To maximize efficiency, power company suppliers must minimize the energy loss between power generation and customer distribution. Some of these losses include non-technical losses, such as losses caused by power theft. Some of the most common methods of stealing electricity include tampering with e-meters, which are relatively easy to find.

To maximize efficiency, power company suppliers must minimize the energy loss between power generation and customer distribution. Some of these losses include non-technical losses, such as losses caused by power theft. Some of the most common methods of stealing electricity include tampering with e-meters, which are relatively easy to find.

There are many ways to tamper with the meter. In addition to intrusive tampering methods, Electronic meters can also be tampered with non-invasively without opening the meter casing.

Magnetic tampering is one of the most common forms of non-intrusive tampering. Place a strong magnet near the meter. The strong magnet may saturate nearby transformers and cause them to paralyze. Specifically, strong magnets may paralyze the transformer in the power supply or the current sensor of the current transformer, which may cause the electricity users to pay less than they should actually pay.

In response to magnetic tampering, countermeasures include trying to use Hall-effect sensors to detect the presence of a magnetic field and hardening the meter to prevent magnetic tampering attacks. To detect magnetic tampering, three Hall-effect sensors can detect the presence of strong magnets in all three dimensions. When the system’s backup power is exhausted, it is vital that the average current consumption of the Hall-effect sensor is very low. Hall-effect sensors can achieve low average current consumption through an external duty cycle, or choose a Hall-effect sensor that integrates this duty cycle.

To harden the transformer in the power supply against magnetic tampering, one option is to shield the transformer; however, this is only effective to a certain extent. The second option is to choose a transformer with complete magnetic immunity or magnetoresistance that is sufficient to deal with the expected magnetic tampering attack. For a system that does not draw too much current, the third option is to use a capacitor drop power supply without any magnetic components.

Similar to the transformer in the power supply, in order to harden the current transformer to prevent magnetic tampering, a shielded current transformer can be selected. However, this only works to a certain extent. The best way to obtain magnetic immune current sensing is to use shunt sensors instead of current transformers. Using shunts for single-phase meters is relatively simple: only reference the system with respect to the shunts. For multiphase electricity meters, it is more complicated to use a shunt as a sensor. Since shunts have no inherent isolation, external isolation must be performed to prevent large and destructive differential voltages from appearing on the devices connected to the shunts.

Figure 1 shows the functional components of a three-phase system with isolated shunt sensors. In this architecture, an independent device for each phase measures the voltage on both sides of the shunt sensor. These devices can be isolated delta-sigma modulators or metering analog front-end (AFE) microcontrollers (MCUs). Since the shunt sensor device is isolated, each device must have a separate power supply.
  

TI-Detect and strengthen attacks on non-intrusive tampering

Figure 1: Functional components of a multiphase system with isolated shunt sensors

Back-end device

The back-end device is selected based on its ability to communicate with the shunt sensor device (as shown in Figure 1). For example, if you use an isolated modulator as a shunt sensor device, choose a back-end device with a digital filter. These digital filters can form part of a stand-alone device or be integrated in a metering MCU. Or, if you use the metering AFE as a shunt sensor device, choose a back-end device with a serial peripheral interface or a universal asynchronous receiver transmitter interface.

To calculate the active energy, in addition to the current of the customer’s load, it is also necessary to measure the power supply voltage. A resistor divider usually converts the power supply voltage into a range that can be sensed by an analog-to-digital converter. In a multi-phase system with isolated shunt sensors, you can implement power supply voltage detection on the same device to detect the voltage on the shunt, or if the voltage detection of the device is synchronized with the shunt detection, you can implement it on the back-end device . If the back-end device is sensing voltage, isolation is not required because the voltage can still be measured on multiple phases, and there is no large destructive voltage on the back-end device.

In order to prevent dangerous voltages on the back-end device (because the shunt itself does not have an isolation function), it is necessary to isolate the communication and shunt sensor devices to the back-end device. This isolation can be integrated in the shunt sensor device or a separate digital isolator device.

There are two ways to achieve isolated shunt current sensing. The first method, shown in Figure 2, involves the use of metered AFE. In this method, the metering AFE calculations are mainly metering (voltage, current, power, etc.), rather than letting the back-end devices perform these calculations. Calculating these parameters on the shunt sensor device reduces the processing required by the back-end device and provides a good separation between metering and host functions.

TI-Detect and strengthen attacks on non-intrusive tampering

Figure 2: Isolated shunt sensor using metering AFE

Microcontroller

Digital filter

The second method of isolated shunt sensing is to make the shunt sensing device only detect current and let the metering MCU perform metering calculations. Figure 3 shows an example of this method. The advantage of this architecture is that it is easier to perform parameter calculations between phases, such as measuring the angle between different phases.

TI-Detect and strengthen attacks on non-intrusive tampering

Figure 3: Isolated shunt sensor using isolated modulator

Microcontroller
Metering AFE
Metering AFE
Metering AFE
I2020 power supply (high-side power supply)
Public utilities

in conclusion

We can use shunt current sensors and capacitor drop power supplies to design magnetic immune electronic meters.
By following these anti-tampering technologies, meter tampering events can be prevented or at least mitigated, thereby reducing inefficiency when supplying power.

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