequence between the alternators accurately and
rapidly. The manual methods of synchronization demand a skilled operator. Under
emergency condition such as synchronizing of large machine a very fast
operation become more difficult which may not be possible for human operation.
Thus, there is a need of auto synchronizer in a power station. This project
describes a microprocessor based setup for synchronizing a three-phase
alternator to bus bar. The developed automatic synchronization unit is fast,
cost effective and reliable.

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CHAPTER 1

INTRODUCTION

Introduction

Electrical
power system mainly consists of an alternators/generator, transmission lines,
and supplies large numbers of widely distributed loads. In many cases, there is
a need to connect more than one generator to the system. It is known that load
on a power system not remain constant and varies in a discreate manner. To cope
with requirement of variable load and continuity of supply, synchronization of
alternator is necessary.

 

            Some of the
benefits of operating alternator in parallel with another alternator or bus bar
are increased reliability, expandability, flexibility, serviceability and
efficiency. For, an efficient operation of synchronization, the voltage, phase sequence
and frequency must be in a suitable limit. Severe damage to the alternator as
well as system may result if it is allowed to connect to the system above and
below the safe levels.

 

              Therefore, the
automatic synchronizing device plays an important role in synchronization. For
many years, the researchers have done so much work to develop the high performance-synchronizing
device. The main problems of connecting an alternator to an electrical system are
the limits of the delta phase sequence, the delta frequency, and the delta
voltage magnitude.

 

These problems
are summarized below:

 

1)     
Delta
Frequency

Delta frequency is the relative
frequency of an alternator with respect to the busbar. If the difference
between frequency of alternator and bus bar then this also cause a shock.

 

 

 

 

2)     
Delta
Voltage Magnitude

Delta voltage magnitude is the
relative magnitude of an alternator with respect to bus bar. There are two
cases that may occur in this case

 

                          
i.           
Low
alternator voltage

                        
ii.           
High
alternator voltage

 

Excessively low alternator terminal
voltage during the synchronization could cause stability problems due to the
weak magnetic circuit between the generator and the system.

 

Excessively high alternator terminal
voltage during the synchronization will create a large reactive power flow from
the system to the generator which can damage the generator shaft and mechanical
shock to the stator windings.

 

 

3)     
Delta
Phase Sequence

When we connect an alternator to an
electrical system with a high delta phase sequence between the alternator and
the bus bar causes a shock to the alternator. This shock may create stress on
prime shaft.

 

 

                    Therefore, it is necessary to keep the three synchronizing
parameters within acceptable limits. There are several methods available for
generator parameters measurements; most of them can be categorized into either
hardware based or software based methods.

 

Problem Statement

Synchronization means all the parameters
are matched before the circuit breaker is closed. All the conditions are
clearly illustrated in the previous section. If there is difference between the
frequencies of alternator and bus bar this is called “Slip”.

A faulty synchronization is
that in which all the three conditions are not in acceptable limits. According
to IEEE C50.12 and IEEE C50.13 the faulty synchronization as closing the
breaker outside the following limits:

• Phase: ±10 degrees.

• Voltage: 0 to +5 percent.

• Slip: ±0.067 Hz.

 

For a fast synchronization,
manual methods become insufficient for the synchronization process to do in
required limits that may result in the sever damage or loss. These problems are
serious especially when the alternators are far away from each other.

Objective

         Our main
objective of our project is to make an efficient synchronization device that
will able to connect the alternator to busbar within permissible limits that
are defined. Proposed model is developed with microprocessor 8085. A single
microprocessor can efficiently measure and control the parameters of
synchronization.

          This project will be able to measure
and compare the voltage and frequency between an alternator and the busbar and
able to make necessary changes in the frequency and voltage if any required.
When these two limits become satisfied Instant Inphase Detector will find the
correct instant to shut down the circuit breaker.

 

 

 

 

 

 

 

CHAPTER 2

LITERATURE REVIEW

 2.1           
Synchronization

            In dictionary synchronization is the operation or activity of two or
more things at the same time or rate. In simple words, it is a process of
electrically connecting and matching one alternator with another or to the
busbar.

          If we talk in a precise
manner then it is an act of matching two different alternator’s phase, voltages
and frequencies.

Illustrating the words mathematically, voltages provided by the alternator
is in the form

And the voltage from the busbar that we are obtaining are

For synchronization, the voltages of alternator and bus bar
must be equal that is

=

That implies

=

So all these parameters should be matched.

 

 

 

 

 2.2           
Synchronizing methods

          We can categorize it into two methods which are
manual synchronization and automatic synchronization.

 

Manual synchronization

In manual synchronization, the operator has a full control over
generator speed, and after meeting the synchronization conditions, he is
responsible to operate the breaker closure command. Manual synchronizing is
completely performed by the operator. This type of synchronizing method is
quite simple.

               The main
disadvantage of this method is that it requires well trained operators at the
controls to prevent sever damage to system due to improper synchronization. Manual synchronization can be
performed by the two different ways

1.     Synchronizing lamps

2.     Synchroscope

Synchronizing lamps

     This is the oldest method
used to synchronize the alternator with another alternator or to busbar. This method uses three lamps connected across like phases of the open
breaker, and two voltmeters one to measure the first alternator voltage, and
the other one is used to measure second alternator or busbar voltage to satisfy
the first condition of paralleling.

              Other conditions can
be satisfied using lamps, As the generator speed changes, the lights will
flicker at the frequency proportional to the difference between alternator frequency and
busbar frequency. The lamp would be at maximum brilliance when the alternator
is completely out of phase and completely extinguished when the two voltages
were in phase with identical magnitudes. The procedure steps to follow for the
synchronization in this method are given below

Step1:

The prime mover of the incoming machine starts, and the generator is
brought up to near its rated speed.

Step2:

By adjusting the field current, the terminal voltage of the alternator
is made the same as that of the busbar. The lamp in the circuit will now
flicker at a rate equal to the difference in frequency of the alternator and
busbar. Correct connection of the phases result on synchronous brightening and
blacking of the lamps. If this is not the case, then it means two of the lines
are connected wrongly and they need to be interchanged.

Step3:

Further adjustment of the incoming prime mover is now necessary, until the
lamps flicker at a very low rate, the lamps pulsed as the alternator voltage
rotated with respect to the system voltage at slip frequency.

Step4:

After taking final adjustments, the operator would initiate a breaker
close when the lamps were dark, indicating matching voltages and phase are
matched together and ready to synchronize.

Synchroscope

Synchroscope is a device that indicates the degree to which two
systems are synchronized with each other. It plays a vital role in ensuring
that the two power supplies which are being synchronized are “in
phase” with each other.

      The Synchroscope has a dial with
a pointer which can occupy different positions according to the difference in
the phase angle. The positions are usually compared with the
markings on the clock.

3 ‘O’clock position indicate that the voltages are apart by an angle of
30 degrees.

6 ‘O’clock position indicate that the voltages are apart by an angle of
180 degrees.

When the pointer is at the 12’O’clock position, it indicates that the
difference in phase angle between the two sources is zero. The breaker
connecting the two sources can now be closed.

 

 

 

Working Principle

             The synchroscope
consists of a small motor with coils on the two poles connected across two
phases i.e incoming alternator and bus bar. The bus bar circuit consists of an
inductance and resistance connected in parallel. The inductor circuit has the
delaying current effect by 90 degrees relative to current in resistance.

             These dual currents
are fed into the synchroscope to the armature windings which produces a
rotating magnetic field. The polarity of the poles will change alternatively in
north/south direction with changes in red and yellow phases of the incoming
machine. The rotating field will react with the poles by turning the rotor
either in clockwise or anticlockwise direction.

            If the rotor is moving
in clockwise direction this means that the incoming machine is running faster
than the bus bar and slower when running in anticlockwise direction. Generally,
it is preferred to adjust the alternator speed slightly higher, which will move
the pointer on synchroscope is in clockwise direction. The breaker is closed
just before the pointer reaches 12 o clock position, at which the incoming
machine is in phase with the bus bar.

 

             Sometimes as a
precaution against out-of-step connection of a machine to a system, a “synchro
check” relay is installed that prevents closing the generator circuit breaker unless the machine is within a few
electrical degrees of being in-phase with the system.

The manual system uses two types of sync-check relay:

a)      electromechanical sync-check relays

b)      solid-state sync-check relay

 

Automatic synchronization

Design of an automatic synchronizing device mainly adopt several kinds
of controllers and these are listed below

 

 

1)     
PLC

2)     
DSP

3)     
Microcontroller

4)     
Microprocessor

            Using sensors and PLC
in the control unit increases the cost of the system. But it is most effective
way to do the synchronization.

            Using DSP can realize
the high arithmetic rate, but the cost is expensive, and the developing period
is long.

             An automatic
synchronizer based on dual principles and dual microcontroller is developed.
Both modules monitor the parameters of alternators, and switch is connected
when all parameters are synchronized.

             Using Microprocessor,
we can easily control the voltage, frequency and phase by using some axillary
devices just like

Frequency
Controlling Unit
Voltage Controlling
Unit
Circuit Breaker with
Switching Circuit
Signal Conditioning
Unit
Display unit

 

In order to improve the celerity, veracity and security of the
alternator synchronizing operation, an alternator synchronizing device based on
8085 microprocessors, is developed.

This device is simple in structure and cheap. Only one microprocess is
required to do the required task.