CHAPTER 3 -METHODOLOGY-

CHAPTER 3

3.1  METHODOLOGY

3.1.1 List of equipment

—  Step Down Transformer

—  Voltage regulator

—  Menthol & LED

—  Comparator

—  555 Timer

—  Switch

—  Diode

 TRANSFORMER

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This is a step-down transformer, as evidenced by the high turn count of the primary winding and the low turn count of the secondary. As a step-down unit, this transformer converts high-voltage, low-current power into low-voltage, high-current power. The larger-gauge wire used in the secondary winding is necessary due to the increase in current. The primary winding, which doesn't have to conduct as much current, may be made of smaller-gauge wire

COMPARATOR

Potential dividers are connected to the inverting and non-inverting inputs of the op-amp to give some voltage at these terminals. Supply voltage is given to +Vss and  – Vss is connected to ground. The output of this comparator will be logic high (i.e., supply voltage) if the non-inverting terminal input is greater than the inverting terminal input of the comparator. If the inverting terminal input is greater than the non-inverting terminal input then the output of the comparator will be logic low.

 555 TIMER

The 555 has three operating modes:

Monostable mode: in this mode, the 555 functions as a “one - shot”. Applications include timers, missing pulse detection, bounce free switches, touch switches, frequency divider, capacitance measurement, pulse-width modulation (PWM).

  Astable  –  free running mode: the 555 can operate as an oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation.

Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is not connected and no capacitor is used. Uses include bounce free latched switches.

 RELAY

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another.

Relays were used extensively in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relay".

 Block Diagram

 Block Diagram Explanation

The project uses six numbers step-down transformers for handling the entire circuit under low voltage conditions of 12v only to test the three phase fault analysis. The primaries of three transformers are connected to a three phase supply in star configuration, while the secondary of the same is also connected in star configuration. The other set of three transformers with its primary connected in star to three phase have their secondary’s connected in delta configuration. The outputs of all the six transformers are rectified and filtered individually and are given to six relay coils.  Six push buttons, one each connected across the relay coil is meant to create a fault condition either at star i.e. Line to Line Fault or three Line Fault. The Normally Closed (NC) contacts of all the relays are made parallel while all the common points are grounded. The parallel connected point of NC are given to pin2 through a resistor R5 to a 555 timer i.e. wired in monostable mode.

The output of the same timer is connected to the reset pin 4 of another 555 timer wired in astable mode. LED’S are connected at their output to indicate their status. The output of the U3 555 timer from pin3 is given to an Op-amp LM358 through wire 11 and d12 to the non-inverting input pin3, while the inverting input is kept at a fixed voltage by a potential divider RV2. The voltage at pin2 coming from the potential divider is so held that it is higher than the pin3 of the Op-amp used as a comparator so that pin1 develops zero logic that fails to operate the relay through the driver transistor Q1.

While the board is powered from a three phase supply all the six relay coils get DC voltage and their common point disconnects from the NC and moves on to the Normally Open (NO) points there by providing logic high at pin2 of 555 timer U1 i.e. that is kept on monostable mode. While any push button across the relay is pressed it disconnects that relay and in the process in common contacts moves to the NC position to provide a logic low at trigger pin of 555 timer to develop an output that brings the U3 555 timer which is used in astable mode for its reset pin to high such that the astable operation takes place at its output which is also indicated by flashing D11 LED.

If the fault is off temporary in nature i.e. if the push button pressed is released immediately the U1 monostable disables U3 the output of which goes to zero in the event of any push button kept pressed for a longer duration the monostable output provides a longer duration active situation for U3 the astable timer the output of which charges capacitor C13 through R11 such that the output of the comparator goes high that drives the relay to switch off three phase load.

The output of Op-amp remains high indefinitely through a positive feedback provided for its pin1 to pin3 through a forward biased diode and a resistor in series. This results in the relay permanently switched on to disconnect the load connected at its NC contacts permanently off. In order to maintain the flow of DC supply the star connected secondary set DC’S are paralleled through D8, D9 & D10 for uninterrupted supply to the circuit voltage of 12v DC and 5v DC derived out of voltage regulator IC 7805.

 Flow Chart

 Flow Chart Explanation

After pick up the title, the research begin with some article for literature view and after get the circuit the simulation begin. If the simulation did not work so the research keep continue until the right progress made and after simulation done the construction of the circuit start then the circuit will be test and if it is not working the trouble shoot will be made to find error and after the circuit working so the analysis will be do and finally the report will be made.