Electric motor vibration diagnostics is a non-destructive testing method in which the condition of the bearings, rotor, couplings and magnetic system is determined from the vibration spectrum of the machine body. At industrial enterprises in Tashkent, vibration diagnostics remains the most informative way to identify emerging defects before the engine fails. According to statistics from the Elektromotors service center, timely vibration control prevents up to 70% of unplanned downtime of pumping and compressor equipment.
Types of vibrations of an electric motor
Before choosing a device and measurement points, you need to understand the nature of vibrations. All vibrations of an electric machine are divided into two large groups - mechanical and electromagnetic. Their frequency range and phase pattern differ, and this is what allows the diagnostician to localize the defect.
Mechanical vibrations
- Rotor imbalance - rotation frequency 1×frev, amplitude increases with the square of the speed.
- Miscentering of the shafts - harmonics 2×fvr and 3×fvr, axial component is high.
- Defects in rolling bearings - characteristic frequencies BPFO, BPFI, BSF, FTF in the range of 500–10,000 Hz.
- Loosening - broadband spectrum with a whole range of harmonics.
- Shaft bending or deflection - growth 1×fb in the radial and axial direction simultaneously.
Electromagnetic vibrations
- Air gap eccentricity - peaks at double network frequency 2×fc (100 Hz).
- Breakage of the short-circuited cage rod - side bands around 1×fvr at a frequency of 2sfc.
- Stator interturn short circuit - increase in 100 Hz and odd harmonics of the supply network.
- Power asymmetry - spectrum modulation by sliding frequency.
It is easy to distinguish the electromagnetic nature from the mechanical one: when the power is turned off, the electromagnetic component disappears instantly, and the mechanical component fades as the rotor runs out. This is a basic test that an Elektromotors engineer performs on every visit to the customer's workshop.
Vibration measurement equipment
The fleet of vibration measuring equipment in Tashkent has been significantly updated over the past twenty years. In production there are both Soviet and modern imported devices - they all have their own niche.
Vibrometer SD-12 and analogues
The domestic device SD-12 and its modifications (SD-21, VVM-201) are two-channel analyzers with piezoelectric sensors. They measure RMS vibration velocity in the range of 10–1000 Hz according to GOST ISO 10816. Suitable for incoming inspection after repair and periodic walk-throughs. Simple interface, autonomous power supply, price lower than imported analogues by 3–5 times.
IRD Mechanalysis
American IRD systems (models 880, 890) have long been the standard in the oil and gas industry. Full spectral analysis FFT up to 20 kHz, envelope for bearings, ability to build trends. For large enterprises in Tashkent, where the engine fleet exceeds 300 units, IRD is still optimal.
SKF Microlog and SKF @ptitude
Modern SKF data collectors (CMXA 75, CMXA 80) are integrated with @ptitude Analyst software. They support route detours, automatic diagnostics using an expert system, and phase angle measurement. For enterprises with a PdM (Predictive Maintenance) system, this is the default choice. Also popular are the Adash A4400 VA4 Pro and the Russian SM-3001 Baltech.
Vibration standards according to ISO 10816
The main international document is ISO 10816 (in Russia and Uzbekistan it acts as GOST ISO 10816). The standard divides machines into four classes based on power and rigidity of supports and establishes vibration zones: A (new machine), B (long-term operation without restrictions), C (limited operation), D (dangerous condition, immediate stop required).
| Machine class | Power | Zone A, mm/s | Zone B, mm/s | Zone C, mm/s | Zone D, mm/s |
|---|---|---|---|---|---|
| Class 1 | up to 15 kW | ≤ 0.71 | 0.71–1.8 | 1.8–4.5 | > 4.5 |
| Class 2 | 15–75 kW | ≤ 1.12 | 1.12–2.8 | 2.8–7.1 | > 7.1 |
| Class 3 | > 75 kW, rigid foundation | ≤ 1.8 | 1.8–4.5 | 4.5–11.2 | > 11.2 |
| Class 4 | > 75 kW, flexible foundation | ≤ 2.8 | 2.8–7.1 | 7.1–18.0 | > 18.0 |
In practice, for a new 55 kW motor, after rewinding the winding we achieve a vibration velocity of 1.0–1.2 mm/s. If the reading exceeds 2.8 mm/s, rotor balancing or alignment check is required.
Spectral analysis basics
The temporal vibration acceleration signal is converted into a frequency spectrum using the fast Fourier transform (FFT) method. Spectrum analysis allows you to “decompose” the total vibration into individual sources. Basic rules of interpretation:
- Determine the rotation frequency 1×frev = n/60, where n is revolutions per minute.
- Find the peaks at 1×, 2×, 3× fvr - these are mechanical harmonics.
- Check 100 Hz and its harmonics - this is the electromagnetic component.
- For bearings, enable the envelope spectrum in the range of 500–10,000 Hz.
- Compare the spectrum in three directions: vertical, horizontal, axis.
An experienced diagnostician makes a diagnosis with an accuracy of 85–90% within 5–10 minutes using the spectrum. Confirmation is obtained by repeat measurement after adjustment or bearing replacement.
Table of fault symptoms
| Defect | Peak frequency | Direction | Additional feature |
|---|---|---|---|
| Rotor imbalance | 1×fvr | Radial | Phase is stable, amplitude increases with n² |
| Parallel misalignment | 2×fvr | Radial | Phase shift 180° between supports |
| Angle misalignment | 1× and 2×fwr | Axial | High axial component |
| Shaft bend | 1×fv | Axial + radial | Axial > 50% radial |
| Bearing wear (outer ring) | BPFO | Radial | Side stripes in envelope |
| Bearing wear (inner ring) | BPFI | Radial | Reverse frequency modulation |
| Gap eccentricity | 2×fс (100 Hz) | Radial | Disappears when the network is turned off |
| Broken rotor rod | 1×fvr ± 2sfc | Radial | Side stripes on sliding |
| Looseness | 0.5×, 1×, 2×, 3× fwr | Vertical | Wide range of subharmonics |
| Coupling defect | 1× and 2×frev | Axial | Increase in coupling temperature |
When to order vibration diagnostics
At Tashkent enterprises, we recommend three scenarios: scheduled walk-throughs every 30–90 days for critical equipment, monitoring after any repair of an industrial electric motor and emergency departure in the event of noise, heating or an increase in current consumption. For crane electric motors cyclic mode, the schedule is drawn up individually taking into account the duty cycle.
If the vibration background has increased at your production site in Tashkent, a hum has appeared, or current protection has tripped, contact Elektromotors specialists. We will measure vibration velocity and vibration acceleration, build an FFT spectrum, decipher the defect and propose a elimination plan. More information about the service can be found on the page electric motor diagnostics or by phone in the contacts section.