Insulation Deterioration Detection in Electric Machines
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Solution Overview
Problem
Existing methods for detecting insulation deterioration in electric machines, particularly inverter-controlled ones, are either offline and not continuous or complex and time-consuming, lacking a reliable and cost-effective online monitoring solution.
Innovation Solution
A method and device that apply a stepped voltage to the machine windings, using existing current sensors to detect the current and its derivative, oversampling at high frequencies to analyze characteristic parameters like overshoot, natural frequency, and damping constant for early detection of insulation deterioration, without requiring additional high-precision sensors or complex setups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offline testing methods like Surge Test are used to detect insulation deterioration, then measurement precision is improved, but productivity deteriorates because tests cannot be carried out continuously and only at long time intervals
Solution Approach 1:
The patent applies preliminary action by performing insulation testing during the motor startup phase before the motor begins rotating. The surge voltage is applied to the windings during this idle period, allowing continuous online monitoring without interrupting normal operation. This resolves the contradiction by enabling frequent testing (high productivity) while maintaining accurate insulation detection (measurement precision).
Solution Approach 2:
The patent implements continuity of useful action by integrating the insulation testing function into the regular motor operation cycle. Instead of separate offline tests, the surge testing is continuously performed at each startup or idle moment, providing ongoing monitoring. This enables both continuous detection capability and maintains measurement accuracy through repeated measurements.
2Reliability
If additional expensive equipment like PD method is used for online detection, then reliability is improved, but device complexity worsens
Solution Approach 1:
The patent applies universality by designing a testing system that uses the existing motor startup infrastructure for dual purposes: normal motor operation and insulation testing. The surge voltage generator and measurement circuits serve both the motor control function and the insulation detection function. This eliminates the need for separate dedicated PD detection equipment, reducing device complexity while maintaining reliable online monitoring.
Solution Approach 2:
The patent implements self-service by using the motor's own startup process and existing electrical infrastructure to perform the insulation testing. The system tests itself during normal operation without requiring external specialized equipment. The surge voltage applied during startup serves both to energize the motor and to stress-test the insulation, providing reliable detection with minimal additional hardware.
3Measurement precision
If multiple pulses with increasing voltage level are applied as in online surge testing, then measurement precision is improved, but loss of time worsens making the process time-consuming
Solution Approach 1:
The patent applies partial action by using a single surge voltage pulse or limited number of pulses during motor startup instead of multiple progressively increasing voltage levels. The startup surge provides sufficient stress to detect insulation defects without requiring the extended multi-stage voltage escalation. This reduces testing time significantly while maintaining adequate detection precision through the high dv/dt characteristic of the startup surge.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables continuous, reliable, and cost-effective online detection of insulation faults, including inter-turn insulation issues, allowing for immediate identification of potential failures and preventing damage to windings and lamination cores.
Implementation Method 1
the resulting current and/or the time derivative thereof is detected as a measurement signal... following which the signal obtained by the oversampling is analysed with regard to characteristic parameters of the transient process, such as overshoot and/or natural frequency and/or damping constant
Implementation Method 2
by means of an inverter, a stepped voltage is applied to the winding(s) of the machine and the resulting current... is detected as a measurement signal
Data Source
AI summary
The invention relates to a method and a device (1) for the online-detection of a deterioration in the state of an insulation in an electric machine (2). A stepped voltage is applied to the winding(s) (3) of the machine (2) with the aid of a converter (41), and the current (i) induced in this manner, and/or the time derivative (di/dt) thereof, is acquired as a measurement signal with the aid of at least one sensor (6, 7, 8) and is then oversampled with a frequency higher than the frequencies characteristic for settling. The signal obtained by said oversampling is then evaluated with regard to parameters of the settling process such as overshooting (Ah) and/or natural frequency (1/ΔT) and/or a damping constant, in order to detect any deterioration in the insulation.