Capacitive Bushing & Online Partial Discharge Monitoring
Capacitance, tan delta and PD from the bushing test tap.
Bushing failure is one of the leading causes of catastrophic transformer failure, and it does not happen without warning. Capacitance and dissipation factor drift as the capacitive layers degrade, and partial discharge activity rises before the final breakdown. The problem is the sampling interval: an offline measurement every one to three years can miss a degradation that develops in months. This monitor measures capacitance, dissipation factor (tan δ), partial discharge and leakage current continuously.
Four channels run simultaneously, three phases plus one leakage current, over an input range of −20 V to +20 V with 2 MHz bandwidth at the 3 dB point and at least 128 GB of storage. It connects to the bushing test tap, and once the tap adapter is fitted no outage is required. The unit works with OIP, RIP and RIS capacitive bushings from the major manufacturers. Partial discharge measurement references IEC 60270, bushing requirements follow IEEE C57.19.01 and C57.19.100, and field testing follows IEEE C57.152. Data goes out over IEC 61850, DNP3.0 or Modbus on Ethernet RJ-45, with an optional fiber-optic converter where the substation environment demands it.
Why it matters
The drift that precedes a bushing failure is measurable, and continuous monitoring catches it between the offline test intervals where it currently hides.
Dielectric trending and PD activity in one instrument means one set of connections and one time base, so a capacitance change and a discharge event can be correlated.
Connection is at the test tap, so after the adapter is fitted the asset stays in service.
Compatibility with OIP, RIP and RIS bushings covers a mixed fleet without a per-bushing engineering study.
IEC 61850 and DNP3.0 output puts the result on the substation bus, where the alarm reaches the operator instead of a laptop in the maintenance office.
Ratings
Measured quantities: Capacitance, dissipation factor (tan δ), partial discharge and leakage current
Input range: −20 V to +20 V
Bandwidth: 2 MHz (3 dB point)
Channels: 4 simultaneous — three phases plus one leakage current
Storage: ≥128 GB
Bushing compatibility: OIP, RIP and RIS capacitive bushings from the major manufacturers
Communication: IEC 61850, DNP3.0, Modbus; Ethernet RJ-45 with optional fiber-optic converter
Installation: Connects to the bushing test tap — no outage required after the tap adapter is fitted
Standards
IEC 60270 (PD measurement)
IEEE C57.19.01 / C57.19.100 (bushings)
IEEE C57.152 (field testing)
IEC 61850
Applications
Transmission and generator step-up transformers
Shunt reactors
Critical substation assets without redundancy
Condition-based maintenance programs
Questions engineers ask
How does online bushing monitoring connect without taking an outage?It connects to the capacitive test tap that the bushing already provides. An outage is needed once, to fit the tap adapter, and after that the monitor reads capacitance, dissipation factor, partial discharge and leakage current with the transformer in service. That is what makes continuous trending practical on an asset you cannot switch out.
Which bushing types are supported?OIP, RIP and RIS capacitive bushings from the major manufacturers are supported, so a substation with a mixed population does not need a different monitor per bushing type. Four channels are measured simultaneously, covering the three phases plus one leakage current input, with 2 MHz bandwidth at the 3 dB point.
Technical documentation
Download HVEX Transformer Bushing and Online PD Monitor datasheet (English, PDF)
