Replacing motors with third-level energy efficiency with second-level energy efficiency motors does not result in energy savings
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At present, the company has replaced a batch of new motors with secondary energy efficiency ratings. During use, it was found that the operating current under the same conditions was higher than that of motors with tertiary energy efficiency ratings. Electricity meter readings showed that, over several days, the average daily consumption was only 1 kilowatt-hour less compared to motors with tertiary energy efficiency ratings. I would like to ask everyone: Is the energy efficiency value indicated on the motor’s nameplate referring only to its efficiency at rated power? If the motor does not operate under its rated conditions, could its efficiency be lower than, or even equal to, that of a conventional three-star energy-efficient motor? What I want to ask is: under the same operating conditions but at a power level other than the rated one, does a motor with class 2 energy efficiency necessarily use less power or be more efficient than a motor with class 3 energy efficiency? Has anyone else encountered this? Please share your insights!
@yaohero @qhwangyz @sdykghlxc @dongyihao2008 All the experts, please come and take a look at what’s going on :lol
Ahah, dear sea friend, the efficiency on the motor’s nameplate definitely refers to that at the rated supply voltage and current! Under the same operating conditions, the current drawn by the motor is higher than that of a motor with grade 3 energy efficiency, which indicates an increase in the motor’s active power output and a reduction in its mechanical or electrical losses (an additional 1A is used for active power output), resulting in improved efficiency! This is equivalent to increasing the motor’s output power, which is used to drive equipment to perform work; the benefits may include an increased flow rate of the pump, a higher rotation speed, or more products being produced, among other things. Conversely, the originally chosen non-energy-saving motors consumed too much reactive power, forcing him to opt for motors with higher power ratings; now, it’s possible to reduce the rated power of the motors chosen (depending mainly on the shaft power required by the equipment!) At the same time, the motor’s output current increases, the active power rises, and its power factor improves; as a result, less reactive power compensation is required by the system. The transmission of reactive power over the lines is reduced, allowing for a more optimized capacity of the overall power system (especially in large projects with numerous electrical devices, where this optimization leads to lower investment costs). When the motor operates under non-rated conditions, with a load factor of 0.6 to 1, its efficiency will certainly be higher than that of conventional three-level energy-efficiency motors!
First of all, thank you for your reply; I still gained something from it. But there are still doubts. It wasn’t specified when the post was made. 1. The motor in question is a 15KW motor with a rated current of 29.6A, an efficiency of 90.6%, and a power factor of 0.85; it belongs to the fourth class of motors. The operating current, as determined by three measurements, averages 24.3A, with a speed of 1240 ； After replacement, it has a power of 15Kw, a rated current of 28.8, an efficiency of 92.1%, and a power factor of 0.86. The operating current is 25.8A, obtained as the average of three measurements, with a speed of 1266. The operating current is 1.5A higher than before; how can this be explained? 2. The rated current of the new motor is lower than that of the old motor! Why is the current of the new motor higher under the same operating conditions (as I think, though it might not be correct)? According to your explanation, the current of the new motor should be higher than that of the old motor both at rated load and under the part-load conditions mentioned earlier! 3. Our pumps are heat transfer oil pumps that regulate temperature; if the pump rotates too fast and pumps out too much fluid, my control valve will automatically adjust, so my load can be considered constant.
Ahaha, hello there, sea friend! Based on the data you provided, we can calculate that the actual output power of the motor before replacement was 12.316 KW, while after replacing it with an energy-saving model, the actual output power of the motor reached 13.45 KW. Under the same operating conditions, since the motor’s output power is higher, the flow rate output by your pump will definitely increase. Perhaps the opening degree of your control valve isn’t very significant; however, if there is a flow meter, it will definitely show an increase in flow rate – there should be a trend of increase. If there is a cumulative flow function, it definitely should be displayed! Let me give you an example. When riding a bicycle, those who have more strength – in other words, higher power output – will definitely ride faster. That is, within the same amount of time, they cover a greater distance; their efficiency is different! This is also why high-efficiency motors have a higher rated speed! With this explanation, it should be understandable now!