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Current Transformers

The Power Diagnostix line of coupling devices includes quadrupoles, current transformers, and coupling capacitors to adapt Power Diagnostix PD detectors to different measurement tasks. The coupling device in a PD measuring circuit provides the means of sensing the partial discharge pulse and sending it as a voltage signal to a preamplifier for conditioning.

Current Transformers

When a current transformer is used instead of a quadrupole, the current transformer can be placed around a coupling capacitor terminal or around a part of the test object itself. A current transformer has the advantage of providing galvanic isolation between the ICMseries PD detector and the high voltage circuit. Power Diagnostix offers current transformers as separate modules or integrated with a coupling capacitor into a single unit.

The CTs are a low-impact PD sensor option since no interruption of the power connection is required. Such installation is even possible under on-line conditions, as the CT100 is a clamp-on current transformer that can be opened and clamped around a connecting cable, a ground lead, or even a feeding medium-voltage cable with a high-voltage motor installation.

Standard Sizes

Type Transfer Ratio at 50 Ω Primary Window Bandwidth at -3 db Bandwidth at -6 db
CT1 1:10 15 mm 0.5-80 MHz 0.3-100 MHz
CT100(/R) 1:10 100 mm 2-25 MHz 1.2-40 MHz
CT125R 1:10 125 mm 2-25 MHz 1.2-40 MHz
CT150R 1:10 150 mm 2-25 MHz 1.2-40 MHz


Current transformer CT33

The CT33 was designed to meet the requirements of permanent on-site installations in cross link cable boxes and other online PD monitoring applications. It picks up partial discharge (PD) pulse signals in a wide frequency band. Providing a galvanic isolation between the PD detector or PD online monitoring system and the high voltage circuit reduces the risk of unwanted damages on the sensitive measurement equipment. The housing of this newly introduced PD sensor is made of flame retardant PU material. The output signal can be transferred via coaxial cable to an accessible position. Typically, a coupler termination box, like the CTB1A, is placed in a small cabinet to give access to all signals of all three phases for service purposes. Permanent online monitoring with an ICMmonitor or temporary measurements with an ICMcompact (incl. SPEC option) or ICMsystem are the most common ways of data analysis and PD failure recognition in combination with this kind of HFCT.