Study & Analysis for Load Flow, Short Circuit and Relay Coordination in New Zealand

Performing a combined load flow, short-circuit, and relay coordination study follows a consistent sequence, whatever the size of the facility.

It starts with a single-line diagram of the network — every generator, transformer, cable, and switchgear device, with its rating. From there, all quantities are converted to a common per-unit base so that components at different voltage levels can be compared directly, and the network is represented as a set of nodes connected by impedances (an admittance/Ybus model, in the language the software uses). With that model built, load flow is solved iteratively — the Newton-Raphson method is the standard approach — to find the steady-state voltages, power flows, and losses for the system's normal operating condition. The same model is then used to calculate short-circuit current at each bus for different fault types, which gives the fault current magnitude every protective device downstream needs to handle safely. Finally, relay coordination checks each protective device's time-current curve against those fault currents and against the neighbouring devices upstream and downstream, confirming that the device closest to a fault trips first and that no two devices are set to trip at effectively the same time for the same fault.

For a New Zealand facility, this sequence gives a documented, AS/NZS 3000-aligned basis for how the network behaves both under normal load and under fault conditions, and for whether the existing protection settings are still correctly coordinated. Carelabs performs the full sequence in ETAP. Get in touch if it's been a while since your facility's protection settings were last reviewed against its current load and fault-current profile.