What is a smart grid?

A smart grid is an intelligent power grid that connects energy generators, storage systems and consumers.

These include:

• Wind turbines
• Solar power plants
• Gas-fired power plants
• Photovoltaic systems on buildings

Since these facilities generate energy at different locations, the power grid must monitor their energy flows. To do this, sensors measure the voltage and energy flow throughout the entire grid.

What role do voltage sensors play in the smart grid?

Smart grids must detect changes in voltage and power flow within the grid. Voltage sensors provide the necessary measurement data for this purpose.

They perform three key functions:

• Detecting grid fluctuations: Voltage sensors provide data on the condition of the grid. This data supports monitoring at the municipal and medium-voltage levels.

• Locating Faults and Damage: Sensors can pinpoint faults in high-voltage networks to smaller sections of the line. This shortens the search distance for long cross-connections.

• Monitoring bidirectional energy flows: Smart grids must track energy flows in both directions. This also applies to the charging and discharging of vehicle batteries. During bidirectional charging, the electric vehicle draws energy from the grid. Later, it can feed stored energy back into the grid.

Why use resistive voltage dividers instead of capacitive voltage dividers?

Earlier voltage sensors often used capacitive voltage dividers. With increasing demands on measurement accuracy, many applications today rely on resistive dividers. They enable more precise voltage measurement and help meet the accuracy classes required by modern smart grids.

For high-precision voltage sensors, resistors must maintain their electrical value as constant as possible, even in the face of temperature fluctuations. Even the slightest deviations can affect measurement accuracy. That is why particularly stable, high-precision resistors are used in smart grid applications.

How are high-precision resistors manufactured?

The resistor for a voltage sensor in a smart grid is fabricated in several steps on a circular ceramic substrate. Aluminum oxide ceramic is often used as the material.

The resistor pattern is then applied using screen printing. The paste contains metallic components and glass particles. Among other things, the pattern determines the final resistance value. The thick film is approximately 10 µm thick.

The layout is then sintered at approximately 850 °C. During this process, the material bonds permanently to the carrier substrate.

After sintering, a protective coating is applied to the resistor. This protects the component from external influences. Next, the electrical connections are made.

The entire production cycle can take up to three weeks. The exact duration depends on the quantity and the required process steps.

How are resistors for smart grid applications tested?

Resistors for smart grids are tested using the lightning impulse test. The required accuracy class and the behavior under short high-voltage pulses are key factors in this test.

Background: In actual use, resistors must withstand high electrical stresses.

Depending on the size of the voltage sensor, different test voltages are used:

• Test voltages start at 95,000 volts for a 39-mm sensor.
• For a custom resistor measuring approximately 300 mm, they can reach up to 325,000 volts.
• One test set was even tested at 1.25 million volts.

The test values depend on the sensor size and the intended application. This allows us to determine whether the resistor can withstand the electrical stresses.