How Extended Range CTs Help Reduce Inventory

How Extended Range CTs help you Reduce Inventory

By Steve Lindsay

The Alta Series of metering current transformers by Peak Demand are designated as both high accuracy and extended range.  These designations have two distinct benefits.  First, high accuracy means utilities will gain more revenues.  These CTs exceed the IEEE C57.13 standard for accuracy.  This will lead to increased revenues for utilities, especially under light loads, as explained in the following article.  The second advantage is that extended range CTs help utilities reduce their inventory.

Extended range current transformers are unique because they allow utilities to standardize on fewer ratios and to cut back drastically on the number of different types of CTs they need to keep on hand in inventory.  With an Alta Series CT, a utility can reduce the number of ratios down from 8 to only 1 or 2 thus limiting the chance of a stock out.  An additional benefit is reducing the chance for incorrectly sizing a CT installation.

Let’s look at the benefits of extended range CTs by looking closely at the COS-6.  The COS-6 is commonly used in meter boxes and is popular due to its smaller size.  A standard accuracy COS-6 will have up to 8 different ratios, from 50:5 to 1200:5.  The Alta Series COS-6 unit, however, will have just one ratio that will cover as much as all of the 8 ratios – and more accurately.

On the low side, a 50:5 ratio CT with a rating factor of 4 will meter with 0.3% accuracy from 50A to 200A.  It will meter as low as 5A with 0.6% accuracy.  On the high side of current, the COS-6 1200:5 ratio unit with a rating factor of 1 will meter up to 1200A.  The Alta Series COS-6 unit, on the other hand, will handle that whole range.  A single 600:5 ratio will deliver 0.15% accuracy down to 6A and 0.3% accuracy down to 3A.  The Alta Series COS-6 600:5 has a rating factor of 2 allowing it to meter loads as high as 1200A, all at an accuracy level of 0.15%.

So, the high accuracy and extended range Alta series of metering CTs allows the utility to reduce part numbers and carry only one ratio to (more accurately) meter loads from 6A to 1200A.

In addition to the extra revenue that a high accuracy CT gives a utility, the opportunity to standardize on fewer ratios and simplify inventory and ordering has been seen as a huge advantage.  These two benefits are what has been driving utilities to adopt high accuracy, extended range CTs for the last several years.