Design And Construction Of A High And Low Voltage Cut-Off With Time Delay

ABSTRACT

The power line fluctuations and cut-offs causes damages to electrical appliances connected to the line. It is more serious in the case of domestic appliances like fridge and air conditioners. If a fridge is operated on low voltage, excessive current flows through the motor, which heats up, and get damaged.

High and low voltage cut off is a device designed to protect electrical appliances from over voltage as well as under voltage. The under/over voltage protection circuit with time delay presented in this work is a low cost and reliable circuit for protecting such equipments from damages. Whenever the power line is switched on it gets connected to the appliance only after a delay of a fixed time. If there is hi/low fluctuations beyond sets limits the appliance get disconnected. The system tries to connect the power back after the specific time delay, the delay being counted from the time of disconnection. If the power down time (time for which the voltage is beyond limits) is less than the delay time, the power resumes after the delay: If it is equal or more, then the power resumes directly.

This circuit has been designed, built and evaluated by me to use as a protector for my home refrigerator. This is designed around readily available semi-conductor devices such as standard bipolar medium power NPN transistor (D313/SL100/C1061).

The complete circuit is consisting of various stages. They are: – Dual rail power supply, Reference voltage source, Voltage comparators for hi/low cut offs, Time delay stage and Relay driver stage.

CHAPTER ONE

INTRODUCTION

High and low voltage cut off is a device designed to protect electrical appliances from over voltage as well as under voltage. The under/over voltage protection circuit with time delay presented in this work is a low cost and reliable circuit for protecting such equipments from damages. Whenever the power line is switched on it gets connected to the appliance only after a delay of a fixed time. If there is hi/low fluctuations beyond sets limits the appliance get disconnected. The system tries to connect the power back after the specific time delay, the delay being counted from the time of disconnection. If the power down time (time for which the voltage is beyond limits) is less than the delay time, the power resumes after the delay: If it is equal or more, then the power resumes directly.

This work provides few circuit ideas that can provide low voltage and over voltage protection to connected electrical assets. Though these circuits won’t be able to stabilize the input voltage, even so may prove very effective in providing total safety to your precious electrical home appliances against dangerous input voltages.

The first design of a low voltage indicator circuit may be used to indicate the presence of dangerous low voltage conditions.

A low voltage may appear to be something that is lower in magnitude and power, but that is what makes it more lethal. For example a refrigerator working at 230 volts AC mains will never “like” voltages below 190, since in such cases its compressor due to the lack of sufficient voltage, will try to compensate by drawing heavy currents and may get damaged if the situation persists. The same is true for other types of AC operated motors.

Also in vehicles, for example a car, if the battery voltage falls below 9 volts, it may be quite harmful for the life of the battery itself and moreover the vehicle will just not start at that voltage.

1.2                                          OBJECTIVE OF THE PROJECT

The objective of this work is:

• Provide a solution to under voltage and over situation faced by residents of high density areas of Nigeria by designing and constructing an effective and comparatively cheaper voltage stabilizer which will have a cost price of less than total cost obtained which could be afforded by most low income earners.
• To regulate the voltage of there is any over voltage or under voltage an regulate the voltage that will suit the purpose the analysis design, construction and cost comparison have been done and necessary tests have been satisfactory out.

1.3                                        SIGNIFICANCE OF THE STUDY

As a student of electrical and electronic engineering, working on this project have expose my knowledge to function and working principle of many electrics components such as voltage comparator, transistor, and mainly to auto-transformer.

It has made me to understand the working principle and application of s of over and under voltage cutout if for both in homes and industries.

1.4               APPLICATIONS OF HIGH-AND-LOW VOLTAGE CUT-OUT

Over or under voltages in electricity is one of the major problems that affect their production. Due to high demand of electricity to sustain their operations, it results to low or high voltage output which can damage equipments. Therefore, these companies need specialized devices to help them protect their equipments from early wear and tear. High-And-Low Voltage Cut-Out is an electromechanical constituents that control the regular voltage outputs. During peak consumption of electricity, the sudden flow of power can damage electric or electronic machines. On the other hand, if there is low output of voltage, a machine may fail to function. It  provide safe output to guard varieties of equipments including ultra modernized music systems, medical equipments LCD, Home Theater, industrial machines and more. They are designed with special features to protect equipments which include line noise spike protection, primary switching technology, auto reset, and overload cutoff protection. In order to preserve the life of machines, these devices are recommendable in any operation. They assure that machines are working well all the time especially in peak timings.

1.5                     ADVANTAGES AND APPLICATIONS OF THE PROJECT

1. Cost is less as compared to voltage stabilizers
2. Consumes less power.
3. This circuit is used in homes and offices to protect equipments from high voltages and low voltages.