Low-voltage incoming cabinets play a crucial role in power systems, responsible for converting high-voltage electricity into low-voltage power and safely delivering it to various electrical equipment. With the continuous development of power technology, the design and performance of low-voltage incoming cabinets have been constantly improving to meet the growing demand for electricity.

In the design of low-voltage incoming cabinets, safety is always the top priority. By employing advanced electrical protection technologies and equipment, these cabinets can effectively prevent electrical accidents and ensure the stable operation of the power system. Additionally, low-voltage incoming cabinets are known for their reliability and durability, capable of operating steadily under harsh conditions to guarantee uninterrupted power supply. But have you ever wondered why a low-voltage incoming cabinet might need seven current transformers (CTs)? Let’s explore this question together.

This discussion is based on a single-line diagram from an actual engineering project.

Below is the excerpted diagram. Without straying off-topic, let’s focus directly on the core issue.
The diagram shows seven circular symbols with slashes next to them. These represent current transformers (CTs).

Note: (The functions of CTs have been discussed in previous articles, so they won’t be elaborated on here.) It’s worth noting that CTs must be installed in the correct orientation when integrated into circuits.

In general, CTs are usually arranged in groups of three, with one group dedicated to power circuits.
Now, let’s analyze the purpose of these CTs in detail:

1. First Group of CTs

Function: These three CTs are located next to symbols like KWh (active energy meter) and KVarh (reactive energy meter). This indicates that they are used to provide current for energy metering.

2. Second Group of CTs

Function: These three CTs are associated with three "A" symbols, which stand for ammeters. This group supplies current to the ammeters installed on the front panel of the low-voltage cabinet.

3. Last CT

Function: The seventh CT stands alone with no immediate connections shown on the diagram. This CT is used to provide sampling current to the smart controller of the adjacent capacitor compensation cabinet. (Understanding the principle of capacitor compensation will make this clearer.)

Additional Notes

1.Can Groups (1) and (2) Share a Set of CTs?

Answer: No, they cannot. Combining the CTs would compromise the circuit's impedance within acceptable limits, reducing measurement accuracy.

2.Accuracy Requirements for CTs in Different Groups:

CTs for energy metering (Group 1) require higher precision for billing and monitoring purposes.

CTs for ammeters (Group 2) serve as reference tools for users, so their precision can be lower.

By using separate CTs tailored for specific tasks, low-voltage incoming cabinets ensure accurate measurement and reliable functionality, contributing to the overall safety and efficiency of the power system.