Transmission Injection and Withdrawal Studies in Power Systems (TIR & TWR Guide)

1. Introduction: Why Injection & Withdrawal Studies Matter More Than Ever

As power systems transition toward renewables, storage, and electrification, the ability to inject and withdraw power reliably from the grid has become one of the most critical technical challenges in modern energy infrastructure.

Transmission systems are no longer passive carriers of electricity—they are actively managed, constrained, and optimized networks. Every new project—whether it is a solar farm, battery energy storage system (BESS), or HVDC transmission line—must prove its compatibility with the grid through detailed engineering studies.

At the core of this evaluation are two fundamental concepts:

• Transmission Injection Rights (TIR) – the ability to inject power into the grid 
• Transmission Withdrawal Rights (TWR) – the ability to withdraw power from the grid 

These rights are not simply contractual—they are earned through rigorous system impact studies, governed by ISO interconnection procedures such as those outlined in PJM Manual 14H.

2. Understanding Transmission Injection and Withdrawal Rights

2.1 Transmission Injection Rights (TIR)

TIR defines how much power a facility can safely inject into the transmission system. It is primarily associated with:

• Utility-scale solar and wind plants 
• Battery discharge from BESS 
• Merchant transmission imports 
• Conventional generation 

Injection capability is not equal to plant capacity. It is constrained by:

• Transmission line ratings 
• System stability 
• Voltage limits 
• Congestion conditions 

2.2 Transmission Withdrawal Rights (TWR)

TWR defines how much power can be withdrawn from the grid at a specific location. It applies to:

• Industrial loads 
• Data centers 
• Export facilities 
• Storage charging 

Withdrawal rights are increasingly critical due to:

• Growth of large load centers 
• Electrification of industry 
• AI/data center expansion 

2.3 Firm vs Non-Firm Rights

Both TIR and TWR are categorized as:

• Firm Rights → Guaranteed delivery under normal conditions 
• Non-Firm Rights → Subject to curtailment during congestion 

PJM requires developers to explicitly define these MW values during application submission. 

3. The Interconnection Study Process: Where Engineering Meets Market Rules

The PJM interconnection process is structured as a Cycle Process, which ensures that all projects are evaluated consistently and fairly.

3.1 Key Phases

1. Application Phase 
2. Phase I System Impact Study 
3. Decision Point I 
4. Phase II System Impact Study 
5. Decision Point II 
6. Phase III System Impact Study 
7. Decision Point III 
8. Final Agreement Negotiation 

Each phase progressively refines:

• Injection capability 
• Withdrawal limits 
• Required upgrades 
• Cost allocation 
  

4. System Impact Studies: The Backbone of Injection & Withdrawal Analysis

Transmission rights are determined through multi-stage engineering studies.

4.1 Phase I Study (Screening Level)

• load flow analysis 
• Identifies: 

• Thermal overloads 
• Initial congestion 

• Establishes feasibility 

No stability or short circuit analysis at this stage.

4.2 Phase II Study (Detailed Engineering Analysis)

Includes:

• Voltage analysis 
• Short circuit analysis 
• Stability analysis 
• Interconnection facilities study 

This is where inverter-based resources (IBRs) such as solar and BESS face the most scrutiny.

4.3 Phase III Study (Final Validation)

• Confirms all system upgrades 
• Finalizes injection/withdrawal limits 
• Determines cost responsibility 

At this stage, results become binding for interconnection agreements.

5. Key Technical Analyses for Injection & Withdrawal

5.1 Load Flow Analysis

Evaluates steady-state conditions:

• Line loading 
• Transformer capacity 
• Power transfer limits 

Used to determine:

• Maximum injection capability 
• Feasible withdrawal levels 

5.2 Short Circuit Analysis

Ensures system protection:

• Evaluates fault current contribution 
• Prevents equipment damage 

Critical for:

• HVDC converters 
• Large BESS installations 

5.3 Stability Analysis

Examines dynamic behavior:

• Rotor angle stability 
• Voltage recovery 
• Frequency response 

Mandatory for:

• Solar PV plants 
• Wind farms 
• Battery systems 

5.4 Deliverability Analysis

Determines whether injected power can reach load centers without violating constraints.

Key criteria:

• Flowgate loading < 100% 
• Contribution < threshold limits 
  

6. Network Upgrades and Cost Allocation

Injection and withdrawal often require system upgrades such as:

• Transmission line
• Transformer additions 
• Reactive compensation 
• Substation expansion 

Key Rules:

• Developers pay 100% of interconnection facilities 
• Network upgrades are: 

• Shared among projects 
• Allocated based on impact 

Cost allocation is determined using:

• DFAX (Distribution Factor) 
• Contribution to violations 

7. Merchant Transmission and HVDC Considerations

The Breaker Rating Module is designed to streamline checking circuit breaker ratings against the short-circuit currents they must interrupt. The material states that the module has been merged into the main OneLiner executable since Version 11 and is enabled through licensing under the Check → Circuit Breaker Short Circuit Rating command.

For Keentel Engineering  this is important because breaker adequacy is a fundamental part of protection engineering. A relay may detect and clear a fault correctly, but if the breaker interrupting rating is inadequate, the protection system is not acceptable.

A breaker rating study typically evaluates:

• Symmetrical interrupting current 
• Momentary current 
• Close-and-latch capability 
• X/R ratio impact 
• Fault current contribution from generation 
• System changes that increase available short-circuit current 
• Replacement or mitigation requirements 

In renewable interconnection work, breaker duty can become an issue when new generation is added to an existing substation. Even inverter-based resources may affect fault levels and system topology in ways that require verification. A breaker rating module integrated with the short-circuit model reduces manual checking and improves consistency.

8. Risks in Injection & Withdrawal Studies

8.1 Technical Risks

• Stability failures 
• Voltage violations 
• Thermal overloads 

8.2 Financial Risks

• High upgrade costs 
• Deposit forfeiture 
• Re-study expenses 

8.3 Schedule Risks

• Delays in study phases 
• Queue congestion 
• Dependency on other projects 

8.4 Withdrawal Risks

Projects may be withdrawn if:

• Requirements are not met 
• Deposits are not submitted 
• Study results are unfavorable 
  

9. Engineering Best Practices (Keentel Insights)

Early Feasibility Studies

Perform pre-application modeling to:

• Estimate injection limits 
• Identify congestion 

High-Fidelity Modeling

Use tools like:

• PSSE + TSAT 
• PSCAD 
• PowerFactory 

Dynamic Model Compliance

Ensure models meet:

• Grid operator requirements 
• Stability guidelines 

Strategic POI Selection

Choosing the right Point of Interconnection can:

• Reduce upgrade costs 
• Improve injection capability 
  

10. Case Studies

Case Study 1: 200 MW Solar PV Plant 

Project Overview

• Capacity: 200 MW 
• Technology: Utility-scale solar PV 
• POI: 230 kV substation 

Challenge

• Limited transmission capacity 
• High congestion in the region

Study Findings

• Phase I: 

• Thermal overload on 230 kV line 

• Phase II:

• Voltage instability during low-load conditions 

• Phase III: 

• Required: 

• New transformer 
• Reactive compensation 

Outcome

• Injection limited to 170 MW initially 
• Network upgrades increased cost by $25M 

Keentel Insight

Early reactive power modeling could have reduced costs significantly.

Case Study 2: 150 MW / 600 MWh BESS Project

Project Overview

• Discharge: 150 MW 
• Charging: 120 MW 
• Location: Near load center 

Challenge

• Bidirectional power flow 
• High fault current contribution 

Study Findings

• Load Flow: 

• Charging caused reverse congestion 

• Short Circuit: 

• Exceeded breaker ratings 

• Stability: 

• Required inverter tuning 

Outcome

• Reduced charging capacity to 100 MW 
• Installed fault current limiting controls 

Keentel Insight

BESS projects must model both:

• Injection (discharge) 
• Withdrawal (charging) 
  

Case Study 3: HVDC Project

Project Overview

• 500 MW HVDC link 
• Interconnecting two regions 

Challenge

• Cross-border system impacts 
• Dynamic stability concerns 

Study Findings

• Phase I: 

• Minimal thermal issues 

• Phase II: 

• Stability concerns due to control interactions 

• Additional Studies: 

• Harmonics 
• SSR (Sub-Synchronous Resonance) 

Outcome

• Required advanced control systems 
• Granted both TIR and TWR rights 

Keentel Insight

HVDC projects require significantly more dynamic modeling and validation.

11. Future Trends in Injection & Withdrawal Studies

Growth of Large Loads

• Data centers driving TWR demand 

Increased IBR Penetration

• Stability becoming dominant constraint 

Hybrid Projects

• Solar + BESS requiring complex modeling 

Grid Congestion

• Injection rights becoming more limited 
  

12. Why Choose Keentel Engineering

At Keentel Engineering, we specialize in:

• Interconnection studies (PJM, ERCOT, CAISO, SPP) 
• Load flow, short circuit, and stability analysis 
• High-fidelity modeling (PSSE, PSCAD, TSAT) 
• NERC compliance and grid code support 

We help clients:

• Maximize injection capacity
  
• Minimize upgrade costs
  
• Navigate interconnection processes
  
• Achieve faster project approvals
  

13. Conclusion

Transmission Injection and Withdrawal studies are the gateway to grid access.

They determine:

• Whether your project is viable 
• How much power you can deliver 
• How much it will cost 

As grids become more constrained and complex, engineering excellence is no longer optional it is critical

Technical FAQ (Engineering-Focused)