Power terminal system

Power terminal system

Power in the terminal

The KL8001 power terminal, together with a power contactor, forms a complete distributed motor starter with any fieldbus connection. Apart from all the protective functions of a motor protection relay, the power terminal contains comprehensive diagnostics. By means of values such as current, voltage, active-power input and apparent power consumption or load condition, the control programmer is able to regulate the drive or a machine component in the best possible way and to protect them from damage and failure. At first sight the power terminal looks to the control engineer like a conventional motor protection relay and is fitted to a contactor in exactly the same way. The additional functions are available with little effort. The Bus Terminal block is fitted with a KL9060 adapter terminal instead of a KL9010 end terminal. The KL9060 is connected to a power terminal using a simple ribbon cable. Up to ten power terminals can be driven by one KL9060. No other wiring is necessary apart from a ground cable. The power terminal is supplied using the K-bus and the 24 V control voltage. The status of the contactor is mapped by a bit in the process image. A setting range for the nominal motor current from 0.9 A to 9.9 A covers a wide range normal motors operating on three-phase 400 V AC mains. That represents a motor rating from approximately 300 W up to the maximum switching capacity of the contactor being used (typically 4 kW to 5.5 kW). The connection mechanism of the KL8001 power terminal of the KL8xxx series is particularly suitable for Siemens contactors of the Sirius 3R series. Other power terminals are adapted for other contactor manufacturers. The power terminal switches the installed contactor and takes over all the functions of the motor protection relay. The power terminal can imitate the standard class 5, 10, 15, 20, 25 and 30 trip classes and switch the overloaded motor off via the contactor. Further motor operation is possible only after a cooling-down period and switching on again via the controller. The protective response is configurable using software and makes it possible to achieve optimum compatibility of the motor to the application. A write protection in the power terminal prevents inadvertent alteration of the set values. It is possible to set the motor current directly on the power terminal manually and this has a higher priority than the software settings. Apart from its purely protective function of switching-off the motor when overloaded, the power terminal can carry out numerous diagnostic functions on the motor. Apart from the function of measuring the current, the power terminal can also indicate the supply voltage. From the current and voltage the power terminal calculates the apparent and active power of the connected motor. These values can be transmitted as instantaneous values for an application with very critical loading of the motor and make it possible to react very rapidly to changes. The calculation of the true effective value in the power terminal makes useful information available in the process image, which does not presuppose high computing power on the part of the controller. Even non-sinusoidal voltage and current curves can be read-in with a practical accuracy of 1 % to 5 %, depending on the type of curve. The cut-off frequency of the calculations amounts to 2 kHz. The evaluation for each of the three phases takes place independently. The power terminal recognises failure of one conductor or unbalanced current. Earth leakages with a fault current of more than 0.5 A are recognised and lead to the immediate switching-off of the motor. Using a status word, the controller can ascertain the condition of the motor with a few program steps. Even after the motor has been switched off, the information is retained through the power terminal, simplifying the fault finding.