The advantages of the Power Terminal are its low space requirement and the possibility of communication over a fieldbus. It is true that there are other device power junctions on the market capable of protecting drives without the aid of motor protection relays, but they are far less compact than the new Power Terminal, which means that the control cabinet can be made smaller. Furthermore, there is ”the plus with the bus“: Communication over the fieldbus provides information on all the relevant motor data such as its current consumption, active- power input, loading status or start-up behavior. Also, the user does not have to wire a separate power lead to each motor, but can use the Power Terminal to wire the motor directly to the power distribution rail in the distributed terminal box.

The Power Terminal offers all-around value
Instead of the motor protection relays that have been utilized until now, the Power Terminal can be mounted directly on the contactor. Moreover, it is used for a wide range of regular contactor types. Because of the wide range over which the nominal motor current can be adjusted, from 1.0 A up to 10 A, only one device type is needed for all motors up to 4 kW power. The terminal is convenient to order since very few accessories are needed for its assembly. Only the KL9060 adapter terminal and a connecting cable for each KL8001 are required. The benefit is that the number of different components that need to be stocked is significantly reduced, ensuring high availability. These are important cost factors, and should not be underestimated. The Power Terminal offers increased value from the functional point of view, while it performs many more functions than those of a motor protection relay.

The KL8001 protects more than just the drive from damage. It automatically measures the motor current and manages safely switching it off in the event the maximum value is exceeded, i. e. if there is an overload. The terminal switches the contactor directly like a digital 24 V DC output. Just like a standard Bus Terminal, the KL8001 can be operated by any Bus Coupler, and therefore by any of the common fieldbus systems. It provides important motor operating data to the fieldbus communication and allows comprehensive diagnosis of the drive. The machine operator is immediately informed about the state of the drive and thus of the machine. The terminal gives him all the values related to current consumption, voltage, active power and the maximum value of the current since switching on. The operator is able to rapidly assess the loading of the machine.

Four LEDs give a clear indication of the state of the drive, allowing quick, visual, on-the-spot diagnosis. Excess current, failure of one phase, or a missing supply voltage are indicated immediately. Green LEDs indicate correct communication with the fieldbus and show whether or not the motor is switched on. If the KL8001 switches the drive off because of an overload, an OVERLOAD LED is illuminated until the user acknowledges this state, either manually or via the fieldbus.

Control cabinets are getting smaller
The KL8001 allows a complete power control cabinet together with a standard contactor to be constructed a good deal faster and more compactly. Alternatively, the installation can be decentralized into small switching boxes. The user can fit the following varieties of motor starter: A direct starter with the KL8001 terminal plus a contactor, or a reversing starter with a KL8002 terminal and two contactors. A contactor with a Power Terminal fitted can be connected to any of the extension modules of the particular contactor series, with no restrictions. A further option is whether or not to work with two locally operating 24 V DC inputs. These inputs can, for instance, be used to implement a fast stop on slide valve gear. The signal states are transmitted to the higher-level control system in parallel with the stop event.

And, just like the whole Bus Terminal system, a distributed implementation of the ”power“ side, i.e. 400 V, three phase power, in small terminal boxes is now possible. The motor leads can be wired directly to the bus terminal row, without an additional terminal strip. This makes for a very efficient installation. The KL8001 appears on the fieldbus with 24 input and output bits. 16 bits provide the information on current, power or mains voltage to be read, while another 8 bits indicate the state of the motor and the KL8001 terminal in a simple form. One output bit can be used to operate the contactor. All the parameters such as the motor current, switch-off threshold, time constants, response characteristic, measuring cycle times and the over-voltage and under-voltage thresholds can be set over the fieldbus. Write-protection prevents the settings from being accidentally overwritten.

Preventive maintenance ensures availability
Anyone who wants to ensure the availability of a machine or of plants will want to make use of preventive maintenance. Thanks to the terminal, the expected remaining service life of the contactor can here be predicted within narrow limits: From the number of switching cycles and the current loading, the KL8001 estimates the wear on the contactor, and provides a guide value via the fieldbus communication. The user can in turn use this for service life prediction, and can in that way significantly reduce failures resulting from wear. A valuable practical point is that just as the machine can be configured, the user can set the nominal motor current locally over the fieldbus. Selection switches are provided for this setting, and these can even be operated when powered down. Nominal motor current can be set using the selection switch over a range from 1 A to 9.9 A, with a resolution of 0.1 A. The terminal is supplied with a factory setting for configuration via the fieldbus, but the hardware setting always takes precedence. The current setting can be read at any time over the fieldbus.

Innovative solution for distributed automation
The important advantages of the new Power Terminal can be summarized as follows: It can be used with all types of fieldbus, and for different mains voltages from 300 to 550 V. It can be used for either direct or alternating current of up to 100 Hz, and also for non-sinusoidal currents. The terminal can be fully integrated into the TwinCAT control software, and the user can perform settings in the System Manager. The KL8001 significantly reduces the amount of wiring and permits genuine decentralization, because it fits into a terminal box. Together with a contactor it is in fact only about 75 mm x 45 mm x 100 mm in size, which is about the same as the dimensions of four Bus Terminals. It can also do its job with less power dissipation than a motor protection relay, as the internal resistance is less than 1 m. All of this allows a high packing density inside the control cabinet so that smaller and more compact housings can be used. Unlike a motor protection relay, the Power Terminal provides an adjustable response characteristic that eases optimization of the drive. When installing on site, the value of this feature becomes readily apparent. It will make a significant contribution to the future replacement of motor protection relays. Because the guiding principle of distributed automation is that less is more.