OVERLOAD PROTECTION. All electrical circuits must have some means of protecting against overload.

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1 AN OVERLOAD PROTECTION CIRCUIT FOR AN INVERTER OR AN ELECTRIC FUSE FOR THE A.C. MAINS SUPPLY WITH A RESET BUTTON. PROJECT NO. 103 BY OPIYO LYDIA ACHIENG EXAMINER : PROF. M.K. MANG OLI SUPERVISOR: DR. C. WEKESA BY OEA ACHIENG

2 Outline Objectives What is an overload Overload protection Forms of overload protection Inverter and the mains supply Desirable features of an overload protector Basic building blocks

3 objectives To conceive and implement an overload protection circuit with a reset button Designing a simple circuit set up which performs the function of an overload sensor. Designing a circuit that trips under an overload condition. Designing a circuit that provides visual indication of the overload condition. Designing a circuit which is can be used to manually reset the system

4 OVERLOAD PROTECTION All electrical circuits must have some means of protecting against overload. Electrical circuit overloads is a type of overcurrent where more amperage is put across an electrical wire or circuit than it can handle leading to excessive generation of heat, and the risk of fire or damage to equipment.

5 Fuses are one-use only. As a circuit breaker is a complex mechanical device, outfitting an electrical panel with breakers is more expensive compared to other forms of overload protection. If a circuit breaker fails, you ll have to remove the breaker and wire in a new one. Fuse selection is prone to human error.

6 INVERTER OVERLOAD PROTECTION An overload condition in an inverter may permanently damage the power transistor array or burn off the transformer.. Block diagram of a basic inverter

7 An overload protection system for an inverter utilizes a circuit for monitoring current to the load from the inverter to detect an overload and shut off the inverter when an overload condition is detected.

8 AC Mains overload protection In the case of AC mains, an overload protection circuit acts as fuse by disconnecting the load from the main supply making sure that the loads connected do not exceed the maximum power ratings, protecting the appliance connected. The AC output voltage and frequency of a inverter is often regulated to be the same as the grid line voltage, even when there are changes in the load that the inverter is driving.

9 DESIRABLE FEATURES OF AN OVERLOAD PROTECTION CIRCUIT One that automatically shuts down the inverter or disconnects the load from the mains supply incase of an overload. Provides a visual indication of the overload condition. Continues to give visual warning, until the overload condition is cleared. Manual reset button. No replacement of circuit components in case of an overload.

10 BASIC BUILDING BLOCKS Overload sensing element An isolator Relay 555 Timer Resistors Diodes Capacitors Transistors

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13 PRINCIPLE BEHIND THE DESIGN It s a two pat circuit; The 12v power supply Supply s the low voltage side of the circuit The main overload protection circuit The mains supply to the load is routed via the N/C contacts of relay 1.

14 CONTINUED In the case of an inverter, the relays contacts are used as the inverter s oscillator OFF/ON control. The resistor R 1 acts as the overload sensing element. = ( + )

15 CONTINUED The overload limiting point is set by the preset VR 1. When the potential at the wiper of preset VR 1 becomes greater than V Z + V be, it causes forward biasing of transistor T 1. This results in the collector of transistor T 1 to be pulled down to ground thus triggering IC555, connected in the bistable mode. The output of the 555 timer causes the overload indicating LED1 to light up and forward bias transistor T 2 to energize the relay R 1. Once the output of the 555 timer goes high, it remains at this state unless it is reset pushbutton S 1 The circuit being so sensitive, capacitor C 1 acts as a bypass capacitor

16 Results With the overload limit set at 55wwatts i.e. I MAX =0.25A When a bulb rated 40 watts 220 volts is connected in the circuit and the circuit switched on, the bulb lights up and continues to light unless disconnected from the circuit. When a bulb rated 100 watts 220 volts is connected in the circuit and the circuit switched on, the bulb lights up and then goes off immediately

17 CONCLUSION The circuit described as an efficient one in terms of cost, making use of readily available electrical components in the market. The circuit instantly trips incase of an overload condition, offering overload protection to whatever load is connected to it, making it quite effective.

18 RECOMMENDATIONS The reset button could be replaced with an auto-reset button Circuit configured in such a manner that when an overload condition occurs, the trips then circuit resets itself automatically after some delay time has elapsed. The timing circuit could also be configured in a way that the overload protection circuit trips and stays off if there is a certain number of overload condition occurring in the circuit successively.

19 THANK YOU