Department of Electrical Engineering

Guided by :- Mr. Ashish Agrahari (Asst. Prof.) Himakar Tiwari

Anurag PatelDurgesh Pandey

THREE PHASE SYSTEM OVER VOLTAGE AND OVER FREQUENCY PROTECTION

EN :- 4TH Year

Submitted by :-

Overview • Introduction• Overvoltage • Types of over voltage• Over frequency & it’s type• Over voltage & over frequency protection• Block diagram• Circuit diagram• Component• Advantage & application

Three phase system over voltage and over frequency protection

INTRODUCTION

Sudden fluctuation in supply is a very big problem in industries and domestic applications. It causes a major loss for industries, offices and homes.

This project gives a low cost and powerful solution for this problem. This Circuit protects refrigerators ,ACs, Microwave ovens as well as other appliances from over and under voltage fluctuations.

WHAT ARE OVERVOLTAGES?

According to IEEE standard for Insulation Coordination, Overvoltage is defined as:

“ Voltage between one phase and ground or between two phases, having a crest value exceeding the corresponding crest of maximum system voltage.”Overvoltages may be classified by shape and duration as either temporary or transient.

Overvoltage

types

internal

Switchingo.v

Temporary

o.v

external

lightening

An Oscillatory phase-to-ground or phase-to-phase overvoltage that is at a given location of relatively long duration(seconds, even minute) and that is undamped or only weakly damped. Temporary overvoltage usually originate from switching operation or faults (e.g. load rejection, single-phase fault, fault on a high-resistance ground or ungrounded system) or from nonlinearities ( harmonics), or both. They are characterized by the amplitude, the oscillation frequencies, the total duration or the decrement.

Temporary Overvoltage:-

Temporary over voltages (sustained over voltages)differ from transient switching over voltages in that theylast for longer durations, typically from a few cycles toa few seconds.

A transient overvoltage in which a slow front, short-duration, unidirectional or oscillatory, highly damped voltage is generated (usually by switching or fault).

Switching Overvoltage:-

With the increase in transmission voltages needed to fulfill therequired increase in transmitted powers, switching surgeshave become the governing factor in the design of insulationfor EHV and UHV systems.According to the International Electro-technical Commission(IEC) recommendations, all equipment designed foroperating voltages above 300 kV should be tested underswitching impulses (i.e., laboratory-simulated switchingsurges).

Lightening Lightning is produced in an attempt by nature

to maintain dynamic balance between the positively charged ionosphere and the negatively charged earth This is then counteracted by thunderstorms, during which positive charges are transferred upward in the form of lightning. During thunderstorms, positive and negative charges are separated by the movements of air currents forming ice crystals in the upper layer of a cloud and rain in the lower part.

There are always a chance of suffering an electrical power system from abnormal over voltages. These abnormal over voltages may be caused due to various reason such as, sudden interruption of heavy load, lightening impulses, switching impulses etc. These over voltage stresses may damage insulation of various equipments and insulators of the power system. Although, all the over voltage stresses are not strong enough to damage insulation of system, but still these over voltages also to be avoided to ensure the smooth operation of electrical power system.

These all types of destructive and non destructive abnormal over voltages are eliminated from the system by means of overvoltage protection.

Over voltage Protection

WHAT IS OVER FREQUENCY & O.F. FAULT?

When in any power system network the

Value of input and output frequency isChanges then very serious fault

occursThat comes in frequency fault.

• There are mainly two types of frequency fault occurs.

Frequencyfault

Over frequency

fault

Under frequency

fault

We can summarize over & under frequency in a mathematical concept to understand and memorize as below-Production > Load demand = frequency highProduction < Load demand = frequency lowProduction = Load demand = frequency stable.

Block diagram:-

CIRCUIT DIAGRAM

Components:-

TRANSFORMERIC 7812LM 324 (OPERATIONAL AMPLIFIER)RELAYZENER DIODE N-P-N TRANSISTORRESISTORS ,CAPACITORS AND DIODES

TRANSFORMER

Step down transformer 230V/12VOperating frequency is 50HZ.Voltage is converted from 230v to 12v.Current rating is 1A.

Output current in excess of 1A.Output Voltages of 12V.current Internal thermal overload

protection.No external components required.Output transistor safe area protection.Internal short circuit limit.

IC 7812

IC LM324 (OPERATIONAL AMPLIFIER)

Features : Large DC voltage gain:100 dB Wide power supply range: Single supply:3VDC to 32 VDC Dual supplies:±1.5VDC to ±16VDC Differential input voltage range equal to the power supply voltage Power drain suitable for battery operation Large output voltage swing:0VDC to VCC-1.5VDC

Its rating is 12v, 200 ohm spdt relay.

•SPDT – Single Pole Double Throw. A common terminal connects to either of two others. Including two for the coil, such a relay has five terminals in total.

A relay is an electrically operated switch.

Diodes

Resistor

capacitor

WORKING

This proposed system will trip the load in the event of the input voltage falling below/above a set value. Two comparators are used as window comparator formed out of one quad comparator IC. This delivers an error output if the input voltage to them crosses the range beyond the voltage window. A relay is then operated to cutoff the load for safety reasons. A lamp is used as load in this project. It is extended by integrating an alarm, which sounds when the tripping takes place

It can also be enhanced in future by interfacing with a GSM modem to convey alert message to the user via SMS to take appropriate action.

For the variation of frequency we use very easy and simple concept as given below :-

Concept is simple - Use capacitor to charge up and discharge.More the threshold voltage, more time is required for capacitor to achieve it. ( Capacitor charging depends on current not voltage & charging current here depends only on Vcc, R. & C, not on Threshold voltage. )

So by controlling Threshold voltage, you will be controlling Time taken for capacitor to reach threshold voltage. And frequency is inverse of time. So you have obtained frequency in terms of Voltage.

CONT…

ADVANTAGES:Highly sensitiveFit and Forget systemLow cost and reliable circuitComplete elimination of manpowerCan handle heavy loads up to 7AAuto switch OFF in abnormal conditionsAuto switch ON in safe conditions

APPLICATIONS:-Industrial machineryHouse hold items like TV, refrigerator, ACAgriculture MotorsWater pumps

CONCLUSION: It is helpful in protecting electrical appliances in very effective way.

Thank You