1.0 Introduction
The design and construction of a phase fault detector for a power transformer relates to system for detecting faults in power signals, and responding appropriately. More specifically, the construction relates to system for detecting phase and / or amplitude faults in multi-phase power lines that provides power to items of equipments (power transformer) at an installation, and with a corresponding response to cut off the power in order to prevent damage to the equipment (power transformer).
1.1 The Concept of Phase Fault Detection
Suppliers of electricity such as public electric utility companies typically provide electric power to users in the form of a multi-phase AC voltage. Typically such voltages are of frequencies 50 or 60Hz, amplitude 230/ 240 or 460/480-volt and 3-phase. It is well known that such multi-phase AC voltages are susceptible to a variety of electrical disturbances which may damage an electrical installation. For example, one or more phase of the voltage may experience a sudden increase of reduction in amplitude.
Furthermore, brown-outs and power surges may occur. Also, one of the phased may actually dropout, or even reverses in phase. There could be also be a total loss of power on all phases. Each of these disturbances can induce instantaneous voltages and currents to be experienced in the equipment which can damage costly component , even if the disturbances are experienced only for a short-time. The duration of disturbance that the transformer can withstand depends substantially on the nuture of the disturbance or fault. Different types of phase or amplitude fault detection systems are in use.
However, such known systems have typically been unduly complex and for at least that reason, have lacked in reliability. Further, the response of the known systems have often been inappropriate, cutting power off when such a drastic response was not warranted for a given installation, or conversely responding too slowly when a damaging amplitude or phase fault is encountered. Perhaps, worst of all is that some fault detection systems lack the ability to reliably detect a wide range of phase faults. Thereby allowing a continued supply of power which is capable of damaging the power transformer. Hence, there is the need to provide a simple reliable and comprehensive phase faults detection and response system which can detect a variety of phase faults quickly.
Of concern to the equipment is the fact that, after the disturbance is experienced, the supplier may not restore electric power in its proper phases in a uniform manner. For example, after a total power failure the three phases may not all be restored simultaneously.
The amplitude of each phase may not be uniformly and simultaneously restored to proper levels. These occurrences is of concern because many known fault detection systems may not operate properly long after the power failure. In such system, when electrical power is interrupted to detect the state of remaining power which still reaches the transformer, possibly, damaging it. After a total power failure, the lack of power to the detection system may lead to equipment damage in the time period immediately after power is restored but before the detecting system begins to function.
Therefore, there is a need to provide an electrical amplitude and phase fault detection system which allows the use to be assured that electrical power has been fully and properly restored before providing that power to the power transformer.
1.2 Common Application of Fault Detector
Electrical power is supplied through multi-phase AC lines. These lines are associated with a variety of faults. In power systems, there are some expensive items of equipment which aid the transmission and distribution of electrical power. Amongst these is the power transformer which is very relevant in the project. The power transformer is a very important and expensive component /items in power system. The power transformer receives the power or AC voltage from the lines. This AC voltage carrying lines have faults associated with them.
Phase fault detectors are applied on the power system to protect the power transformer in the event of failure of fault on the power transformer and other electrical devices in the system. This faults detector has the capability to sense and detect faults on each phase of a multi- phase system in order to prevent damages to the power transformer.
1.3 Aim of the Project
The aim of this project is to provide a reliable simple and comprehensive electrical phase and amplitude faults detection and response system. The system includes means for detecting any of the various electrical faults.the equipment will also provide power cut-off at an appropriate time after a given fault has been detected. This prevents premature power restoration when the line power has not been fully restored to normal; thus protecting the power transformer and other equipment in the system.
1. 4 Methodology
The design of a phase fault detector for a power Transformer consists of the construction of a power transformer, a fault sensing circuit , and a power supply circuit . The power transformer consist of many turns of coil wound on the same limb of a laminated iron core and insulated from the iron and from each other. The core has no air gap and the windings are arranged concentrically on the limbs of the laminated magnetic rectangular frame constituting the core. The transformers was constructed, tested and confirmed due and good for the detector system.
The power supply circuit is comprised of a signal transformer, a full wave bridge rectifier circuit, a filter and a voltage regulator circuits. An AC voltage (240)v is fed to the signal transformer, then a steady dc voltage is obtained by full wave rectification. The rectified D.C voltage is filtered DC voltage in fed into the regulator circuit to obtain a desired fixed dc voltage which is required for the system.
This regulation is obtained from a 7805IC voltage regulator, which takes in a dc voltage and provides a somewhat lower dc voltage which remains constant even if the input dc voltage varies or the output load connected to the dc voltage changes. Below shows the block diagram of the power supply with produced signal.
The regulator voltage with less ripple is fed to the main detector circuit which is the load in the block diagram. The detector circuit and associated components are the fault sensing devices.
The circuit is constructed in a way that the fault to the circuit is simulated through the soft touch switch, which sends signal to the processor which activates the relay. The relay is normally open, and close to completes the circuit and energizes the power transformer.
When the fault signal is sensed in the processor, the buzzer makes an audible sound and the LED will lit to indicate the presence of fault in the system. When the transformer is energized, the lamp which acts as load to the transformer lights and the fault in the system cuts off the light.
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