Mastering Circuit Breaker Failure Protection Scheme

Description

The circuit breaker failure protection provides a backup protection in the case, that the local circuit breaker fails to clear a system fault.

In this training we have started from basic concepts, explained circuit breaker symbol and how circuit breaker look like in substation. We have discussed in training how to represent circuit breaker by ANSI code, difference of circuit breaker and line isolator. What are different functions that are performed by circuit breaker, what is arc, how to quench arc, what are media to quench arc, what will happen if arc is not quenched.

We have discussed different components of circuit breaker that include CB closing coil, tripping coils, auxiliary contacts, normally open and normally close contacts, simplified protection system consisting of DC battery banks/charger, relays, Current and voltage transformers, why CT & VTs are required at substation, what do you understand by CT ratio 1000/1, use of redundant DC supplies, why DC is used not AC for control & trip functions, how circuit breaker spring is charge, circuit breaker operation, what is trip free/ready to trip function of CB, Trip Circuit Supervision feature, DC supply supervision, trip coil supervision, TCS Relay, control & protection DC supplies & Tripping coils, what is typical tripping and closing time of circuit breaker.

What are different types of breaker failure that can occur in power system:

• Circuit Breaker Failure due to Mechanism Fail

• Circuit Breaker Failure due to non-interruption of fault current

• Circuit Breaker Failure due to DC control/trip supply fail

• Circuit Breaker Failure due to tripping coil failure

• Circuit Breaker Failure due to low DC voltage

• Circuit Breaker Failure due to Aux contact failure

• Circuit Breaker Failure due to Fire

• Circuit Breaker Failure due to delayed tripping

• Circuit Breaker Pole Discrepancy

What is Circuit Breaker Pole Discrepancy:

• Single pole & three pole circuit breaker operated mechanisms

• advantages of single pole tripping & reclosing

• How single pole reclosing support system

• What is meaning of pole discrepancy

• How pole discrepancy is detected in system

• Pole discrepancy circuit working

• Timer circuit in pole discrepancy

• Stage 1 & Stage 2 operations of pole discrepancy

• Pole discrepancy during closing command & tripping command.

• Re-trip and 2nd stage

• What is typical time settings for Pole discrepancy

• Creation of 3I0 zero sequence current during pole discrepancy condition

• How Pole Discrepancy can lead to indiscriminate tripping in the network

Busbar Schemes:

In order to understand it is good idea to learn about busbar schemes, we will go through following busbar schemes.

• Single Bus Single Breaker Scheme

• Double Bus Single Breaker Scheme

• One and half breaker scheme

• Mesh Breaker schemes

• double bus and double breaker

• How to change over load from one bus to another bus without interruption

• Advantages of different busbar scheme

Circuit Breaker Fail Philosophy:

• Circuit breaker failure protection using relay coordination at low / MV levels

• What to do & protect if one breaker fail

• Understand basic concept of breaker failure, if some one understand well can design and understand all CBF protection schemes & logic

• CBF protection example in one and half breaker scheme,  how to protect system if middle breaker fail , How to protect system if main breaker fail.

• CBF protection example in double bus double breaker busbar, consider the case of bus coupler & bus sectionalizer.

Circuit Breaker Failure Logic, Function:

• Circuit Breaker Failure logic block

• CBF initiation function

• CBF current guard

• CBF Low current mode

• CBF CB Aux contact input

• CBF timer

• CBF stage 1 & Stage 2

• CBF for Mechanical Protection not involving current

• CBF protection and End fault protection

• CBF Re-trip & 2nd stage faulty CB isolation from sources

• CBF when Circuit Breaker is faulty

• CBF and lockout function, 86 close block relay

• CBF & CB close blocking

• CBF typical times for stage 1 & stage 2 & when CB faulty

By completing this course you will be able to understand circuit breaker failure relay function, Circuit breaker failure scheme/trip matrix, how CBF stage 1 & 2 operate, CBF protection for different busbar schemes.

I wish you best of luck for the course.

Best Regard

Elite Engineering

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