Schneider LTMR08MFM Motor Management Controller

Schneider TeSys‑T (LTMR Series) Motor Management Controller — Application Scenarios

TeSys‑T is an intelligent motor‑protection & monitoring unit. Core values: comprehensive motor protection + I/O logic control + Modbus RTU bus for motor‑data & fault‑log upload. It targets three‑phase asynchronous motors requiring fine‑grained protection, remote monitoring and predictive maintenance. An external contactor is required for motor start‑stop.

Product Status: Planned Obsolete, End‑of‑Life Date: Sep 30, 2026

Series: TeSys‑T Intelligent Motor Management Unit, Modbus‑RS485 communication, 0.4‑8A motor circuit protection & monitoring

1. Model Code Breakdown

1. Main Electrical & Hardware Specifications

III. Built‑in Protection Functions

Thermal overload long‑time protection, locked‑rotor protection, phase loss, phase unbalance, phase‑reversal, earth‑leakage protection

Recordable data: fault events, starting current, operating hour counter, trip context, residual thermal capacity; pre‑alarm supported

Expansion: with LTME expansion module for voltage measurement, power‑factor and load‑variation protection

1. In‑depth Operating Principle
2. Current acquisition: Built‑in 3‑phase current transformers measure motor true RMS current; integrated earth‑fault current detection.
3. Thermal model: Embedded motor thermal‑memory algorithm simulates motor temperature rise for overload protection; cooling delay applied after tripping.
4. I/O logic: 6 DIs receive external start/stop / local‑remote commands; 3 relay outputs drive contactor coils; fault relay provides alarm signal.
5. Modbus bus: Upload current, thermal status, fault codes, operating status; receive remote start‑stop and parameter modification commands.
6. Local blue TEST/RESET push‑button: manual fault reset & local test; front‑panel LED indicators (POWER / RUN / ALARM / FAULT).

Note: This unit performs only protection & logic control. Main‑circuit contactor must be externally wired to build a complete motor starter circuit.

1. Key Terminal Definitions (Summary)

A1/A2: Controller power supply, 100‑240 VAC

C1‑C6: 6 logic input channels (DI)

21‑24, 31‑34: 3 NO relay outputs (for contactor driving)

95‑96‑97: Fault relay, 1NO+1NC

Modbus: Dual‑port RS485 (RJ45 + terminal block), supports daisy‑chain networking

1. Upgrade & Replacement Solution (Official TeSys‑Tera New‑generation Series)

TeSys‑Tera adopts separated architecture: controller body + external CT sensors. Direct‑pin‑to‑pin hardware replacement against legacy LTMR is not feasible; current‑sensing wiring modification is required.

⚠ Upgrade Risks:

1. Old LTMR integrates internal CT; new Tera uses external CT, cabinet wiring modification required.
2. Modbus register mapping & parameters are not fully compatible; PLC program modification & commissioning are mandatory.
3. I/O terminal layout is completely different; secondary‑wiring inside control cabinet must be reworked.

VII. Typical Application Scenarios

Three‑phase asynchronous motors such as pumps, fans, compressors and conveyors; water treatment, metallurgy, oil‑gas, chemical, cement industries; critical motor loops requiring PLC‑based bus access for motor‑protection status and fault‑log reading.

VIII. Selection Notes & Boundary Conditions

1. Max measuring current 8 A; not applicable for motors with rated current higher than 8 A.
2. DIs are AC‑voltage inputs, not dry‑contact inputs; external supply voltage is required for contact closure.
3. Max relay output switching frequency: 2 Hz; unsuitable for high‑frequency cycling applications.
4. Cabinet‑level protection is required for condensation‑prone or corrosive environments.
5. Planned end‑of‑life: Sep‑30‑2026; new‑project designs shall adopt TeSys‑Tera preferentially.
6. General‑process Industrial Equipment (Most Common)
7. Fan & Pump Circuits

Circulating pumps, cooling pumps, sewage pumps, makeup‑water pumps, smoke‑exhaust fans, supply‑return fans, cooling‑tower fans.

Values: overload, locked‑rotor, phase‑loss & earth‑fault protection; upload running current, fault status and runtime; underload protection for pump dry‑run prevention.

Industries: HVAC, wastewater treatment, water‑works, building MEP.

2. Conveyors, belt feeders & screw feeders

Belt conveyors, scraper conveyors, screw feeders, bucket elevators.

Values: fast trip upon mechanical jamming; phase‑unbalance & earth‑fault protection; fault history for jam‑incident analysis; interlock‑logic support.

Industries: mining, building materials, grain storage, logistics handling, chemical processing.

3. Compressors & refrigeration units

Screw air compressors, refrigeration compressors, process compressors.

Values: prevent locked‑rotor / overload caused by liquid‑slugging; thermal‑model winding protection; upload motor status to PLC / SCADA via fieldbus.

2. Water‑treatment & Municipal Industry (High‑volume TeSys‑T deployment)

Lift pumps, return‑flow pumps, agitator motors for chemical dosing, aeration blowers, bar screens, scrapers.

Site features: large quantity of geographically distributed motors; remote monitoring of current & faults to reduce on‑site inspection; high incidence of phase‑loss & earth‑fault faults.

Typical architecture: Modbus‑RTU multi‑drop networking with PLC, aggregating motor‑protection data to SCADA host.

3. Chemical & Pharmaceutical Industry

Reactor agitators, circulation pumps, metering pumps, material transfer pumps, centrifuges.

Values:

1. Earth‑leakage protection mitigating motor damage from process‑media leakage.
2. Complete fault event log for process traceability and GMP compliance.
3. Phase‑reversal protection to prevent reverse rotation after maintenance phase swapping.

Note: Controller body cannot be installed directly in hazardous explosive areas; explosion‑proof enclosures / contactors are required.

4. Metallurgy, Cement & Building‑materials

Dust‑removal fans, cooling fans, distributing actuators, unloading drives, small roller‑table motors.

Operating conditions: heavy shock‑loading, high dust; frequent locked‑rotor & phase‑loss events; combined thermal‑overload & fast locked‑rotor trip safeguards motor windings.

5. Power‑plant Auxiliary Drives

Small auxiliary motors: cooling fans, lube‑oil pumps, seal‑water pumps.

Values: critical auxiliary equipment; pre‑alarm & fault‑snapshot recording for root‑cause analysis after incidents.

6. Logistics‑packaging & Plastics Machinery

Conveyor belts, agitators, feeders, auxiliary drives for small extruders.

Advantages: local / remote mode selection via DI; contactor‑coil driving via DO eliminates numerous intermediate relays.

✅ Selection Criteria for TeSys‑T

Choose LTMR if any condition below applies:

1. Fieldbus communication required: read current, thermal‑capacity percentage, operating hours, fault codes and fault snapshots.
2. Valuable motors requiring full‑scope protection: thermal overload, locked‑rotor, phase‑loss, phase‑unbalance, phase‑reversal, earth‑fault, underload.
3. Local‑remote dual control mode plus complex interlock logic; reduce intermediate‑relay count.
4. On‑site requirement for fault logging for post‑event troubleshooting.
5. Multi‑motor centralized monitoring network connected to PLC / SCADA.

❌ Unsuitable Application Scenarios

1. Only simple thermal‑relay protection needed without communication or fault logging: select low‑cost LRD thermal overload relays instead.
2. Motor full‑load current far exceeds built‑in CT range (max integrated‑CT LTMR:100 A). Use new‑generation TeSys‑Tera with external CT for higher‑current motors.
3. High‑frequency motor cycling: relay DO max switching frequency 2 Hz; contact wear will accelerate.
4. Intrinsically‑safe hazardous zones: controller body cannot mount inside hazardous area.
5. Single‑phase‑motor protection: TeSys‑T targets three‑phase induction motors.

📌 Old‑vs‑New Generation Summary

Legacy: LTMR series (e.g. LTMR08MFM), planned EOL Sep‑30‑2026, built‑in current transformers.

New: TeSys‑Tera (LTMT series), external‑CT architecture, broader current coverage; preferred for new‑project engineering.

Thermal‑Overload Protection Principle of Schneider TeSys‑T (LTMR)

TeSys‑T does not rely on physical bimetallic‑strip deformation like conventional thermal relays. It implements thermal‑overload protection via electronic thermal‑model (virtual‑motor thermal‑memory algorithm) + true‑RMS three‑phase‑current sampling.

1. Hardware Acquisition Stage
2. Built‑in three‑phase current transformers sample true RMS stator current (not simple peak values).
3. Integrated earth‑fault‑current detection circuit.
4. Analog‑current signals are digitized by MCU for periodic load‑current refresh.

For LTMR08MFM: internal CT measuring range:0.4‑8 A for direct stator‑loop current measurement.

2. Core: Virtual‑motor Thermal‑Model (Thermal Memory)

The controller runs a mathematical model simulating motor‑winding heat accumulation and heat dissipation:

theta_{virtual} \propto \int(I^2 \cdot t)dt

Heat accumulation: thermal‑capacity percentage rises when operating current exceeds motor rated current.

Heat dissipation: thermal‑capacity percentage decreases during stop or light‑load operation, simulating natural motor cooling.

Two key configurable parameters drive model behaviour:

1. Motor rated current Ir: set according to motor nameplate full‑load current.
2. Trip Class (5/10/15/20/30), defines inverse‑time tripping characteristics.

📌 Thermal‑capacity percentage: internal variable 0‑100 %; overload trip triggers at 100 %. This value can be read via Modbus register.

Trip‑Class Definition

3. Overload Handling for Two Typical Operating Conditions

① Continuous running overload (persistent over‑current)

Motor runs continuously with I＞Ir; virtual thermal‑capacity accumulates until reaching 100 %. The controller outputs trip command, de‑energizes contactor‑coil relay outputs and stops the motor. Over‑load fault code plus fault snapshot (3‑phase current & thermal‑capacity at trip instant) are stored.

② Overload during motor start‑up (high‑magnitude starting inrush current)

Configured Trip‑Class permits short‑term high starting‑current without nuisance tripping; thermal‑model decays accumulated heat after start‑up completes.

⚠ Critical Feature: Thermal‑memory retention

After overload trip, virtual thermal‑capacity value does not reset immediately even if controller power supply remains alive. Model‑simulated cooling‑time must elapse or manual RESET is required.

Practical case: after motor trips from overload, windings remain hot. Instant reset & restart risks motor burnout. Thermal‑memory prevents premature restart and mimics real‑motor cooling behaviour.

4. Pre‑alarm Function (Overload Early Warning)

Configurable thermal‑capacity threshold (e.g. 80 %). When virtual thermal‑capacity exceeds threshold, overload pre‑alarm activates without tripping. Warning signal can be transmitted via relay DO or Modbus for predictive maintenance before unplanned shutdown.

5. Comparison: Conventional Bimetallic Thermal Relay vs TeSys‑T LTMR Electronic Thermal‑model

6. Boundary‑conditions & Limitations
7. Overload protection protects motor‑winding thermal accumulation, not power cables; separate circuit‑breaker required for cable‑conductor protection.
8. Phase‑loss / phase‑unbalance accelerates thermal‑model accumulation and advances trip threshold.
9. Locked‑rotor and earth‑fault are independent protection functions, not part of overload logic.
10. Adjust Trip‑Class if actual motor‑cooling condition deviates from internal model (e.g. forced‑air‑cooled motor).
11. LTMR thermal‑model is designed for standard three‑phase induction motors. Direct reuse for VFD‑fed or special‑purpose motors is invalid; parameter tuning is mandatory.
12. Fault‑reset Logic
13. Auto‑reset: parameter‑enabled; reset occurs only after thermal‑model cools down to safe thermal‑capacity level.
14. Manual reset: local front‑panel RESET button, DI terminal reset signal, or Modbus‑bus reset command.

Forbidden operation: repeated forced restarts before motor cools after thermal trip.

8. Fault Code

Thermal‑overload trip fault code: OL1. Fault log stores timestamp, three‑phase current and thermal‑capacity percentage, retrievable via Modbus.