Standard 10 hp, 1800-rpm, 208-230/460-V, 3-phase electric motor in 215TC frame size with feet. This model is totally enclosed and fan cooled, with a NEMA F-1 mounting for the junction box.
The obvious point is that the electric motor is a critical part of any power unit. Therefore, understanding the basic parameters of electric motors is key when specifying one for a particular HPU application. Five basic factors must be considered:
1. Horsepower — the designation of power you need from your system — 5 hp, 10 hp, 20 hp, etc. Note that a service factor (1.15 on standard units) lets motors run above their rated horsepower for intermittent periods.
Locked-rotor torque, also called startup torque, is an issue when any motor must start under load. The common locked-rotor torque is 100% of full-load torque, but we recommend that you select a motor that is designed to provide a more generous 140% or greater locked-rotor torque.
2. Rotational speed (rpm) — how many complete revolutions the motor shaft makes in a 60-second period. Most ac motors run at nominal fixed speeds of 3,600, 1,800, 1,200, or 900 rpm. Most hydraulic pumps for industrial applications are designed to run at 1,800 or 1,200 rpm. These lower-speed motors are more efficient, and have fewer balance problems than those operating a higher speeds.
3. Voltage and phase — determined by the electric service that will power the motor. Most motors operate at 230 or 460 Vac, 3-phase. When specifying voltage for an electric motor, always cite the number of phases. Single-phase is normally associated with residential and commercial power, whereas 3-phase is associated with industrial power — and is most commonly used in power unit applications.
4. Frame size and configuration — the National Electrical Manufacturers Association (NEMA) has established detailed standard motor dimensions for interchangeability. The motors on most power units mount to the pumps via flanges and are supported by feet. However, some mountings require no feet. Make sure you specify feet (or base) or no feet (round body) when ordering. (Many designers select direct coupling to attach the motor to a pump because this arrangement saves space.)
Also, where is the junction box on the motor? When looking at the motor from the shaft end, the standard location for the junction box on the left hand side (designated an F-1 mount). If you need a motor with the junction box on the right-hand side, make sure that you specify an F-2 mount.
Finally, a short shaft (known as a TS frame) should be specified on all 1800- or 1200-rpm motors. This may require a modification of the basic motor. It’s important to note that most manufacturers do not stock special motors, so some extra lead time should be expected on F-2 mount, short shaft, or round body models.
5. Enclosure — protect the motor’s internal parts from moisture, while still allowing cooling. Open drip-proof motors (which are cooled by the outside atmosphere) can be used where ambient conditions are fairly friendly. The more-expensive alternative, totally enclosed fan-cooled motors afford maximum protection even in a hazardous or aggressive environment. After the five basics have been established, you can request several different documents from your motor vendor to help you finalize your selection — and provide information for the end user if he or she will be someone else.
