Product Core Brief
- Model: RXEDK 2H, Full OEM part number: 1MRK000841-KA
- Brand: ABB Hitachi Energy
- Series: Classic COMBIFLEX modular secondary protection relay system
- Core Function: Microprocessor-based two-stage voltage measuring relay, independently configurable for overvoltage (59) or undervoltage (27) protection for each stage. Widely applied for generator neutral displacement voltage earth fault supervision, busbar over/undervoltage monitoring, flashover protection, stator winding earth fault protection and grid anti-islanding supervision in thermal/hydro power plants and distribution substations. The 1MRK000841-KA variant is equipped with built-in third-harmonic filter, optimized for 100% generator stator earth fault protection matching REX010 injection equipment and REG series generator IEDs.
- Product Type: COMBIFLEX plug-in modular voltage protection relay
- Key Specs: Dual independent protection measuring stages; Stage 1 supports inverse definite minimum time (IDMT) / definite time (DT) characteristics; Stage 2 fixed definite time (0–10s adjustable); built-in 3rd harmonic filter; low measurement burden; high reset ratio; universal wide-range auxiliary power; COMBIFLEX standard 19-inch rack plug-in mounting
- Note: Mature legacy power plant protection device, still active production for traditional COMBIFLEX relay panel renovation projects; factory sealed new modules and fully bench-tested surplus units are supplied for thermal power, hydropower and industrial self-generation station maintenance.
Key Technical Specifications
| Parameter | Value |
|---|---|
| Full OEM Article Code | RXEDK 2H 1MRK000841-KA |
| Measuring Stage Layout | 2 fully independent voltage measuring stages (Stage 1 + Stage 2) |
| Function Mode Per Stage | Each stage switchable for overvoltage OR undervoltage operation |
| Time Characteristic – Stage 1 | Two selectable curves: Inverse definite minimum time (IDMT) / Definite time (DT) |
| Time Characteristic – Stage 2 | Fixed definite time, adjustable range: 0 s ~ 10 s |
| Built-in Filter (KA suffix) | Integrated third harmonic suppression filter for generator neutral voltage measurement |
| Reset Ratio | High reset ratio, enables tight setting close to rated nominal voltage |
| Measuring Circuit Burden | Ultra-low burden, no extra load on VT secondary circuits |
| Auxiliary Supply Range | Wide-range AC/DC universal power supply for substation cabinet standard power |
| Output Contacts | Multiple independent Form-C changeover relay contacts for alarm and trip signal output |
| Mechanical Mounting | Standard COMBIFLEX 19-inch rack plug-in drawer structure |
| Operating Ambient Temperature | -10 °C ~ +55 °C continuous cabinet operation; storage temperature -40 °C ~ +70 °C |
| Humidity Tolerance | <95% RH non-condensing, indoor control room rated |
| Compliance Standards | IEC 60255 protection relay standard, KEMA type-tested, CE certified |
Product Introduction
The RXEDK 2H 1MRK000841-KA is a dedicated dual-stage voltage protection relay within ABB’s COMBIFLEX modular relay family, specially customized with a third-harmonic filter for generator neutral point voltage monitoring applications.
Core Functional Advantages
- Dual Independent Configurable StagesEach measuring stage can be individually set to overvoltage or undervoltage without mutual restriction. Stage 1 supports both inverse-time and fixed-time delay curves for selective backup protection coordination; Stage 2 adopts fixed short-time delay for fast critical fault tripping, realizing hierarchical voltage fault protection logic.
- Third-Harmonic Filter Optimized For Generator Earth Fault DetectionThe KA suffix integrated third-harmonic filter eliminates fundamental frequency interference in neutral displacement voltage signals, perfectly matching the REX010+REX011 injection system. It accurately detects 5% neutral-point dead zone stator earth faults that conventional single-stage voltage relays cannot identify, achieving full 100% stator winding insulation monitoring for large synchronous generators.
- Wide Application ScenariosBesides generator neutral earth fault supervision, it is widely used for: medium/high voltage busbar over/undervoltage protection, grid frequency-dependent voltage supervision, overhead line flashover fault detection, distributed generation anti-islanding voltage blocking protection and transformer tap-changer voltage limit supervision.
- Low Burden & High Stability DesignUltra-low VT secondary circuit burden avoids voltage signal distortion caused by excessive load on voltage transformers. The high reset ratio prevents false operation caused by minor transient voltage fluctuations, greatly improving protection stability under normal grid fluctuation conditions.
The plug-in COMBIFLEX structure allows quick replacement without full cabinet rewiring, compatible with all standard COMBIFLEX test switches (RXDS4) and auxiliary relay modules, forming a complete secondary protection circuit solution for power plant main generator bays.
QA & Testing SOP (Transparency Building)
- Incoming Visual Inspection: Cross-check full part number RXEDK 2H 1MRK000841-KA and serial number against ABB power system spare parts database to reject counterfeit mismatched relays; inspect front adjustment dials, internal third-harmonic filter circuit, relay output contacts and conformal PCB coating for burn marks, corrosion or deformation; record serial numbers and production batches for full traceability.
- Full Performance Bench Test: Install the relay on standard COMBIFLEX 19-inch test rack, supply matched auxiliary power, input adjustable VT voltage signal; run 24-hour cyclic testing covering Stage 1 IDMT/DT curve switching, Stage 2 fixed time delay adjustment, third-harmonic filter interference suppression, overvoltage/undervoltage trigger and contact output linkage, verify no false operation under normal voltage fluctuation simulation.
- Electrical Insulation Test: Use insulation resistance tester to confirm isolation resistance ≥ 10 MΩ between measuring voltage circuits, auxiliary power and relay output contact circuits; test chassis ground continuity resistance below 0.5 Ω.
- Setting Record Backup: Photograph front panel voltage/time adjustment dial definitions, record built-in filter hardware version and COMBIFLEX base terminal wiring pinout for field commissioning reference.
- Final QC Packaging: Wipe relay housing with anti-static microfiber cloth, cover all front adjustment terminals and rear plug connectors with insulating dust caps, place the unit into independent ESD shielding bag, attach unified printed QC test tag with technician ID and full 24-hour cyclic test runtime timestamp, then pack into foam shockproof carton for long-distance power plant transportation.
Installation Pitfalls & 4-Step Replacement Guide
Common Installation Hazards
❗ VT Secondary Circuit Open-Circuit Risk: Before extracting the RXEDK 2H relay, activate the CT/VT shorting function of the matched RXDS4 test switch to avoid abnormal high voltage on VT loops during disassembly.❗ Filter Version Mismatch: Only the KA suffix model carries third-harmonic filter; direct replacement with standard RXEDK 2H without filter will cause severe measurement distortion and generator earth fault protection failure.❗ Auxiliary Power Polarity Reversal: Incorrect positive/negative wiring of DC auxiliary power will damage internal microprocessor and filter circuits instantly.❗ ESD PCB Damage Risk: Wear certified anti-static wrist strap during disassembly and installation; bare hand contact with internal filter and measuring chips leads to permanent signal processing failure.❗ Improper Stage Curve Setting: Misconfigured IDMT/DT characteristic of Stage 1 breaks protection coordination between generator main protection and backup voltage relay, resulting in selectivity loss during grid faults.
4-Step Plug-in Relay Replacement Guide
- Pre-install Preparation: Lock out and tag out the relay cabinet auxiliary power supply, engage VT shorting links via RXDS4 test switch, wear ESD wrist strap, photograph rear COMBIFLEX plug terminal wiring of VT measuring circuits, auxiliary power and trip/alarm output contacts.
- Removal Operation: Unlatch the COMBIFLEX plug-in drawer locking handle, pull the old RXEDK 2H relay fully out of the rack base socket (the base wiring remains fixed on the cabinet rack).
- Installation & Wiring: Insert the new RXEDK 2H 1MRK000841-KA module into the original COMBIFLEX base socket, push fully to lock the drawer handle; cross-check all VT, power and control wiring matches photographed terminal sequence without misconnection.
- Power-on Commissioning Test: Restore cabinet auxiliary power, input rated nominal VT voltage signal to verify no alarm/trip output; simulate overvoltage and undervoltage fault signals respectively, test Stage 1 time curve and Stage 2 fixed delay trigger performance, validate third-harmonic filter anti-interference function, confirm stable trip/alarm signal transmission to DCS/SCADA system.
FAQ
Q: What is the unique feature of 1MRK000841-KA compared to standard RXEDK 2H variants?A: The KA suffix integrates a dedicated third-harmonic suppression filter, which is mandatory for generator neutral displacement voltage stator earth fault protection. Standard RXEDK 2H models without this filter cannot filter harmonic interference and are only suitable for general busbar voltage supervision, not generator main winding fault monitoring.
Q: What is the difference between RXEDK 2H and single-stage RXEDK 1H relays?A: RXEDK 1H only has one measuring stage with single definite time characteristic, limited to simple undervoltage alarm. RXEDK 2H provides two independent protection stages with flexible time curve selection, realizing hierarchical primary trip + backup alarm logic for critical generator and transmission bay protection schemes.
Q: Can RXEDK 2H be hot-swapped under energized cabinet power?A: Not permitted. The relay is connected to live VT secondary measuring circuits and auxiliary power loops; extraction under energized conditions will cause abnormal voltage surge and permanent damage to internal filter and microprocessor hardware. Full auxiliary power lockout and VT shorting are required before replacement.
Q: What warranty applies to stocked RXEDK 2H 1MRK000841-KA modules?A: Factory-new original COMBIFLEX relays carry 12-month official ABB manufacturer warranty covering measuring circuits, third-harmonic filter hardware, time delay logic and relay output contacts. Bench-tested surplus modules provide 6-month functional warranty; damage caused by VT open-circuit voltage shock, power polarity reversal or ungrounded ESD handling voids all warranty terms.
Q: Has ABB discontinued RXEDK 2H series production?A: No formal EOL notice issued; RXEDK 2H is still supplied as standard spare parts for legacy COMBIFLEX generator protection panel renovation. New digital substation projects adopt REF615/RET670/REG670 series IEDs with built-in voltage protection algorithms instead of discrete COMBIFLEX relays.
Q: What typical faults indicate a defective RXEDK 2H 1MRK000841-KA relay?A: Common failure symptoms: Constant false neutral earth fault alarms under normal generator operation (filter circuit failure), no trip output when over/undervoltage threshold is reached, time delay deviation exceeding factory tolerance range, Stage 1 IDMT curve switching failure, no response to third-harmonic fault signal injection from REX010 equipment.
