Maritime Protection Systems on Modern Vessels: From Theory to Real-World Testing

Electrification has turned today’s ships into compact, highly stressed microgrids. Integrated Power Systems (IPS) connect propulsion, hotel loads, and auxiliary systems to common main switchboards, often in closed rings with multiple generators feeding the same busbars.

That architecture is fantastic for efficiency and redundancy… but only if the protection system really does what its settings promise.

This post turns the findings of “Protection of Electrical Power Systems in Maritime Applications – Analysis of Directional Overcurrent Protection Methods” into practical guidance for shipowners, yards, and system integrators.

We’ll look at:

• Why directional overcurrent (ANSI-67) is a cornerstone for shipboard selectivity

• How protection behaves in closed-ring, multi-infed configurations

• Concrete testing procedures for key elements (generators, busbars, feeders, motors, breakers)

• Where EuroSMC equipment like Quasar, Mentor 12, ROOTS, Raptor, Prime, and PME can help you turn theory into reliable practice at sea

  

• 1. What makes maritime power system protection different?

The thesis highlights several characteristics that make shipboard systems quite unlike typical terrestrial grids:

• Integrated Power Systems (IPS): generators, propulsion and hotel loads share common main switchboards, often arranged in a closed ring with multiple infeeds.

• Short electrical distances: cables are often <100 m. Fault currents are strong and appear almost simultaneously at several relays.

• Variable short-circuit power: depending on how many gensets are on line, fault levels and relay operating times can change significantly.

• High penetration of motors and drives: propulsion motors can represent up to 90% of the total load; starting and fault behaviour can strongly influence voltages and currents.

• Insulated or high-resistance grounding: earth-fault currents are low, so phase-to-phase (PP), double-phase-to-ground (PPG) and three-phase (3P) faults are often the dominant protection concern.

The conclusion from the thesis is clear: continuity of service depends on fast and selective protection, and that protection must remain reliable across different system configurations and loading conditions.

2. Directional overcurrent (ANSI-67): the backbone of selectivity at sea

Because distances are short and CT saturation can limit differential schemes, distance protection (ANSI-21) is often impractical on ships. Differential (ANSI-87) remains important for machines and sometimes busbars, but using it everywhere can be costly and CT-sensitive. This leaves directional overcurrent (ANSI-67) as a key tool for selective protection of busbars, ties and feeders in closed-ring systems.

The thesis focuses on how ANSI-67 behaves in maritime conditions and compares several polarisation methods:

• Positive-sequence polarisation (V₁ / I₁)

• Cross-polarisation (Vyz / Ix)

• Self-polarisation variants (Vx / Ix, Vxy / Ix, Vxy / Ixy)

Key findings:

• Positive-sequence and cross-polarisation deliver reliable directionality and fast pickup (typically <1 period) for PP and 3P faults in the studied 8-bus closed-ring model.

• Self-polarisation can lose its directional element during phase-to-phase faults, especially for bolted faults with very low fault impedance.

• The main challenges in maritime applications are not the polarisation methods themselves, but coordination in closed rings and configuration changes (generators in/out, loop open/closed).

Crucially, the thesis doesn’t stop at simulation: the author validated a commercial medium-voltage relay (DEIF MVR-215 with ANSI-67 based on positive-sequence polarisation) using a hardware test set that replayed COMTRADE fault records in real time.

That same philosophy—simulate realistic faults, replay them into the actual relay, and verify the response—is exactly where EuroSMC units can add value for shipboard projects.

3. From thesis to engine room: testing procedures by element

Below is a pragmatic test approach by component type, and how EuroSMC equipment can support it.

3.1 Generators and main switchboard busbars

Protection functions typically involved (per the thesis and marine practice): ANSI-50/51 (OC), 67 (directional OC), 32 (directional power), 27/59 (UV/OV), 24 (overfluxing), 81 (frequency), 87 (differential).

Testing objectives

1. Verify pick-up and time-current characteristics for all overcurrent functions (50, 51).

2. Confirm correct directional behaviour of ANSI-67 for forward/reverse PP and 3P faults under different generator configurations.

3. Check coordination of generator, busbar and feeder relays with the time-grading logic used in your closed-ring scheme.

Recommended tests (secondary injection)

Using a relay test set such as Quasar or Mentor 12 together with ROOTS software, you can:

• Static pickup tests

  • Inject three-phase currents with incremental ramps to confirm 50/51 and 67 pickup levels (usually 1.1–1.2 × In).

• IDMT curve verification

  • For each 51/67 element, apply several current points (e.g. 2, 5, 10 × In) and measure operating time. Compare against SI/VI/EI curves used on board.

• Directional tests (forward/reverse)

  • Recreate fault scenarios from your own short-circuit study or directly from time-domain simulations in RMS/EMT tools.

  • Export as COMTRADE and replay with Quasar/Mentor, just as the thesis did with an OMICRON unit.

  • Test PP and 3P faults at different locations (generator terminals, busbars, ring cables) and confirm that each relay and interlocking logic trips—and only where it should.

• Frequency deviation and fault impedance sweeps

  • The thesis shows that deviations in frequency and fault impedance can affect relay timing and sometimes push polarising angles towards zone limits.

  • With ROOTS, you can automate test sequences that sweep frequency (e.g. 58–62 Hz) and increase fault resistance, checking that relays still pick up in time.

Where this sparks debate

• Do you currently test your ship’s protection only at nominal frequency and bolted faults?

• What evidence do you have that settings remain selective when only two gensets are online—or when the loop is opened for maintenance?

These are questions your classification society and your own internal safety reviews will increasingly ask.

3.2 Propulsion and large motor drives

In many IPS vessels, propulsion motors dominate the load profile and strongly influence system dynamics.

Relevant protections: 50/51, 49, 51R, 27, 40, 47, 55, 81, 87.

Testing objectives

• Distinguish clearly between motor start currents, short-time overloads, and true faults.

• Verify that motor protection and upstream feeder/busbar protection coordinate properly—no unnecessary blackout of an entire main switchboard due to a single thruster.

Recommended tests

With Quasar or Mentor 12 + ROOTS:

• Simulate a realistic start profile (inrush, acceleration, normal running) and verify that only the intended elements (thermal, 51R) respond.

• Inject locked-rotor and phase-loss conditions to verify trip times and selectivity.

• Combine current and voltage ramps to test undervoltage / reduced-voltage starts, checking that 67/51 elements upstream do not trip unintentionally while the propulsion drive is starting.

This is where having automatic templates in ROOTS becomes powerful: every time you commission or refit a propulsion system, you can replay the same test plan and directly compare results.

3.3 Feeders, cables and ring bus ties

The thesis devotes significant attention to closed-ring-multiple-infed configurations and shows how directional OC, reverse blocking, and CB interlocking can deliver selective protection without full differential schemes.

Testing objectives

• Validate forward and reverse 67 elements at each end of key cables.

• Confirm that reverse-blocking and permissive-trip logic correctly isolates cable and busbar faults without splitting the ring more than necessary.

Recommended tests

Again using Quasar or Mentor 12:

• Perform end-to-end directional tests on each ring cable:

  • Inject a simulated fault from the “sending” side with appropriate voltage polarisation.

  • Confirm that the local relay trips and the remote relay blocks as intended (or vice versa, depending on your scheme).

• Use logic testing / binary I/O to verify that your programmable logic (reverse-blocking, interlocks, busbar trip conditions) behaves exactly like the scheme tables drawn in your design documents.

• Replay the same COMTRADE scenario into several relays (sequentially or simultaneously) to check that overall system behaviour matches the study that justified the settings.

EuroSMC units are particularly strong here because they can combine precise three-phase injection with automatic logic checking, and ROOTS can generate consistent reports that are easy to present to yards, owners and classification societies.

3.4 Circuit breakers and switchgear: primary injection and timing

Even a perfectly set relay is useless if the breaker doesn’t open in time.

In compact shipboard microgrids, every millisecond of fault clearing time matters: long clearing times quickly translate into thermal stress, voltage collapse and potential loss of synchronism.

Testing objectives

• Verify breaker timing under realistic currents.

• Check contact resistance and mechanical condition.

• Prove that primary paths (main busbars, tie breakers, generator breakers) can carry full load and fault currents safely.

Recommended tests (primary injection)

Using Raptor, Prime 600/200, or PME-500-TR / PME-600-T / PME-700-TR:

• Timing tests

  • Inject high current through the breaker poles and measure opening/closing times against relay trip signals.

  • Confirm that overall fault clearing time (relay + breaker) matches the assumptions used in your coordination study.

• Dynamic resistance measurements (DRM)

  • Especially important for high-duty breakers whose contacts see many short-circuit interruptions.

• Busbar and joint verification

  • Perform primary injection through bus sections and tie-lines to validate connections, CT polarity and saturation performance.

These tests not only support safety; they also open a useful conversation: are the margins you assumed in your coordination study still valid after five or ten years of operation?

3.5 Ground faults in high-resistance or insulated systems

The thesis notes that with high-resistance or insulated grounding, ground-fault currents are usually low, so PG faults may not exceed overcurrent thresholds and are sometimes treated more like insulation issues than high-energy faults.

Testing objectives

• Confirm sensitivity and directionality (where used) of 51G/67N elements.

• Validate alarms and trip logic for first-fault / second-fault philosophies.

Recommended tests

With Quasar or Mentor 12:

• Inject low-level residual currents and offsets to check sensitivity.

• Verify the transfer from alarm-only to trip when a second fault or higher level is detected.

Because ground-fault strategy is often specific to each ship and classification society, this area is ideal for constructive debate between designers, owners, and yards—EuroSMC equipment becomes the neutral “truth meter” to validate whichever philosophy you adopt.

4. A practical roadmap for shipyards and operators

Putting everything together, a realistic test program for a newbuild or major retrofit might look like this:

1. Before sea trials

   • Use Quasar/Mentor 12 + ROOTS to validate all relay settings (generators, busbars, feeders, motors) with automated test plans.

   • Execute primary injection tests with Raptor/Prime/PME on main breakers and busbars.

   • Store test reports as part of the vessel’s technical file.

2. After first year in service

   • Re-run a shortened version of the relay test plan focusing on critical loops (ring ties, propulsion feeders, emergency generator).

   • Repeat breaker timing tests on the most critical breakers.

3. Every dry-dock / major refit

   • Review the coordination study considering any new drives, generators or consumers.

   • Update relay settings where needed and re-run ROOTS automated tests.

   • Use primary injection to confirm that any new switchboards or bus-couplers perform as designed.

Over time, you build a traceable history of protection performance—a powerful asset when discussing risk, availability, and compliance with owners and class.

5. Opening the discussion

To close, here are a few questions you can use internally—or with us—to spark constructive debate:

• Are your directional relays tested in all realistic genset configurations (harbour, transit, DP, emergency)?

• Do your time-grading margins still make sense once you measure actual breaker times with primary injection?

• How do you demonstrate, with evidence, that a fault on one propulsion bus will not black out the entire vessel?

• Is your current test strategy based on a single relay brand’s philosophy, or on a system-level view like the one developed in the thesis?

If these questions resonate with you, we’d love to help.

Using EuroSMC relay and primary injection test systems, plus ROOTS automated testing, we can work with your team, your yards and your partners to turn advanced protection theory for maritime applications into a repeatable, documented testing strategy—from design office to engine room.

And that’s where reliability at sea really starts.