Mitchell Instrument Co. - best price for Test and Measurement, Safety, NFPA 70E Arc Flash

Skip to Main Content »

Search Site
For the Very Best Price, Call us at: (888) 270 2690

Phase Sequence and Motor Rotation

Phase Sequence Indicators

The phase sequence indicator is a device used to compare the phase sequence of three-phase generators or motors. The indicator is typically a small three-phase induction motor with three leads labeled 'A', 'B', and 'C' that are colored red, white and blue.The rotor in the instrument can be observed through the three ports as it turns so that you can note the direction in which it rotates.   The rotor can be started by means of a momentary contact switch: it, stops again when you release the switch. Whichever  light  is  on indicates the phase sequence of the voltage in the conductors that the instrument is connected to; for example, the light labeled "ABC" indicates one phase sequence,  while  the  other  light,  labeled  "BAC," indicates another.

Motor Rotation Direction

When installing a motor, determining the rotation direction is critical to the operation of the motor. A phase rotation meter compares the phase rotation of two different 3-phase connections. Three leads, labeled "A," "B," and "C," are connected to the test unit's side labeled "MOTOR." Three other leads are labeled the same but are connected to the opposite side of the test unit, which is labeled "LINE." The meter contains a zero-center voltmeter, with one side labeled "INCORRECT" and the other labeled "CORRECT." Correct motor installation is dependent on this proper phase hook-up.

Example Operation
Motor Connection for a 9-Wire, 3-Phase, Dual-Voltage, Single-Speed, Delta Connection.
In the delta-connected winding, one terminal in each group is common to two winding sections. This terminal can be identified by using the motor rotation circuit as a bridge. Connect all three MOTOR leads together. Set the selector switch to the MOTOR position. Operate the ZERO ADJ. control to bring the meter pointer to zero (center). Connect the three MOTOR leads to the three terminals of the group in any order. Observe the meter deflection. Reverse the A and B MOTOR leads. Again observe the deflection. Reverse the B and C MOTOR leads. Note the deflection. Return to the connection that gave the smallest deflection of the meter. At this point, the B MOTOR lead is connected to the common terminal. Now make a motor rotation test with the leads connected as above ; rebalance the tester if necessary, using the ZERO ADJ. control, and then turn the motor slightly in the direction in which it is desired to run. If no preferred direction is specified, turn it clockwise when viewed from the drive end. If the deflection is in the INCORRECT direction, reverse MOTOR leads A and C. When the CORRECT deflection is obtained, the terminals in the group should be marked according to the MOTOR lead markers. The number 1 should be used as a prefix to identify the group. Thus, the terminal connected to the A MOTOR lead is marked 1A. The common terminal is marked 1B, and the remaining terminal 1C. Select a second group of leads. Determine the common terminal and rotation in the same manner as described above. In tagging these terminals, the prefix number is temporarily omitted. The terminals are tagged A, B, C. If done properly, B will mark the common lead. At this stage, the identification of terminals has reached the point shown in the figure. It remains to be determined whether this second group belongs in the 2 or 3 position. This can be determined by an induced voltage test that indicates whether coil A-B or coil B-C is in phase with coil 1B-1C. By continuing to apply similar steps, the entire configuration can be determined. Similarly, appropriate modifications of the general procedure can be employed to determine other types of winding configurations.

Items 1 to 9 of 16 total

per page
Page:
  1. 1
  2. 2

Grid  List 

Set Descending Direction

Items 1 to 9 of 16 total

per page
Page:
  1. 1
  2. 2

Grid  List 

Set Descending Direction
Thank You For Shopping with Mitchell Instrument Company Inc.® - 1570 Cherokee St. San Marcos CA 92078 - Phone: (760) 744 2690 - Fax (760) 744 0083