Why is it so important to maintain Primary and Secondary CT connections? Why must we always have a closed secondary – and what happens when we don’t?
The answer is surprisingly straightforward.
When a Current Transformer isn’t connected to a closed circuit, it becomes a Voltage Transformer. The 600:5 CT on a 480 Volt primary now tries to deliver 288,000 volts on the secondary. Unfortunately, the typical CT has a basic impulse level (BIL) of only 10,000 volts. What happens next?
- If we’re “lucky”, the CT fails and the immediate hazard passes – though dangerous voltages can still be present if the upstream breaker doesn’t trip.
- If we’re not, someone in the arc path is injured – or worse. Unfortunately normal service work can unintentionally disconnect the secondary, so many of us have stories that begin, “Remember when Bob opened…”
The event typically disrupts the process or application supplied until you replace the CT. You know the cost of a new CT and can calculate your costs to de-energize and replace the CT, but there is a simpler way to avoid the risk of injury and potential replacement expense.
Apply Open Circuit Protection (OCP) to maintain a closed secondary connection in the event of other actions. Of course, it must have minimal impact on the measurement accuracy…
OSI’s OCP-35 is such a device and available at a very reasonable cost.
Talk with OSI Tech Support Team today to understand how adding OCP to your system can avoid the personnel risk, expense and disruption of a failure. [email protected] | 614-777-1005. DOWNLOAD OCP35 SPEC SHEET HERE