This document summarizes a seminar presentation on numerical analysis of short circuit testing and verification of molded case circuit breakers (MCCBs). It discusses the need for protection systems, types of faults, MCCB components and testing, short circuit current calculation methods, and test results. The presentation covers minimum electric shock levels, MCCB construction, standard tests including temperature rise and breaking capacity tests, and concludes that product testing improves quality and provides technical comparison data.

1. NATIONAL INSTITUTE OF TECHNOLOGY
SRINAGAR(J&K)
A seminar on
Numerical Analysis of short circuit testing &
verification of a MCCB
Presented By:
RAJEEV KUMAR
M.Tech(EP&ES)
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2. Contents
 Introduction
 Electric Shock
 Need of protection system
 About MCCB
 Types of fault
 Selection of circuit breakers
 Kind of tests
 Short circuit current calculation
 Block diagram of SC Lab
 Results
 Conclusion
 References
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3. Introduction
 Testing is a process of measuring the properties or
performance of the products.
 Product testing might be accomplished by a manufacturer, an
independent laboratory or by a government agency etc.
 Tests are performed on the basis of relevant standards such as
BIS, IEC, KEMA, ASTA & UL.
 CPRI(Central power research institute) is a government
agency. It functions as a center for applied research in
electrical power engineering assisting in the product
development & quality assurance.
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4. Electric Shock
 The minimum current a human can feel at least 5 mA of AC at
50 Hz.
 The minimum voltage level for shock is 50V.
 Current will take 50ms time to travel from top to bottom in a
human body.
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Min Voltage Level Min Current Level Min time Result
 50V  50mA  50ms Fatal Shock

5. Need of protection system
Protection schemes are generally divided into equipment
protection and system protection.
The main function of equipment protection is to selectively and
rapidly detect and disconnect a fault on the protected circuit
to:
 Minimize damage to the primary plant.
 Prevent damage to healthy equipment that conducts fault
current during faults.
 Restore supply over the remaining healthy network.
 Sustain stability and integrity of the power system.
 Limit safety hazard to the power utility personnel and the
public.
 Provide uninterrupted power supply to the consumers.
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6. Moulded Case Circuit Breaker(MCCB)
 A moulded case circuit breaker is an automatically
operated electrical switch designed to protect
an electrical circuit from damage caused by
overload or short circuit.
 Rated current up to 1000 A
 MCCBs provide overload and short-circuit protection
for all applications. The thermal & magnetic elements,
adjustable over a wide band, make these MCCBs
ideal for any distribution application.
 MCCB is made of BMC material. BMC(Bulk molding
compound) is a fiber reinforced thermoset polyester
material used in injection & compression molding & is
corrosion resistant.
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7. Cross sectional View of MCCB7
100A
Icu 240V 25kA
Icu 415V 10kA
Ics 415V 5kA
IS / IEC 60947-2

8. Types of fault
 Over load fault
When current exceeds from the rated value, this fault occurs.
 Bimetal mechanism used to clear this type of fault.
 Short circuit fault
The prospective short circuit current is the highest
electric current which can exist in a particular electrical system
under short-circuit conditions.
 Magnetic tripping mechanism is used for clear this type of
fault. The current flows through the contacts also flows through
a conductor that passes closed to the circuit breaker’s trip
unit. At fault current level, the magnetic field surrounding this
conductor provides sufficient force to unlatch the trip unit &
trip the breaker.
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9. Selection of Circuit Breaker
 What is the
 Frame size (measured in amperes)
 Continuous Current (amperes trip)
 Rated Voltage (240V, 480V, 600V)
 Interruption capacity/Braking Capacity (measured in kA)
 No. of poles(1,2,3,4)
 Accessories (under voltage shunt trip, bell alarm)
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10. Kind of tests(As per IEC 60947)
 Type test
 Temperature rise test
 Tripping limits and characteristics
 Operational performance capability
 Overload performance
 Short-circuit breaking capacities
 Dielectric properties
 Routine test
 Mechanical operation
 Verification of the calibration of overcurrent releases
 Verification of the operation of under voltage and shunt releases
 Dielectric tests
 Verification of clearances
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11. Short Circuit current calculation
 Determine the transformer full load amps (F.L.A.) from the
following formulas,
𝑰 𝑭.𝑳.𝑨. =
𝒌𝑽𝑨 × 𝟏𝟎𝟎𝟎
𝑬 𝑳−𝑳 × √𝟑
; 𝑰 𝑺.𝑪. =
𝑰 𝑭.𝑳.𝑨.
%𝒁
Exp: 3- 𝜱, 480V,1500kVA Transformer, %Z=3.5;
𝑰 𝑺.𝑪.= 𝟓𝟏, 𝟓𝟒𝟎 𝑨
 Let 𝑰 𝑪𝑼=25kA, CosΦ=0.25, Voltage=240V;
𝑪𝒐𝒔𝜱 =
𝑹
𝒁
; 𝒁 = 𝑹 𝟐 + 𝑿 𝟐; V=I×Z
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R=9.30mΩ; L=0.023mH

12. Block diagram of a short circuit lab
Gen Make S/W ACB R-Load L-Load MCCB Recording
(LabVIEW)
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13. Simulation Result13
Prospective Voltage
Fault Current
Recovery VoltageVoltage Sag
Tripping time

14. Contd..(As per IEC 60947)14
Test Current I (kA)
Power Factor
Time
Constant(ms)
SC Test
Operational
Performance
Capability
Overload SC Test
0.8 0.5
I ≤ 3 0.9 5
3 ≤ I ≤ 4.5 0.8 5
4.5 ≤ I ≤ 6 0.7 5
6 ≤ I ≤ 10 0.5 5
10 ≤ I ≤ 20 0.3 10
20 ≤ I ≤ 50 0.25 15
50 < I 0.2 15
TABLE: Values of power factors and time constants corresponding to test currents

15. Tripping Characteristics of MCCB15

16. Conclusion
In a competitive industry, a business need to use all the
resources they have, including skills and knowledge. Product
testing improves the quality of the products. Some of the main
results of product testing are;
 Validate suitability of end-use.
 Provide a basics for technical communication.
 Provide a technical means of comparison of several options.
 Provide standard data for other scientific, engineering &
quality assurance functions.
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17. References
 IEC 60947 Standard Part 1 & Part 2.
 S.S. Rao, Switchgear Protection & Power Systems.
 U.A. Bakshi, Protection & Switchgear.
 CPRI website: www.cpri.in
 HAVELLS MCCB Catalogue.
 MAT Lab Simulink, GUI development environment for V-I curve.
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18. Thank you
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