understand protection 1

8/11/2019 Understand Protection 1

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Power Research & Development Consultants Pvt Ltd. #1

Understanding Protectionthrough

Digital Simulation

Power Research & Development Consultants Pvt Ltd.


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Contents of presentation

Introduction

Resources required

Case studies


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Introduction

Reliability of a power system operation :

Reliable : Equipment used in the system are in operation andperform the function for which they are designed for.

Reliability Index : Performance index measured in terms ofcustomer load affected in a year or particular duration.


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X

X

X

X X

33 33/11 220/33

Transmission Sub Transmission Distribution --Primary --Secondary

Transmission & Distribution System


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Methods to enhance reliability

Duplicate every thing Minimize the outage time during faults

Economics ?


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How to achieve minimum outage ?

1. A good and integrated performance of power system relays.

2. Successful operation of relay for all short circuits in its zone.3. Adequate backup protection for the faults in the adjoiningsection.

Operations involved in protection engineering :Periodic fault studies Relay setting calculationChecking and co-ordination studies


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Difficulties :

* Wide variety of relays in operation.* Functionality, Manufacturer, technology.* System operational changes.* System growth.

It is just impossible to overcome the above difficulties by ahuman (Operator).

Only solution is through computer applications.



Resources required

Man Power Computer

softwareComputer hardware

Resources required



Sl.No.

Cricket Field (Fielding side Bowler)

Protection field(Protection Engineer)

1. Positions the fielders Designs the system and sets the relays

2. Bowls the ball Charges the system3. Batsman hits the ball Fault occurs4. Mid-off stops/fails Primary relay operates/ fails5. Long-off stops/ fails Backup relay operates / fails6. Boundary (Dropped?) Has to face enquiry commission

Protection - Cricket Field Analogy



Co-ordination with different departments:

Finance

ProtectionEngineer

Manufacturer /supplier

FieldEngineer

Planning/

Design

OperationalLoad Despatch



SystemOperationalRelay

RESULTS

SLDZooming

WindowingReports

Graphs

LoadflowShort CircuitRelay Co-ordinationTransient Stability

Over voltage

Degitizer MousePrinter Plotter

GUI (Graphic User Interface) Peripheral supports stem

Analysis Tools

Database

Computer Software



Database organisation

Load flow

Short Circuit Results

Results

Relay co-

ordination setting Transient Stability

Studies

Large Volume of data handling

Centralized Database Management System [CDMS]



Requirements of CDMS :

Easy and simultaneous access to multiple users. Consistency in the data representation with proper read/write

permissive. Fast access and updating on user request.

Application program and hardware independent data structure.



Case Studies :


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Power flow to know1. Normal load current2. Worst contingency load current3. Steady state over voltage


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Fault calculation to determine1. Fault current from various sources2. Post fault voltage

3. Earth fault current4. Primary and back up relay current5. Temporary over voltage (during

single line to ground fault)


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Fault study

1. Symmetrical AC current2. DC off set current3. Asymmetrical AC current


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DC off set current1. Maximum at voltage zero2. Minimum at voltage maximum


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Stability study1. To determine the critical clearing time2. To find the voltage and frequency variation in the grid.3. Helps in relay setting calculations


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Frequency plot

1. Under frequency and over frequency relay setting2. Operate the system around designed values.


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Impedance seen by the distance relay

1. Helps in distance relay setting calculations

2. Re-shaping the relay characteristic to avoidthird zone load encroachment


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Out of step operation1. Out of step protection for the machine2. Pole slipping relay


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Sustained fault on the machine terminal1. Sub-transient current2. Transient current3. Steady state current


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Loss of excitation1. Machine draws very large reactive power from the grid.2. Stator gets heated up


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Loss of excitation relay1. Off set mho relay2. Off set of xd/2 3. Diameter of xd


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Capacitor charging


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Inrush current capacitor charging


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Magnetizing inrush current


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VCB current chopping and voltage raise problem


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P R h & D l t C lt t P t Ltd

Conclusions:

Simulation studies help to understand the protection philosophy better

and increases the analytical skills. It is possible to conduct post-mortem analysis on the gridfault to arrive at better relaying functions and schemes.

understand protection 1

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