A Report of Workshop on
“Industrial Application of Protective Relays and Circuit Breakers”
Department of Electrical & Electronics Engineering (EN) at ABES Engineering College organized a workshop on “Industrial Application of Protective Relays and Circuit Breakers” for the students of B.Tech-3rd and 4th year of EN department in Seminar Hall-2, Bhabha Block on 6th September 2019. The speakers for the workshop were Ms. Anupama Singh, Manager, Training; Mr. Uttam Saha, Manager, Sales, and Mr. Avdesh, Technical In-charge Legrand India Pvt. Ltd.
Ms. Anupama initiated her lecture with an overview of Protective Equipment and emphasized on Circuit Breakers and its types. The session was made interactive by thought-provoking questions posed by Ms. Anupama Singh to the student audience and presenting them a gift for every correct answer.
Later, Ms. Anupama and Mr. Uttam explained about different types of circuit breakers, their protection schemes and working. The lecture was mainly focused on two types of faults i.e. overcurrent Faults and Overload Faults and their protection.
Four types of circuit breakers were described for the protection of over current and overload faults are as follows –
1. MCB (Miniature Circuit Breaker) – An automatic switch that stops the flow of electric current in a suddenly overloaded or otherwise abnormally stressed electric circuit.
There is two arrangement of operation of the miniature circuit breaker. One due to thermal effect of over current and other due to electromagnetic effect of over current. The thermal operation of the miniature circuit breaker is achieved with a bimetallic strip whenever continuous overcurrent flows through MCB, the bimetallic strip is heated and deflects by bending. This deflection of bimetallic strip releases a mechanical latch. As this mechanical latch is attached with operating mechanism, it causes to open the miniature circuit breaker contacts. But during short circuit condition, the sudden rising of current causes electromechanical displacement of plunger associated with tripping coil or solenoid of MCB. The plunger strikes the trip lever causing an immediate release of latch mechanism consequently open the circuit breaker contacts.
MCB is characterized into three types according to its tripping current and operating.
These types of MCBs are tabulated below –
Type Tripping Current Operating Time
Type B 3 To 5 time full load current 0.04 To 13 Sec
Type C 5 To 10 times full load current 0.04 To 5 Sec
Type D 10 To 20 times full load current 0.04 To 3 Sec
MCBs are of following types according to poles:
1. Single Pole
2. Pole (with N)
3. Pole (DP)
4. Pole (TP)
5. Pole with N (TPN)
6. Pole (4P)
Ratings – 6A – 100A
2. MCCB (Molded Case Circuit Breaker)- A molded case circuit breaker, abbreviated MCCB, is a type of electrical protection device that can be used for a wide range of voltages, and frequencies of both 50 Hz and 60 Hz. The main distinctions between molded-case and miniature circuit breaker are that the MCCB can have current ratings of up to 2,500 amperes, and its trip settings are normally adjustable.
MCCB has three main functions:
• Protection against overload – currents above the rated value that last longer than what is normal for the application.
• Protection against electrical faults – During a fault such as a short circuit or line fault, there are extremely high currents that must be interrupted immediately.
• Switching a circuit on and off – This is a less common function of circuit breakers, but they can be used for that purpose if there isn’t an adequate manual switch.
Ratings – upto 2500A
3. RCCB (Residual Current Circuit Breaker) – A Residual Current Circuit Breakers is another different class of Circuit Breakers. A Residual Current Circuit Breaker (RCCB) is essentially a current sensing device used to protect a low voltage circuit in case of a fault. It contains a switch device that switches off whenever a fault occurs in the connected circuit.
The underlying fundamental principle behind the operation of RCCB is that in ideal situations the current flowing into the circuit through live (hot) wire should be the same as the returning current from the neutral. In case of an earth fault, the current finds a passage to earth through accidental means (such as accidental contact with an open wire etc.). As a result, the returning current from neutral is reduced. This differential in the current is also known as “Residual Current”. RCCB is designed such way that it continuously senses and compares for difference (residual current value) in current values between the live and neutral wires. Any small change in the current value on account of such an event would trigger the RCCB to trip off the circuit.
Ratings – The most widely used are 30 mA (milliamp) and 100 mA.
4. RCBO (Residual Circuit Breaker and Overload Protection) – It is a combination of a residual current device and a miniature circuit breaker. When a current leakage fault occurs the internal residual current detecting element will trip the whole circuit. Equally, if the circuit is overloaded the internal thermal/magnetic circuit breaker parts are able to trip the device in the same way.
Different industrial-grade MCB, RCB, and MCCB were shown and their brief working was also discussed during the workshop.
At last, there was a questionnaire session in which individual student was awarded for the correct answer.
Dr. Hemant Ahuja HOD (EN) introduced the speaker and the topic of the lecture to the students. Prof. Gajendra Singh, Dr. Amit Agarwal, Dr. Vikas Bhadoria, Ms. Pragati Deb and Ms. Nitika Ghosh (faculty EN Deptt.) also attended the program.
Dr. Vikas Bhadoria coordinated the overall program.