RXPPK Reverse Power Protection Relay

Description

Product Model: RXPPK
Product Brand: ABB
Product Series: RXPPK Reverse Power Protection

Key Features:

• Microprocessor-based time-directional reverse/underpower detection
• Continuous setting range from ~0.3 % to ~15 % of rated current
• Dual time delay stages with optional “hold” function
• Blocking features: undervoltage block, undercurrent block

• (Often sold under variant “RXPPK 2H 1MRK001615-AA”)

Applications & Industry Context

When a prime mover (turbine, engine, or synchronous motor) loses sufficient torque, the machine can begin drawing real power from the grid — a phenomenon known as reverse power. In generator settings, that is a harmful state: the rotating machinery starts to “motor,” which can lead to overheating, bearing damage, lubricant starvation, or mechanical stress. The RXPPK series relays are designed to sense that reverse power condition (or dangerously low forward power) and issue a trip to protect the prime mover.

You’ll find RXPPK devices deployed in power plants, hydropower stations, gas/steam turbine facilities, and large synchronous machines. For example, in a hydroelectric plant, if water flow suddenly drops (e.g. gate closure or upstream flow loss), the generator may begin to draw reversal power. The RXPPK module monitors power direction and will trip the generator breaker to protect the turbine blades and bearings.

In thermal plants or combined cycle plants, sudden fuel cutoff, control valve failure, or other transient events may push the machine toward motoring. Without reverse power protection, the prime mover may try to maintain rotation by drawing from the grid, leading to internal overheating or damage to auxiliary systems.

Another context is in standby diesel or gas generator sets that are parallel-connected to a grid or another generator. If load changes or synchronization phases shift, a generator might attempt motoring. The RXPPK is used as a guard against that, acting independently or in coordination with other protection relays.

Operators often note that while reverse power is relatively rare, when it occurs without protection, it can cause very expensive damage in a short time. Thus, RXPPK relays, though niche, are critical in any comprehensive generator protection schema.

Product Role & System Fit

The RXPPK is a reverse power / underpower protection relay. Its primary function is to detect the direction of active power and issue trip commands when the flow reverses or falls below a safe forward threshold.

In a protection scheme, RXPPK sits alongside other protective devices (overcurrent, differential, over/under voltage, loss-of-excitation, etc.). It’s typically mounted in the generator control bay, wired to CTs (and perhaps VTs or voltage sensing) to sample current/voltage, compute active power, and decide direction.

In ABB’s COMBIFLEX or modular relay panel systems, the RXPPK is packaged to be modular and compatible with standard mounting and powering arrangements. In many system architectures, the RXPPK becomes part of the “reverse power protection assembly” often paired with auxiliary relays such as RAPPK (for redundancy or complementary logic).

It is particularly useful because, compared to electromechanical or simple directional relays, it provides digital precision, adjustable settings, block logic and multi-stage timing. This flexibility allows protection engineers to coordinate it cleanly with upstream and downstream protection elements without undue nuisance trips.

Technical Features & Benefits

Based on the ABB literature and distributor listings, here are the salient features of the RXPPK relay:

• Time‐directional reverse power detection: The relay senses forward vs reverse real power (active power) by comparing phase quantities (current, voltage) and determining whether the generator is motoring.
• Continuous sensitivity / setting range: The RXPPK can operate with a sensitivity (Is) setting from roughly 0.3% up to 15% of rated current.
• Scale constants / variants: Some variants support different scale constants (e.g. Is = 0.1, 0.4, 0.7, 1.0 A; or alternately 0.5, 2.0, 3.5, 5.0 A) to match different CT/relay currents.
• Dual stages of delay (t1, t2): The relay supports two time delay stages:
  • t1: adjustable from 0 to ~4 seconds
  • t2: adjustable up to ~30 seconds
  This allows a two-level trip logic or coordination with other protective devices.
• Hold / time-hold for t2: For stage t2, there is a hold function (0 or 5 s) which keeps the second timer from resetting immediately if the start condition is removed prematurely.
• Blocking logic:
  • Undervoltage block – the RXPPK will inhibit its operation when voltage falls below ~40 V, reducing false operation during voltage sag or power disturbances.
  • Undercurrent block – if the measured current is below a small fraction (~0.25% of rated current), the relay will block to prevent misoperation under light load/noise conditions.
• Microprocessor-based logic: Because it’s digital, it is less prone to drift, and can maintain consistent performance over years.
• Compatibility with existing relay systems: The RXPPK is designed to integrate into ABB’s modular protection schemes (COMBIFLEX) and can share power / mounting / interlocks.

Together, these features deliver a protection relay that is precise, discriminating, and adaptable to modern generator control systems. The dual-stage timing and blocking logic allow it to be tuned tightly so as not to nuisance-trip during transient swings but still protect under legitimate reverse power conditions.

Technical Specifications

Installation & Maintenance Insights

Here are field-proven tips and cautions when installing or maintaining an RXPPK relay:

• Powering & auxiliary circuits: The RXPPK often depends on DC supply modules within a relay rack (e.g. ±24 V supply modules). Ensure the relay rack is equipped with adequate power provisioning. The relay itself does not usually provide its DC source.
• CT & VT wiring integrity: Because reverse power logic is sensitive to phase relationships, careful phasing, shielding, and proper wiring practices are essential. Any mismatch or CT vector error can lead to false detection.
• Blocking settings tuning: The undervoltage block and undercurrent block thresholds should be tuned so that normal fluctuations, voltage sags, or low load conditions don’t inadvertently trigger the relay.
• Timer coordination: Use the dual-stage timers thoughtfully. For example, set t1 for fast tripping when reversal is severe, and t2 for delayed operation if you need coordination with upstream breaker or protection logic. The hold time can prevent spurious resets.
• Commissioning test: Always perform reverse power simulation in test mode (or via injection) to verify that the relay logic, direction detection, timers, blocks, and trip outputs are functioning as intended.
• Panel environment: Keep the relay environment clean, cool, and vibration-limited. Relays in dusty or high-heat locations may age faster or suffer drift.
• Periodic checking: Although digital relays typically require less frequent maintenance than analog ones, it’s wise to test function periodically (bench test if possible), inspect wiring, verify settings, and monitor for any logged reverse-power events or near-trigger conditions.
• Version / variant awareness: Because RXPPK has variants (e.g. 2H, possibly others), always check that your replacement or backup unit matches the correct version (same scale constant, wiring layout, firmware or design) to avoid misfit or mismatched behavior.

In one real-world retrofit of a hydropower facility, technicians initially installed an RXPPK module whose undervoltage block was set too low, resulting in nuisance trips during startup voltage sags. The block threshold was adjusted upward, resolving the false trips while preserving protection functionality. This kind of fine-tuning is typical and expected.