Grounding Module
Grounding of the neutral marked a turning point in the evolution of the modern power grid, transforming earlier ungrounded systems into safer networks. This comprehensive module explores both ungrounded and grounded system design and operation, covering their principles, behaviour during faults, detection methods, and practical implementation challenges. It examines solid, resistance, reactance, and resonant grounding methods, along with special grounding transformers such as Zig-Zag and Star-Delta. Real-world case studies, numerical examples, and “fairy tale” Q&A sessions bring complex concepts to life. Generator neutral grounding practices are discussed in depth, highlighting their impact on protection, zero-sequence current circulation, and core damage severity. The module blends theory with practical design insights, enabling one to make informed grounding decisions in diverse power system contexts.
INR 7500/-
INR 5000/-
Grounding Module
7 Hours of Training
In the early stage of development, Power System operated as ungrounded. Grounding of neutral made a tectonic shift in development of modern Power Grid. This module covers various aspects of ungrounded and grounded system design and operation
In this module, you will learn:
1. Ungrounded System
- Definition of Neutral, Relationship between Neutral voltage and zero sequence voltage
- Neutral shift and phase over voltage during ground fault
- Open delta PT connection for ground detection in AC System
- Ground fault location methods in AC System
- Off-line and on-line ground fault detection and location in DC systems
- Ferro-Resonance and Neutral Inversion
- Advantages and disadvantages of ungrounded system,
2. Grounded System
- Reasons for grounding.
- Measure of Grounding Effectiveness – Factors K F and E F
- Definition of Effectively Grounded System
3. Solidly Grounded System
- Magnitude of ground fault current, Neutral shift, K F and E F in solidly grounded system
- Examples of Solidly grounded system – EHV System, MV systems without rotating machines, LV systems
- Disadvantages of Solidly grounded system - Zero sequence current Circulation and Core damage curve for rotating machines
4. Resistance and Reactance grounded System
- High Resistance Grounding – Use of Neutral Grounding Transformer and resistor across NGT secondary
- Low Resistance Grounding – Use of Neutral Grounding Resistor, Caution regarding Resistor Enclosure earthing
- Comparative features of different type of earthing - K F , Transient Over voltage, PT Voltage Factor, Core & Winding damage in rotating machines, possibility of multiple ground faults
- Reactance grounding
- Resonant grounding – Peterson Coil – Difficulty in practical implementation
5. Grounding of ungrounded System – Zig Zag NGT
- Zig and Zag winding connection, Impedance offered to flow of Positive or Negative and Zero sequence currents.
- Limiting Ground fault current by inserting resistor or reactor in neutral of NGT,
- Voltage Vector Diagram & Specification of MVA rating of Zig Zag Transformer
- Ground fault current distribution in the presence of NGT o Sample calculation for sizing of NGT
6. Grounding of ungrounded System – Star Delta Transformer
- Application of Star delta transformer for only grounding purposes
- Ground fault current distribution based on the Ampere-Turns Balance Principle o Limiting Ground fault current by inserting Resistor in star neutral or across open delta., Numerical example for sizing of Resistor in both cases.
- Illustration of inadvertent grounding o Behavior of delta connections in response to zero sequence current flow
- Variation of positive, and zero sequence voltages from source to fault
7. Fairy Tales
- Basic concepts of grounding are explained with a series of questions and answers, of increasing complexity.
- Interesting case studies of transformers involving, Star-Star, Star – Delta, and Star – Zig Zag vector groups are presented.
8. Generator Neutral Grounding practices
- Relationship between sequence components and harmonics,
- Third Harmonic Current and Zero Sequence current, Need for Neutral connection to ground
- Circulation of fundamental and zero sequence currents between generators connected to a common bus
- Different grounding methods for generators connected to a common bus: Common NGR for all the units, High and Low Resistance NGR for each unit and NGT + NGR with Delta-Star GT for each unit; advantages and disadvantages of each connection
- Evolution of common Zig Zag Grounding Transformer
- Zero sequence current circulation in LV generators connected to TPN system
- Sensitivity of ground fault protection in Low Resistance grounded generators
- Numerical example for design of high resistance grounding for large utility scale generators
- Hybrid grounding – mix of high and low resistance grounding
- Perils of grounding mix up.
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