SDV free standing vacuum breakers
Author: Steven Hawkins
08/01/2006 - Volume III - Issue II
The SDV-3, 4, and 4A models have been popular, robust distribution breakers for 15.5 - 27.6 kV applications. The SDV is a single dead tank vacuum distribution breaker designed for the typical utility distribution substation. Since the introduction of SDV-3 in 1989 (welded enclosure) through the present SDV-4A design (bolted cabinet and ventilation provisions), the SDV has been installed in virtually all states as well as in Europe and Asia.
SDV-3 welded enclosure ventilation modification
In several instances at locations with moderate to severe conditions, the SDV-3 has been found to retain moisture/humidity once the gasketed doors are closed. Even with working heaters set at 104 degrees F, evidence of condensation or water intrusion has been observed. Siemens has designed a ventilation modification kit for customers who observe the described condensation.
The ventilation modification kit (18-829-309-803) includes small round vents for the HV compartment, rectangular vents for the control cabinet, and comes with all installation components, drawings, and written instruction. With the appropriate crew and tools and the unit de-energized, it should take on average two hours to install the ventilation kit, clean-up, and prepare the breaker for re-energization.
The increased air flow from the installation of the ventilation kit, as well as the continuation of heater energization, has resolved all instances of the described condensation.
SDV-3 high-voltage compartment door seals
Over the last few years, several customers have advised that the neoprene weather stripping, used on the SDV-3 HV compartment door seals, has allowed water to penetrate into the HV compartment. This may have also contributed to the condensation described above, necessitating the ventilation modification kit.
A customer was successful in utilizing the self gripping bubble type gasket Siemens currently uses on the SDV-4A HV panel. First, they removed the existing weather stripping from inside the HV compartment door panel. Next, they applied a continuous run of the bubble type gasket on the lip extending from the SDV-3 HV compartment, essentially moving the seal from the door to the unit side. Since the SDV-3 is no longer in production, this method has not been tested in the factory. However, customers have reported that this field fix has alleviated water ingression via the door seal on the SDV-3 HV compartment.
SDV-3 and 4 field stroke measurements
Stroke is defined as the distance that the movable contact must travel before touching the fixed contact. There are two methods used for measuring stroke: static and electronic. Siemens Wendell, NC manufacturing facility measures stroke on vacuum interrupters (VI) by electronic measurement. This procedure takes into consideration the operating speed of the mechanism, the synchronization of the phases, and the stroke itself.
Measuring stroke is not a formal prerequisite to commission new equipment in the field. However, customers who wish to measure stroke should carefully follow the instructions found in the operation and maintenance manual provided with the breaker. Customers typically re-measure stroke following adjustment, replacement, or other operating linkage services. Please note that 20-30% deviations from the contact gap in Appendix F may be experienced.
There are two additional methods that yield repeatable results:
- The best way to statistically measure VI contact stroke is to fasten a piece of tape to the moving stem (or any part fastened to the moving stem that operates linearly) and scribe a line on the tape in both the open and closed positions using a single datum.
- An alternate way to measure VI contact stroke, although less accurate, is to utilize the depth measuring portion of a dial or digital calipers. In both the open and closed positions, measure the distance from the top of the flex shunt clamp to the support ring. The difference should be repeatable and approach the given contact gap referenced in the operation and maintenance manual provided with the breaker. Again, there will be variations in the values derived based on operator differences. Please note that deviations in the 10-20% range may be experienced. This method has been tested recently in the manufacturing facility within specification results.
Siemens Wendell, NC manufacturing facility measures stroke using a linear transducer (Novo Technick) and recording equipment (Rochester). Siemens deems this measurement accurate, typically to three decimal places in centimeters. Please note that this measurement is from the start of movement to "contact touch." This distance is typically less than those measurements captured by manual or static measurements. This information is captured and retained in our QA retention records. During the complete movement of the breaker operator shaft, additional pressure is applied to the vacuum bottle contacts. The differences between measurements made at this point in time versus the electrical measurements come from the various components that stretch, compress, and change references of angularity (such as the movable contact stem).