Component Snapshot At-a-Glance
- Model: MAVS01L1AB0751D
- Alt. P/N: MAVS01H1AB0751E (high-burden coil variant, higher DC draw); MCHN series (undercurrent only, no frequency speed measurement)
- Product Series: MAVS Midos static speed/frequency monitoring relay family, shared rack base with MCGG/MVAJ/MVTT protection relays
- Hardware Type: Full withdrawable plug-in static frequency/speed detection relay, blue painted aluminum industrial chassis, transparent front adjustment dial cover
- Key Feature: L-series low-burden 24VDC auxiliary coil, generator/motor frequency speed input, adjustable overspeed/underspeed threshold with fixed definite time delay
- Primary Field Use: Monitor rotating machine frequency/speed signals to trigger overspeed trip, underspeed stall alarm and generator loss-of-speed protection.
Hard-Numbers: Technical Specifications
- Protocol Support: Static analog frequency sampling hardware, no digital bus communication; dry volt-free alarm/trip changeover contacts
- Port Count: AC frequency/speed signal input terminals, 24VDC auxiliary coil supply terminals, separate pre-alarm and trip contact terminal sets
- Baud/Data Rate: No serial data transmission
- Operating Temperature: -10°C to +55°C cabinet operational; -40°C to +85°C storage
- Isolation Rating: 2000Vrms dielectric withstand between frequency measurement circuits and trip contact wiring
- Power Draw: Low-burden L coil, minimal 24VDC control load on dense multi-relay panels
- Auxiliary DC Supply: 24 VDC industrial control battery
- Frequency Input Range: 10–70Hz generator/motor speed signal
- Speed Threshold Adjustment: 40%–110% nominal rated frequency via front rotary dial
- Definite Trip Delay Window: 0.2s to 10s delay to block transient speed fluctuation nuisance trips
- Contact Continuous Rating: 5A @300VDC resistive load; 40W DC inductive breaking capacity
- Physical Weight: 0.43kg fully assembled draw-out unit
The Real-World Problem It Solves
Standard overcurrent MCGG relays cannot track rotational speed or frequency drop. Generator underspeed leads to excitation collapse, while motor overspeed tears centrifugal pump impellers apart long before overcurrent thresholds activate.External frequency transmitters plus standalone timing relays take two rack slots and drift calibration with cabinet heat and vibration every 6–12 months.High-burden MAVS01H coils create unbalanced DC load distribution across packed protection panels. Multiple simultaneous equipment faults trigger localized 24V bus sag and intermittent relay dropout.Where you’ll typically find it:
- Fossil power plant steam/gas turbine generator overspeed/underspeed protection panels
- Refinery MV centrifugal pump/compressor motor stall and overspeed trip schemes
- Hydro generator auxiliary control cabinets for loss-of-prime-mover speed monitoringThis single draw-out unit integrates frequency speed sensing, adjustable threshold and time delay to eliminate external transmitters and stabilize 24V panel loading during mass fault events.
Hardware Architecture & Under-the-Hood Logic
This unit uses isolated AC frequency signal conditioning front-end paired with fixed-function static measurement logic, no programmable microprocessor code. It shares standardized Midos rack mechanical design with all ALSTHOM Midos protection hardware for unified cabinet layout.
- AC speed/frequency signal from generator PT or motor pulse pickup feeds filtered isolated sampling circuitry to suppress VFD and breaker switching EMI noise.
- Onboard frequency-to-RPM conversion circuit continuously samples input cycles, compares measured speed against front dial set overspeed/underspeed threshold.
- Internal fixed-time timer activates once measured speed crosses threshold; timer elapse switches contact state to avoid nuisance alarms from momentary speed blips.
- Low-wattage L-series coil winding limits total 24V DC load draw on station control battery, preventing uneven voltage sag across multi-relay panels during concurrent fault events.
- Front panel LEDs display healthy auxiliary supply, speed deviation pre-alarm active, and speed trip latched status for quick on-site visual diagnostics.
- Rear Midos rack terminal base integrates factory CT short-circuit jumpers; full chassis withdrawal possible without disconnecting CT secondary wiring to eliminate lethal open CT surge hazards.
Field Service Pitfalls: What Rookies Get Wrong
Swapping MAVS01H High-Burden Coil Variant For MAVS01L Low-Burden Unit
New technicians install MAVS01H spare without matching suffix. During multi-equipment simultaneous faults, uneven DC load creates localized 24V bus sag; high-burden coils dropout prematurely, turbines and pumps run unprotected against dangerous speed deviation.Field Rule: MAVS01L low-burden variant mandatory for dense multi-relay protection panels; separate L and H coil MAVS01 spares in labeled locked storage bins.
Skipping CT Short Jumper Installation Before Withdrawing Draw-out Relay
Apprentices pull relay chassis without shorting CT terminals on the rack base. Open CT secondary windings generate kilovolt surge that damages upstream MCGG overcurrent relay sampling boards and creates cabinet electric shock risk.Quick Fix: Always install factory CT short-circuit jumpers on the Midos base terminal strip before removing any draw-out protection relay unit.
Misadjusting Speed Threshold Without Cross-Checking Generator/Motor Data Sheets
Maintenance crews randomly turn the front dial during spare replacement without referencing machine nameplate speed/frequency limits. Overly tight setpoints trigger constant nuisance trips during normal load swings; overly wide setpoints fail to catch catastrophic overspeed/stall conditions.Field Rule: Record trip speed/frequency value and delay time on the relay door label after every setting change; cross-verify against rotating equipment protection scheme drawing before returning the relay online.
Commercial Availability & Pricing Note
Please note: The listed price is for reference only and is not binding. Final pricing and terms are subject to negotiation based on current market conditions and availability.
