The Doble M5500 is the current flagship Sweep Frequency Response Analyzer (SFRA) from Doble Engineering. It is the successor to the widely used M5400 and is designed to detect mechanical failure or winding movement in transformers.
The M5500 performs SFRA (Sweep Frequency Response Analysis). It injects a low-voltage signal into one end of a transformer winding and measures the response at the other end across a wide frequency spectrum.
- What it finds: “Hidden” mechanical issues that standard electrical tests (TTR, Winding Resistance) often miss, such as:
Hoop buckling (from high fault currents).
Core shifting or grounding issues.
Winding telescoping or deformation.
Shipping damage.
Frequency Range: 10 Hz to 25 MHz (User selectable).
Standard diagnostic range is typically 20 Hz – 2 MHz.
Dynamic Range: >150 dB (Significant upgrade from the older M5400’s >90 dB). This high dynamic range is critical for seeing deep nulls in the high-frequency response.
Sweep Speed: 15 – 30 seconds per test. This is one of the fastest sweep times on the market, reducing the total time required for a full transformer test plan.
Source Impedance: 50 Ohms.
The M5500 runs on Doble SFRA Software v6.
- This software is backward compatible; it can open and compare results from older M5200, M5300, and M5400 units.
It includes the Leakage Channel Analysis tool, which helps diagnose short-circuit radial deformation automatically.
If you are used to the older gray/blue M5400 units, the M5500 offers three main differences:
Speed: It is significantly faster per sweep.
Size: It is smaller and lighter (approx. 7 lbs / 3.2 kg).
Connectivity: It supports Wireless connection to the controlling laptop, so you don’t have to stand right next to the bushing with a USB cable.
