ABB RXPDK21H 1MRK000844-BB Protection Relay

ABB RXPDK21H 1MRK000844-BB Protection Relay for COMBIFLEX

In modern industrial control system design, protection relays are not standalone devices — they are integral nodes within a layered automation architecture. The ABB RXPDK21H (1MRK000844-BB) is a precision-engineered protection relay purpose-built for deployment within ABB’s COMBIFLEX modular relay system, where it functions as a critical element in the protection and control layer of electrical switchgear, motor control centers, and substation automation systems. Understanding where this relay sits within the broader system hierarchy is essential for engineers designing reliable, maintainable, and scalable industrial installations.

Product Specification Table

System Compatibility Notes

The ABB RXPDK21H does not operate in isolation. Its value is realized when it is correctly positioned within a coordinated control architecture that spans multiple system layers. In a typical COMBIFLEX-based protection panel, the RXPDK21H is mounted on a compatible relay socket such as the RXMVB2 or RXMVB4, which provides the mechanical interface and terminal connectivity to the panel wiring. This socket-relay combination forms the fundamental building block of the COMBIFLEX system, enabling plug-in replacement without rewiring — a critical advantage for maintenance efficiency in live substations.

At the control layer, the RXPDK21H works in coordination with ABB’s REF615 feeder protection relay or the RET615 transformer protection relay, which handle primary protection functions such as overcurrent, earth fault, and differential protection. The RXPDK21H typically serves as an auxiliary relay — extending the output contact capacity of these primary relays, providing signal multiplication, or implementing interlocking logic between protection zones. This division of function between primary and auxiliary relays is a standard architecture in IEC 61850-compliant substations.

At the I/O and signal layer, the relay’s hardwired contacts interface directly with ABB AC500 PLC I/O modules or third-party DCS digital input cards, feeding status signals — trip confirmation, alarm states, and interlock conditions — into the supervisory control layer. In more advanced installations, an ABB COM600 substation gateway or RTU560 remote terminal unit aggregates these hardwired signals and maps them to IEC 60870-5-104 or DNP3 protocol frames for SCADA communication, ensuring that the protection events captured by the RXPDK21H are visible at the control room level in real time.

For power supply integrity, the COMBIFLEX panel typically relies on an ABB UNO-PS or PSMB series 24 V DC power supply to energize the relay coils and auxiliary circuits. Stable DC supply voltage is essential for consistent relay pickup and dropout characteristics, and any voltage deviation can affect protection coordination timing. Engineers should verify that the panel power supply is sized to handle the inrush current of multiple relay coils energizing simultaneously during a fault event.

At the human-machine interface layer, an ABB CP600 HMI panel or a SCADA workstation running ABB Ability System 800xA provides operators with real-time visibility into protection relay states, alarm histories, and interlock statuses. The RXPDK21H’s contact outputs, once wired into the I/O layer, contribute to the alarm and event log that operators monitor during normal operations and fault investigations.

Industrial Application Notes

The ABB RXPDK21H 1MRK000844-BB finds application across a wide range of industries where reliable electrical protection and control interlocking are non-negotiable. In power distribution and substation automation, it is used as an auxiliary relay in medium-voltage switchgear panels, extending the trip and alarm contact outputs of primary protection relays to circuit breaker coils, alarm annunciators, and remote indication systems. Its plug-in COMBIFLEX format allows rapid relay replacement during maintenance windows without panel rewiring, minimizing substation downtime.

In petrochemical and oil & gas facilities, the RXPDK21H is deployed in motor control centers and emergency shutdown (ESD) panels, where it provides hardwired interlock signals between protection systems and process control systems. The relay’s robust contact ratings make it suitable for switching inductive loads such as contactor coils and solenoid valves in hazardous area control panels.

In water treatment and pumping stations, the relay supports pump motor protection schemes, providing auxiliary contacts for motor run confirmation, fault indication, and remote start/stop interlocking. Its compatibility with standard COMBIFLEX sockets means that maintenance teams can carry a single spare relay type to cover multiple protection functions across the facility.

In mining and metallurgical plants, where electrical systems are subject to high fault currents and frequent switching operations, the RXPDK21H’s durable contact construction and wide operating voltage range make it a reliable choice for auxiliary protection and control functions in high-voltage motor starters and transformer protection panels.

All units supplied by ZYPLC are sourced from verified supply channels, undergo pre-shipment functional testing, and are covered by a warranty terms confirmed during quotation, ensuring that engineers can deploy the RXPDK21H with confidence in both new installations and retrofit projects.

Product Compatibility FAQ

Q1: Is the ABB RXPDK21H compatible with all COMBIFLEX relay sockets?
The RXPDK21H is designed for use with ABB COMBIFLEX plug-in relay sockets, specifically the RXMVB2 and RXMVB4 series. Before installation, verify the socket type installed in your panel against the relay’s pin configuration to ensure mechanical and electrical compatibility. If you are retrofitting an existing panel, the COMBIFLEX socket system allows direct plug-in replacement without rewiring, provided the socket type matches.

Q2: How does the RXPDK21H integrate into a system with ABB REF615 or RET615 primary protection relays?
The RXPDK21H functions as an auxiliary relay that extends the output contact capacity of primary protection relays such as the REF615 or RET615. It is wired to receive a binary output signal from the primary relay and then multiplies that signal across multiple hardwired contacts for trip coil activation, alarm annunciation, and interlock logic. This architecture is standard in IEC 61850-compliant protection panels and does not require any special configuration of the primary relay — only correct wiring of the auxiliary relay socket terminals.

Q3: What does the warranty terms confirmed during quotation cover, and what is the testing process before shipment?
Every ABB RXPDK21H unit supplied by ZYPLC undergoes pre-shipment functional testing to verify coil pickup voltage, dropout voltage, contact continuity, and insulation resistance. The warranty terms confirmed during quotation covers manufacturing defects and functional failures under normal operating conditions. Units are shipped with test records available upon request. For replacement or warranty claims, contact ZYPLC directly at plc.sales@zyplc.com or +86 19859288691.