OMICRON CMC 256plus High Precision Relay Test Set

Posizionamento: Combined high-precision relay test set & general calibration source (OMICRON, Austria)

Successor model: CMC500; Last order cutoff for NET-2 version: 31 Dec 2026, manutenzione & calibration support until 2036

✅ Core Channel Specifications

Uscita corrente: 6 channels × 12.5 UN / 80 VA; combinable: 3 × 25 UN / 1 × 75 UN

Uscita in tensione: 4 channels × 300 V, combinable into 2 × 600 V

Precisione: Errore tipico <0.015% of reading +0.005% of range. Suitable for 0.2S energy meters, transducers, PMUs and power quality equipment calibration

Built-in 10-channel analogue acquisition & transient waveform recording; integrated Ethernet port for IEC 61850 OCA / SV sampled value simulation and subscription

Optional LLO-2 module: Ulteriori 6 low-level output channels for simulating Rogowski coils, low-level ECT/EVT signals; capable of driving external CMS356 power amplifier

Amplitude, phase angle and frequency of all channels can be adjusted independently and continuously; integrated short-circuit, overtemperature and external high-voltage surge protection

✅ Applicazioni tipiche

1. Relay protection testing for all types: elettromagnetico, statico, numerical relays and 61850 intelligent IEDs (sovracorrente, distanza, differenziale, busbar auto-switch, reclosure, ecc.)
2. Metering equipment calibration: 0.2S energy meters, AC/DC transducers, PMU synchrophasor units, PQ power quality analysers
3. Type testing, R&D testing and laboratory reference source for manufacturers
4. Closed-loop IEC 61850 simulation for smart substations

✅ Supporting Software

Test Universe: Mainstream定值-based automated protection test software (PTL test library, Advanced Distance / Differential modules)

RelaySimTest: System-level grid fault simulation, relay-model independent

CMControl P: Manual quick commissioning via tablet / mobile phone

EnerLyzer Classic: Waveform recording and power quality analysis

CMEngine: Open API for secondary development and automated bench integration

✅ Version Identification (Critical for Spares & Manutenzione)

CMC256plus PAR-1: Older parallel port variant, end of sale 2014, manutenzione & calibration support terminated

CMC256plus NET-1x: Early Ethernet version, end of sale 2014, maintenance support until 31 Dec 2028

CMC256plus NET-2: Revised Ethernet hardware, available for order until end 2026, longest maintenance & calibration coverage (until 2036)

✅ Cross-Series Replacement Reference

Equivalent accuracy for metering + protezione: CMC430 (portable)

Mainstream new-generation replacement: CMC500 (official successor of CMC256plus by OMICRON)

Heavy-duty IEC 61850 digital simulation: CMC850

✅ Common Accessories

CMS356 power amplifier, CMGPS588 synchronisation clock, assorted test lead sets, dedicated CT/PT test accessories, CEI 61850 optical modules

OMICRON CMC256plus Troubleshooting Checklist (On-site Version, Prioritised)

Precautionary Safety Rule: In case of reverse external high voltage, smoke, abnormal odour or persistent overtemperature lockout, cut power immediately. Do not repeatedly power on for output. External voltage >42 V applied to output terminals triggers the front-panel high-voltage alarm lamp.

Self-test logic: Automatic hardware self-test on power-up and after connection to Test Universe. Failed self-test triggers pop-up error messages, accompanied by internal relay click sounds. Record the full error text, firmware version and serial number before further action.

1. Accensione & Boot Faults
2. Unit no power, indicatore di alimentazione spento

Controllo: AC inlet, power cord, external circuit breaker; internal instrument fuse (inside chassis, on-site disassembly for replacement is not recommended); confirm input voltage 100–240 V AC

Risoluzione dei problemi: Swap with a known-good power cord; verify wall socket voltage with multimeter. Root causes: blown fuse, failed power supply board

Azione: Blown fuse usually caused by lightning strike or reverse high voltage. Return to factory; never short the fuse.

2. Fan runs on power-up, but unit fails to start, self-test hangs, yellow lamp stays on

Controllo: Associate pairing status of Ethernet port; faulty LLo module / connected CMS356 amplifier; USB drives or peripherals plugged near Ethernet port

Risoluzione dei problemi: Remove all external modules, test leads and peripherals, power up bare unit only; verify A/B status LEDs for NET variants

Azione: Steady yellow lamp on NET models usually indicates corrupted firmware. Firmware reflash with OMICRON dedicated tool, cannot be fixed on site.

3. Repeated reboot on startup

Controllo: Supply voltage drop, undersized extension cables; blocked cooling vents; ageing power supply board

Risoluzione dei problemi: Plug directly into wall socket, remove power strips / long cables; clean intake filter

Rischio: Bulging capacitors on PSU will cause progressive damage if operated continuously

2. PC Communication / Test Universe Connection Failure (Most frequent for NET-1 / NET-2)

NET variants of CMC256plus use fixed MAC binding via Associate. Rebinding is required after changing PC or network adapter.

1. Software cannot locate instrument, connection timeout

Controllo: Cavo Ethernet, interruttore; PC NIC IP subnet; correct MAC bound in Associate; firewall or antivirus blocking Test Universe processes

Standard procedure:

① Direct PC connection, bypass switch; use Cat5e or better shielded cable

② Set static IP on PC NIC within the same subnet, avoid DHCP cross-subnet

③ Press front-panel Associate button, yellow LED flashes, re-pair in OCC

④ Disable Windows firewall or add allow rules for OMICRON programs

Distinction for legacy PAR parallel version: Check PCI parallel port card, driver and parallel cable (rare today)

2. Connected but frequent disconnection / intermittent dropouts

Controllo: Oxidised RJ45 contacts, incorrect shield grounding; strong on-site EMI (VFD, DC panels); NIC sleep policy

Risoluzione dei problemi: Disable “Allow the computer to turn off this device to save power” for network adapter; single-end grounding for shielded cable; route away from power cables

3. CMControl P tablet cannot connect

Controllo: Same LAN; instrument and tablet on the same switch; remote control permission enabled inside OCC

3. Output Channel Alarms: Sovracorrente / Sovraccarico / Cortocircuito, Channel Fault (CU/CI Alarms)

Current channels: open-circuit, protezione da cortocircuito e sovraccarico. Voltage channels: protezione da sovraccarico. LLo low-level channels also have overload protection with software warning popups.

1. Current channel reports Overload / Cortocircuito

First step: Stop output, disable output in Test Universe before disconnecting leads. Never remove CT terminals while energised.

Controllo: Shorted test leads, open CT secondary (critico! Open CT secondary generates reverse high voltage which can easily damage channels); VA loading exceeds 80 VA per channel; incorrect wiring for paralleled channels

Verifica: Remove all field wiring, output small current at no load

✅ Normal at no load → external short circuit / open CT / carico eccessivo

❌ Still overload alarm at no load → damaged power amplifier board or sampling circuit, requires repair and recalibration

2. Voltage channel overload alarm

Controllo: Reverse PT secondary voltage, external backfeed voltage, short circuit inside DUT IED, wrong wiring in 600 V series mode

Nota: External voltage >42 V at voltage terminals illuminates red high-voltage warning lamp; stop testing immediately

3. Individual channel amplitude inaccuracy, phase drift, three-phase unbalance without explicit fault alarm

Controllo: Contatto scarso, unequal lead resistance, unlinked neutral reference, temperature drift, expired calibration certificate

Self-check: Run built-in Hardware Test in software and save report

Distinzione: Hardware Test Pass, error only appears on site → wiring / interference issue; Hardware Test Fail → hardware fault, return for calibration and repair

4. Abnormal LLO-2 low-level output (CMS356 drive or ECT simulation)

Controllo: Secure LLo ribbon cable, bent pins; external amplifier power supply; shorted LLo load; firmware compatibility with LLo module

4. OverTemperature Alarm (Common on Older Units)

Sintomo: Software popup overtemperature warning, output power derating, severe cases lock output

Controllo: Blocked intake/outlet vents; fan stall / rumore anomalo; temperatura ambiente >40℃; continuous full-VA operation

Azione: Power off and cool for 30 minuti; low-pressure compressed air to blow filter and ducting (do not blast directly onto PCB); replace fan if non-functional

Importante: Repeated overtemperature causes permanent channel drift, power transistor failure and invalid calibration

5. Acquisition Circuit, Waveform Recording & AI Analogue Input Abnormality (Integrato 10 Acquisition Channels)
6. Acquisition reading zero, jittering or inaccurate

Controllo: Polarity of acquisition leads, terreno comune, acquisition range setting, external transducer supply; run acquisition channel hardware self-test

Critical pitfall: Never mix acquisition terminals and output terminals, reverse high voltage will destroy acquisition board

2. EnerLyzer recording fails to trigger or recorded files corrupted

Controllo: Trigger settings, synchronisation clock, PC disk space, known software bugs (upgrade Test Universe)

6. CEI 61850 OCA / SV Digital Simulation Faults (Smart Substation Work)
7. GOOSE subscription receives no messages, GOOSE status change fails to trigger relay

Controllo: Optical module / electrical port VLAN, switch IGMP, port mirroring; matching APPID & GOID; SCD revision; PC time synchronisation

Risoluzione dei problemi: Capture packets on the same switch with Wireshark, verify CMC transmission and IED subscription; confirm time sync between instrument and IED

2. Abnormal SV sampled value output, relay reports sampling out-of-sync or jittering samples

Controllo: SV sampling rate, ASDU configuration, sync source (CMGPS588); locked status of PTP / IRIG-B; optical power, dirty fibre endface

Typical root cause: Unlocked GPS → severe SV phase drift; bent fibre or contaminated endface → packet loss

3. Optical module not recognised

Controllo: Re-seat optical module, module firmware; only OMICRON original compatible transceivers work reliably, third-party modules frequently fail identification

7. Synchronisation Clock, GPS / IRIG-B / PTP Timing Faults
8. Sync indicator not locked, phase drift, PMU test failure

Controllo: GPS antenna placement, feeder cable, LNA; IRIG-B polarity and level; PTP switch support for transparent clock

Risoluzione dei problemi: Confirm lock status on CMGPS588 first; test with internal clock as reference. If internal clock works normally, fault lies in external sync link

2. Time jumping, inaccurate sequence timing, excessive timing error for reclosure tests

Key note: Synchronisation reference is critical for PMU, differential and distance closed-loop testing. Unstable sync invalidates all phase and timing results.

8. Intermittent Hard-to-Reproduce Faults

Sintomo: Works normally after reboot, error occurs after running for some time

Checklist:

1. Sciolto / oxidised terminals, modules and ribbon cables (LLo, amplificatori, optical modules)
2. Ageing PSU capacitors, voltage sag under load
3. Intermittent fan operation leading to periodic overtemperature protection
4. Cold solder joint on Ethernet PHY chip (high failure rate on older NET-1 hardware)
5. Transient reverse high voltage from PT/CT secondary on site

Localisation method: Long-duration no-load ageing test with Hardware Test running; swap Ethernet cable, change supply and isolate from field interference

9. Software / Firmware Faults (Test Universe)
10. Project load error, PTL library fails to open, template crash

Check matching TU version and CMC firmware, corrupted project file, user permission, missing runtime libraries

Rule: Do not mix mismatched major firmware and TU versions (per esempio. old NET1 firmware with new TU release)

2. Automated test stops mid-sequence and does not proceed

Check binary input (BIN) feedback wiring and threshold, GOOSE feedback packet loss, overly short software timeout settings

3. Front-panel CMControl6 local control inactive

Check front panel ribbon cable, panel firmware; control permission mutually exclusive if OCC takes control from PC

10. On-site Acceptance Checklist (After Repair / Second-hand Unit Receipt)
11. Power off and rest → power on, confirm clean boot self-test with no errors
12. Run full Hardware Test from OCC, export report, confirm all channels Pass
13. No-load output test: 6I and 4V channels output rated value one by one, verify amplitude and phase
14. Synchronisation lock test, simple GOOSE/SV send/receive test
15. Short-duration full-load test, confirm no false overload or overtemperature alarms
16. Verify calibration certificate validity
17. Fault Information Template for OMICRON Support

Modello, serial number, hardware revision NET-1 / NET-2 / PAR

CMC firmware version, Test Universe version

Full error screenshot or text message

Condizione di guasto: no-load or loaded, LLo/CMS356 attached, GPS connected or not

Wiring scheme, test type (conventional protection / SV & OCA / PMU calibration)

Ambiente: substation site, history of reverse high voltage, calibration expiry date

Supplementare: Common False Alarms (Not Instrument Faults)

Open CT secondary → overload alarm triggered, root cause is external circuit, not tester failure

Unlocked sync source causes phase deviation, easily misdiagnosed as channel inaccuracy

Windows NIC sleep / auto-adaptation causes random communication dropouts

Parallel multi-channel output without enabling parallel mode in software → abnormal VA distribution and overload alarm

OMICRON CMC Full Model List (Relay Test Set Mainline, Sub-Versions & Stato del ciclo di vita)

Nota: CMS356 is external power amplifier and not part of CMC main unit series; CMGPS, LLO and optical modules are accessories and excluded. CMC500 is the new flagship replacement for CMC256plus / 356 / 353.

1. Currently Available New Models
2. CMC 500 (modulare, 5 base configurations: USH / UHH / USX / UHX / VHX)

Posizionamento: Successor to CMC256plus / CMC356 / CMC353. Supporta fino a 10 current channels, 7 voltage channels and IEC 61850 digital functions

2. CMC 430 (ultra-light high precision, 8.7 kg, dual use for protection + 0.2S metering calibration)
3. Previous Generation Classic Units (End of Sale, PAR / NET Sub-Versions, CMC256plus belongs here)
4. CMC 256plus

Sub-models: PAR-1 (legacy parallel port, support terminated), NET-1x (early Ethernet), NET-2 (revised Ethernet, last order 31 Dec 2026)

Posizionamento: 6I+4V, combined high-precision protection & metering source, compatible with LLO-2 low-level module

4. CMC 356

Sub-models: NET-1x, NET-2

Posizionamento: General protection commissioning, higher output power, mainstream substation tester

5. CMC 353

Sub-models: NET-1x, NET-2

Posizionamento: Compact three-phase tester, cost-effective for site commissioning

6. CMC 310

Sub-models: NET-1x (NET1 only)

Posizionamento: Basic three-phase testing and on-site meter calibration, entry lightweight unit

7. CMC 850

Sub-models: NET-1x (digital-only)

Posizionamento: Pure IEC 61850 digital tester, no high-power analogue outputs, only SV/GOOSE simulation, for smart substation closed-loop testing

3. Very Early Legacy Models (Rare in circulation, official calibration & repair fully terminated, found only in old documentation / second-hand market)
4. CMC 156 / CMC156 EP (early parallel port, 3-corrente di fase)
5. CMC 256-6 (predecessor of CMC256plus, without “plus”)

Lifecycle Summary Table