Case C2 - Condition monitoring of drainage pumps

The aim of this case was to develop and test models for monitoring the performance and condition of drainage pumps in hydropower plants. Even though drainage pumps usually are not considered as the most critical equipment of hydropower plants, they play an important role for protecting the power station from flooding. The drainage system is designed as a redundant system with two or several pumps in parallel, and an ejector as the last barrier if all pumps fail. If one of the pumps has failed, it must be quickly replaced to maintain the high reliability of the redundant system, since the reliability of a redundant (i.e. parallel) system drops significantly if one of the components fail.

The drainage system is usually not specifically equipped with sensors and monitoring systems. The information that often is available is the on and off signal for the pumps and/or the water level of the drainage pit. Some other signals, such as the motor current, may be available in some cases. The on and off cycles of the pump result in a quite regular pattern (see the left part of the figure) given that the pump and the surrounding systems work faultless. The pump pattern will change when the inflow changes (e.g. due to changed operating conditions of the plant, seasonal effects, or increased leakage water inflow to the drainage pit from faulty surrounding equipment) or when the capacity of the pump changes (e.g. due to pump degradation) [1]. Thus, the analysis of the pump cycles and the inflow pattern can indicate problems with the surrounding equipment, and the analysis of the pump capacity can indicate problems with the drainage pumps and drainage system.

Raw data, i.e. drainage sump water level (left), and pump capacity (right). Courtesy of K. Prajapati [2].

In a master student project carried out by NTNU master student Kishan Prajapati [2], a model for estimating the pump capacity was developed. This model considers the inflow and outflow of the drainage pit as a function of different operating conditions. Thus, it can – in addition to detecting changes in the pump capacity – also be used for detecting abnormal changes of the inflow. The model was developed and tested with data from Brattset power plant (2 x 40 MW, Francis, head: 273 m) were two drainage pumps are installed. The two pumps are used alternately. The estimated pump capacity is shown in the right part of the figure, where both the estimates for pump 1 (red) and pump 2 (blue) are illustrated.

Changes of the pump capacity can be seen at the points in time indicated in the diagram (1 September and 6 December). The pump capacity dropped significantly, by 5 to 7 %. The reason for this is not clarified, but maintenance carried out at the plant is a likely cause. Nevertheless, the example indicates that the approach may be used for detecting pump capacity changes, whether caused by maintenance, degradation of the pumps or other factors.

[1] F. Kvinen, "Model for condition monitoring of pumps in hydropower plants," Norwegian University of Science and Technology, Trondheim, Specialization project, Department of electric power engineering, 2017.
[2] K. Prajapati, "Condition monitoring of pump in hydropower plants," Norwegian University of Science and Technology, Trondheim, Specialization project, Department of electric power engineering, 2018.