Maritime protection systems on modern vessels: from theory to real-world testing

Introduction: from the single-line diagram to blackout… or reliability

Electrification has turned the modern ship into a highly stressed microgrid.
Integrated Power Systems (IPS) connect propulsion, hotel loads and auxiliaries to common main switchboards, often in closed-ring configurations with multiple generators feeding the same busbars.

This architecture is extremely efficient and redundant, but only under one condition:

The protection system must do exactly what its settings promise, in every realistic operating configuration.

The thesis “Protection of Electrical Power Systems in Maritime Applications – Analysis of Directional Overcurrent Protection Methods” shows that the real key is not only a sound short-circuit study, but verifying relay behaviour under realistic conditions.

This article turns those conclusions into practical guidance for shipowners, yards and system integrators, and explains how to use EuroSMC tools (Quasar, Mentor 12, Raptor, Prime, PME, ROOTS, PTE-50-CE Pro) to move from theory to a repeatable, documented and class-friendly testing strategy.

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1. What makes shipboard protection different?

Compared to a typical land-based MV network, shipboard systems show some unique features:

• IPS and closed rings: generators, propulsion and auxiliaries share common main switchboards, often with multiple infeeds in a ring.

• Short electrical distances: cable runs <100 m lead to high fault currents and almost simultaneous effects at several relays.

• Variable short-circuit power: fault levels change significantly with the number of gensets online (harbour, transit, DP, emergency).

• High penetration of motors and drives: propulsion motors may account for up to 90 % of total load, strongly influencing system dynamics.

• Insulated or high-resistance grounding (IT/HRG): earth-fault currents are low; PP, PPG and 3P faults typically dominate protection design.

The bottom line:

Service continuity depends on fast and selective protection that remains robust across different operating configurations and loading conditions.

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

On land MV systems, we often combine differential (ANSI-87) and distance (ANSI-21) for high-end selectivity. On ships:

• Distance (21) is often problematic: short lines, changing fault levels and contribution from multiple infeeds make distance reach tuning difficult.

• Differential (87) is excellent for machines and sometimes busbars, but using it everywhere on a ship can be costly and CT-sensitive.

That leaves directional overcurrent ANSI-67 as the workhorse for:

Selective protection of busbars, ties and feeders in closed-ring shipboard IPS.

The thesis compares several polarisation methods (V1/I1, cross-polarised, self-polarised) on an 8-bus closed-ring model and concludes:

• Positive-sequence (V₁/I₁) and cross-polarisation provide reliable directionality and fast operation (<1 cycle) for PP and 3P faults.

• Self-polarised variants may lose directionality during PP faults, especially with bolted faults and very low fault impedance.

• The main challenge is not the polarising method itself but coordination in closed rings and configuration changes (gensets in/out, ring open/closed).

The work goes beyond simulation by testing a commercial MV relay (DEIF MVR-215 with ANSI-67 based on positive-sequence polarisation) using a hardware test set that replays COMTRADE fault records in real time.

That “simulate → replay → verify” philosophy is exactly where EuroSMC units like Quasar and Mentor 12, combined with ROOTS, deliver high value.

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Conceptual diagram 1 – Closed-ring IPS with ANSI-67

This helps visualise where directional relays sit and where it is critical to test direction, blocking and time-grading.

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3. From thesis to engine room: test strategy by component

Below is a practical test approach by system element, and how EuroSMC equipment can support it.

Table 1 – System elements vs. functions and EuroSMC tools

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3.1 Generators and main switchboard busbars

Typical functions: 50/51, 67, 32, 27/59, 24, 81, 87.

Objectives

• Verify pickup and time-current curves for 50/51.

• Confirm correct forward/reverse operation of ANSI-67 for PP and 3P faults under different genset configurations.

• Check coordination between generator, busbar and feeder relays.

• Assess the impact of frequency deviations and fault impedance on relay timing.

Secondary injection with Quasar / Mentor 12 + ROOTS

• Use linear or binary ramps to determine pickups for 50/51/67.

• Automatically verify IDMT curves (SI/VI/EI) at 2, 5 and 10×In.

• Use Fault / Fault Playback to reproduce realistic Pre-fault / Fault / Post-fault scenarios, including COMTRADE playback directly from your RMS/EMT tools.

• Sweep frequency (58–62 Hz) and fault resistance to explore boundary conditions.

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3.2 Propulsion and large motor drives

Objectives

• Clearly distinguish motor start currents, short-time overloads and true faults.

• Ensure proper coordination between motor protection and upstream feeders/busbars, avoiding unnecessary blackouts.

With Quasar / Mentor 12 + ROOTS

• Simulate realistic start profiles (inrush, acceleration, normal running).

• Inject locked-rotor and phase-loss conditions, verifying trip times and selectivity.

• Combine current and voltage ramps to test undervoltage / reduced-voltage starts, ensuring upstream 51/67 elements remain stable during motor starting.

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3.3 Feeders, cables and ring bus ties

Objectives

• Validate forward and reverse 67 elements at each cable end.

• Confirm that reverse blocking and interlocking logic isolate the faulty section with minimal ring splitting.

• Compare actual scheme behaviour to the design study.

With Quasar / Mentor 12 + ROOTS

• Perform end-to-end directional tests:

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

  • Verify local relay trip and remote relay block.

• Use binary I/O and IEC-61850 GOOSE (in the case of Quasar) to validate blocking, permissive and bus trip logics.

• Replay the same COMTRADE scenario into several relays to check system-level behaviour.

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3.4 Circuit breakers and switchgear: primary injection & timing

Objectives

• Verify breaker timing under realistic currents.

• Check contact resistance and mechanical health.

• Prove that busbars and CTs can safely carry full-load and fault currents.

With Raptor, Prime-600 and PME analyzers

• Raptor: modular primary injection system delivering up to 15 kA via pass-through technique and MS/SL modules, ideal for CBs, busbars and CTs.

• Prime-600: high-current micro-ohmmeter with DRM to assess the condition of main and arcing contacts in sealed breakers without opening them.

• PME-500-TR / PME-600-T / PME-700-TR: breaker analysers combining:

  • Trip/close coil control,

  • Contact timing and synchronism,

  • And for PME-700-TR, 10 A four-wire contact resistance measurement on three poles.

This allows you to compare actual clearing times (relay + breaker) against your coordination margins and build a lifetime record of critical CBs.

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3.5 Ground faults in HRG/IT shipboard systems

In insulated or high-resistance grounded systems, the first ground fault often behaves more like an insulation issue than a high-energy fault.

With Quasar or Mentor 12 you can:

• Inject low-level residual currents to test 51G/67N sensitivity.

• Validate alarm-only vs. trip logic for first-fault / second-fault strategies.

This is usually a good starting point for a constructive discussion between designers, owners and yards.

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4. A practical roadmap for yards and operators

A realistic test programme for a newbuild or major retrofit might look like this:

Before sea trials

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

• Perform primary injection with Raptor / Prime-600 / PME on main breakers and busbars.

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

After the first year in service

• Run a shortened relay test plan focusing on critical loops (ring ties, propulsion feeders, emergency generator).

• Repeat breaker timing tests on the most critical units.

Every dry-dock / major refit

• Review your coordination study including any new drives, generators or large consumers.

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

• Use primary injection to confirm that any new switchboards or couplers behave as designed.

Over time, you build a traceable protection performance history, a powerful asset when discussing risk, availability and compliance.

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5. Questions to open the discussion

• 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, EuroSMC can help.

Using EuroSMC relay and primary injection test systems (Quasar, Mentor 12, PTE-50-CE Pro, Raptor, Prime-600, PME) plus ROOTS automated testing, we can work with your team, your yards and your partners to turn advanced maritime protection theory into a repeatable, documented testing strategy—from design office to engine room.