The Sun Factor: Photovoltaic Systems Measurements
Facts:
- Modern photovoltaic (PV) plants comprise two main components: The PV array made of solar modules for converting the irradiating sun energy into electrical energy and an inverter system that converts the direct current of the solar module and couples it into the AC grid. Large plants are often implemented with central inverters.
- These large inverters have a capacity of approximately 500 kW and can be modularly equipped up to the megawatt range. While just a few years ago, solar arrays supplied system voltages of up to 1000 V and currents of several hundred amps per inverter, today they generate system voltages of up to 1500 V. Therefore, inverters must correspondingly be rated for input voltages of up to 1500 V DC.
Safe Operation of Photovoltaic Systems with High-Voltage Isolation Amplifiers
Protecting Personnel and Equipment
For solar plant operators the challenge is finding the perfect balance between achieving the highest possible energy yield at the lowest cost but without compromising safety, reliability and efficiency.
To detect malfunctions and to control power output, currents and voltages are measured on the DC side. The above-mentioned system voltages require a suitable isolation of the measurement system to protect both the operating personnel as well as the control and evaluation systems. The measurements are taken downstream with high-voltage transducers (or isolation amplifiers) with a correspondingly high galvanic isolation.
The 1000 V plants require a protective separation of 1000 V AC/DC according to EN 61140. With an increase of the system voltage to 1500 V, the requirements placed on protective separation increase accordingly.
Protective separation is achieved through double insulation, which guarantees a safety margin of 100 percent.
For cost reasons, a safety margin is omitted in some plants. However, this can lead to dangerous conditions with severe consequences for the manufacturer and the operator. Products that guarantee standard conformant protective separation even for the coming 1.5-kV plants are readily available.
Protective Separation up to 1800 Volt
The high-voltage transducers of the VariTrans P 41000 series (current measurement) and VariTrans P 42000 (voltage measurement) from Knick provide protective separation up to 1100 V according to EN 61140 (overvoltage category OV III / pollution degree PD 2). In the P 41100/P 42100 versions, protective separation is guaranteed up to 1800 V AC/DC (OV III and PD 2). With these high-voltage transducers, PV systems that comply with applicable safety standards, can now be constructed. A failure rate (MTBF) of 96 years makes them safe and dependable.
Return on Investment
- High operational safety through protective separation up to 1100 or 1800 V AC/DC
- Centrally installed current and voltage metrology in the inverters based on isolation amplifiers increases efficiency while saving money because it makes decentralized measurements superfluous.
- Calibrated range selection provides flexibility and minimizes inventory costs
- String failures can be easily located with portable measurements on site and then immediately repaired.
- A centralized layout of measurements significantly simplifies plant concept and brings along corresponding cost benefits
