Protection Coordination Study
We compare the time-current curves of relays, fuses and breakers on one plot and prepare a selective setting proposal and setting table, so that on a fault only the device closest to it trips.
Which questions does this study answer?
Protection coordination determines both continuity and safety: a wrong setting means either needless outages or high arc flash energy.
Do the devices operate selectively?
The margin between the time-current curves of upstream and downstream devices is checked; the aim is that only the nearest device trips on a fault.
Are clearing times reasonable for arc flash?
A longer clearing time means higher incident energy; ways of shortening clearing time without giving up selectivity are assessed.
Do the settings match changes in the plant?
After a change in load, transformer or source, it is checked whether the existing settings are still valid.
Is there agreement with the grid side?
Agreement with the utility's protection settings at the connection point is verified separately.
Required data
A setting proposal depends on the accuracy of the existing device and setting information.
- Single-line diagram and current short-circuit study results
- Relay, breaker and fuse model information and existing settings
- Current and voltage transformer information
- Motor starting and transformer inrush information
- Grid-side protection setting information
Working steps
The steps are sequential: the output of each is the input of the next.
01
Inventory of existing settings
Device models and settings are collected; the actual field settings are checked against the single-line diagram.
02
Plotting the time-current curves
Device curves are shown on one plot together with fault current levels and load limits.
03
Selectivity check
The time margin between upstream and downstream devices is checked; overlapping regions are flagged.
04
Setting proposal
Settings that give selectivity and shorten clearing time as far as possible are proposed; the arc flash effect is compared.
05
Reporting
The existing and proposed setting table is delivered with the curves and assumptions, document-controlled.
Reference standards
The frameworks below are referenced. This is a reference framework, not a certification or accreditation statement.
- IEC 60255
- Measuring relays and protection equipment
- IEEE 3000 series
- Collection of recommended practices for industrial and commercial power systems, including protection and coordination
Delivered documents
- Time-current coordination curves
- Existing and proposed setting table
- Selectivity assessment
- Statement of assumptions and limitations
- Document control record (prepared by / checked by / approved by, revision)
Scope and limits
- A setting proposal depends on the device manufacturer's setting ranges and on grid-side coordination; cross-verification is needed before implementation.
- Entering settings into relays and commissioning tests are a separate scope.
- Results depend on the input data; they must be updated when the plant changes.
Protection coordination rests on the short-circuit study; if its results are not current, that study is done first.
Protection coordination for your facility
Let us review your existing settings and single-line diagram together and clarify the scope.
Request a technical pre-assessment