Smart motor controls are needed that can maximize resilience and uptime of machinery in the next generation of Industry 4.0 manufacturing, metals and basic materials processing, mineral extraction and mining, and critical infrastructure like drinking water and wastewater plants.
The motor controls in these applications must be able to control and protect motors between 75 horsepower (HP) and 700 HP. Comprehensive protection, including overload protection, ground fault protection, and phase imbalance protection, is needed to support resilient operation.
They should also include self-diagnostics for contact wear and coil over/under voltage detection with visible indicators to support predictive maintenance and have modular designs for faster servicing to maximize uptime. Compliance with National Electrical Code (NEC), UL, and Internation al Electrotechnical Commission (IEC) short circuit current rating (SCCR) is needed to ensure electrical equipment can withstand high currents without damage and that it’s safe.
These motor controls must also comply with IEC 60947-4-1, which covers the safety of electromechanical contactors and starters, including motor protective switching devices (MPSD), instantaneous-only motor protective switching devices (IMPSD), and actuators of contactor relays.
This article begins with an overview of SCCR requirements. It then takes a deep dive into a recently developed family of smart motor controls from Schneider Electric, including modular contactors and overload relays detailing the operation of the protective functions and how self-diagnostics is implemented.
It looks at how those overload relays meet the requirements of IEC 60947-4-1 and presents how the modular design speeds preventative maintenance. It closes by looking at how two contactors can be used to assemble a reversing assembly, enabling bidirectional control of AC motors.
The SCCR is an essential characteristic when specifying a control panel that contributes to overall dependability. It’s used when sizing power components like contractors and conductors. IEC 60947-4-1 details three phases for calculating the SCCR (Figure 1):
- Identify the SCCR of each protection and/or control component and each block and element in the distribution system.
- Determine the SCCR of each branch circuit. Based on the values of the components in the circuit.
- Determine the SCCR of the complete control panel. Based on the values of the circuits.
[FIGURE 1: SCCR calculations begin with individual component ratings (yellow boxes), move up to determine the SCCR of branch circuits (red dashed box), and then consider the SCCR needs of the completed control panel (grey rectangle). (Image source: Schneider Electric)]
TeSys Giga contactors are available with ratings from 115 to 900 amps (A) in both 3-pole (3P) and 4-pole (4P) configurations. They have SCCRs rated up to 100 kiloamps (kA) and 480 volts (V), with the specifics for various protection devices and ratings listed in a table on the side of the contactor. Additionally, the 4P contactors show the AC-3 and HP motor ratings. These contactors are available for two load categories:
- AC-1 – This applies to AC loads where the power factor is more than 0.95. These are primarily non-inductive or slightly inductive loads, such as resistive loads. Breaking the arc results in minimal arcing and contact wear.
- AC-3 – This applies to squirrel cage motors with breaking during normal running of the motor. On closing, there’s an inrush current of up to seven times the rated full load current of the motor. On opening, the contactor breaks the motor’s rated full load current.
TeSys Giga contactors can be supplied by an alternating current (AC) or direct current (DC) control voltage and have built-in surge suppressors. There are two versions of contactors, standard and advanced. Standard contactors are designed for general usage. Examples include:
- LC1G1154LSEN, 4P for AC-1 loads. Rated for 250 A with a 200-500 V AC/DC wide-band coil
- LC1G225KUEN, 3P for AC-3 loads. Rated for 225 A with a 100-250 V AC/DC coil
Advanced TeSys Giga contactors have additional features like a greater selection of coil voltages, lower coil power consumption, a programmable logic controller (PLC) input, and a cable design that enables maintenance without removing cables or busbar connections.
Advanced models are also compatible with the optional Remote Wear Diagnosis (RWD) module discussed in the next section. Examples of advanced contactors include:
- LC1G115BEEA, 3P for AC-3 loads. Rated for 115 A with a 24-48 V AC/DC coil
- LC1G800EHEA, 3P for AC-3 loads. Rated for 800 A with a 48-130 V AC/DC coil
All TeSys Giga contactors include a Diagnosis LED on the front panel for quickly evaluating fault conditions (Figure 2).
[FIGURE 2: Typical TeSys Giga contactor showing the Diagnosis LED in the top center of the unit. (Image source: DigiKey)]
Contact Wear Diagnosis and RWD
Contacts experience wear every time they break the current in the power circuit. A contact failure results in loss of motor control. The contact wear algorithm in TeSys Giga controllers continuously calculates the remaining service life of the contacts. When the remaining life is below 15%, an alert is issued, enabling preventative maintenance to be scheduled:
- A local alert is visible on the Diagnosis LED on the front of the contactor.
- An optional RWD module can be used with advanced contactors.
Control Voltage Diagnosis
The control voltage monitors for undervoltage and overvoltage conditions. The diagnosis indication is remotely available on units with part numbers ending in LSEMC using an optional remote device management (RDM) module. An undervoltage is defined as a supply voltage below 80% of the minimum specification, and an overvoltage is defined as greater than 110% of maximum.
Internal Functioning Diagnosis
Continuous blinking of the Diagnosis LED indicates any internal malfunction of the control circuitry.
Motor protective switching devices
Smart motor controls like TeSys Giga contactors are an important part of Industry 4.0 installations. The use of MPSDs is also an important consideration to ensure maximum productivity and availability.
In IEC 60947-4-1, MPSD refers to a device designed with a delay to protect a motor from overload conditions. A second type of device, an IMPSD, is a specific type of MPSD that trips immediately upon detecting an overload. IMPSDs are not usually associated with AC motor protection.
Depending on the application, motor starting can take a few seconds or several tens of seconds. The MPSD must be specified to meet the application requirements for safety while avoiding nuisance tripping.
To satisfy specific application needs, IEC 60947-4-1 defines several classes of overload relays. The trip class indicates the maximum amount of time it takes for the relay to open when there is an overload.
There are also differences between North American and IEC trip classes. For example, class 10 is a North American trip class that trips the overload within 4-10 seconds of detecting 600% of the overload current setting. Class 10A is an IEC trip class that trips the overload within 2-10 seconds of detecting 720% of the overload current setting (Table 1).
Trip classes 10A and 10 are suited for normal-duty motors. Class 20 is recommended for heavy-duty motors to avoid nuisance tripping. Class 30 is used with a very long starting motor.
| 1.05 x lr | 1.2 x lr | 1.5 x lr | 7.2 x lr | |
| Class | Time to trip from a cold start | |||
| 10A | >2 hr | <2 hr | <2 min | 2s< to <10s |
| 10 | >2 hr | <2 hr | <4 min | 2s< to <10s |
| 20 | >2 hr | <2 hr | <8 min | 2s< to <20s |
| 30 | >2 hr | <2 hr | <12 min | 2s< to <30s |
TABLE 1: Examples of thermal overload relay classes based on rated current (Ir). (Table source: Schneider Electric)
TeSys Giga Overload Relays
TeSys Giga thermal overload relays are highly flexible and designed for use with AC motors. Settings for ground fault protection, phase imbalance protection, and trip class (5, 10, 20, and 30) are configurable on the front panel. The front panel also includes alarm and status LEDs. They have wide adjustable thermal overload protection ranges that enable four overlapping models to handle applications from 28 A to 630 A (Figure 3):
LR9G115, adjustable from 28 to 115 A
LR9G225, adjustable from 57 to 225 A
LR9G500, adjustable from 125 to 500 A
LR9G630, adjustable from 160 to 630 A
[FIGURE 3: The front panel of TeSys Giga overload relays includes status LEDs and protection adjustments. (Image source: DigiKey)]
Thermal overload protection is used with single-phase and three-phase asynchronous motors. The current level for thermal overload protection can be adjusted based on the model of the overload relay being employed. In addition, the trip class and associated delay are adjustable. Thermal overload protection can be set for automatic or manual resetting.
Phase loss
Phase loss protection is used to protect three-phase asynchronous motors from overheating. The overload relay continuously monitors the current in each phase. When the current value in one of the phases is lower than 0.1 of the rated current (Ir), and the current value in another phase is greater than 0.8 Ir, the overload relay triggers within 4 ±1 seconds. Phase loss protection cannot be disabled and must be reset manually.
Phase imbalances
Phase imbalances cause overheating of an asynchronous motor. Common causes include:
- Long main supply line
- Defective contact on the incomer switch
- Imbalanced network
When the imbalance ratio exceeds 40%, the overload relay triggers in 5 ±1 seconds. Phase imbalance protection must be reset manually.
Ground faults
Ground-fault protection is used to protect three-phase asynchronous motors. A ground fault occurs when the insulation on the load circuit becomes ineffective due to vibration, moisture, or other factors. The overload relay monitors the ground current (Ig). When the Ig exceeds more than 10% of Ir, the relay trips in 1 ±0.2 seconds. Ground fault protection must be reset manually.
Modularity
The modular design of TeSys Giga contactors can be especially useful if excessive contact wear is experienced or if an overload or other abnormal operating conditions damage the controller. Control modules can also be replaced to adapt to different coil voltages, and the switching module can be switched out to replace worn-out poles.
A cable memory function can be implemented with an optional kit to facilitate rapid maintenance. Once installed, the control or switching module can be replaced quickly without removing the cables.
Going in reverse
Reversing contactors are used to change the direction of rotation of AC motors in applications like conveyors, elevators, and packaging lines. They work by reversing the polarity of the connections, causing the motor to rotate in the opposite direction.
A reversing contactor can be made using two mechanically interlocked standard contactors. The interlock prevents the contactors from turning on simultaneously (Figure 4).
For example, the following components can be used to build a reversing contactor rated for 200 HP at 460 V with a 100-250 V AC/DC coil (Figure 4):
- LC1G265KUEN, TeSys Giga motor controller, two required
- DZ2FJ6, contactor lug kit
- LA9G3612, spreaders
- LA9G3761, reverser bars
- LA9G970, mechanical interlock
[FIGURE 4: Two TeSys Giga contactors interlocked to form a reversing contactor for AC motors. (Image source: Schneider Electric)]
TeSys Giga contactors and overload relays are highly versatile devices that can maximize resilience and uptime in a wide range of applications. The contactors have ratings from 115 to 900 A in 3P and 4P configurations. They have SCCRs up to 100 kA 480 V, and their modular design speeds maintenance.
The programmable overload relays have wide operating current ranges, enabling a small number of devices to satisfy the needs of many applications. Finally, bidirectional motion control can be realized by connecting two TeSys Giga contactors with a mechanical interlock system.
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