Industrial site
Protection coordination and relay verification
MV protection coordination and on-site check of the settings.
Study
Protection coordination study
When a fault occurs, only the nearest protection should trip, and fast enough for the equipment to withstand it.
We check protection coordination (selectivity) in the worst-case configuration, with maximum and minimum short-circuit currents and maximum load current. A single calculation case is not enough.
Four types of discrimination exist and are often combined. Current discrimination relies on thresholds, time discrimination on time delays, typically 250 to 300 ms between stages. With logic discrimination, the downstream protection blocks the upstream one. Differential protection monitors a closed zone and operates instantaneously.
Earth faults are treated separately. Their current depends on the neutral earthing arrangement and is sometimes too low for conventional functions. We check the current transformers at the same time, because a saturating CT distorts every calculated time.
01What we do
Method
- Maximum and minimum fault currents
- Time-current curves per protection chain
- Current, time and logic discrimination
- Verification of current transformer performance
Results
- Deviations found and corrections
- Proposed settings
- Curves per voltage level
02Examples
03Our offer
Usual content of an offer for this type of assignment. The exact scope, deliverables and price are set in the quotation.
- Package 1Data and fault currents
Maximum and minimum currents, three-phase and earth, per busbar.
- Package 2Protection chains
Relays, CTs and settings, from feeder to incomer.
- Package 3Time-current curves
Margins at the critical points, CT verification.
- Package 4Proposed settings
Justified corrections and updated settings schedule.
04How we work
- 01Fault currents
Maximum and minimum, three-phase and earth, per busbar.
- 02Protection chains
From feeder to incomer, each relay and its CT.
- 03Time-current curves
Margins measured at the critical points.
- 04Settings
Proposed corrections, updated settings schedule.
05References
General contractor
Protection plan, 240 MVA data centre
Selection of protection functions, current transformer sizing, settings, follow-up of testing through to commissioning.
06Frequently asked questions
Protection coordination or protection plan?
Coordination checks that the settings work together. The protection plan goes further and also covers the choice of functions and current transformers, as well as the settings schedule.
Do you check the settings actually in place?
Yes, on site with our injection test sets (see Protection, tap changer and automation testing).