EXPLORE THE STORY · 4 MIN READ
The relay can make the right decision while the wider system still needs checking. Where does its information come from—and what happens next?
How Clean Air Current Transformers Work
A current transformer steps down high current for safe measurement and protection relay input. The Clean Air Current Transformer by Trench Group operates at voltage levels up to 420 kV and primary currents up to 6000 A, using a gas mixture of 20% oxygen and 80% nitrogen—essentially the same air we breathe—as the insulation medium. Unlike traditional CTs insulated by mineral oil or sulphur hexafluoride (SF6), this approach eliminates greenhouse gas emissions and the risk of insulation aging, providing both technical and environmental benefits.
Core Technical Features
– Designed for bar-type high-current applications, minimizing voltage drops in the primary winding and accommodating demanding load and fault conditions.
– Composite insulator and aluminum housing, painted to customer specification, help meet mechanical and environmental requirements.
– Engineered to operate without regular maintenance for over 30 years, reducing operational costs and onsite servicing.
– Explosion-proof per IEC 61869-1 Class II, with a rupture disk to release excess internal pressure, supporting enhanced substation safety.
– No F-Gas regulation compliance overhead or leak documentation required.
Illustrative Substation Scenario: Application in a 420 kV Busbar Protection Scheme
Imagine a high-voltage substation where protection, control, and metering rely on accurate current measurement. Installing a Clean Air Current Transformer as part of a busbar protection scheme allows for safe, continuous current monitoring up to 6000 A. In the event of a high-magnitude fault, the CT’s bar-type primary conductor and robust insulation prevent insulation failure and hazardous gas emissions. If an internal arc occurs, the rupture disk safely relieves pressure, protecting surrounding equipment and personnel. The engineering lesson is clear: clean air insulation combines safety with environmental responsibility and can cut costs associated with maintenance, regulatory compliance, and end-of-life disposal.
Limitations and Practical Lessons
While the clean air insulation has a global warming potential (GWP) of zero and requires no aging-related maintenance, it is essential to verify that specified ratings and environmental tolerances match site conditions. Always confirm technical requirements for voltage, current, and climate before specifying or commissioning a Clean Air CT.
Reporting and Disposal Simplified
With no SF6 or oil present, compliance documentation and skilled HazMat handling are unnecessary. This reduces complexity during routine testing, life extension, or end-of-life dismantling.
For further guidance, always verify up-to-date product specifications and site suitability with the manufacturer’s official literature before making design or equipment selection decisions.
THE ENGINEERING CORNER
A relay decision is only one link in the chain
Protection begins with measurements. Current transformers (CTs) provide scaled current signals; voltage transformers provide scaled voltage signals where required. A relay evaluates those inputs using its configured protection functions and settings.
A trip output is a command. It does not, by itself, prove that the circuit breaker moved, that current stopped flowing or that equipment is isolated. Those are different claims and need the appropriate evidence. The useful engineering question is: what has actually been measured, and what has merely been requested?
For protection-zone discussions, locate the relevant CTs on the single-line diagram before judging which equipment a scheme covers. Compare that drawing with the actual scheme documentation rather than assuming that a relay name defines the complete boundary.
When equipment or network conditions change, the design and coordination assumptions need review. That does not mean every setting must automatically change. A study may confirm the existing settings or identify a justified revision; neither result can be inferred from a news headline alone.
THE ENGINEERING CORNER
Read the application before the product list
A company profile can introduce useful equipment families, but the engineering assessment starts with the duty. Identify what the device must do, the system it will connect to, and the conditions it must withstand. Similar-looking products may serve different applications.
Build a short comparison table from the relevant manufacturer documentation: intended function, electrical ratings, interfaces, environmental limits and the stated test or conformity evidence. Keep the document revision beside the figures so that a later change is visible.
One useful distinction: a manufacturer’s portfolio statement is not the same as approval of a particular model for a particular project. Likewise, the presence of a product category on a website does not establish every voltage rating, certification or service capability you might need.
For a substation application, follow the interface with the rest of the scheme. Equipment selection involves how a device works with measurement, control, protection and the connected circuit. The aim is to turn a broad product description into specific questions that can be answered from the exact model’s current documentation.