MAXREFDES38#: ECT/EPT current fault sensor

Introduction

To realize the vision of a truly smart electricity grid, utilities must find new ways to increase the speed at which they locate, isolate, and fix faults. The electronic current transformer/electronic potential transformer (ECT/EPT), or current fault sensor, fulfills this vision. The ECT/EPT is a low-power sensor that may be placed at many points in the grid thereby increasing the granularity grid health data and fault location. These sensors must be ultra-low power, because they generally receive energy from batteries or nearby fiber optic lines. Although power is readily present in the lines being measured, converting power from the kilovolts in the distribution lines is not feasible. In addition to low-power operation, these sensors must also maintain accuracy and performance, as they provide valuable grid health information during both faults and normal operation.

The term ECT/EPT refers to a variety of technologies applied to grid measurement applications. MAXREFDES38# specifically provides the low-power, high-speed, high-accuracy analog front-end designed for the ECT/EPT or current fault sensor application.

The MAXREFDES38# features a low-power, 16-bit, high-accuracy, three-channel analog input. Input channels can be configured as ±3V_P-P single-ended or ±6V_P-P differential. The MAXREFDES38# design integrates a three-channel analog switch (MAX14531E); a quad precision low-power buffer (MAX44245); a 16-bit fully differential ADC (MAX11901); an ultra-high-precision, 3V voltage reference (MAX6126); a low-noise precision op amp (MAX44241); a STM32L1 microcontroller; a supervisory circuit (MAX16058); a 64kB SRAM, a FTDI USB-UART bridge; a dual-output step-down DC-DC converter (MAX1775); a switched-capacitor voltage converter (MAX1044); and -3V, 1.8V, 3.3V, 3.38V, 4.5V power rails (MAX1735/MAX8891/MAX8881/MAX8902B/MAX16910). The entire system typically operates at less than 85mW and fits into a space roughly the size of a credit card. The MAXREFDES38# targets for the ECT/EPT and current fault sensor applications that require low-power high-accuracy data conversion. A block diagram of the system is shown in Figure 1.

Figure 1. The MAXREFDES38# reference design block diagram.

Features

• High accuracy
• Low power
• Accepts 3V_P-P single-ended signal or 6V_P-P differential signal
• Optimized layout and size
• Device drivers
• Example C source code
• Test data

Applications

• ECT/EPT
• Current fault sensors

Competitive Advantages

• Ultra-low power
• Small size