Design and Application of Auto Recloser Relay

Project Title

Design and Application of Auto Recloser Relay

Project Area of Specialization Electrical/Electronic EngineeringProject Summary

This project develops an automatic tripping mechanism for three-phase transmission system. There may occur several failures in a three-phase supply system due to some faults which may be temporary or permanent. A fault in a power system can be referred to any abnormality in the electric current flowing in it. For example, if the current is interrupted by some failure in the circuit, the resulting fault is an open circuit fault. If the current in the circuit bypasses the normal load, it results in a short circuit fault. Due to these faults, the power system suffers considerable damage which may lead to disturbance in power supply. The proposed system can overcome such problems, by detecting the faults automatically and disconnects the system from the supply so that a large scale of damage to the system equipment can be avoided. The system automatically differentiates between a temporary disturbance and a permanent fault and appropriately cuts the supply for a short duration or long respectively.

Project Objectives

• To develop an automatic mechanism for a three-phase transmission system which senses the fault automatically and differentiate between a temporary and permanent fault.
• To develop such a mechanism which after sensing and differentiating the fault automatically disconnect the healthy circuit from the faulty part of the circuit.

Project Implementation Method

This project uses 6 step-down transformers for handling the entire circuit under low voltage conditions of 12V only. The primaries of 3 transformers are connected to a 3 phase supply in star, while the secondary of the same are also connected in star. The primaries of other 3 transformers are connected to a 3 phase supply in star, while the secondary of the same are connected in delta. The outputs of all the 6 transformers are rectified and filtered individually and are given to 6 relay coils.

6 push buttons i.e. fault switches, every button connected across the relay coil, is meant to create a fault condition either at star or delta i.e. LL Fault or 3L Fault.

            The Normally Closed (NC) contacts of all the relays are made parallel while all the common points are grounded. The parallel connected points of NC are given to pin2 through a resistor 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 a stable mode. LEDs 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 a potential divider RV2 keeps the inverting input at fixed voltage. The voltage at pin2 coming from the RV2 (potential divider) is held such that it is higher than the voltage at pin3 of the Op-amp used as a comparator. As a result, pin1 develops zero logic that fails to operate the relay through the driver transistor Q1. This relay Q1 is 3CO relay i.e. it disconnects the load to indicate fault condition.

Benefits of the Project

1. It automatically disconnects the faulty part of the circuit from the healthy one.
2. It differentiates automatically between a permanent fault and a temporary fault.
3. It resets the circuit automatically in case of temporary fault.
4. It trips the circuit completely in case of permanent fault.
5. It is time saving in comparison with the manually operated system.
6. It is more reliable and efficient than manually operated system.

Technical Details of Final Deliverable

The board is powered from a 3 phase supply but all the 6 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. kept on monostable mode. When any push button across the relay is pressed, it disconnects that relay and in the process in common contacts moves to the NC position.

It provides a logic low at trigger pin of 555 timer to develop an output that brings the U3 555 timer which is used in a stable mode, for its reset pin to high such that the stable 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 U1monostable disables U3. The output then 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 stable timer, the output of which charges capacitor C13 through R11 such that the output of the comparator goes high so that it drives the relay to disconnect the 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. As a result, the relay is 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 DCs 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.

Final Deliverable of the Project Hardware SystemCore Industry OthersOther IndustriesCore Technology OthersOther TechnologiesSustainable Development Goals Industry, Innovation and InfrastructureRequired Resources

Item Name	Type	No. of Units	Per Unit Cost (in Rs)	Total (in Rs)
			Total in (Rs)	33900
Fault switches	Equipment	6	550	3300
Timers	Equipment	2	800	1600
Regulator	Miscellaneous	2	700	1400
Resistors	Miscellaneous	50	90	4500
LEDs	Miscellaneous	12	75	900
Transformer	Equipment	6	1300	7800
Arduino UNO	Equipment	1	3000	3000
LAMPS	Equipment	8	300	2400
Capacitors	Equipment	18	200	3600
Diodes	Equipment	15	200	3000
PCB	Equipment	2	1200	2400