Discrimination Studies in Melbourne
ARA Electrical Services provides protection discrimination studies for industrial plants, commercial buildings, and utility infrastructure across Melbourne and Victoria. Studies are carried out by engineers with direct experience in protection system design and analysis, using specialist power system software to model device behaviour across the full range of fault conditions relevant to the installation.
AS/NZS 3000 requires discrimination to be achieved as far as practicable. On industrial and commercial installations of any complexity, that means a properly conducted engineering study, not assumptions based on rating ratios or standard device combinations.
Study Methodology
ARA models the protection system from the point of supply through to final subcircuits, entering circuit breakers, fuses, protection relays, cable impedances, and transformer impedances to produce accurate time-current characteristic comparisons at each level of the distribution hierarchy. Fault current is calculated at each node using IEC 60909 short-circuit methodology, covering both maximum and minimum fault conditions.
The study verifies grading margins between upstream and downstream protective devices across the full fault current range, identifies where time-current curves overlap and selectivity is lost, and assesses whether existing or proposed device settings achieve the required discrimination for the fault levels present in the system. Where relay-based protection is involved, relay characteristic curves, time multiplier settings, and instantaneous element thresholds are included in the coordination analysis.
Data Requirements
Accurate study outputs depend on complete and accurate system data. ARA requires the following to complete a discrimination study:
• Single-line diagrams reflecting the current or proposed system configuration
• Available fault level at the point of supply, or network impedance data
• Cable data including conductor size, length, and installation method
• Protective device specifications, ratings, trip unit types, and current settings
• Protection relay model numbers, characteristic curves, and existing settings
• Transformer impedance data and winding configuration where applicable
Where fault level data is not available, ARA can calculate available fault current from network impedance data supplied by the distribution network service provider.
When a Discrimination Study Is Warranted
Discrimination studies are applicable across a broad range of project and operational scenarios:
• New LV or HV distribution systems where protection coordination needs to be established before energisation
• Switchboard and MCC replacements where existing protection settings need to be reviewed against the new device complement
• Site expansions or load additions that change fault levels at existing protection nodes
• HV and LV protection coordination across substation transformer feeders
• Investigations into nuisance upstream tripping under downstream fault conditions
• Essential services installations where supply continuity to critical loads must be maintained during a downstream fault
• New protection relay commissioning requiring verified grading margins
Study Outputs
ARA delivers a written study report covering the discrimination performance of the system at each protection level, grading margin analysis between device pairs, identified selectivity deficiencies, and specific recommendations for device selection changes or setting adjustments required to achieve the required level of coordination. Where software-generated time-current characteristic plots are included, these are presented alongside the written findings to support review by the client engineering team.
Discrimination Studies in Melbourne
ARA Electrical Services provides protection discrimination and selectivity studies for industrial and commercial clients across Melbourne and Victoria. If your site requires a new study, a review of existing protection settings, or coordination analysis as part of a switchboard or infrastructure upgrade, contact ARA to discuss your requirements.
