Notes on the alarm settings and shutdown setting values for the cooling tower reducer oil level

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Points to note regarding the setting of oil level alarm values and shutdown values for cooling towers: There are generally two types of data related to the oil level of the lubricating oil in the cooling tower’s reduction gearbox: one is the level when the unit is at rest, and the other is the level when it is in operation. Due to the high viscosity and poor fluidity of the lubricating oil, the oil level in the gearbox changes significantly at the beginning of operation. The lubricating oil fills the gaps around the bearings; more importantly, the rotation of the gears and the planetary gear set inside the gearbox causes the lubricating oil to be lifted and thrown against the inner walls of the gearbox. Because of its high viscosity, this oil cannot settle back down immediately, resulting in a significant drop in the oil level. Therefore, the oil level alarm values and shutdown thresholds cannot be set based on fixed values from before; they must be determined based on the oil level under static conditions as well as the data obtained under dynamic operating conditions. Generally, oil is added to the gearbox between the lowest and highest oil levels. However, since the markings for indicating the oil level are not very precise, it is sufficient to fill it within the specified range; as a result, the oil filling level varies from one gearbox to another. When the reduction gearbox starts operating, the amount by which the oil level in each gearbox decreases will vary. In such cases, when setting the alarm values and shutdown values, it is necessary to use the minimum oil level as a reference. For example, for three cooling tower reducers, the oil levels at rest are 27 mm, 38 mm, and 22 mm. When the machines start operating, the oil levels drop to 14 mm, 23 mm, and 10 mm respectively. If we use the conventional fixed values – an alarm threshold of 30 mm and a shutdown threshold of 20 mm – then the cooling towers will trigger alarms and shut down automatically. However, if the alarm threshold is set to 5 mm and the shutdown threshold to 2 mm, this problem can be avoided. It is also possible to set the shutdown value to 0 mm; although 0 mm represents the level at which fueling should stop, it is not recommended to set the shutdown value at this level. After all, there is a margin of error in the probe, and for the sake of having a higher safety factor, it is better to set the value to something greater than 0 mm. In the case of the probe with the three-parameter combination, if the length of the probe rod is not customized based on the lowest and highest oil levels in the gearbox, then a longer probe rod will result in less noticeable drops in the detected oil level. If the shutdown point is set at 20 mm, it might be possible to avoid shutdowns caused by alarms in the cooling tower; however, the oil level readings will then be inaccurate. As a consequence, when the gearbox actually starts leaking oil to levels below zero, the readings will still indicate a level above zero, which can lead to abnormal wear of the gears and even their destruction. Therefore, for manufacturers of three-parameter combination probes, it is essential first to ensure high detection accuracy and precise measurements by the probe rod; the shutdown settings are relative and are determined based on parameters under static and dynamic conditions. This approach not only ensures detection accuracy but also prevents cascading shutdowns. Technical Department of Changzhou Tianchuan Electromechanical Technology Co., Ltd. 2020-05-08