The motor magnetic structure and- windings are designed to obtain certain desired characteristics of torque and speed. *Over-voltage (at higher noise) can be tolerated better than under-voltage provided current is limited to nameplate rating. This table shows nominal voltage for which polyphase motors are usually made, and the maximum voltage range over which they can be operated (10% variation from nominal rating). If the voltage loss in any phase is more than 3% check for high resistance in wiring, connections, fuses, circuit breaker, or disconnect switch.
ELECTRIC MOTOR WINDING DATA SHEET FULL FULL
With the motor running at full load, compare the voltage of each phase at the motor with voltage readings taken at the power line entrance. If unbalanced more than 3½% at that point, call the utility company for an inspection and corrective measures. Corrective measures may be taken as follows:Ĭheck for voltage unbalance of each phase where the power line enters the building. If the higher voltage advances with the re-connection, the power line is unbalanced. Then, advance all power lines by one phase and repeat the measurements. To determine where the fault lies, first measure the voltage of all phases. If the voltage, at full load, is unbalanced between phases, either the motor is defective or the power line is unbalanced. On installations where the motor s running at or very near full HP, an unbalance of as little as 3½% between the highest phase voltage and the average of all three voltages may result in a temperature rise of about 25% above the normal rated rise, causing damage to the insulation. Also, the motor noise will greatly increase, and may be objectionable. The wiring, fusing, and thermal overload protection will have to be sized accordingly. However, its starting current and breakdown current (at stall) will be higher than normal. If the motor is not loaded beyond nameplate HP, the full load current will be lower than rating and the motor will run cooler than its rating. Therefore, it should be de-rated to 0.945 × 25 = 23.6 HP (plus service factor if applicable).Įffects of High Voltage. For permanent operation on a voltage source known to be low, the HP rating should be reduced by the same percentage that the voltage is low.Įxample: A 25-HP, 220 volt meter on a 208-volt line has only 94½% of its rated voltage. Motors can usually accommodate as low as 90% of rated voltage, and although there will be an abnormal temperature rise, it will not be great enough to damage insulation. If the voltage is too low, then to produce rated HP the current becomes too high, and this causes an abnormal temperature rise. HP output is a combination of voltage times current. Nameplate HP rating is based on full voltage being available. Any operating condition such as low voltage, wrong frequency, or torque overload, which causes current in excess of nameplate rating to flow, will cause an abnormal temperature rise.ĭesign B motors (most often used on pump drives) can start under full load, but if they must be started frequently, the pump should be unloaded until the motor starts, to prevent high starting current from overheating the motor.Įffects of Low Voltage. Current is also responsible for temperature rise in the windings. Torque is produced by current flow the higher the current the greater the torque output. Except for a small amount of speed slip at full load condition, it will not run at slower speeds with out severely overheating.ĭesign B Motor Speeds - Synchronous and Full Loadįull load RPM in the chart has been calculated on a drop in speed (slip) of about 3% from the theoretical or synchronous speed. The motor runs at a constant speed determined by the line frequency (Hertz) and by the number of pairs of magnetic poles which it has.
All windings are on the stator which is also constructed of iron laminations with various numbers of north and south poles (in pairs). This type motor has a rotor made up of iron laminationsbut does not have a winding on the rotor therefore, it has no brushes, commutator, or slip rings. Information in this issue applies only tothis type and may not be applicable to other types. The motor type used on most hydraulic pump drives is the 3-phase, squirrel cage, induction motor, of integral HP in therange of 1 to 500 HP. Motor housings, fusing, thermal overload protection, and motor starters will be covered in a later issue. Additional information in the present issue covers other important areas which may affect the selection of the best motor type for a specific job.
ELECTRIC MOTOR WINDING DATA SHEET FULL HOW TO
3-PHASE, INDUCTION-TYPE, ELECTRIC MOTORS FOR PUMP DRIVEĭesign Data Sheet 3 shows how to determine motor HP required to drive a hydraulic pump rated for (so many) GPM at a certain PSI level.