General contractor
Protection plan, 240 MVA data centre
Selection of protection functions, current transformer sizing, settings, follow-up of testing through to commissioning.
Study
Protection plan
Selection of the protection functions, sizing of the current transformers and calculation of the settings, from the HV substation to the MV feeder.
The protection plan is the reference document for testing, commissioning and operation. It states which protection sees which fault, in what time, and what happens if it fails to operate.
It is built by zones (line, busbars, transformers, feeders). Each zone is bounded by its current transformers, and the zones overlap around the circuit-breakers to leave no blind spot. Each zone has a main and a backup protection, and we check what happens to fault clearance if a circuit-breaker fails to open (breaker failure, 50BF).
At HV, the plan must also meet the network operator's requirements at the connection point, which cover mandatory functions, clearing times and exchanges with the upstream substation.
Neutral earthing
The neutral earthing arrangement determines the earth-fault protection. With an impedance-earthed neutral, the fault current is known and 50N/51N residual overcurrent protection is suitable. A neutral compensated by an arc-suppression (Petersen) coil, now common on the public MV network, gives a very low fault current and requires directional or wattmetric zero-sequence protection. An isolated neutral, still found on industrial networks, goes with permanent insulation monitoring and discrimination by directional protection. At HV, the neutral is solidly earthed.
Changing the neutral earthing arrangement, or connecting a private network to a compensated public network, requires a review of the earth-fault protection plan, the surge arrester withstand and the touch voltages.
01What we do
Design
- Functions per zone: 87T, 87B, 87L, 21, 50/51, 50N/51N, 67N, 27/59, 81, 50BF
- Earth-fault protection suited to the neutral earthing arrangement
- NF C 13-100 main protection and interface protection
- CT and VT sizing
- Redundancy of the trip chains
Settings
- Calculation of thresholds and time delays
- Settings schedule per relay
- Manufacturer configuration files on request
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 1Protection principle
Zones, main and backup functions, neutral earthing, redundancy.
- Package 2Current and voltage transformers
Ratio, class, burden, accuracy limit factor verified.
- Package 3Settings calculation
Justified thresholds and time delays, coordination verified.
- Package 4Settings schedule
Per relay, ready for configuration and testing.
04How we work
- 01Principle
Zones, main and backup functions, redundancy.
- 02Current transformers
Ratio, class, burden, accuracy limit factor verified.
- 03Settings calculation
Justified thresholds and time delays, coordination verified.
- 04Settings schedule
Per relay, ready for configuration and testing.
05References
Data centre operator
225 kV GIS substation
Design review and review of the studies (VISA). We found deviations on the voltage transformers and on trip circuit redundancy.
Integrator, West Africa
Four PV plants
Load flow, short-circuit, neutral earthing, earthing, stability and protection plan for each plant.
06Frequently asked questions
Do you supply the configuration files?
Yes, for the main product ranges on the market, based on the settings schedule. See Protection, tap changer and automation testing.
Do you follow commissioning?
Yes, through to testing and energisation.