Short Circuit and Relay Coordination Study for a Paper Manufacturing Facility with 23.5 MW Captive Generation
A combined Short Circuit and Relay Coordination Study for an integrated pulp and paper manufacturing facility, assessing the addition of a proposed 15 MW turbine generator alongside 8.5 MW of existing captive generation.
Project Overview
Power Projects was engaged to perform a comprehensive Short Circuit and Relay Coordination Study for an integrated pulp and paper manufacturing facility in Uttar Pradesh, India.
The facility receives its normal utility supply at 33 kV and has an extensive 11 kV and LV distribution network. The plant also includes multiple captive turbine generators:
- TG-1Existing 2.5 MW
- TG-2Existing 6 MW
- TG-3Proposed 15 MW
With the addition of the proposed 15 MW turbine generator, the electrical network would operate with significantly different source configurations. Depending on the operating condition, the plant could operate with the utility grid and captive generators together or entirely from captive generation.
The engineering assessment therefore focused on two key requirements:
- Determining whether existing electrical equipment could safely withstand the revised fault levels
- Developing coordinated protection settings capable of selectively clearing faults across the expanded network
System Configuration
The study covered a multi-source industrial electrical network comprising:
- 33 kV utility interconnection
- 7.5 MVA, 33/11 kV main transformer
- 11 kV plant distribution system
- 433 V and 690 V LV distribution systems
- Multiple distribution transformers ranging from 2 MVA to 4 MVA
- TG-1: 2.5 MW · TG-2: 6 MW · TG-3: Proposed 15 MW
- Process substations, MCCs and LV distribution boards
- New paper machine-related electrical distribution
The proposed 15 MW TG-3 was intended to operate alongside the existing turbine generators and support independent plant operation when the utility grid was unavailable.
Short Circuit Assessment
The addition of captive generation introduced additional sources capable of contributing current during a fault.
Power Projects performed short-circuit simulations for different utility and generator operating configurations to establish the fault currents throughout the network. The assessment included:
- Three-phase faults
- Line-to-ground faults
- Line-to-line-to-ground faults
The calculated short-time and peak fault currents were then compared with the corresponding switchgear withstand and making-current ratings.
This assessment was particularly important because the effect of additional generation was not limited to the 33 kV and 11 kV systems. Increased fault contribution also propagated into downstream LV sections through the distribution transformers.
The study identified specific LV sections where the calculated fault duty exceeded the available equipment withstand rating when critical source combinations were considered. This provided a technical basis for identifying equipment requiring further engineering review or rating enhancement before operation under the proposed generation configurations.
Relay Coordination Assessment
The second part of the study focused on protection coordination throughout the plant distribution network. The assessment covered:
- IDMT overcurrent protection
- Instantaneous overcurrent protection
- IDMT earth fault protection
- Instantaneous earth fault protection
- LV protection release coordination
- Transformer feeder protection
- Incomer protection
- Generator protection
Protection coordination was performed in accordance with IEEE 242-2001, while the short-circuit calculations were based on IEC 60909-2016.
The calculated fault levels were used as the basis for developing coordinated protection settings. Time Current Curves (TCCs) were reviewed to establish appropriate grading between downstream and upstream protective devices. Separate coordination philosophies were considered for load feeders, capacitor feeders, incomers, transformer HV protection and generators.
Detailed relay setting values and equipment-specific protection parameters are intentionally excluded from this case study.
Engineering Challenges
Increased Fault Contribution from Captive Generation
The proposed 15 MW generator increased the number of sources capable of feeding a fault. Depending on the operating configuration, a plant fault could receive contribution from the 33 kV utility grid, TG-1 (2.5 MW), TG-2 (6 MW) and TG-3 (15 MW). As a result, equipment that was adequately rated under the original configuration required reassessment under the proposed generation configuration.
Multiple Operating Configurations
Fault levels were dependent on which sources were in service. The assessment therefore considered different operating configurations rather than relying on a single fault scenario. One critical configuration considered simultaneous operation of the utility grid with TG-1, TG-2 and TG-3. Another configuration considered operation entirely from the captive turbine generators with the utility disconnected.
Protection Selectivity Across the Industrial Network
The plant contains multiple stages of protection between generators, incomers, transformers and downstream process loads. The coordination assessment was therefore developed to ensure that the protective device nearest to the fault could isolate the affected section while maintaining appropriate upstream backup protection. For a continuous-process manufacturing facility, maintaining selectivity is particularly important because unnecessary upstream tripping can affect multiple downstream production systems.
ETAP-Based Engineering Approach
A detailed ETAP 24.0.0 simulation model was developed using the electrical data and single-line diagram provided for the project. The model incorporated:
- Utility source
- Turbine generators
- Main transformer
- Distribution transformers
- Cables
- Switchgear
- Plant loads
The available engineering inputs were reviewed and validated before performing the studies. Different utility and generator combinations were then simulated to establish the fault duty imposed on each section of the network.
The resulting short-circuit levels were assessed against equipment ratings, while the same fault-level information provided the basis for the relay coordination assessment. Time Current Curves were reviewed to evaluate the coordination between downstream and upstream protective devices and to develop recommended protection settings for the network.
Key Outcomes
The combined assessment provided important findings for the proposed generation configuration.
Equipment Fault-Duty Assessment
The short-circuit study identified specific LV sections where the calculated fault duty exceeded the available equipment withstand rating under critical source combinations. This demonstrated the importance of assessing the complete electrical distribution network when additional captive generation is introduced. The findings provided the engineering basis for identifying equipment requiring further review or rating enhancement before operation under the proposed configurations.
Protection Coordination
The relay coordination study established revised protection settings for the network. The recommended settings were developed to:
- Improve protection selectivity
- Maintain sensitivity to abnormal conditions
- Safeguard electrical equipment
- Minimise damage within the faulted protection zone
- Avoid unnecessary upstream tripping
The final Time Current Curve assessment demonstrated coordination between the protective devices, with the device nearest to the fault intended to isolate the affected equipment as early as practical while maintaining upstream backup protection.
Integrated Protection and Equipment Assessment
The value of performing the two studies together was the ability to assess both the electrical equipment capability and the protection response under the revised generation configuration. The Short Circuit Study established the fault currents and equipment fault duty. The Relay Coordination Study used these fault levels to develop coordinated protection settings across the network. Together, the studies addressed two critical aspects of the protection design:
Equipment Capability
Can the electrical equipment withstand the available fault current?
Protection Selectivity
Can the protection system detect and isolate the fault without unnecessarily disconnecting healthy sections of the network?
Project Delivery
The project was planned for completion within four weeks from receipt of the required engineering inputs and commercial authorisation.
The engineering workflow included:
- Collection and review of electrical system inputs
- Development and validation of the ETAP network model
- Short-circuit simulations for relevant operating configurations
- Equipment fault-duty assessment
- Relay and LV release coordination
- Time Current Curve review
- Development of recommended protection settings
- Submission of Short Circuit and Relay Coordination Study reports
The final Short Circuit Study report was issued as Revision 2 in May 2026, while the Relay Coordination Study report was issued separately.
Conclusion
The integration of additional captive generation can significantly change the fault levels and protection behaviour of an existing industrial electrical network.
For this 23.5 MW captive-generation configuration, the proposed 15 MW TG-3, together with the existing 2.5 MW TG-1 and 6 MW TG-2, required the network to be assessed across different source configurations.
Through detailed ETAP 24.0.0-based Short Circuit and Relay Coordination Studies, Power Projects identified network sections requiring attention due to increased fault duty and developed coordinated protection settings for the expanded electrical system.
The study provided the engineering basis for assessing operation with the utility supply and captive generation under different configurations while maintaining appropriate equipment protection and selective fault isolation.
Most importantly, the assessment identified potential equipment limitations before the proposed generation configuration was placed into service, allowing corrective engineering decisions to be considered before those limitations could become an operational or safety concern.
Power Projects — Electrical Power System Studies
Power Projects provides engineering services in short-circuit analysis, relay coordination, protection studies and electrical system assessment for industrial and power-sector facilities. Our approach combines detailed electrical system modelling with study-specific engineering assessment to support safe, reliable and coordinated electrical network operation.
