Overload Relays

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SMM™ Smart Motor Manager

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Click to enlarge - 825-2_9-1
Smart Motor ManagerCat. No. 825-MÄ


Bulletin 825 SMM™ Smart Motor Manager


The Bulletin 825 SMM™ Smart Motor Manager provides the tools necessary to obtain optimal utilization of motors that operate critical processes. The Smart Motor Manager can minimize unplanned shutdowns with its comprehensive protective, monitoring, warning, and diagnostic capabilities. Protective features include: thermal overload, phase loss, phase reversal, phase imbalance, rapid trip/mechanical jam, ground (earth) fault, short circuit, over-temperature (thermistor input), underload, stator and bearing RTD monitoring, start time monitoring, stall during start, and multiple starts. Some of these features require the installation of an option card.

Thermal Overload

Two-Body Simulation

Most thermal overload protective devices employ a one-body thermal simulation model. This model assumes that a motor’s thermal response is uniform throughout. The Smart Motor Manager uses a two-body simulation to calculate a more precise representation of a motor’s thermal condition during all modes of operation. A twobody simulation incorporates the temperature rise characteristics of both the stator

windings and the iron mass of the motor into the thermal image.

Starting: In a two-body simulation, the fast rise in the winding temperature and the much slower conduction of heat to the iron during starting are correctly simulated.

Running: While the motor is running, both the iron and current imbalance losses are entered into the model. The optional addition of the ambient temperature into the simulation improves the level of motor use, even in cases where the temperature is subject to considerable fluctuations.

Stopped: The different cooling rates of a self-cooled motor while running and at rest are taken into account by two separate time constants. The simulation includes the faster cooling of the windings relative to the temperature of the iron mass after switching off the motor, as well as the slower cooling of the motor as a whole.

Thermal Capacity Utilization

Thermal capacity utilization is the motor I2t value that the Smart Motor Manager calculates with the two-body simulation. This value can be accessed via the front panel keypad/LCD under the Actual Values menu. When the value reaches 100%, a thermal (overload) trip occurs.

Adjustable Settings

To allow maximum utilization of a motor, the Smart Motor Manager provides the following adjustable settings that allow the installer to match the electronic thermal overload protection to the time-current response of the motor:


The thermal capacity of the iron is particularly important at low-level overloads; allowance for it in the thermal image enables the overload reserves of the motor to be used without risking a premature trip.

Adjustable Ratio of Cooling Time Constants

The ratio of the cooling time constant when the motor is stationary to the cooling time constant when the motor is running allows for the different cooling rates in each of these states. The factory-programmed default value is 2.5; this value is correct for the majority of self-cooled motors. For forced-cooled and special motors, especially those that respond either very quickly or slowly, it may be necessary to modify this value.

Tripping Time Display

In conditions when an overload is likely to occur, the time to trip is continuously displayed on the Smart Motor Manager’s front-panel LCD. This allows corrective action to be taken so that production may continue uninterrupted.

Reset Time Display

Following a thermal trip, the Smart Motor Manager cannot be reset until the temperature in the thermal image has fallen to the reset level, which has a factory-programmed default value of 50% of thermal utilization.

Thermal Warning

The Smart Motor Manager provides the capability to alert in the event of an impending overload trip. The thermal warning level has an adjustable range of 50…99% of thermal utilization, and the warning can be assigned to any of the available auxiliary relays.

Motor Temperature Monitoring

Direct motor temperature monitoring can provide enhanced protection against influences that are independent of current, such as ambient temperature and obstructed motor ventilation. Doing so requires a motor with temperature sensors embedded in the windings. The Smart Motor Manager offers two options for direct temperature monitoring.

Thermistor Input: The option card (Cat. No. 825-MST) allows connection of a maximum of six positive temperature coefficient (PTC) thermistors in series. The resistance of a thermistor increases immediately when its rated response temperature is exceeded. The Smart Motor Manager provides an instantaneous trip when the measures thermistor response resistance level is achieved.

RTD Input: The option card (Cat. No. 825-MMV) allows connection of six 100 W platinum resistant temperature detectors (RTDs) for monitoring motor winding and bearing temperature. A seventh input for monitoring the ambient temperature is also available. User-adjustable settings are provided for programming separate warning and trip temperature values. The monitored temperatures are displayed through the Actual Values menu.

Ground Fault

Motor insulation breakdown usually results in a leakage current to the grounded parts of the machine or, in the case of a power cable, the protective conduit. In grounded power systems, the fault current that develops can rise rapidly to a very high value. The Smart Motor Manager offers the following ground fault sensing options.

Residual Method (Holmgreen)

The Smart Motor Manager uses the Holmgreen method with the basic unit as standard. This method calculates the ground fault current by summing the individual phase currents. In a "healthy" motor where there is no residual current flowing to ground, the three-phase currents sums to zero. The Holmgreen method is best suited for use on either solidly grounded power systems or those grounded through a low impedance. The trip setting has an adjustable range of 10…100% of the motor’s full load current rating.

Zero Sequence Method (Core Balance)

The option card (Cat. No. 825-MST) allows the user to connect a core balance transformer (Cat. No. 825-CBCT), which measures the ground fault current directly from the three-phase motor conductors passing through it. This method is best suited for use on high-impedance grounded power systems. It is also preferred when a sensitive measurement is required. Both trip and warning settings are available with adjustable ranges from 5 mA…50 A.

Imbalance/Phase Loss

The Smart Motor Manager continuously monitors and calculates the current imbalance of an operational motor. The measured current imbalance is entered into the thermal image calculation to simulate the resulting increased motor heating.
User-adjustable trip and warning settings for current imbalance are available with a preset range of 5…80% of full-load current.
Phase loss, a severe form of imbalance, is one of the primary causes of motor failure. A phase loss can occur as a result of a blown fuse or a poor electrical connection. Under a phase loss condition, the current draw of the remaining two powered phases increases by as much as 1.73 times the normal operating current.
The Smart Motor Manager offers two options for obtaining phase loss protection.
Basic Unit: With the basic unit, phase loss protection is gained by using the current imbalance (asymmetry) settings.
Cat. No. 825-MLV: This option card provides terminals for connection to the threephase power system. With the connection made before the motor-starting contactor, a phase loss condition is recognized even while the motor is stopped. The Smart Motor Manager’s phase loss protection provides a preset delay of 2 s prior to a trip.

Rapid Trip/Mechanical Jam

When a driven load is jammed, causing the motor to stall, undue stress is applied to the transmission elements (gears, bearings, motor shaft, etc.). Additionally, as the motor stalls, its current draw begins to increase to the level of its locked rotor current rating.
The Smart Motor Manager provides the capability to quickly take a motor off line in the event of a mechanical jam, thereby reducing the potential for mechanical damage. It can also monitor and warn of impending jam situations. User-adjustable trip and warning settings are available with a range of 1…6 times the motor full-load current.

Underload

A sudden drop in motor current can signal conditions such as:


In these instances rapid fault detection can help minimize damage and aid in reducing production downtime.
Additionally, monitoring for underload can provide enhanced protection for motors that are cooled by the medium being handled (e.g., submersible water pumps). Such motors can become overheated despite being underloaded. This can result from an absence or insufficient amount of the medium (due to clogged filters, closed valves, etc.).
The adjustment range of the underload trip and warning settings is 25…100% of the motor’s full load current rating.

Short Circuit

In the event of a short circuit (phase-to-phase or phase-to-ground), excessive currents, typically much greater than a motor’s locked rotor current rating, are generated. Given the magnitude of this current, it is generally preferable or necessary to interrupt three-phase power to the motor through the branchprotecting circuit breaker rather than the motor-starting contactor due to the differences in the short-circuit withstand rating.
In the event of a short circuit, the Smart Motor Manager trips output relay #1 of the option card (Cat. No. 825-MST) regardless of other protective functions, actuating the circuit breaker with adequate breaking capacity. To prevent the contactor from opening under short-circuit conditions, its main relay is blocked from operating at currents greater than or equal to 12 times the motor’s full-load current rating. Tripping is delayed by 50 ms.

Start Time Monitoring

The Smart Motor Manager furnishes a setting for the installer to define the time that the motor should accelerate the load to full speed. The adjustment is 1…240 s. Start time monitoring begins when the motor’s starting inrush current is recognized (current is greater than 110% of the motor’s full-load current rating). Acceleration to full speed is deemed to have been completed when the starting inrush current has fallen below 110% of the motor’s full-load current rating.
Start time monitoring is independent of thermal overload protection.

Speed Switch Input

The Cat. No. 825-MST option card provides input terminals for connection of a speed switch. This enables the Smart Motor Manager to detect a stalled motor during start and react immediately to take the motor off-line; this reduces the risk of damage to either the motor or the driven load.

Two-Speed Motor Protection

In the case of two-speed motors, the Smart Motor Manager provides a second motor current rating setting. Activating control input #2 of the option card signals the Smart Motor Manager to begin protection based on this second setting.

Control Functions

Contactor Operation

The Smart Motor Manager allows control relays #2 and #3 on the Cat. No. 825-MST option card to be operated over an automation network (e.g., DeviceNet via the Cat. No. 825-MDN communication card). The relays will actuate the motorstarting contactor(s).

Wye-Delta Control

With the Cat. No. 825-MLV option card installed, the Smart Motor Manager can control the transition from wye to delta. The command to transition is issued when the starting current has dropped to the motor’s full-load current rating, thus minimizing the associated current transients.

Emergency Restart

If a critical process requires the restart of the motor, the Smart Motor Manager provides two terminals that, when bridged, return the stored thermal capacity utilization to zero so that an emergency restart can be initiated.

Outputs

Output Relays

The basic unit provides a main relay and an alarm relay. The main relay can be operated either as electrically held or non-fail-safe. The Cat. No. 825-MST option card offers three additional auxiliary relays. Two additional auxiliary relays are available with the Cat. No. 825-MLV option card.

Isolated Analog Output

The Cat. No. 825-MST option card provides an isolated 4…20 mA analog output signal. This can be set to indicate one of the following:


Monitoring and Diagnostic Display

The Smart Motor Manager provides the following useful operating motor data via the Actual Values and Recorded Values menus.

Actual Values


Recorded Values


Communications

The Smart Motor Manager provides a dedicated communication expansion slot for connection to the following automation networks:


This can enhance process operation by allowing the user to do the following via the network:


Basic and Optional Features

Features¬  Basic
Bulletin 825 		Option Cards
Cat. No. 825-MST Cat. No. 825-MLV Cat. No. 825-MMV
Thermal Overload ¬  — — —
Phase Imbalance (Asymmetry) ¬  — — —
Jam (High Overload/Stalling) ¬  — — —
Underload ¬  — — —
Ground (Earth) Fault (Holmgreen) ¬  — — —
Starting Time Monitor ¬  — — —
Limited Starts Per Hour ¬  — — —
Emergency Start ¬  — — —
Short Circuit — ¬  — —
Ground (Earth) Fault (Core Balance CT) — ¬  — —
Stalling During Start — ¬  — —
Thermistor Input (PTC) — ¬  — —
Analog Output for Thermal Utilization — ¬  — —
Two-Speed Motor Protection — ¬  — —
Wye-Delta (Star-Delta) Starting — — ¬  —
Phase Reversal (Sequence) — — ¬  —
Phase Failure — — ¬  —
100 W Platinum RTD Inputs #1…#6
(Stator/Bearings) 		— — — ¬ 
100 W Platinum RTD Input #7
(Ambient Temp.) 		— — — ¬ 
  
¬ Available

Possible Combinations of Option Cards with Basic Unit

Basic
Bulletin 825Ä 		Option CardsT 
Cat. No. 825-MST Cat. No. 825-MLV Cat. No. 825-MMV
¬  ¬  ¬  —
¬  ¬  — ¬ 
¬  ¬  — —
¬  — ¬  —
¬  — — ¬ 
¬  — — —
 
¬ The features and protective functions provided by each option card can be monitored through the communication network with any of the communication cards.
T A single communication card can be used with any combination of option cards.
‡ Available in shown combination.