Overloading motors

Line Starters and Combination Starters A line starter consists of a contactor (motor-starting switch) and motor-overload relays, (Contactors are capable of canving and interrupting normal motor-starting and -running currents they are not, hovv ever, normally capable of interrupting short-circuit currents. They must be backed up by fuses or a circuit breaker for this function,... 

Individual fans are capable of operating over a range of volumes and pressures which are interrelated, the performance being shown in manufacturers tables and curves. Venturing outside the recommended area of operation may, depending on the type of fan, result in motor overload, motor under-cooling, vibration or stall. 

Motor overload indication through integrated temperature sensors. 

In addition to the basic control loops, all processes have instrumentation that (1) sounds alarms to alert the operator to any abnormal or unsafe condition, and (2) shuts down the process if unsafe conditions are detected or equipment fails. For example, if a compressor motor overloads and the electrical control system on the motor shuts down the motor, the rest of the process will usually have to be shut down immediately. This type of instrumentation is called an interlock. It either shuts a control valve completely or drives the control valve wide open. Other examples of conditions that can interlock a process down include failure of a feed or reflux pump, detection of high pressure or temperature in a vessel, and indication of high or low liquid level in a tank or column base. Interlocks are usually achieved by pressure, mechanical, or electrical switches. They can be included in the computer software in a computer control system, but they are usually hard-wired for reliability and redundancy. 

But there is a bigger problem than motor overload when increasing a fan s speed. The blades themselves are rated only for a maximum centrifugal force. This force increases with increased fan RPM. At some maximum speed, the blades fly apart. Gentle reader, you can imagine how I became so smart on this subject. 

The control system is designed to sense certain component and system failures. Pressure switches are located to sense overpressure, excessive suction, low chlorine pressure, and low eductor vacuum. A flow switch senses low flow. Motor starters sense motor overloading. Evaporator low-temperature switch senses low water temperature. 

Check motor overload (3) Should be energized, if not, problem is... 

For most evaporative units, the steam flow is directly proportional to the production rate and to the temperature rise in the recirculation system and the AT" in the heat exchanger. Both of these values have an important influence on the scaling rate in cases where materials of inverted solubility are being handled or where there are scale-forming components within the system. In systems where this value is critical, the AT can be monitored and used to reset the steam rate. An interlock should be provided that will cut off the steam flow to the system if the circulating pump or propeller circulator in a draft tube baffle unit is off due to motor overload or power failure. 

Motor overload protection, settings, status, pre-alarms and time to trip. 

Oh, come on, Andre, you can t use this again. The motor overloaded when Erick dumped the atmosphere. There s no telling what internal damage the voltage spike caused."... 

PRESSURE REGULATOR, SUCTION (REFRIGERATION COMPRESSORS) -An automatic valve designed to limit the suction pressure to prevent motor overload. 

Feeder screw conveyor Shear pins on feeder drive break screw diameter < exit hole from bin. Motor overload on feeder drive screw conveyor diameter < exit... 

Feeder belt feeder from the bottom of a hopper Belt feeder initially starts but suddenly stops with motor overload gap between the belt and hopper interface edge is too small/belt sags between pulleys/large FDI and small % difference between FDI and BDI. 

POSSIBLE CAUSES Motor not running Unload solenoid valve not closed Pump/shaft damaged REMEDY A Check disconnects, motor overloads, motor A Replace A Replace pump... 

As the actual flowrate increases beyond the design point, a decrease occurs in the NPSH available to the pump because of additional pressure drop in the suction piping. At the same time, the NPSH required by the pump is increasing with flowrate so that the NPSH-available and NPSH-required curves intersect as shown in Figure 25-6. This point of intersection represents the onset of cavitation because of formation of vapor bubbles. Motor overload may also occur at unexpectedly high flow rates. 

Multiple discrete sensors are connected in series to a single input and the sensors all monitor the same process condition (for example, motor overloads). 

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