* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Instructions For Rotation Check of Large Motors
Survey
Document related concepts
Switched-mode power supply wikipedia , lookup
Electric machine wikipedia , lookup
Opto-isolator wikipedia , lookup
Power engineering wikipedia , lookup
Electrification wikipedia , lookup
Alternating current wikipedia , lookup
Mains electricity wikipedia , lookup
Tektronix analog oscilloscopes wikipedia , lookup
Oscilloscope history wikipedia , lookup
Voltage optimisation wikipedia , lookup
Electric motor wikipedia , lookup
Three-phase electric power wikipedia , lookup
Brushless DC electric motor wikipedia , lookup
Oscilloscope types wikipedia , lookup
Brushed DC electric motor wikipedia , lookup
Induction motor wikipedia , lookup
Transcript
Oscilloscope Method for motor phase rotation check by electricpete Problem Statement: Commercial motor phase rotation meters require manually accelerating the rotor from rest very rapidly, in order to clearly distinguish the direction of initial deflection of the meter needle. This works well for small motors, but does not work for large motors which cannot be rapidly accelerated rapidly due to high inertia. The commercial phase rotation meter gives ambiguous or subjective results for large motors. Solution: An alternate method is presented which does not require rapid acceleration, and therefore is suitable for large motors. This alternate method uses an oscilloscope to monitor the steady-state sinusoidal voltages generated by the rotor residual magnetism when manually rotating the motor slowly in the normal direction of rotation. This method has been successfully applied to verify rotation on several large motors including 2 Reactor Coolant Pump motors at our plant. Theory: The rotor core retains a small amount of residual magnetism which will induce a few hundred millivolts of voltage in the stator when the rotor is manually rotated. The phase rotation sequence of the voltage generated during manual rotation of the motor in the normal direction is the same as the phase rotation sequence of the voltage which would cause the motor to rotate in the normal direction when energized from the power system. This principle is exploited in the methods below. Phase-To-Neutral Voltage Method: If the motor neutral is accessible, then phase-to-neutral voltages could be monitored with an oscilloscope while manually rotating the motor in the normal direction. Table 1 illustrates the two possible outcomes, which are described as motor phase rotation sequence T3/T2/T1 or T1/T2/T3. Table 1 - Phase to neutral voltages while rotating motor forward for T3/T2/T1 and T1/T2/T3 motor sequences Motor T3/T2/T1 Sequence Motor T1/T2/T3 Sequence The motor-to-power-system connection T1-A, T2-B, T3-C can be used in either of the following situations: Motor is T3/T2/T1 sequence and power system is C/B/A sequence Motor is T1/T2/T3 sequence and power system is A/B/C sequence For the remaining 2 scenarios (Motor is T3/T2/T1 and power system is A/B/C…. OR motor is T1/T2/T3 and power system is C/B/A), then motor leads should be relabeled or an alternate connection should be selected (for example T1-B, T2-A, T3-C). However, neutral leads are not always available, so a method which relies on phase-to-phase voltages rather than phase-to-neutral voltages is preferred. The remainder of this whitepaper/procedure will address the phase-to-phase method. Phase-To-Phase Voltage Method: This method is more general since it can be applied regardless of whether neutral leads are available. A 2-channel oscilloscope is selected since it is more readily available than a 3-channel oscilloscope. As shown in Figure 1 of the detailed procedure below, oscilloscope channel A will record Vab=Va-Vb and oscilloscope channel B will record Vbc=Vb-Vc. Phasor Diagrams are shown in Table 2 below. For these diagrams, the direction of phasor rotation is arbitrarily assumed to be CCW (this need not correspond to direction of motor rotation). These phasor diagrams prove that if the motor generates voltage in a T3/T2/T1 sequence, then channel B will lead channel A…. and if the motor generates a T1/T2/T3 sequence then channel A leads channel B. Table 2 - Phasor Analysis (T3/T2/T1 Sequence... Ch B leads Ch A) Phasor Drawing Ch A T2 Ch B T1 N T3 Ch B N T2 T3 Phasor drawing, redrawn to emphasize relationship of Channels A and B (T1/T2/T3 Sequence... Ch A leads Ch B) Ch B Ch A T1 Ch A Ch A Ch B Expected oscilloscope pattern Description of Channel B leads channel A Channel A leads channel B oscilloscope pattern Motor sequence is compared to power system sequence in a similar manner to the phase-to-neutral voltage test above. The entire phase-to-phase voltage method is described in a detailed procedure below which is suitable for craft instructions. Detailed Procedure For Rotation Check of Large Motors (Phase-to-phase method) Equipment: Fluke 199B 2-channel Scopemeter or equivalent isolated-channel instrument. (Almost any modern battery-powered oscilloscope has isolated channels). Hookup up test equipment as shown in Figure 1 (T1 to Channel A+, T2 to channel A- and channel B+, T3 to channel B-). For the Fluke 199B, double-ended probes (Figure 3) should be connected to “input A” and “input B” ports (Figure 4). Figure 1 – Connection of 2-channel oscilloscope to motor T1 Motor + + T2 Channel A Two Channel Oscilloscope Channel B T3 Set up oscilloscope for monitoring two channels. Suggested steps for Fluke 199B are as follows: Reset Fluke 199B to factory default settings as follows: Start with the Unit Off Press and hold User. Press/Release On button briefly. Unit comes on and beeps twice. Release user. The unit will now be on, in scope mode, monitoring channel A. Add channel B trace as follows; Press B, Press F2, and Press B again Use the vertical move buttons to separate the A and B traces. Adjust horizontal time scale to aprox 1 second per division by pressing left side of the “time” button (labeled second) several times. Adjust range button (V or mV) to adjust vertical range to approx 100 mV per division. Energize oil lift pump, if applicable. Rotate motor in normal direction of rotation. Observe oscilloscope pattern (The “save” button may be used to freeze the display on the Fluke 199B). Compare results to Figure 2 to determine if the motor voltages sequence is T3/T2/T1 or T1/T2/T3. Figure 2- Interpretation of Oscilloscope Results Ch B leads Ch A, signifying T3/T2/T1 motor sequence Ch A leads Ch B, signifying T1/T2/T3 motor sequence How to connect motor to power system: The connection T1-A, T2-B, T3-C can be used in either of the following situations: Motor is T3/T2/T1 sequence and power system is C/B/A sequence (STP has C/B/A sequence) Motor is T1/T2/T3 sequence and power system is A/B/C sequence For the remaining 2 scenarios (Motor is T3/T2/T1 and power system is A/B/C…. OR motor is T1/T2/T3 and power system is C/B/A), then motor labels should be relabeled or an alternate connection should be selected (for example T1-B, T2-A, T3-C). (contact Engineering prior to relabeling or alternate connection). Figure 3 - Photo of Double-Ended Oscilloscope Probes and Connections Figure 4 - Fluke Inputs Figure 5 - B leads A indicating T3/T2/T1 Sequence