Summary Highlights
- Maximum–minimum short circuit current calculations and equipment endurance/breaking capacity control in HV/MV systems
- Relay selectivity (protection coordination) studies: time-current curves, tripping sequence and setting optimization
- Technical conformity assessment according to the fault level of circuit breakers, fuses, MCCB/ACB, protection relays and contactors
- Analysis-reporting for new facility, power increase, transformer replacement, generator/SPP integration and revision projects
- Modeling, field data verification, relay setting list preparation and commissioning support with ETAP/similar software
Service Details
Short circuit analysis and relay selectivity studies are basic engineering studies in terms of safe operation, equipment protection and energy continuity in electrical facilities. Especially in industrial facilities, production lines, hospitals, data centers, shopping malls, hotels and large commercial buildings; It is difficult to ensure healthy operating safety without technically verifying which protection element will open in which order in case of failure.
What is short circuit analysis? Short circuit analysis; It is the process of calculating the expected fault currents in fault scenarios such as three-phase short circuit, phase-ground, phase-phase and two phase-ground that may occur in the electrical system. These calculations are made by taking into account transformer power and impedance, network short circuit power, cable lengths and cross-sections, motor contributions, generator/SPP contributions and system topology.
What is relay selectivity study? Relay selectivity (protection coordination) study; It is an adjustment and coordination work that ensures that in case of a fault, the protection element closest to the fault opens first, and the protection elements at the upper level are activated only when necessary. The aim is to isolate only the faulty area without blacking out the entire facility.
Why are these studies important? If the short circuit level is calculated incorrectly, the selected breaker or protection element may be inadequate in the event of a fault. If selectivity is not done correctly, the main breaker may open due to a minor malfunction and the entire facility may be left without power. This leads to production loss, equipment damage, occupational safety risks and unplanned downtime costs.
Within the scope of the service, firstly, single line diagram, transformer information, MV/LV panel data, cable lists, protection element types, existing relay brand-model information and current setting values, if any, are collected. Project documents are compared with the data obtained from the field; If there is missing or outdated information, the model is revised for accuracy.
During the modeling phase, mains supply, transformers, generators, motor loads, cables, busbars and protection elements are represented in the software environment. Operating scenarios (normal operation, generator feeding, ring opening/closing status, parallel transformer operation, etc.) are evaluated separately and fault currents are calculated for each scenario.
Short circuit analysis outputs are not limited to giving fault current values only. At the same time, the interrupting capacity of the equipment, thermal-dynamic resistance adequacy, busbar/cable strains and suitability of the measuring ranges of the protection devices are also checked. Thus, it is seen whether the equipment selection is sufficient in terms of engineering.
In relay selectivity study, protection relays, fuses, MCCB/ACB electronic trip units and, if necessary, motor protection elements are evaluated together. Trip thresholds and delays are coordinated on time–current curves (TCC); Overcurrent, short circuit, ground fault and directional protection functions are optimized according to the application.
When conducting selectivity studies, not only theoretical coordination but also business priorities are taken into account. For example, while continuity is prioritized in lines feeding critical loads, a special protection approach may be required for loads such as fire pumps, process safety, UPS supply routes or critical production lines. Therefore, the work is not a job of copying a standard setting; It is engineering optimization according to the operating scenarios of the facility.
Short circuit and selectivity studies are critical for correct equipment selection in new facility installations. In revision projects, it must be checked whether the existing protection level is damaged after transformer power increase, panel replacement, new machine addition, generator integration or SPP connection. Current settings may remain inadequate or overly sensitive after a system change.
At the reporting stage; The assumptions and assumptions used, the system model, short circuit calculation results, equipment conformity assessment, coordination curves, relay adjustment recommendations and revision items that need to be applied are clearly presented. If desired, investment priorities can be determined by comparing the 'current situation' and 'proposed situation'.
Field application and commissioning support is also an important part of this service. In order to ensure that the relay settings do not remain only in the report, coordination is maintained with the field teams, relay parameter entries are checked, a primary/secondary test plan is created if necessary, and the expected tripping behavior of the protection functions is verified. Thus, the analysis work turns into a protection system that works in practice.
Short circuit analysis and relay selectivity studies; It makes a big difference not only in MV systems, but also in LV main distribution panels, MCC panels and critical sub-distribution systems. Especially in facilities with transformers with high short circuit power, LV side protection coordination can be vital to prevent the spread of the fault and maintain business continuity.
As Pow-Sys, we offer this service through a systematic process consisting of field data collection, single line verification, software modeling, short circuit calculations, protection coordination, relay setting optimization, reporting and field application support. Service according to need; We can carry out relay tests, energy quality measurements, harmonic analyses, thermal controls and periodic maintenance work in an integrated manner.
If you would like to get detailed information about short circuit analysis and relay selectivity studies, request a technical evaluation for your existing facility or request a quote for your new project, you can contact us. When shared with your single line diagram and essential equipment list, we can quickly clarify the scope and create an actionable work plan.
Frequently Asked Questions
What is short circuit analysis and what does it do?
Short circuit analysis; It is an engineering study that calculates the expected fault currents in case of faults that may occur in the electrical system. Thanks to this study, it is checked whether the breaker, fuse, busbar, cable and other equipment are sufficient to withstand the fault level; The risk of damage due to wrong equipment selection and malfunction is reduced.
Why is relay selectivity (protection coordination) study necessary?
Selectivity operation aims to leave only the faulty area de-energized in the event of a fault. If correct coordination is not made, the upper level protection elements that are remote from failure may trip and the entire facility may be disabled. This creates unnecessary power outages, production losses and operational risks.
In which facilities should short circuit and selectivity studies be carried out?
This study is recommended for industrial facilities with substations, factories, hospitals, shopping malls, hotels, data centers, large commercial buildings and all MV/LV electrical systems with critical loads. In addition, the work should be updated after transformer power increase, panel revision, generator/SPP integration or new machine addition.
What information is required for this study?
Generally, a single line diagram, transformer power and impedance information, network short circuit data (if any), panel and breaker brand-model information, cable lengths/sections, relay types, current relay settings and operating scenarios are required. Missing data/data discrepancies can be completed by verification in the field.
Is it mandatory to use ETAP?
ETAP is a widespread and powerful analysis platform; However, short circuit and selectivity studies can also be done with different engineering software. The important thing is that the methods used are correct, the model represents the field, and the output is converted into an applicable technical report and setting list.
What outputs are delivered at the end of the study?
According to the scope; Short circuit calculation results (maximum/minimum fault currents), equipment conformity evaluation, time-current curves (TCC), selectivity/coordination comments, relay adjustment recommendation lists, revision recommendations and engineering report are delivered. If desired, field application and testing support can also be provided.
Can selectivity be achieved without changing existing relay settings?
In some facilities, existing settings may be sufficient; however, in many cases optimization is required due to system changes, different equipment characteristics, or incorrect historical settings. As a result of the study, whether to maintain the current settings, revise them or recommend equipment replacement is determined according to technical data.
Are short circuit analysis and arc flash analysis the same thing?
No. Short circuit analysis and selectivity study; Evaluates protection coordination with fault current levels. Arc flash analysis focuses on determining possible arc energy levels, approach distances and PPE requirements. However, short circuit and protection data is an important input for arc flash operation.
When should the study be updated?
Short circuit and selectivity studies should be reviewed when transformer change/power increase, new panel or line addition, generator/SPP integration, large engine addition, protection equipment change or significant change in the operating topology is made. Otherwise, the current settings may not be suitable for the new system.
Can relay selectivity study be done together with field tests?
Yes. The healthiest approach; It is the combination of analysis, adjustment recommendation, field parameter application and relay test/verification steps. In this way, it is checked that the protection behavior recommended in the report actually occurs in the field and the commissioning is completed safely.