VIPER|SSTI SCREENING

Sub-Synchronous Torsional Interaction
Screening. Before You File.

Your 500 MW data center interconnection could trigger a multi-year SSO study if it lands near the wrong generators. VIPER's SSTI screening module computes Unit Interaction Factors across every vulnerable generator in the network — so you know the risk before you commit to a site.

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HOW IT WORKS

UIF-Based SSTI Screening: From Bus Selection to Risk Classification

STEP 01
Select Interconnection Point

Choose any bus from 226 nodes across ERCOT and Eastern Interconnect, or enter coordinates for the nearest bus match.

STEP 02
Specify Load Size

Enter the proposed load (MW) for your data center, industrial facility, or other large-load interconnection.

STEP 03
Screen Generators

The engine computes UIF scores for every vulnerable generator in electrical proximity, flags those above EPRI thresholds.

STEP 04
Review Risk Assessment

See risk tier (LOW/MEDIUM/HIGH/CRITICAL), flagged generators, short-circuit capacity, and contingency sensitivity.

INPUTS

Screening Inputs: Location, Load Size & Region

Four inputs drive the SSTI screen. The engine handles the rest — admittance matrices, generator classification, and short-circuit estimation are all computed from the solved network model.

Bus / Location

Select from 226 nodal buses or enter a GPS coordinate. The engine identifies the nearest electrical bus and all generators within the study area.

VIPER Map · Click or Search
Load MW

The nameplate capacity of the proposed load interconnection. Drives the UIF numerator — larger loads produce higher interaction factors.

Numeric · MW
Load Type

Data center, industrial, or generic large load. Load type informs harmonic profile assumptions and converter topology considerations.

Dropdown · Category
Region

ERCOT (187 county-level buses) or Eastern Interconnect (39 state-level buses). Each region uses its own solved production cost model.

ERCOT · Eastern
OUTPUTS

Screening Outputs: UIF Scores, Risk Tiers & Generator Flags

Every screen produces a complete SSTI risk profile — not just a pass/fail, but the underlying data you need to make siting decisions or prepare for a formal interconnection study.

📊
UIF Scores
Unit Interaction Factor for every vulnerable generator — the primary SSTI screening metric per EPRI guidelines
🎯
Risk Tier
Overall site classification: LOW, MEDIUM, HIGH, or CRITICAL based on max UIF, flagged generator count, and grid strength
⚠️
Flagged Generators
List of generators exceeding UIF thresholds, with type, capacity, distance, and individual UIF values
⚡
Short-Circuit Capacity
MVA fault level at the interconnection bus — measures the electrical stiffness of the grid at your point of connection
📈
Short-Circuit Ratio (SCR)
SC MVA divided by load MW. SCR < 5 indicates a weak grid point with elevated oscillation risk
🔄
Contingency Sensitivity
How UIF scores change under N-1 generator outages — identifies fragile screening results that depend on a single unit
METHODOLOGY

EPRI-Based UIF Screening with Production Cost Model Data

Unit Interaction Factor (UIF)

UIF = (MWload / MVAgen) × (1 − SCwithout_gen / SCtotal). This captures both the relative size of the load versus each generator and the electrical coupling between them.

A generator that contributes a large fraction of the short-circuit capacity at the load bus is tightly coupled — and more likely to experience adverse torsional interaction.

Short-Circuit Estimation

Short-circuit MVA is computed from the network admittance matrix (Ybus) using the diagonal of Zbus = Ybus-1. Generator contributions use typical transient reactance (x'd) values by fuel type.

Typical x'd: coal 0.30 pu, CCGT 0.25 pu, OCGT 0.20 pu, nuclear 0.30 pu. These are conservative values per IEEE Std 3002.3.

EPRI Risk Thresholds

Risk classification follows EPRI screening guidelines:

LOWUIF < 0.01
MEDIUM0.01 ≤ UIF < 0.1
HIGH0.1 ≤ UIF < 0.3
CRITICALUIF ≥ 0.3
Generator Vulnerability Classification

Only synchronous generators with multi-mass turbine shafts are susceptible to SSTI. The engine automatically classifies every generator in the network by fuel type and capacity.

Vulnerable: coal, CCGT, OCGT, nuclear, oil, biomass. Not susceptible: solar, wind, battery, hydro. Classification is conservative — all thermal units are screened.

USE CASES

Who Needs SSTI Screening: Data Centers, Hyperscalers & Interconnection Planning

Data Center Site Selection

Screen 10 candidate sites for SSTI risk in minutes. Eliminate locations near vulnerable generators before investing in land options or interconnection applications.

Hyperscaler Interconnection Planning

Your 500 MW campus needs to interconnect without triggering a multi-year SSO study. SSTI screening identifies the lowest-risk buses in your target market.

Utility Interconnection Study Pre-Screening

Run UIF analysis before a formal interconnection request to anticipate study requirements, flagged generators, and potential mitigation needs.

PE Due Diligence

Evaluating an acquisition or development site? SSTI screening provides a quantitative risk metric for the interconnection viability component of your diligence.

VIPER INTEGRATION

SSTI screening lives inside VIPER's nodal map.

Toggle to SSTI mode and every bus on the map is color-coded by risk tier. Click any bus to see flagged generators, UIF scores, and short-circuit capacity. Adjust load MW in real time to see how risk changes with interconnection size.

Risk Heatmap
Every bus colored LOW (green) to CRITICAL (red) based on max UIF score at your specified load size
Generator Detail
Click a bus to see every flagged generator — name, type, capacity, UIF score, and electrical distance
Dynamic Sizing
Adjust load MW with a slider and watch risk tiers update across the entire network in real time
Try SSTI Screening in VIPER

Know the SSTI risk before you commit to the site.

226 buses. Every vulnerable generator screened. UIF scores in seconds — not months.

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