Burlington Electrical Testing

Field Services


Sweep Frequency Response Analysis (SFRA)

Frequency response analysis (often referred to as FRA or SFRA) is an effective to test the mechanical integrity of transformer cores and windings. Every electrical network has a unique frequency response. Network faults or vibrations can cause changes in this frequency response.

Comparing the frequency measurements taken at various phases or on multiple identical transformers, as well as comparing measurements with past frequencies of the same transformer, provide indications of any mechanical or electrical changes.

Burlington Electrical Testing (BET) recommends initial acceptance testing of the frequency response to obtain a baseline signature curve. Then especially after transporting transformers and after faults at high currents have occurred. BET uses the Omicron FRANEO 800 SFRA test device to help detect winding displacement and deformation (among other mechanical and electrical failures) on power and distribution transformers - without opening the unit

Frequency response analysis measures the impedance of the transformer windings over a wide range of frequencies. The measurements are compared with a reference set and the differences are highlighted. The differences may indicate mechanical damage to the windings, such as winding displacement or loose windings, and electrical faults.

Frequency response analysis can be achieved by either injecting a low voltage impulse into the winding (impulse response method) or by making a frequency sweep using a sinusoidal signal (swept frequency method). For frequency response analysis to be useful, a baseline reference set of measurements need to be determined and periodic tests need to be conducted to compare the differences.

The SFRA test is non-intrusive (non-destructive) test. SFRA is an offline test, which can be carried out for any voltage rating of power transformers, generator transformers and distribution transformers.

The measurement of SFRA can be a part of regular transformer maintenance. The SFR Analyzer identifies the following abnormalities in the transformer before they lead to failure,

  • Core movement.
  • Winding deformation and displacement
  • Faulty Core ground
  • Partial winding collapse
  • Hoop buckling
  • Broken or loosened clamping structures
  • Shorted turns and open winding

The Technique of SFRA is a proven technique for making accurate and repeatable measurements. The test can be carried out:

  • Pre-commissioning check.
  • To record initial signature of the transformer sweep frequency response for future reference.
  • Periodical measurement as a maintenance check, usually bi-annually.
  • Immediately after a major external Short Circuit, especially those closer to the transformer.
  • Transportation or re-location of transformer.
  • Earthquakes or other major disturbance to the transformer.


NFPA 70E 2021

Is your site NFPA 2021 compliant? Is your staff "qualified" or "unqualified" to work on electrical equipment?

Burlington Electrical Testing conducts onsite Arc Flash Hazard Awareness training which provides an understanding of the federal laws (OSHA), potential dangers, as well as the accepted safety practices when personnel are to be exposed to electrical hazards.

This includes defining an arc flash and its effects on the human body, complying with Arc Flash labeling, and the selection and use of Personal Protective Equipment (PPE).

The Arc Flash Hazard Awareness class is to be part of your overall electrical safety program; therefore, your staff will require a working knowledge of the electrical equipment at their facility, along with the tools, test equipment and available PPE.

The one day class is presented by an instructor certified by NFPA, and the NJACT / NECA to instruct Electrical Safety Related Work Practices based on NFPA70E 2018. Curriculum follows the accompanying Electrical Safety-Related Work Practices text modules and will focus on:

1. Electrical Safety Culture
2. Electrical Hazard Awareness
3. OSHA and NFPA 70E concepts
4. Electrical Safety Program
5. The Control of Hazardous Energy
6. Arc Flash Hazard Analysis
7. Personal Protective Equipment
8. Existing Electrical Equipment

For scheduling and quotations please call:
(215) 826-9400

About Us

Burlington Electrical Testing is a testing and verification firm with more than 35 years of experience in electrical maintenance testing, acceptance testing, electrical certification, and engineering evaluations of electrical distribution equipment.


Burlington Electrical Testing
300 Cedar Avenue
Croydon, PA 19021
Phone: (215) 826-9400
Fax: (215) 826-0964