understand protection 1
TRANSCRIPT
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Understanding Protectionthrough
Digital Simulation
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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.
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Resources required
Man Power Computer
softwareComputer hardware
Resources required
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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
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Co-ordination with different departments:
Finance
ProtectionEngineer
Manufacturer /supplier
FieldEngineer
Planning/
Design
OperationalLoad Despatch
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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
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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]
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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.
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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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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.