Permanent Magnet Synchronizing Motor for UG, PSG, and SG Governors

Description

The permanent-magnet synchronizing motor is used to provide remote speed adjustment for an SG, PSG, or UG governor. The motor allows a switchboard operator to match the frequency of an alternator to that of other alternators or to change load distribution with other units when operating in the droop mode.

The synchronizing motors run only on nominal 24 Vdc power, but models are available with self-contained rectifiers which allow use of 110 Vac and 220 Vac supply. A potentiometer is included in most models. This allows the installer to match the motor with the type of supply available, and to set the motor speed within an adjustable range.

Four different PM motors have been used to adjust the speed setting of the governor. The S40, MM40, and MM4A have been used in the past. The current model is the SMM40. The SMM40 is directly interchangeable with any former speed-setting motor.

The SMM40 permanent-magnet motor operates on a nominal 24-Vdc supply. Rectifiers are included in models built to operate with ac supply. In addition a potentiometer is included with the unit which adjusts dc voltages to an acceptable level. An adjustable speed is achieved when a PM or APM motor control is added to the system.

Product Specifications

82044 APM Motor Control

82499 Adjustable Voltage Converter for 24 Vdc PM Motor Control

Adjustment

A friction-type slip clutch between the motor shaft and the governor allows speed adjustment by the regular manual speed-setting method or by the electrically driven PM motor. If this coupling has too little friction the motor drive will slip. With too great friction the manual speed adjustment will be too hard to turn or set.

The slip clutch also prevents damage to the governor or the speed adjusting motor when a maximum or minimum stop is attained. (The motor can continue to run for a short period after a physical stop has been reached.)

The clutch should be adjusted for about 0.5 Nm (4.5 lb-in) of friction. Individual governor manuals contain instructions on the maintenance and setting of the friction clutch.

Adjustment Procedure

(There are no adjustments on the MM4A.)

Unscrew the four round head screws (828, 515, 605) that hold the cover plate (825, 519, 602) on the potentiometer portion of the unit.

Loosen the lock nut (866, 511, 603) on the potentiometer, turning it counterclockwise. Turn the potentiometer adjusting shaft (865, 608, 530) clockwise (toward F on the Bakelite board (834, 510, 601) to increase motor speed, or counterclockwise (toward S) to decrease motor speed.

When the slot in the shaft points toward the white spot on the Bakelite board the potentiometer adjustment will be at about the rated speed.

After the adjustment has been satisfactorily completed, lock the nut on the shaft and replace the cover and four round-head screws removed in step 1 of this procedure. (Do not operate the engine for any extended period of time with the potentiometer and wiring exposed.)

Power Connection

If ac power is used for speed adjustment connect one line from the ac source to terminal "C" on the receptacle (831, 522, 609). The rectifiers (843, 518, 606) may burn out if the unit is incorrectly wired. (Review the wiring diagram on the next page and check against the wiring before applying power to the motor for the first time.)

Terminals "A" and "B" are connected to the respective output poles of the speed control switch.

Bearing Lubrication

Ball bearings are permanently packed with a high-quality grease. Repacking or periodic oiling is not required.

Gear Lubrication

The speed reduction gear housing (846, 528, 640, 733) is filled with enough lubricant to last about two years. Clean out the old grease every two years or as required and refill with Alvania No. 2 grease or its equivalent.

Troubleshooting

The speed setting motor is extremely long lived and reliable. Most problems perceived as caused by the motor are in reality caused by either the power supply to the motor or the friction clutch and speed-setting linkage in the governor.

Do not disassemble the motor until after all other causes have been thoroughly investigated. Make sure that the correct power is being delivered to the motor. Check the connection between the motor and the power source.

Excess load or low supply voltage will slow the speed of the motor. Motor load can be caused in the governor as well as in the sealed gears on the motor. Always check for load in the governor by trying to turn the manual speed setting knob before assuming that excess load is in the motor and attached gears.

Motor heat can be caused by low voltage, excess load, or internal wiring. Always check causes outside of the motor before determining that the motor is at fault.

Applied voltage can cause motor overspeed. Overspeed conditions are seldom caused by the motor itself.

Irregular motor speed can be caused by a slipping clutch, problems in the voltage supply to the motor, of by the motor itself.