How to Perform Power System Analysis for Load Flow, Short Circuit and Relay Coordination for a Company in New Zealand

An electrical system rarely gets a full power system study on its own initiative — it usually gets one because a change is coming. A planned expansion, a new production line, a standby generator being added, or simply a facility old enough that no one currently on staff has seen the original design calculations are all common triggers for a New Zealand business to commission a combined load flow, short-circuit, and relay coordination review before the change goes ahead.

The reason the three studies are done together rather than one at a time: a planned change typically shifts both how the system behaves under normal load and how much current is available at a fault. Load flow analysis models the network's steady-state condition — voltages, power flows, and losses — for the load configuration the change will create, confirming existing cabling, transformers, and switchgear can carry it without exceeding rated limits. Short-circuit analysis then recalculates fault current at every bus under the new configuration, since adding generation or transformer capacity generally increases the fault current available at that point. Relay coordination is reviewed last, because settings that were correct for the old fault-current profile can become incorrect once that profile changes — either too slow to protect equipment, or tripping more of the facility than the fault requires.

Carelabs runs this sequence in ETAP: single-line diagram, per-unit modelling, iterative load flow solution, short-circuit calculation at each bus, and a relay coordination check against the results — delivered as a report aligned with AS/NZS 3000. If your facility has a change planned and no recent study to check it against, contact our engineering team before the change goes ahead.