Automatic short-circuiting of the transformer before the measuring circuit is disconnected – approved according to IEC 60947-7-1 Annex D – safety-relevant components captively connected to the modular terminal block

In power transmission and distribution, current and voltage transformers are used primarily for protection and measurement functions. Weidmüller has developed the new Klippon® Connect measuring transformer terminals of the TTB series for this application, for particularly simple and safe wiring – even within complex circuits. Avoiding operating errors during operation is a top priority here, as they can have serious consequences for personnel and equipment.  For this purpose, the Klippon® Connect measuring transformer terminals of the TTB series feature a unique disconnect lever mechanism, the “close-before-open” contact. It increases system availability and extends the life cycle of the entire switchgear. An IEC 60947-7-1 Annex D approval underlines the quality claim.

New forced short-circuit functionality

The measuring transformer terminals of the TTB series have been specially developed for use in secondary circuits of measuring transformers. For safe application when disconnecting or isolating protection and measuring devices, the terminal short-circuits the current transformer and thus prevents high voltages from occurring in the secondary winding. One of the most important advantages of the new transformer terminal is the “close-before-open” contact for up to four connections. It ensures that the current transformer within the terminal is short-circuited before it is disconnected from the rest of the transformer circuit. This prevents the voltage at the current transformer from running up and protects it from damage or even destruction. After short-circuiting the CT side and simultaneously disconnecting the primary side, the meter can be easily and safely replaced or a protective relay test can be performed.

The combination of disconnecting lever, short-circuit bridge and lever connection in a single system, i.e. the forced short-circuit functionality, guarantees particularly simple and safe wiring.

Safe comparison measurement

It is just as easy, for example, to connect a reference measuring device for a comparative measurement. Thanks to the patent-pending CM (Comparative Measurement) lever connection, two terminal blocks can be selectively disconnected in order to interconnect a calibrated measuring device. After the measurement, the captive lever is reset to the original position, leaving the “close-before-open” contact active. A unique feature of the TTB series that guarantees the highest safety for personnel and equipment.

The switching state of the TTB series instrument transformer terminals is easily visible in all lighting conditions. The disconnect lever can be operated by hand or with a standard screwdriver. It also facilitates the realisation of multi-pole actuations. All other features of the compact clamp are also designed for maximum safety, ease of operation and convenience, as required by such demanding measurement applications. All functional and safety-relevant components are captively connected to the terminal block.

A switching lock blocks the disconnect lever in the respective position, thus preventing the unintentional opening and closing of circuits. Cross-connection channels upstream and downstream of the disconnect point ensure maximum flexibility. This means that even more complex circuit requirements can be implemented with standardised accessories such as short-circuit bridges, lever connectors and test sockets. To complement this, Weidmüller also offers a PE terminal with the same contour, which can be used to install a star point very quickly and easily. Generous marking areas and an extensive colour palette for coding terminals and accessories provide a clear overview during installation and service work.

The measuring transformer terminal blocks of the TTB series also adapt flexibly to different customer specifications. The integrated combination foot allows mounting on the two common mounting rail profiles G 32 and TH 35. In addition, the terminal blocks are available with either PUSH IN or screw connection. A transparent protective cover system is available for particularly sensitive applications. Its cover can only be fixed when all connection components are in their initial position. In this way, the assembly is comprehensively protected against incorrect operation, unauthorised access and contamination without impairing visual inspection.

Data-supported product configuration and accessory selection

In the planning phase of plants and systems, intelligent interaction between digital article data and interlinked engineering tools is essential. The Weidmüller Configurator (WMC) provides all data sets in full for simple preparation and article selection in the planning phase. The simple assistance function guarantees a reliable configuration of the strip, even if the user knows neither the product name nor the article number. The WMC is additionally characterised by a particularly rational product configuration as well as the simple selection of safety-critical accessory items. The extensive database of the measuring transformer terminals of the TTB series is already integrated into the WMC.