Offline Testing on Rotating Electrical Machines
Rotating electrical machines are critical for power generation and running critical processes in industrial applications. However, performance and reliability can be compromised over time due to the thermal, electrical, ambient and mechanical stresses motors and generators are continuously subjected to when in operation.
We have identified a set of essential off-line electrical diagnostic methods that will help you to perform complete on-site condition assessments of your motors and generators.
Partial Discharge Measurement and Analysis on Rotating MachinesShow more
Partial Discharge Measurement and Analysis on Rotating Machines
Partial discharge (PD) occurs in the stator insulation system of rotating machines, where local electric field stress exceeds the local electrical strength. Compared with other dielectric tests, the differentiating character of partial discharge measurements allows localized weak points of the insulation to be identified.
PD measurements based on IEC 60034-27 standards can be performed off-line on motors and generators by energizing each winding successively during standstill of the machine.
Dissipation/Power Factor and Capacitance (TanDelta) Measurement on Rotating MachinesShow more
Dissipation/Power Factor and Capacitance (TanDelta) Measurement on Rotating Machines
The insulation is the most sensitive part of rotating machines. The lifetime of a stator winding depends on how effectively the electrical insulation can prevent any occurrence of winding faults.
Aging processes, changes in the structure of the insulation or moisture ingress can, for example, increase the dissipation factor. With capacitance and dissipation factor measurements, also known as tan-delta measurements, changes in the insulation can be reliably diagnosed.
Stator Electrical TestsShow more
Stator Electrical Tests
In addition to dissipation/power factor measurements, partial discharge measurement and analysis and dielectric response analysis, there are other common stator electrical tests that can be performed. They assess the insulation integrity and help to identify connection problems and weak points in the stator winding.
These additional tests include voltage withstand testing, insulation resistance, polarization index and dc winding resistance measurements, as well as inter turn fault detection.
Electromagnetic Imperfection TestingShow more
Electromagnetic Imperfection Testing
The electromagnetic imperfection test (also known as a stray flux measurement) is performed to detect stator core interlamination imperfections that can eventually cause overheating and damage to the stator core of motors and generators when in operation.
Stator core measurements should be performed on a regular basis to evaluate the insulation integrity between the stator core layers of a machine during factory acceptance testing and commissioning, as well as after the machine is in service.
Contact Resistance Measurement on Rotating MachinesShow more
Contact Resistance Measurement on Rotating Machines
Contact resistance measurements are performed to detect loose connections as well as oxidized or damaged contact surfaces on machine pole connectors. These defects generate hot spots, which can lead to disconnection of the poles. DC current and DC voltage are measured at the same time for each pole connector of the rotor.
These measurements are compared to one another and to previous measurements to calculate the contact resistance.
Pole Drop Testing on Rotating MachinesShow more
Pole Drop Testing on Rotating Machines
Mechanical stress in rotor windings cause inter turn faults (short circuits), which can lead to magnetic imbalance in generators and motors. This causes higher shaft vibrations, resulting in stress and damage to the bearings. Similar to sweep frequency response analysis (SFRA), the pole drop test is performed on single pole windings when the machine is in a standstill condition.
An AC current is injected into the slip rings to energize the pole windings. By measuring the voltage drop of every pole between the pole winding connectors, the impedance can be determined.
Inter Turn Fault Detection on Rotating MachinesShow more
Inter Turn Fault Detection on Rotating Machines
Sweep Frequency Response Analysis (SFRA) is used to detect inter turn faults caused by mechanical stress in the pole windings and stator windings of electrical machines.
The electrical circuits in the stator and in the rotor are complex network of capacitance, inductances and resistors with their own frequency response. Any defects in the windings result in a change of the corresponding frequency response. The measurements of different poles enable fault detection.