Temperature Measurement in Hydropower Plants: These 6 points must use PT100 sensors

In temperature measurement systems for hydroelectric power plants, PT100 platinum resistance thermometers are almost a "standard" component. But do you know that not all temperature measurement points require the use of PT100? Selecting the wrong sensor for certain points can lead to issues ranging from minor data drift and false alarms to severe consequences such as bearing burnout or unit shutdown. Which specific points must utilize Pt100 Sensors? And what key considerations should be kept in mind when selecting these sensors? This article provides a comprehensive explanation on all these aspects.

I. The long-standing challenge of temperature measurement in hydroelectric power plants

Many hydroelectric power plant O&M personnel have encountered the following scenario: the DCS temperature display suddenly jumps to 300°C at full scale; upon opening the insulation sleeve, it is discovered that the PT100 lead wire has been broken by immersion in the oil tank; or, when the actual bearing temperature is already 75°C, the displayed value is only 42°C—due to condensation within the temperature measurement insulation sleeve, resulting in poor heat transfer. Even more problematic is that some older power plants still utilize Cu50 copper resistors, which suffer from poor accuracy, are prone to damage, and frequently trigger false alarms and tripping events.

The root cause of the problem lies in: selecting an incorrect sensor type for the temperature measurement point, or using an installation method that does not meet the operating conditions. The DL/T 1107-2019 standard "Basic Technical Conditions for Automation Components in Hydropower Plants" explicitly specifies that thermoresistors for temperature measurement in hydropower plants should preferably be Pt100 Sensors with Class A accuracy and a three-wire output configuration. However, the specific requirements may vary depending on each individual measurement point.

II. For these 6 critical temperature measurement points, PT100 sensors must be used.

1. Thrust bearing pad temperature – the "lifeline" of the power unit

The thrust bearing bears all the axial loads of the unit and serves as the most critical temperature-monitoring point for hydro-generator units. According to the requirements of GB/T 11805, each thrust pad on large and medium-sized units shall be equipped with two PT100 sensors (implementing a redundant design), with one sensor dedicated to monitoring and the other dedicated to protection tripping. The alarm setpoint is typically set between 65–75 °C, while the trip setpoint is set between 85–90 °C.

Why must the PT100 be used? Because thrust bearing temperature monitoring is directly critical to the safety of the unit, requiring Class A accuracy (±0.15 + 0.002 |t| °C) and long-term stability. The PT100 platinum resistance thermometer exhibits minimal drift—its resistance variation over 50,000 hours is <0.02%—which is unattainable with thermocouples or Cu50 sensors.

2. Upper guide, lower guide, and water guide bearing pad temperatures – the three "sentinels"

The guide bearings are responsible for constraining the radial displacement of the spindle; each of the three guide bearings (upper guide, lower guide, and water guide) is equipped with 4–10 PT100 temperature sensing points. A dual-bearing configuration is also required; the lead-out wires must be routed directly to the exterior of the oil tank without any joints, and mesh shielding cables shall be used to protect against oil contamination and vibration.

The most significant challenge at the site is the continuous flow of turbine oil within the guide bearing oil tank combined with shaft bearing vibration, which can easily lead to oil leakage or contact failure at the rear connector of standard sensors. Therefore, the PT100 must employ a root-sealed welded construction, and the wiring must be made of oil-resistant fluoroplastic rather than conventional PVC wire.

3. Oil tank oil temperatures – the "thermometer" for bearing health

Each of the upper oil guide groove, thrust lower oil guide groove, and water-guided oil groove is equipped with two PT100 sensors to monitor the temperature of both the cold and hot oils. An abnormally elevated oil temperature often serves as an early indicator of bearing wear, enabling early warning prior to the activation of the bearing temperature alarm. The oil groove's oil temperature monitoring system requires PT100 sensors that are oil-resistant and possess high insulation properties (insulation resistance> 100 MΩ), with the sleeve material selected as SUS316 stainless steel.

4. Stator winding temperature – the "firewall" against short circuits

Temperature monitoring of generator stator windings directly impacts insulation life and short-circuit protection safety. Standards require PT100 sensors to be installed at the top, middle, and bottom positions of the stator bars, evenly distributed along the circumference; for large-capacity generators, this may involve up to 12–24 temperature measurement points. DL/T 1107-2019 explicitly stipulates that the maximum operating temperature for PT100 sensors used at stator locations shall be ≥150 °C.

Note: For some existing units, the stator temperature measurement employs T-type thermocouples; however, all newly constructed units have now been fully upgraded to using PT100 sensors, as PT100s offer higher accuracy, do not require cold junction compensation, and exhibit far superior long-term stability compared to thermocouples.

5. Stator core temperature – monitors core overheating

The stator core temperature monitoring system is used to detect localized overheating and prevent core burnout. Typically, more than six PT100 embedded temperature sensing points are installed, evenly distributed across both the core teeth and the yoke section. The PT100 sensors must possess excellent thermal conductivity and a thermal response time ≤ 60s to ensure that temperature changes are captured promptly.

6. Air cooler cold and hot air temperatures – a "barometer" for cooling performance

Each inlet and outlet port of the air cooler is equipped with a PT100 sensor to monitor the temperatures of the cold and hot air; large units typically feature 6 + 6 = 12 temperature measurement points. The cooling efficiency of the air cooler is determined by the temperature difference between the cold and hot air; a reduction in this temperature difference indicates a decline in the cooler's efficiency or possible blockage. The PT100 sensors installed at this location must have an IP65 or higher protection rating to withstand humid environments.

III. Overview of PT100 temperature measurement point distribution in the hydropower station

▲ Schematic diagram of the distribution of PT100 temperature measurement points for the hydroelectric power plant's hydraulic turbine generator set

IV. Parameter Table for PT100 Selection for Key Temperature Measurement Points in Hydropower Stations

V. 3 Key Tips for Avoiding Common Pitfalls When Selecting PT100 Sensors

1. For shaft bearing temperature measurement, select the armored sealing type; do not opt for the rear connector structure. The oil tank is subject to long-term vibration and immersion in turbine oil; the connector structure will inevitably leak oil or disengage over time. The lead-out cable must be a single-piece lead-out without joints, with its root section sealed via laser welding.
2. The three-wire system serves as the baseline, while the four-wire system offers greater accuracy. The three-wire system can compensate for conductor resistance errors (deviations exceeding ±5°C); therefore, for key measurement points on medium-and large-scale units, it is recommended to directly adopt the four-wire system. Do not opt for the two-wire system simply to save effort—errors in long-distance transmission can exceed 10°C.
3. For chip selection, opt for the sputtering photolithography process with a Pt100 thin-film layer; do not select the wire-wound type. Thin-film chips exhibit significantly superior vibration resistance, impact resistance, and long-term stability compared to wire-wound types, with a drift of <0.02% over 50,000 hours. Under high-frequency vibration conditions, wire-wound copper resistors (Cu50) are almost guaranteed to fail.

VI. Leave professional matters to professional sensors

The temperature measurement system in hydroelectric power plants serves as the final safeguard for unit safety; therefore, the selection of PT100 sensors must be handled with utmost care. Weilian Fengran Sensing Technology specializes in the research, development, and manufacturing of Temperature Sensors. The PT100 sensors specifically designed for hydroelectric power plants utilize imported thin-film chips, armored sealing structures, and oil-resistant fluoroplastic conductors; these products comply with the IEC 60751 and JB/T 8622 standards and have been operating stably in numerous hydroelectric power plant projects.

If you require a PT100 temperature measurement solution for hydroelectric power plants or product selection support, please feel free to contact our technical team to receive tailored temperature measurement solutions.

#Hydropower Station Temperature Measurement #PT100 Platinum Thermistor #Hydro Turbine Temperature Sensor #Shaft Bearing Temperature Measurement #Stator Temperature Monitoring #Hydropower Station Automation