Basic Of Circuit Breaker Guidelines



Content:
1. Design, function and types of
circuit breakers
1.1. Summary 
1.2. Types of switches 
1.2.1. Manual motor starter and protector or
circuit breaker with motor protective characteristics 1.2
1.2.2. Circuit breaker 1.2
1.2.3. Load break switch 1.6
1.2.4. Disconnector 1.6
1.2.5. Main switch 1.7
1.2.6. Emergency OFF-switch 1.8
1.2.7. Summary: Circuit breaker as load break switch 1.8
1.3. Design of a circuit breaker 1.9
1.3.1. The current path of the circuit breaker 
1.3.2. Thermal overload release 1.10
1.3.3. Electromagnetic overcurrent release 
1.3.4. Main contact system 1.12
1.3.5. Auxiliary contacts 1.15
1.3.6. Operating mechanism 1.15
1.4. Functions of a circuit breaker 1.15
1.4.1. Interrupting short-circuit current 1.16
1.4.2. Reliable protection of motors 1.17
1.4.3. Protection of leads and its optimum utilisation 1.18
1.4.4. Protection of installations 1.19
1.4.5. Integration in the control circuit 1.19
1.4.6. Switching under normal service conditions 1.20
1.4.7. Disconnecting function 1.20
1.4.8. Locking out with a padlock 1.20
2. Circuit breaker technology 2.1
2.1. Summary 2.1
2.2. Short-circuit current in supply systems 2.2
2.2.1. Types of short-circuit 2.2
2.2.2. The peak value of the short-circuit current 2.3
2.2.3. Calculation of the short-circuit current
close to the transformer
2.2.4. Calculation of the short-circuit current in
radial supply systems 2.7
2.2.5. Dynamic stress on the connecting leads
in the case of a short-circuit 2.16
2.3. Short-circuit protection 2.18
2.3.1. The principle of current limitation 2.18
2.3.2. Breaking capacity 2.26
2.3.3. Electrical life (durability) of
circuit breakers 2.26
2.4. Short-circuit co-ordination 2.28
2.4.1. Definitions in accordance with
the IEC 947-4-1 2.28
2.4.2. Conclusions drawn from the
definitions for the user 2.28
2.4.3. Physical significance of the short-circuit
co-ordination 2.30
2.4.4. Requirements of a circuit breaker for a simple
co-ordination of type "2" 2.33
3. Fields of application of circuit breakers 3.1
3.1. General procedure for the selection of
correctly rated circuit breakers 3.1
3.2. Circuit breakers for motor protection 3.2
3.2.1. Protection of motors with direct-on-line starting 3.3
3.2.2. Protection of motors with star-delta starting 3.4
3.2.3. Protection during heavy-duty starting 3.8
3.2.4. Circuit breaker with a motor protective
device connected downstream 3.8
3.2.5. Protection of motors in explosive environments 3.12
3.2.6. Protection of motors with phase controlled
starting (soft starter) 3.13
3.2.7. Protection of frequency controlled motors
(frequency converter) 3.14
3.3. Circuit breakers for the protection of
connecting leads and for group protection 3.16
3.3.1. Protection of the connecting leads 3.16
3.3.2. Group protection
3.4. Circuit breakers for capacitors 3.17
3.5. Circuit breakers for transformers 3.18
3.5.1. Protection of transformer: primary side 3.18
3.5.2. Protection of transformer: secondary side 3.18
3.6. Circuit breakers for generators 3.18
3.7. Circuit breakers for special supply frequencies 3.19
3.7.1. Breaking capacity at frequencies below 50/60Hz 3.19
3.7.2. Breaking capacity at frequencies above 50/60Hz 3.20
3.8. Interruption of direct current 3.20
3.9. Breaking capacity at higher supply voltages 3.21
3.10. Selectivity (discrimination) 3.21
3.10.1. Selectivity between circuit breakers 3.21
3.10.2. Selectivity between circuit breaker and fuse 3.24
3.10.3. Selectivity between fuses 3.25
4. Arguments in favor of the circuit breaker 4.1
4.1. Summary 4.1
4.2. Comparison of the functions:
circuit breaker / fuse 4.2
4.2.1. Time-current characteristics 4.2
4.2.2. Comparison of Joule-integrals 4.3
4.2.3. Comparison of the ultimative tripping current 4.4
4.2.4. Table of comparison 4.4
4.3. Arguments in favour of the circuit breaker 4.6
4.3.1. Prevention of accidents with the help of
circuit breakers 4.6
4.3.2. Ready to be switched on again without delay 4.8
4.3.3. All pole interruption 4.9
4.3.4. No ageing 4.9
4.3.5. Reduction of the conductor cross-section 4.10
4.3.6. Simplified planning of installations 4.14
4.3.7. Reduction of costs of installations and
optional costs

A circuit breaker, as we shall understand in the following text consists of a
thermal overload release, an electromagnetic short-circuit release, a tripping
(operating) mechanism, the main contact system and the auxiliary contacts.
These are the most important functional blocks.

By integrating all these functional blocks in a single unit, it is possible to replace
many individual components in an installation with one single device, viz. the
circuit breaker. The combination of fuse, contactor and thermal overload relay
will be replaced by the starter combination of circuit breaker and contactor.

One single device, the circuit breaker, fulfils the following functions :

• Short-circuit protection
• Motor protection
• Protection of connecting leads
• Protection of installations
• Signalisation of the switching state
Tripping indication
• Switching under normal service conditions
• Remote switching
• Disconnecting
• Locking out with padlock (mandatory for main switch)
Hence, it can be used not only as a circuit breaker, but also as circuit breaker for
motor protection, as load-break switch or as disconnector. 
 

Basics of Circuit Breaker Guidelines

Circuit breakers are essential components of electrical systems, designed to protect circuits, equipment, and personnel by interrupting power flow in the event of a fault. This guide provides an overview of the types, functions, and essential guidelines for selecting, operating, and maintaining circuit breakers.

1. Purpose of Circuit Breakers

  • Protection: Automatically disconnect electrical circuits during faults such as short circuits, overloads, and ground faults.
  • Safety: Prevent damage to equipment and reduce the risk of fire or injury.
  • Control: Enable manual and automatic control of power flow.

2. Basic Working Principle

A circuit breaker detects abnormal current flow (e.g., overload or short circuit) through sensing mechanisms like thermal or electromagnetic devices. Once a fault is detected, the breaker trips, creating an open circuit that stops current flow.

3. Types of Circuit Breakers

Based on Voltage Level:

  1. Low Voltage Circuit Breakers (LVCB):

    • Used in domestic and industrial applications for voltages below 1 kV.
    • Examples: Miniature Circuit Breakers (MCBs) and Molded Case Circuit Breakers (MCCBs).

  2. Medium Voltage Circuit Breakers (MVCB):

    • Operate between 1 kV and 52 kV.
    • Common in distribution networks.

  3. High Voltage Circuit Breakers (HVCB):

    • Used in transmission systems for voltages above 52 kV.
    • Examples: Gas-Insulated Circuit Breakers (GIS) and Air-Blast Circuit Breakers.

Based on Operating Mechanism:

  1. Thermal Circuit Breakers: Operate based on heat generated during an overload.
  2. Magnetic Circuit Breakers: Use an electromagnetic force to trip during a short circuit.
  3. Hybrid Circuit Breakers: Combine thermal and magnetic mechanisms.

Based on Arc Quenching Medium:

  1. Air Circuit Breakers (ACB): Use air to extinguish the arc.
  2. Oil Circuit Breakers (OCB): Use insulating oil for arc suppression.
  3. Vacuum Circuit Breakers (VCB): Operate in a vacuum, ideal for medium voltage.
  4. SF6 Circuit Breakers: Use sulfur hexafluoride gas for high voltage applications.

4. Selection Guidelines for Circuit Breakers

When selecting a circuit breaker, consider the following factors:

A. Electrical Ratings

  1. Voltage Rating: Must match or exceed the system voltage.
  2. Current Rating: Continuous current capacity of the breaker.
  3. Breaking Capacity: Maximum fault current the breaker can interrupt safely.
  4. Frequency: Compatible with the system’s operating frequency (e.g., 50 Hz or 60 Hz).

B. Application Requirements

  1. Type of Load: Resistive, inductive, or capacitive loads.
  2. Operating Environment: Indoor, outdoor, or hazardous conditions.
  3. Standards Compliance: Conformance to standards like IEC, ANSI, or IEEE.

C. Additional Features

  1. Trip Settings: Adjustable for overload and short circuit protection.
  2. Interlocking Mechanisms: Prevent improper operations.
  3. Remote Operation: Compatibility with SCADA or automation systems.

5. Installation Guidelines

  1. Location: Ensure accessibility for operation and maintenance.
  2. Mounting: Follow manufacturer recommendations for proper alignment.
  3. Wiring: Use cables of appropriate size and insulation.
  4. Clearance: Maintain sufficient spacing between breakers and other equipment to prevent overheating.
  5. Labeling: Clearly mark breakers for identification.

6. Operation Guidelines

  1. Pre-Operation Checks:

    • Inspect for physical damage and ensure proper connections.
    • Verify settings for overload and short circuit protection.

  2. Switching Operations:

    • Avoid frequent manual tripping or closing.
    • Use appropriate tools for remote-controlled breakers.

  3. Monitoring:

    • Observe breaker behavior during normal operation for unusual noises, vibrations, or temperature rise.

7. Maintenance Guidelines

Regular maintenance ensures reliability and extends the life of circuit breakers.

A. Routine Maintenance

  1. Visual Inspection: Check for signs of wear, corrosion, or loose connections.
  2. Cleaning: Remove dust and debris from external surfaces.
  3. Lubrication: Apply grease or oil to moving parts as recommended.

B. Electrical Testing

  1. Insulation Resistance: Verify insulation integrity.
  2. Contact Resistance: Measure resistance of closed contacts.
  3. Timing Tests: Check the time taken to trip under fault conditions.

C. Overhaul

  • Replace worn-out components such as contacts, springs, and arc chutes during periodic overhauls.

8. Safety Precautions

  1. Lockout-Tagout (LOTO): Isolate breakers before maintenance.
  2. Personal Protective Equipment (PPE): Use gloves, goggles, and insulating mats.
  3. Voltage Testing: Ensure the circuit is de-energized before inspection.
  4. Arc Flash Protection: Maintain safe distances and use arc flash-rated equipment.

9. Common Issues and Troubleshooting

  1. Frequent Tripping:

    • Check for overloads or short circuits.
    • Adjust trip settings if necessary.

  2. Failure to Trip:

    • Inspect trip mechanisms and replace faulty components.

  3. Overheating:

    • Tighten connections and verify load currents.

  4. Noise During Operation:

    • Lubricate moving parts and inspect for misalignment.

10. Standards and Compliance

  • IEC 60947: Standards for low-voltage switchgear and control gear.
  • IEEE C37: Standards for high-voltage circuit breakers.
  • NFPA 70 (NEC): Guidelines for electrical installations in the USA.

Conclusion

Circuit breakers are critical for the protection and control of electrical systems. By following the guidelines for selection, installation, operation, and maintenance, engineers and technicians can ensure the safe and efficient functioning of breakers, minimizing downtime and maximizing the lifespan of the electrical infrastructure.


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