A protection coordination study is an engineering analysis that determines the settings and grading of every protective device in an electrical network — relays, circuit breakers and fuses — so that when a fault occurs, only the device closest to the fault operates, isolating the smallest possible portion of the system. Its purpose is selectivity (also called discrimination): faults are cleared quickly and locally, without tripping the whole installation offline.
Every well-designed power system relies on one, whether it’s a hard-rock mine, a hyperscale data centre or a utility-scale solar farm. Below is what a protection coordination study actually involves, why it matters, and when you need one.
Why does protection coordination matter?
Three outcomes hang on getting coordination right:
Selectivity and continuity of supply. Without proper grading, a fault on one feeder can trip an upstream breaker and take out an entire switchboard — or the whole site. Coordination ensures the fault is cleared at the nearest downstream device, keeping the rest of the network energised. For a mine or a data centre, that difference is measured in lost production or breached uptime guarantees.
Arc flash and personnel safety. The faster a protective device clears a fault, the lower the incident energy released in an arc flash event. Coordination directly governs clearing times, so it’s inseparable from arc flash safety and the PPE categories your people are exposed to.
Compliance and equipment protection. Correct settings keep fault currents within equipment withstand ratings and satisfy the requirements of AS/NZS 3000 and relevant network operator standards. Poorly coordinated protection can leave cables, transformers and switchgear unprotected against damage.
When do you need a protection coordination study?
You need one whenever the protection grading can no longer be assumed correct. Common triggers:
- New installations — every new substation, switchroom or reticulation scheme needs coordination from the outset.
- Network changes — adding a transformer, a large motor, on-site generation or a new feeder changes fault levels and can break existing grading.
- Relay replacement or upgrades — moving from electromechanical to numerical relays is a natural point to re-verify settings.
- After a nuisance trip or a fault that isolated too much — clear evidence the existing coordination is wrong.
- Compliance audits — many operators and insurers now require current coordination and arc flash records.
What is the process for a protection coordination study?
The study is only as good as the model behind it, so it follows a disciplined sequence.
1. Data collection
We gather the network data: single-line diagrams, transformer ratings and impedances, cable sizes and lengths, source strength or generation characteristics, and every existing relay, fuse and breaker with its current settings and manufacturer curves. Accurate data is non-negotiable — guessed impedances produce confident but wrong results.
2. System modelling
The network is built into a validated power system model in SKM PowerTools (PTW) or ETAP. This model becomes the engine for the fault, coordination and arc flash calculations.
3. Fault level analysis
Short-circuit currents are calculated at every relevant point in the network. These fault levels define the current range over which each protective device must coordinate and set the equipment rating requirements.
4. Relay grading
Using time–current curves, each device is graded against the one upstream of it. We apply appropriate grading margins so that for any fault, the downstream device operates first and the upstream device holds — across the full spectrum of fault currents, not just one operating point. This is the core of the study and the part that’s impossible to do properly without the model.
5. Arc flash assessment
With clearing times now established, incident energy is calculated per IEEE 1584. This produces arc flash boundaries and PPE category labelling for each item of switchgear — a direct safety output of the same study.
What are the deliverables?
A protection coordination study typically delivers:
- A settings schedule — recommended settings for every relay and protective device.
- Time–current coordination curves showing the grading and margins.
- A fault level report underpinning the equipment ratings.
- An arc flash report and labels per IEEE 1584.
- A summary of assumptions, findings and any recommendations (for example, equipment nearing its withstand rating).
At JMB Engineering, all protection settings, coordination reports and study outputs are stored on our Protection Database platform, giving your team an auditable, easy-to-access record that makes the next study faster and cheaper.
The bottom line
A protection coordination study is the analysis that makes a network safe, selective and compliant. It ties together fault levels, relay grading and arc flash into one coherent settings regime — the difference between a fault that clears quietly at the nearest breaker and one that takes half the site down. If your network has changed, or you can’t put your hands on current coordination and arc flash records, it’s time for a study.
Need a protection coordination study? Explore our protection engineering capability or review the full power system studies service.
FAQ
What is the difference between a protection coordination study and a fault level study?
A fault level study calculates how much short-circuit current can flow at each point in the network. A protection coordination study uses those fault levels to grade the relays and fuses so the closest device clears a fault first. The fault level study is an input to the coordination study.
What software is used for protection coordination studies?
The industry-standard packages are SKM PowerTools for Windows (PTW) and ETAP. Both build a validated model of the network and generate the time–current coordination curves, fault calculations and arc flash results in one environment.
Does a protection coordination study include arc flash?
Yes — arc flash assessment is a natural output of the same study. Because coordination determines fault clearing times, and clearing time drives incident energy, the arc flash calculation (per IEEE 1584) is usually performed as part of the coordination work.
How often should a protection coordination study be updated?
It should be reviewed whenever the network changes — new transformers, generation, large motors or feeders — and after any fault that isolated more of the system than it should have. Many operators and insurers also expect coordination and arc flash records to be kept current for compliance audits.
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JMB Engineering Pty Ltd — electrical engineering consultancy specialising in power system studies, protection, earthing and modelling for mining, data centres, renewables and heavy industry. Thornton, NSW.
