Component Snapshot At-a-Glance

• Model: MAVS01L1AB0501D
• Alt. P/N: MAVS01H1AB0501E (high-burden 24VDC coil variant, higher DC draw); MCHN series (only undercurrent detection, no frequency/speed measurement)
• Product Series: MAVS Midos static speed/frequency monitoring relay family, shared rack base mechanical footprint with MCGG/MVAJ/MVTT protection relays
• Hardware Type: Full withdrawable plug-in static frequency/speed detection relay, blue painted aluminum industrial chassis, front rotary speed threshold adjustment dial
• Key Feature: L-series low-burden 24VDC auxiliary coil, dual PT/pulse AC speed signal input, independent adjustable overspeed/underspeed threshold with fixed definite time delay
• Primary Field Use: Capture generator PT or motor pulse pickup signals to trigger overspeed trip, underspeed stall alarm and prime mover loss-of-speed protection.

Hard-Numbers: Technical Specifications

• Protocol Support: Static analog frequency sampling hardware, no digital bus communication; dry volt-free pre-alarm / trip changeover contacts
• Port Count: AC speed/frequency signal input terminals, dedicated 24VDC auxiliary coil supply terminals, separate pre-alarm and fault trip contact terminal blocks
• 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 AC frequency measurement circuits and trip contact wiring
• Power Draw: Low-burden L coil, minimal 24VDC control load for densely packed multi-relay panels
• Auxiliary DC Supply: 24 VDC industrial control battery, stable operation at 70%–120% rated voltage
• AC Frequency Input Range: 10–70Hz generator/motor speed signal
• Speed Threshold Adjustment Band: 40%–110% nominal rated frequency via front rotary dial
• Definite Trip Delay Window: 0.2s to 10s fixed time delay to filter transient speed fluctuation nuisance trips
• Operate Response Time: ≤20ms contact state change once speed crosses set threshold
• Contact Continuous Rating: 5A @300VDC resistive load; 40W DC inductive breaking capacity for breaker trip coils
• Physical Weight: 0.43kg fully assembled Midos draw-out unit

The Real-World Problem It Solves

Standard MCGG overcurrent relays only respond to overload and short-circuit current. They cannot track rotational speed deviation; generator underspeed collapses excitation, while pump overspeed tears impellers apart long before overcurrent thresholds activate.External frequency transmitters paired with standalone timing relays occupy two rack slots, and dial calibration drifts every 6–12 months from cabinet heat and vibration.High-burden MAVS01H coils create unbalanced 24V DC bus loading across packed protection panels. Multiple simultaneous equipment faults trigger localized bus sag and intermittent relay dropout, disabling speed protection logic.Non-Midos panel mount speed relays lack integrated CT short-circuit jumpers; swapping them requires full CT wiring disconnection, creating lethal open CT surge hazards during maintenance work.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
• Hydroelectric generator auxiliary control cabinets for loss-of-prime-mover speed monitoringThis single draw-out unit integrates frequency speed sensing, adjustable trip threshold and time delay to eliminate external signal 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 user programmable microprocessor code. It shares standardized Midos rack mechanical design with all ALSTOM Midos protection hardware for unified cabinet layout.

1. AC speed/frequency signal from generator PT or motor pulse pickup feeds filtered isolated sampling circuitry to suppress VFD and breaker switching EMI noise from field wiring.
2. Onboard frequency-to-RPM conversion circuit continuously samples input cycle count, compares measured speed against front dial set overspeed/underspeed threshold.
3. Internal fixed-time timer activates once measured speed crosses threshold; timer elapse switches contact state to avoid nuisance alarms from momentary speed blips during normal load swings.
4. 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.
5. Front panel LED indicators display healthy auxiliary supply, speed deviation pre-alarm active, and speed trip latched status for quick on-site visual diagnostics without workstation access.
6. 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 kilovolt 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 model 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; segregate L and H coil MAVS01 spares in clearly 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 MAVS speed monitoring 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 grid load fluctuations; 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.

Routing AC Speed Signal Cable Parallel To MV Power Cables

Apprentices run unshielded PT/pulse speed wiring alongside medium voltage feeder cables. Inductive EMI distorts frequency measurement readings, relay trips randomly during breaker switching events.Field Rule: Separate speed signal wiring into dedicated control cable trays; use shielded twisted pair for all PT/pulse circuits, single-point ground shield at the PT cubicle only.

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.