ABB RXPDK21H 1MRK000844-BB Current Protection Relay – RX Series

ABB RXPDK21H 1MRK000844-BB — Precision Current Relay for Industrial Protection Circuits

The ABB RXPDK21H (catalog reference 1MRK000844-BB) is a dedicated current measurement and protection relay belonging to ABB’s RXPD series — a product line engineered for high-reliability overcurrent detection in medium-voltage switchgear, motor control centers, and substation secondary protection panels. Unlike general-purpose auxiliary relays, the RXPDK21H is purpose-built around a single-phase current input architecture, where the operating quantity is derived directly from a current transformer (CT) secondary circuit. The relay’s trip threshold is factory-calibrated to IEC 60255-151 inverse-time characteristics, enabling it to coordinate with upstream and downstream protective devices without requiring external timing modules.

In a typical protection loop, the RXPDK21H occupies the measurement and decision layer between the CT secondary and the circuit breaker trip coil. When the monitored current exceeds the set pickup value, the relay’s internal comparator — implemented in hardened analog circuitry — initiates a timed or instantaneous trip output. The output contact is rated for direct coil energization, eliminating the need for an interposing relay in most standard panel configurations. This direct-drive capability reduces the total component count in the protection chain, which statistically lowers the probability of a protection failure caused by auxiliary relay contact degradation.

The RXPD series was designed during an era when ABB prioritized deterministic response time over software-configurable flexibility. As a result, the RXPDK21H exhibits a hardware-fixed operating characteristic that is immune to firmware corruption, communication bus faults, or processor watchdog resets — failure modes that affect modern numerical relays. For applications where protection reliability must be maintained independently of the station automation network, this electromechanical-core design remains the engineering-preferred choice.

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Technical Parameters

Hardware Logical Analysis

The RXPDK21H is constructed around an electromagnetic measuring element with a solid-state output stage — a hybrid topology that combines the inherent robustness of inductive measurement with the contact reliability of static switching. The current input circuit uses a shielded internal CT to galvanically isolate the measuring element from the CT secondary loop. This isolation stage serves two functions: it limits the energy transferred to the relay’s internal circuitry during CT saturation events, and it provides a defined impedance boundary that prevents circulating currents from corrupting the measurement signal during external ground faults.

The relay’s EMC performance is governed by its physical construction rather than software filtering. The COMBIFLEX plug-in case provides a continuous metallic enclosure that acts as a Faraday shield against capacitively coupled interference from adjacent high-voltage busbars. Internal wiring is routed with deliberate separation between the current input loop and the output contact circuit, reducing inductive crosstalk to below the relay’s minimum pickup threshold. ABB’s testing documentation for the RXPD series confirms compliance with IEC 60255-26 (electromagnetic compatibility) at severity level III — the highest standard applicable to substation environments.

The output stage uses a bistable contact mechanism with a mechanical latch, meaning the trip output remains closed after the operating quantity drops below pickup — a critical behavior for protection applications where the fault current may collapse before the circuit breaker has fully interrupted the arc. Reset requires either manual intervention or an auxiliary reset coil, depending on the panel design. This latching behavior eliminates the risk of a protection relay self-resetting during a transient fault, which could allow a damaged circuit to re-energize before the fault has been physically cleared.

System Integration Benefits

• Deterministic trip time: Hardware-fixed time-current characteristic eliminates software scheduling latency; trip initiation is bounded to <40 ms at 2× pickup, independent of processor load.
• CT secondary compatibility: Accepts both 1 A and 5 A CT secondaries without external burden resistors, simplifying retrofit into existing panels with mixed CT ratings.
• COMBIFLEX socket compatibility: Plug-in case design allows relay replacement under live panel conditions without disturbing CT secondary wiring — a critical maintenance advantage in 24/7 process facilities.
• Coordination transparency: Fixed inverse-time characteristic is directly entered into protection coordination software (ETAP, DIgSILENT PowerFactory) using standard IEC curve parameters, with no proprietary data format required.
• Fail-safe output logic: Normally-open trip contact defaults to open on loss of auxiliary supply, preventing spurious tripping during control power interruptions.
• Mechanical flag indicator: Integral drop-flag target provides local visual confirmation of relay operation without requiring HMI access — essential for post-fault inspection in remote substations.
• Low CT burden: Input burden below 0.5 VA at rated current preserves CT accuracy class across the full protection zone, maintaining measurement integrity for both protection and metering functions on shared CT cores.
• No firmware dependency: Protection function is entirely hardware-implemented; relay performance is unaffected by cybersecurity patches, firmware rollbacks, or IED configuration changes elsewhere in the protection scheme.

Quality Assurance & Global Logistics

Every ABB RXPDK21H 1MRK000844-BB unit dispatched from our Xiamen facility is sourced through authenticated supply channels with full batch traceability. Prior to shipment, each unit undergoes a structured inspection protocol: physical label and serial number verification against ABB’s product database, housing and terminal integrity check, contact continuity measurement, and packaging condition assessment. Units that do not pass all four checkpoints are quarantined and not offered for sale.

Our Xiamen warehouse maintains bonded stock with export clearance pre-arranged, enabling same-day or next-business-day dispatch for in-stock quantities. International shipments are handled via DHL Express, FedEx International Priority, or UPS Worldwide Expedited, with full export documentation including commercial invoice, packing list, certificate of origin, and HS code classification (HS 8536.49 for protection relays). For bulk orders exceeding 10 units, sea freight consolidation via LCL or FCL is available with competitive transit times to Southeast Asia, the Middle East, Europe, and the Americas. A 12-month warranty covers all units against manufacturing defects, with replacement or credit issued within 5 business days of confirmed fault diagnosis.

Contact Information

📧 Email: [email protected]
📱 WhatsApp: +86 18359268345
🌐 Web: siemensplc.com
📍 Location: Xiamen, China
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