Amperage load

To prove this to yourself, find the electric circuit breaker for a fan s motor. The amp (amperage) meter on the circuit breaker will have a black needle and a red needle. The black needle indicates the actual current, or amp load. The red needle is the amperage load that will trip the motor, as a result of overamping. Over time, as the tube bundle fouls and airflow through the bundle is restricted, the black needle never moves. 

Normally, increasing the flow from a centrifugal pump, increases the amperage load on the motor driver, as shown in Fig. 23.11. Driver... 

Increasing the size of the impeller by 10 percent will increase the amperage load on the motor driver by 25 percent. For many process pumps, this would require a new motor and breaker, to support the larger impeller. 

The operators were not running the turbine. The turbine was spinning, because it was coupled to the pump, but there was no motive steam to the turbine. The operators reported that the turbine was not needed, as the motor was pulling only 90 percent of its maximum amperage load. The question is, dear reader, whether the pump will run faster if the motive-steam flow is opened to the turbine. And the answer is, no. While the turbine will produce shaft work, and will help... 

This is not quite true. Whenever we start a pump, the starting torque required to get the pump spinning requires a surge of motor amps. To avoid tripping off the motor on high amps, there is a time delay built into the trip mechanism. This delay permits the amperage load to greatly exceed the FLA point, for up to 15 to 30 s. This is too brief a period in which to overheat the motor. 

The cause of this odd behavior is that the water level in the sump had dropped. A layer of oil with a specific gravity of 0.70 had been drawn into the suction of the pump. The feet of head developed by the pump had not changed. But a pump s discharge pressure and the amperage load on the motor driver is proportional to ... 

Another question What happens to the amperage load on a motor-driven centrifugal compressor, when the molecular weight of the gas increases I ask this question in the following context ... 

I hope that you can now see the intimate relationship between surge in a centrifugal compressor and the amperage load on the motor driver used to drive the compressor. Now, let s see if I cannot prove that the Second Law of Thermodynamics is quite in harmony with our practical experience. 

This seems like a rather large loss for a small, 2-psi pressure drop. But after the filter basket was pulled and cleaned, and the compressor was returned to service, the accuracy of the calculation was proved. About 10 percent more moles of gas could be handled, with approximately the same amperage load, on the electric motor driver. A nice example of the Second Law of Thermodynamics in action. 

The 2,000-bhp motor repeatedly tripped off on overload. This motor was driving a propylene vapor compressor. The propylene was being evolved from a propane-propylene splitter. The chief operator explained that whenever the pressure in the splitter tower rose above 105 psig, the motor would pull too many amps and trip off. To correct this situation, the chief pinched back on the block valve located in the compressor suction. The amperage load immediately fell, as did the compressor suction pressure. 

Setting the blade pitch cannot be done with great precision, and it s not too critical. I once increased the blade pitch from 15° to about 22°. Air flow increased by only 5 percent measured by the increased amperage load on the motor driver. 

Was there any reward for my efforts Yes. The amperage load on the cooling water pump motor was reduced from 60 to 50 amps—an improvement that was of no interest to my client. 

Normally, increasing the flow from a centrifugal pump increases the amperage load on the motor driver, as shown in Fig. 34.11. Driver horsepower is proportional to GPM times feet of head. As shown in Fig. 34.10, as the flow increases, the feet of head developed by the pump decreases. On the flat part of the pump curve, the flow increases rapidly, while the head slips down slowly. Hence the product of GPM times feet of head increase. 

As the specific gravity of the oil had dropped by 30 percent, so had the pump discharge pressure. The amperage load on the motor driver is also proportional to the weight of liquid pumped, which also changes with the specific gravity of the liquid. 

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