What is Protective Devices?

Protective devices are devices that are used to safeguard equipment, machinery, components, and devices in electrical and electronic circuits from short circuit, over current, and ground fault. Stability and protection are the two fundamental purposes of protective devices for electrical circuits. The over-current protection is provided via a flexible power supply.

Various protective devices operate as a safeguard, protecting us from a variety of electrical hazards. These technologies, in general, eliminate fire and electrocution risks. Circuit protection devices are available. The majority of the time, this safeguard is against high voltage or current. Circuit protection are electrical devices that limit the flow of superfluous currents and short-circuit currents in electronics.

Need of Protective Devices

To safeguard electrical appliances or equipment from damage, protective devices are required.

• Equipment overloading
• Short Circuit 
• Variations in the supply voltage that are abnormal
• To safeguard the operator from coming into contact with malfunctioning equipment, which could result in a severe shock.

Types of protective Devices

The Protective Devices include the following:

• Fuse
• Circuit Breaker
• PolySwitch
• Residual Current Circuit Breaker (RCCB)
• Metal Oxide Varistor
• Inrush Current Limiter
• Gas Discharge Tube
• Surge Protection device

Fuse

A fuse is an electrical device that is used to prevent a circuit against over-current in electrical circuits. It is made out of a metal strip that melts when a high current flows across it. Fuses are important electrical devices, and there are various types of fuses on the market today based on specific voltage and current ratings, application, response time, and breaking capacity.

Fuse features such as duration and current are chosen to provide effective protection without causing unnecessary disturbance.

Circuit Breaker

A circuit breaker is an electric device that protects an electrical device against short circuits or overloads caused by excessive current supply. It is also one of the type of Protective devices used in power system and in residential purpose. A circuit breaker has a primary purpose is to interrupt current flow when a fault occurs. A circuit breaker, unlike a fuse, can be reset manually or automatically.

Circuit breakers appear in a range of sizes, includes small devices to huge switch gears, and are used to safeguard both low and high voltage circuits.

Poly switch or Resettable Fuse

It is a one of the type of Protective devices. A resettable fuse is a passive electrical equipment that protects electronic circuits from overcurrent errors by allowing them to be reset. A poly switch, multi fuse, or poly fuse is another name for this device. In some instances, these fuses work similarly to PTC (Positive temperature coefficient) thermistors, although they rely on mechanical transformations rather than charge-carrier effects within semiconductors.

Resettable Fuses are utilized in a variety of applications such as computer power supply, nuclear power plants, and aerospace applications where replacement is difficult.

RCCB

The RCD is a residual current device or RCCB is a residual current circuit breaker. It is a safety device or equipment that detects a problem of home's power supply and cuts off the electricity in 10-15 milliseconds to prevent electric shock. Because a residual current device does not provide protection against a circuit short circuit or overload and cannot utilize a fuse in place of an RCD.

RCDs are usually combined with a circuit breaker, such as an MCB (miniature circuit breaker) or a fuse, to protect the circuit from overload current. The residual current gadget is likewise incapable of detecting a human being if both conductors are accidentally touched at the same time.

These equipment are both testable and reprogrammable. After an error state has been cleared, a test button firmly produces a tiny leakage condition, and a reset button reconnects the conductors.

Inrush Current Limiter

This is a type of electrical component or equipment intended to prevent inrush current from damaging equipment and tripping circuit breakers and exploding fuses. Fixed resistors and NTC (negative temperature coefficient) thermistors are excellent examples of inrush current limiter devices.

First, Inrush Current Limiter have a high resistance, which prevents large currents from flowing when turned on. Because the flow of current persists, NTC thermistors heat up, allowing for a large flow of current during normal operation. These thermistors are often far superior to measurement type thermistors, which are designed specifically for power applications in Power system.

Metal Oxide Varistor

A varistor, also known as a VDR (voltage dependent resistor), is an electrical component whose resistance changes depending on the applied voltage. The name varistor comes from the term variable resistor. The resistance lowers as the voltage of this component increases. Similarly, as the extreme voltage grows, the resistance decreases considerably.

These are qualified to protect electrical circuits during voltage fluctuations because of this ability. Both electrostatic discharges and lightning strikes can cause a flow. The most common voltage-dependent resistor is the MOV (metal oxide varistor).

Gas discharge tube

A gas discharge tube, also known as a gas-filled tube, is a set of electrodes enclosed in a temperature-resistant and insulating envelope and immersed in a gas. The Townsend avalanche phenomena is used to ionize the gas with a high enough applied voltage to cause electrical conduction.

Sodium-vapor lamps, fluorescent lamps, metal halide lamps, neon lights, etc. are include in expulsion lamps. Gas-filled tubes known as krytrons, thyratrons, and ignitrons are employed as switching devices in a variety of electrical devices.

The force, geometry of the tube, and composition of the fill gas all influence the needed voltage to start and maintain discharge. Power tubes usually use ceramics, while military tubes frequently use glass wrinkled metal, despite the fact that the cover is normally glass.

Surge protection device

Surge Protection Devices, or SPDs, are one sort of component used in an electrical fitting security system. In the power supply circuit, the SPD device is connected in parallel and can be employed at any level of the power supply system. Surge protection devices are the most common and well-organized type of over-voltage protection devices.

Advantages of Protective Devices

• Operated at high speed.
• Reliable.
• Equally effective in clearing low and high fault currents.
• Consistence performance.
• Automatic switch off under overload and short circuit condition.

Common Mistakes

• Make sure the protective equipment must not have lower rating then required.
• Make sure that protective equipment must not have higher rating then required.
• The periodic maintenance must be done for the health of the equipment.
• In case of the circuit breaker quality of the dielectric must be good enough to withstand the fault conditions.

Context and Applications

The most common application of the topic is in the field of engineering and sciences. The list of the courses are listed below:

• Bacheor of Technology in Electrical Engineering
• Master of Technology in Electrical Engineering

Some of the other applications of the topic are listed below:

• Protective devices are used in Industries as important devices with power equipment.
• In residential and commercial purpose the protective devices are used to ensure the uninterrupted power supply.
• In electrical power transmission the protective devices are used to protect the electrical transformers, transmission lines and many more.
• In substation protective devices are used for protection of the equipment against fault.
• Bachelor of Technology in Electrical Engineering.
• Masters of Technology in Electrical Engineering.
• Bachelor and Masters of technology in Power Engineering

Related Concepts

• Power System Protection
• Circuit Protection
• Types of Protective devices
• Fundamental of Power system Protection
• Earthing System

Practice Problems

Q1. Protective devices are protect the equipment from..........

A. Over-voltage

B. Over-current

C. Short-Circuit Current

D. All of the above

Answer: D

Explanation: The over-current protection is provided via a flexible power supply. Various protective devices operate as a safeguard, protecting us from a variety of electrical hazards. These technologies, in general, eliminate fire and electrocution risks. Circuit protection devices are available.

Q2. What is purpose of protective devices?

A.Equipment overloading

B. Short Circuit 

C. Variations in the supply voltage that are abnormal

D. All of the above

Answer: D

Explanation: To safeguard electrical appliances or equipment from damage, protective devices are required.

Q3. A fuse is an electrical device that is used to prevent a circuit against, ...................... in electrical circuits.

A. Over-voltage

B. Over-current

C. Over-frequency

D. None

Answer: B

Explanation: A fuse is an electrical device that is used to prevent a circuit against over-current in electrical circuits.

Q4. A ..................... is an electric device that protects an electrical device against short circuits or overloads caused by excessive current supply.

A. Fuse

B. Circuit Breaker

C. PolySwitch

D. RCCB

Answer: B

Explanation: A circuit breaker is an electric device that protects an electrical device against short circuits or overloads caused by excessive current supply.

Q5. A .................... is a passive electrical equipment that protects electronic circuits from overcurrent errors by allowing them to be reset.

A. Fuse

B. Circuit Breaker

C. Resettable fuse

D. RCCB

Answer: C

Explanation: A resettable fuse is a passive electrical equipment that protects electronic circuits from overcurrent errors by allowing them to be reset.