Design And Construction Of An Automatic Synchronization System For Low Voltage Generators

1.0 INTRODUCTION
1.1 BACKGROUND OF THE PROJECT
Electrical power systems consist of the interconnection of large numbers of synchronous generators operating in parallel, interconnected by transmission lines, and supplying large numbers of widely distributed loads. When a synchronous generator (SG) is connected to an interconnected system containing many other SGs, the voltage and frequency at its terminals are fixed by the system [1].
Some of the benefits of operating multiple generators in parallel include increased reliability, expandability, flexibility, serviceability and efficiency. The redundancy inherent in parallel power generation provides significantly greater reliability for critical loads. In a parallel configuration, if one generator fails, the most critical loads are redistributed among the other units in the system. Utilizing multiple smaller generators instead of a single large unit offers greater location flexibility. With multiple generators available, individual units can be taken out of service for repair or maintenance without losing standby power for critical circuits. Electrical machines operate at maximum efficiency value close to the rated load. If the load is too low, the efficiency of the SG will decrease. Parallel operation allows operating SGs around their rated load resulting operating with high efficiency [2, 3].

Variety studies related to parallel operation and control of SGs have presented in the literature. These studies include simulation, power control, synchronization and stability of power system including SGs [4, 5]. A standard of synchronization used for power systems is given in [6]. Simulation of parallel connected SGs is presented in [7]. An automatic digital synchronization system has been proposed in [8]. Using sensors and PLC in the control unit increase the cost of the system. A control unit for the parallel operation of AC Generators is developed and presented in [9]. Zero crossing detectors are used for transmit voltage signals of generators to the microcontroller.
In this study, microcontroller based an automatic synchronization unit has been developed for the parallel operation of SGs. The control unit read calculates and evaluates the frequency, voltage, phase sequence of the received input signals and then provides the synchronization for the monitoring parallel connection conditions and parallel operation of generators. The program coded into the microcontroller has developed effectively to eliminate the interface electronics circuit from the system.

Parallel operation of generators is achieved automatically with the control unit when all parallel connection conditions occur. There is no need to use measuring tools, such as voltmeters, frequency meters, phase sequence meter, and synchroscope for monitoring the parallel connection conditions. The proposed automatic synchronization unit is cost effective, quick, reliable, stable and accurate to be used for monitoring, measurement and parallel operation of the SGs.

1.2 PROBLEM STATEMENT
When two ac generators are used to supply energy, It is not possible for the generator to supply power to the electric power system unless or until its voltage, frequency, and other parameters are exactly matched with the network. It is the process of matching parameters such as voltage, frequency, phase angle, phase sequence and waveform of the generator or other sources with a healthy or running power system is known as synchronization.
AC generators have to be synchronized with the grid before being attached to the grid. An out-of-phase generator connecting to the grid would cause a sudden power surge, possibly damaging the grid and/or the generator.

1.3 AIM AND OBJECTIVE OF THE PROJECT
AIM
The main aim of this work is to build an automatic synchronization system for low voltage generators.
OBJECTIVES
The objectives of this study are:
i. To study the matching the speed and frequency of a generators.
ii. To study structure and principle of operation synchronize generators
iii. To learn how to connect generators to utility grid or to another generator

1.4 PURPOSE OF THE PROJECT
The purposes of synchronizing generators are to provide reliability, expand demand, efficiency, expanding capacity, and meeting up with load requirement.

1.5 SIGNIFICANCE OF THE PROJECT
This study has made us to understand how generators synchronization increases the reliability of the power system and allows one or more generators to be removed for shutdown or preventive maintenance

1.6 PROBLEM/ LIMITATION OF THE PROJECT
Poor synchronization causes disturbances in the power system as well as severe damages to the generator and transients in power system. It damages the prime mover and generator because of mechanical stresses caused by rapid acceleration or deceleration. It causes high currents that can cause damage to transformers, power lines and the generator. In the absence of protection schemes, these faults can spread in whole power system thus leading to a blackout.

1.7 BENEFITS OF SYNCHRONIZATION OF GENERATORS
The reasons for synchronization of Generators are enumerated below.

Reliability
Several small units are more reliable than single large unit. This is because, if one alternator is failed, other alternators are still active and hence the whole system will not be shutdown.

Continuity of Service
In case of periodic maintenance, break-down, or repairs of one alternator, it must be shutdown and removed from service. Since the other machines are operating in a synchronize manner, the interruption to supply the load is prevented.

Load Requirements
The load requirements in the central station changes continuously. During light-load periods only one or two generators are operated to supply the load demands. During peak-load demands, other alternators are synchronized to meet the demand.

High Efficiency
Generators run most efficiently when they are loaded at their rated values. Due to the operation of few generators at light-loads and more generators at high peak loads efficiently loads the generators.

Expanded Capacity
As the demand for electric power is increasing continuously, utility companies have been increasing the physical size of the generating plants by adding more alternators. So these alternators have to be connected in synchronize manner with the existing generator equipment.

1.8 SCOPE OF THE PROJECT
Connecting generators in parallel increases the power capacity, control in load management, ease of maintenance, and redundancy. The process involves the physical connection of two or more electric generators, and the synchronization of their outputs. The synchronization matches the waveform of the output voltage of one generator with the voltage waveform of the other generator(s).
When a synchronous generator is connected to a power system, the power system is often so large that nothing the operator of the generator does will have much of an effect on the power system. An example of this situation is the connection of a single generator to the Canadian power grid. Our Canadian power grid is so large that no reasonable action on the part of one generator can cause an observable change in overall grid frequency. This idea is idealized in the concept of an infinite bus. An infinite bus is a power system so large that its voltage and frequency do not vary regardless of how much real or reactive power is drawn from or supplied to it.

1.10 DEFINITION TERMS
HV: High Voltage. This is when any electricity supply in excess of 650volts. Primarily used for the transmission of electricity over long distances.
Kva: Kilo volt amps. A measurement of the electrical ‘pressure’ and ‘quantity’ to a building.
Loads: This is an equipment that is using the electricity supplied to a building.
LV: Low Voltage. This is an Electricity supply from 110volts to 650 volts.
Power cut: this is a failure of the mains electricity by factors outside of your premises.
Single phase power: This is the electricity produced from one phase of a three phase winding or from a dedicated singles phase winding.
Winding: This is the copper wire that produces electricity when it passes through a magnetic field.
Watts: this is the total energy supplied by a circuit.
AVRs. Automatic voltage regulators. The electronic device which controls the output voltage of an alternator.
Base load rating. The rating given to a generator when it is used for continuous supply of electricity at a given load 24/7.
Black out. A national or wide area power failure, causing major disruption. For example.
Brown out. A drop in the mains voltage (not a total failure) that can cause degradation of lighting and electronic equipment.

1.11 PROJECT ORGANISATION
The work is organized as follows: chapter one discuses the introductory part of the work, chapter two presents the literature review of the study, chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.