Protection Schemes for Generators and Recommended Settings Course
Electrical and Power Engineering
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Protection Schemes for Generators and Recommended Settings Course
Course Overview:
This course deals with the design and application of electrical protection schemes for synchronous generators.
It also covers loads, criteria, and damage mechanisms associated with short circuit calculations, differential relays, backup fault protection and ground fault protection. Other advanced topics include unbalanced current protection, motoring protection and field winding protection.
Practical examples and applications as well as setting calculations are included so that the student understands all the protective functions for large and small machines.
This course is targeted at engineers and technical staff who wish to be able to optimize the protection of generators, improve the operability and resolve issues encountered in case of abnormal conditions.
Course Objectives:
The aim of this course is to provide in-depth discussions of the major electrical protection schemes associated with synchronous generators. The principles and criteria presented are applicable to both large and small machines. The discussions include analysis of the damage and damaging mechanisms relating to each protective function. An understanding of these parameters is important not only for the application of protection but also when operability issues arise during or after abnormal operating events.
Who Should Attend?
This course is intended for Electrical and Mechanical/Power Engineers, Project Engineers, Maintenance Engineers, and Supervisors and Operating Staff of electrical substations will find this course very useful for enhancing their knowledge related to transformers and its working principles, design, operation & maintenance. The course will also definitely be beneficial for all the other department people concerned with the plant operations, production, maintenance, and safety. It could be also useful for procurement and quality personnel.
Course Outlines:
Generator Short Circuit Calculations
- Introduction
- Short-Circuit Current Characteristics
- Generator Internal Magnetics
- Generator Magnetic Structures
- Generator Constants
- Fault Current Calculations
- Initial Load
- Fault Calculation Overview
- Determination of Xf and Fault Currents
- Three-Phase Short Circuit
- Phase-to-Phase Short Circuit
- Phase-to-Ground Fault
- Other Fault Conditions
- DC Component of Short-Circuit Current
- RMS Asymmetrical Current
- Voltage Regulator
- Short Circuit Calculation Examples
- Establish Prefault Conditions
- Three-Phase Fault at Generator Terminals
- Effects of the Automatic Voltage Regulator
Generator Differential Relay (87G)
- Introduction
- Ideal Differential Relay
- Practical Considerations
- CT Ratings
- CT Saturation
- CTs and Fault Current Replication
- Percentage Differential Relay
- Relay Characteristics
- Electromechanical Relays
- Solid-State and Microprocessor Relays
- Minimum Operating Current Setting
- Slope Setting
- Requirements for Slope Setting
- Advantage of Low Slope
- Sensitivity and Load Current
- Relay Response to Saturation
- Methods of Choosing Slope Settings
- Manufacturer’s Recommendations
- Qualitative Determination of Slope
- Error Current Calculations for Unsaturated CT
- Mason’s Method
- Example of Mason’s Method
- Fundamental Frequency Analysis
- Sample System Differential Relay
- Sample System Differential Circuit
- Electromechanical Relay
- Specifications for Relay Chosen
- Choosing Slope Static and Microprocessor Relays
- Stabilizing Resistor
- Balancing Burden
- Time Delay
- Frequency Response
Backup Fault Protection
- Purpose and Implementation
- Standard Overcurrent Relays
- Voltage-Dependent Relays
- Electromechanical vs. Electronic Relays
- Voltage Supervised Overcurrent Relays
- Voltage-Controlled and Voltage-Restrained Relays
- Application Options and Fault Sensitivity
- Scheme Sensitivity vs. Potential Transformer (PT) and Current Transformer (CT) Connection
- Sensitivity Related to Relay Type
- Delta Relay Currents
- Settings Considerations
- Basic Requirement
- Automatic Voltage Regulator in Service
- 51 V Transmission System Backup Limitations
- Effects of Wye-Delta Transformer
- Self-Excitation Generators
- Relay Response to Transient Current
- Equipment Protection
- Setting Criteria
- Relay Current and Voltage Calculations
- Relay Current and Voltage Equations
- Sequence Currents and Voltages Calculations
- Sample System 51 V Relay Settings
- Fault Calculations
- Choosing the Undervoltage Setting
- Choosing Overcurrent Setting
- Choosing Time Delay Setting
- Auxiliary PTs to Correct for Wye-Delta Phase Shift
- Distance Relays
- Distance Relay Characteristics
- Z Measured by Phase Distance Relay
- Mho Distance Relay
- System Impedance vs. Relay Characteristic
- Setting Considerations
- Load Limits
- Apparent Impedance
- Influence of an Interposing Wye-Delta Transformer
- Auxiliary PTs to Correct for Wye-Delta Phase Shift
- Other Distance Relay Applications
Generator Ground Fault Protection
- Introduction
- Generator Grounding Considerations
- Ground Fault Current Limitation
- Overvoltage Concerns
- Core Damage Cause by Ground Fault
- Methods of Grounding
- Ungrounded System
- Solidly Grounded/Effectively Grounded
- High-Impedance Grounding
- Distribution Transformer Grounding
- High-Resistance Grounding on Sample System
- Ground Fault Neutralizers
- Low-Impedance Grounding
- Low-Resistance Grounding
- Low-Reactance Grounding
- Grounding Transformers
- Ground Fault Protection
- Alarm vs. Tripping for High-Impedance Grounded System
- Electromechanical and Electronic Relays
- High-Impedance Ground Protection
- Neutral Overvoltage Scheme
- Application of 59GN on Sample System
- Broken Delta Overvoltage Scheme
- Overcurrent Scheme
- Low-Impedance Ground Protection
- Ground Differential
- 100% Stator Protection Schemes
- Third-Harmonic Schemes
- Third-Harmonic Undervoltage Scheme Settings for Sample System 27H Scheme
- Third-Harmonic Overvoltage Scheme
- Third-Harmonic Voltage Ratio Scheme
- Neutral Injection Scheme
Unbalanced Current Protection
- Introduction
- What Is Negative-Sequence Current?
- Effects of Negative-Sequence Current
- Rotor Heating
- Cylindrical Rotor Generators
- Salient Pole Generators
- Pulsating Torque
- Generator Negative-Sequence Capability
- Continuous Unbalanced Capabilities
- Short Time Unbalanced Currents
- Sources of Negative Sequence Current
- Unbalanced Faults
- Open Phases
- In-Service I22t Duty vs. Standards
- Calculation of I22t Duty
- Isolated Generator
- The Interconnected Generator
- The’ venin’s Equivalent Circuit
- Unbalanced Duty on Sample System
- Unbalanced Current Protection
- Negative-Sequence Relay Settings
- Calculation of Open-Circuit Current
- Negative Sequence Relay Setting
Motoring Protection
- Introduction
- Effects of Motoring
- Consequences for a Steam Turbine
- Consequences for Other Prime Movers
- Protection
- Mechanical Protection: Steam Turbines
- Electrical Protection
- Sequential Trip Logic
- Backup Protection
- Setting Device (32)
- Applying Reversed Power Relay on the Sample System
- Field Winding Protection
- Field Ground Protection
- Field Ground Hazard
- Field Ground Protection
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