Cost Effectiveness-The need of an hour
In the present COVID-19 situation, where already our productivity is affected due to most needed force measures like lockdowns and manpower absenteeism because of health issues. On and above this, there has been an increase in prices of commodities like metals and plastics.
All this has affected the costing. Hence, it becomes most important for all of us to look at the cost-effective solution without impacting the quality just by having the right selection of the products we are using.
Higher VA demand from customers
- LT Metering Current Transformers are widely used in the industry & it has been seen that the customers usually ask for a VA rating which is much higher than the actual requirement.
- Customers ask for 5VA, 10VA, 15VA CT’s even if the small ratings or requirement is lesser.
- Higher VA burden unnecessarily affects the cost, accuracy and size, three of the most important aspects of the product selection.
Let us understand…
Actual need and calculations
Analog Panel Meters hardly consume 0.5 VA & the wires used for connection hardly consumes 0.7 VA (Considering 5A, 2.5 sq. mm copper wire, 2-meter length), both together, the max. VA requirement is 1.2VA, even if we use 1.5 or 2 or 2.5 VA CT – it fulfils the requirement. Digital Panel Meter or Multifunction Meter or Digital Energy Meter hardly consumes 0.3VA & the wires used for connection hardly consumes 0.7 VA (Considering 5A, 2.5 sq. Mm copper wire, 2-meter length), both together, the max. VA requirement is 1VA, even if we use 1.25 or 1.5 or 2 VA CT – it fulfils the requirement.
VA burden- core size – accuracy relation
As the VA increases, the core size increases & in turn increases the cost too. In the present situation, it becomes imperative to look at the cost-effectiveness & and we must select the VA as per the system requirement. As per the IEC standard, the CT’s are to be tested at full VA as well as quarter VA @ 1 & 120% input (in case of class S accuracy) or 5 & 120% input (in case of normal class accuracy).
We have tried to understand the impact on accuracy at full VA & quarter VA, it has been observed that the accuracy at full VA is much better than quarter VA.
Hence, it is also clear that even from a system accuracy point of view, it is better to select the CT’s in line with the system VA requirement.
Primary to Secondary phase angle difference
The IEC standard also talks about primary to secondary phase angle difference, the limits are defined under the standard, we must ask the supplier to submit a test report which will have test results of the phase angle difference too, otherwise, the energy & power readings may differ from the actuals.