Frequently Asked Questions

General Atomics Energy Products, a Division of General Atomics Electronic Systems

FREQUENTLY ASKED QUESTIONS
ABOUT HIGH VOLTAGE CAPACITORS

How can a custom capacitor be cost effective?

By designing a capacitor for your application, General Atomics Energy Products (GAEP) can often provide a smaller and less costly capacitor than is available off-the-shelf. In most cases, the capacitor can be built using materials available in our stock.

What is the recommended torque for the terminals on my capacitor?

Torque Specifications
Bushings
C Series low profile 1/2"-13, M12	15.0 ft-lbs	20.0 N-m
C Series low profile 3/4"-16, M16	20.0 ft-lbs	27.0 N-m
C Series Scyllac 1.0"-14	25.0 ft-lbs	34.0 N-m
C Series fluted ceramic 3/8"-16	10.0 ft-lbs	14.0 N-m
DE Series 10-32	1.3 ft-lbs	1.8 N-m
DE Series 3/8"-16	2.5 ft-lbs	3.4 N-m
DM Series ceramic 1/4"-20, M6	2.5 ft-lbs	3.4 N-m
Drawn Metal Cans 10-32	1.3 ft-lbs	1.8 N-m
PD Series 10-32	1.3 ft-lbs	1.8 N-m
PD Series 3/8"-16	2.5 ft-lbs	3.4 N-m
S & SS Series rails 10-32	1.3 ft-lbs	1.8 N-m
Weldnuts
3/8"-16, M10	50.0 ft-lbs	68.0 N-m

Why are GAEP high voltage capacitors oil-filled?

Highly insulating oil is used to suppress partial discharges (corona), increase the dielectric strength, and increase the effective permittivity (dielectric constant) of the capacitor dielectric. Oil-filled film capacitors have high energy density in comparison with other types of capacitors used at high voltage, such as ceramic capacitors. Different types of oils are used with different types of capacitor dielectric and electrode designs.
Can GAEP oil-filled capacitors be operated in any orientation?

GAEP capacitors are completely oil-filled and do not contain an air bubble. They may generally be operated in any orientation.

What is the oil in my GAEP capacitors?

The type of oil may be found on the label or the capacitor specification sheet. Acronyms used are:

CO = castor oil (vegetable oil)
RSO = canola oil (vegetable oil)
IPB, IPBP, MIPB = isopropyl biphenyl
BTDP = benzyltoluene diphenylethane
PXE = phenyl xylyl ethane
SO = silicone oil, (polydimethyl siloxane)
MO = mineral oil (petroleum-based)
EPX = proprietary - contact factory
TCP = tricresyl phosphate
DOP = ethyl hexyl phthalate
DRY = no oil

For other designations, contact the factory

Material Safety Data Sheets (MSDS) for each oil are available by contacting General Atomics Energy Products (858-522-8400). Note that regulations for disposal of oil-filled capacitors differ from locality to locality. For this reason, we are unable to give you advice on proper disposal in your locality.

My Type S capacitor's label indicates that one terminal is the "high potential terminal". What does that mean?

The term "high potential electrode" was chosen because the Type S capacitor is not polarized in the sense that an electrolytic capacitor is polarized, with a definite anode terminal and cathode terminal. Film capacitors such as this can be operated in either polarity (Note: Avoid or minimize reversing polarity).

However, the Type S capacitor, like most wound film capacitors, has a slight asymmetry in its internal construction that results in one of the internal electrodes being closer to the internal surface of the plastic case than the other. There is a larger capacitance between this electrode and external conductors. The voltage potential between this electrode and an adjacent external conductor determines the electric field through the wall of the plastic case.

The "high potential terminal" is connected to the electrode that is buried inside the winding and therefore shielded.

In the case of one terminal being grounded, the "high potential terminal" should be connected to the high voltage source (either positive or negative potential). In the case of multiple capacitors in series, the capacitors should all be connected such that the "high potential terminal" is the one that will experience the highest absolute magnitude voltage, |V|.
Why can't I operate my Type S or SS capacitor at 100 kV in air, if it is rated at 100 kV?

Type S and SS capacitors were originally developed for Marx generators where low inductance was critical to performance. In such applications, it is common to immerse the entire Marx circuit in transformer oil or a pressurized dielectric gas such as SF6 (sulfur hexafluoride), so that spacing between conductors at different polarities can be minimized. The external strike and creep distances between the electrodes of the Type S and SS capacitors were designed for this environment at up to 100 kV. In ambient air, the design is suitable for operation at up to 75 kV.
Can I place the "high potential" side of a Type S or SS capacitor directly on a ground plane to minimize inductance?

This is not recommended. As is the case in many high voltage insulation systems, it is best to use multiple layers of insulation, rather than rely on a single, thick layer such as the plastic case of the capacitor. It is common practice to use multiple layers of polyester (e.g. DuPont Mylar®) or polypropylene sheet between the capacitor case and adjacent conductors or capacitors.

Why are there are two sets of screws in the rails on my Type S capacitor?

One set of screws (A) holds the internal connections and o-ring seals together, and feeds through current to the outer rail. The other set of screws (B) is for external connection to your buswork. If the feedthrough screws (A) are loosened, oil can leak out.

Torque limits for the rail screws (B) are
1.3 ft-lbs or 1.8 N-m

Can I operate my Type S capacitor in any orientation?

The Type S capacitor is completely filled with oil when shipped from the factory, and can be operated in any orientation.

There are situations where gas bubbles can form inside the capacitor, such as after prolonged use in a pressurized gas system followed by release of external pressure, or by fault conditions that produce excessive current flows in the capacitor. Inspect for gas bubbles by holding the capacitor with the terminals at the top, and shining a bright light through the header at the top. If a visible gas bubble is present, the unit should be returned to the factory for a vacuum top-off process. If this is not possible, it is best to operate the unit in the vertical orientation, with rails at the top.
What charge time, hold time, and rep rate are my Type S capacitors rated for?

The nominal conditions used to calculate the life of Type S capacitors are a charge time ≤ 30 seconds and a hold time ≤ 5 seconds. WE recommend that you do not exceed these values. The pulse repetition rate is determined by the capacitor's maximum allowed rms current which is shown on our Series S, SS, & DE page or on individual specification sheets available from GAEP. To determine the rms current for a capacitor in your application, please use our rms current calculator.
Can I connect my Type S capacitors to a parallel-plate transmission line ? What should I use to insulate the line?

This is a common configuration for fast capacitors such as GAEP's Type S. Multiple layers of plastic sheet are typically used for insulation between the parallel plates of such buswork.