PD & RIV Testing of Transformers Using the DDX 9121b

Partial discharges (PD) are evidence of a degrading insulation system, and if left undetected, may eventually lead to very costly repairs or damaging and dangerous in-service failures. Transformers are particularly important and cost-intensive equipment used in power transmission and distribution. PD testing is a valuable tool for factory, acceptance, and regular maintenance testing of transformers to ensure manufacturing quality and for the correct maintenance procedure during the lifetime of the equipment.

Read more on The Basics of Partial Discharge Testing.

In North America Radio Interference Voltage (RIV) testing is still a very common practice for PD testing of transformers according to IEEE C57.12.90 and IEEE C57.113. This practice is based upon an older NEMA 107 standard, which called upon measurement receivers to estimate the disturbance of communication lines. The measurement is similar to IEC 60270, but the quasi-integration of the pulse is conducted at a narrow bandwidth of 9 kHz with a tunable frequency between 10 kHz to 10 MHz. Rather than providing the results in pC, as is common in IEC, RIV results are given in µV. Despite the giant leap in PD measurement technology, RIV testing is still a mandatory requirement for PD testing of transformers in North America.

Read more on Radio Interference Voltage.

The DDX 9121b Partial Discharge Detector provides a complete solution for simultaneously measuring PD and RIV in transformers using the AKV 9310 Measuring Impedance per bushing (bushing tap method) or per phase together with a 9230 Series Coupling Capacitor (coupling capacitance method). Calibration of the circuit can be conducted using the handheld KAL 9531 RIV Calibrator. 

The DDX 9121b is modularly designed to allow for the capability of many measurements to be conducted at the same time. For simultaneous measurements, such as on power transformers, several detectors can be combined, stacked, and connected to a single computer. This means that all bushings of the transformer could be tested simultaneously. For added mobility the detectors can also be fitted into a trolley that can hold up to 4 detectors.

The DDX 9121b also has the option of activating an internal multiplexer (MUX) with 4 total PD inputs. This allows a user to test a transformer as a single-phase test object with the capability to switch between up to 4 different bushings during the test.

Fiber optic communication cables can be used to connect the PD detector with a PC/laptop. This can be used as an added safety feature in which the detectors are left in the HV test area, while the testing and analysis of the results is conducted in a control room.

Solutions for Power Transformers

On power transformers with capacitively-graded bushings, individual AKV 9310 measuring impedances can be connected to the bushings, which is known as the bushing tap method.

Basic Option for Sequential Testing:

The most basic option would be that 1x DDX 9121b be used with internal MUX option and 3 AKV 9310 measuring impedances. This allows a user to test all 3 HV bushings at the same time, phase-by-phase. After testing the HV bushings, the measuring impedances would have to be mounted to the LV bushings and tested.

Basic Option for Simultaneous Testing:

3x DDX 9121b detectors would be stacked and used together with 3x AKV 9310 measuring impedances. This would allow a user to measure the HV and LV bushings separately, but all HV or LV bushings simultaneously. For added safety and mobility, the detectors can be fitted into a trolley left in the test area with fiber optic communication cables drawn into the control room.

Optimized Option for Simultaneous Testing:

A trolley would be fitted with 4x DDX 9121b detectors and 6x AKV 9310 measuring impedances could be attached to each HV and LV bushing. This configuration would enable to measure the HV bushings simultaneously, while measuring the LV bushings phase-by-phase using the internal MUX option.

Customized Option for Simultaneous Testing:

2x trolleys, each fitted with 4x DDX 9121b, and 8x AKV 9310 measuring impedances could be attached to all HV and LV bushings (3 phases plus neutral/null bushing). In this configuration all HV and LV bushings could be measured simultaneously.

Solutions for Distribution Transformers

Basic Option for Sequential Testing:

The most basic option would be that 1x DDX 9121b be used with internal MUX option and 3x 9230 coupling capacitors with AKV 9310 measuring impedances. This would enable the ability to measure the HV side of the transformer phase-by-phase.

Optimized Option for Simultaneous Testing:

A trolley would be fitted with 3x DDX 9121b detectors to be used together with 3x 9230 coupling capacitors with AKV 9310 measuring impedances. This would enable the ability to measure the all phases of the HV side of the transformer simultaneously.

If you would like to learn more, feel free to contact one of our sales managers at 

+1 (703) 365-2330 or hvsales@hvtechnologies.com.