Current Transformers, or CTs, are important elements in power monitoring and protective relaying applications. A CT will step-down higher line currents to a safe level (typically 0-5 A) for use in control panels.
But there is an inherent danger when using CTs. Extreme caution must be taken to prevent an open-circuit on the secondary side of a CT. High voltages will be induced if the secondary side of a CT is opened, or disconnected, while a current is still flowing through the primary side. This poses a significant risk for an electric shock and a potential fire hazard.
To eliminate this risk, a CT shorting block is typically used to allow the technician to manually short out the CT before performing any work on the secondary wiring. CT shorting blocks come in 4-point, 6-point and 8-point arrangements depending on how many CTs are installed, and the wiring method used.
In order for the CT secondary to be safely disconnected, the technician installs a shorting screw into the shorting block for each CT they wish to disconnect. If the CT shorting block was installed and wired correctly, the shorting screw will short the CT’s secondary to ground.
But what if the technician forgot it was a CT circuit, and did not properly short the CT? Or what if the secondary side of the CT opened unintentionally due to a loose connection, or some type of incident?
Automatic CT Shorting Module
Emphatec has developed a CT shorting module, the SIGNEXT CTSM module, which continuously monitors the secondary of a CT and applies a short circuit in the event the voltage increases over approximately 2V. The short circuit can be applied indefinitely.
To ensure integrity in the CT secondary circuit the module uses tension clamp terminations that are vibration proof and locking blocks on the connector so accidental disconnection is not possible.
Another feature is an alarm output (24Vdc @ 40mA). The short circuiting function works even when the 24Vdc for the alarm circuit is not applied to the module.
Each SIGNEXT CTSM module is capable of monitoring a single CT circuit. You will need to install multiple SIGNEXT STSM modules if monitoring 3-phase current and/or neutral/ground current.
Emphatec provides standard off-the-shelf products such as analog signal conditioners, relays and power supplies. Our emphasis is on solutions to your interfacing and automation needs.
Emphatec can also design products specifically for your application. These can be simple power distribution modules, PLC interface products, overvoltage protection modules, analog signal conditioners or microprocessor based controllers.
Looking for more information?
Contact your local automation specialist or account manager at The Reynolds Company to discuss your automation applications. Find your specialist.