Arrester Application

The DynaVar arrester is described by its maximum continuous line-to-ground operating voltage (MCOV). The arrester's most important application criterion is the maximum voltage which can be continuously applied.

For effectively grounded neutral systems, any DynaVar arrester with MCOV equal to maximum line-to-neutral kV is the normal application. For example, a 138kV system usually has a maximum line-to-line continuous voltage of 145kV rms. 145kV divided by v 3 gives 84kV line-to-ground voltage. The appropriate DynaVar arrester for this application is the Dyna- Var 84, with MCOV of 84kV.

For ungrounded or impedance grounded systems, the gapless DynaVar arrester's temporary overvoltage capability is used. For applications where a ground fault is expected to be removed within 30 minutes, the minimum MCOV is maximum system line-to-line voltage divided by 1.25. For extended operation under ground fault conditions up to 2,000 hours but not to exceed five percent of service life, the minimum MCOV is maximum system line-to-line voltage divided by 1.11.

DynaVar arresters are designed to be used where average ambient temperature does not exceed 40°C (104°F) and the daily maximum temperature does not exceed 60°C (140°F).

Switching surge capability of DynaVar arresters is expressed in terms of dissipated energy.

These capabilities assume a two shot energy discharge takes place within one minute.

The indicated current levels are not an arrester limitation, but are related to the indicated energy capability.

Calculations based on the conservative assumption that the entire line length is charged to maximum surge voltage are easily made, and the values obtained seldom exceed the considerable energy capability of the DynaVar arrester.

Temporary Overvoltage Capability

DynaVar arresters are gapless and consist of a column of metaloxide blocks connected between line and ground. The blocks can withstand a significant power frequency overvoltage for a limited time, depending on the magnitude of any immediately preceding surge duty. This duty can be the result of switching surges on higher voltage lines, or from other sources. The energy discharge capability is found in the above table.

All of the TOV curves are available in the Design Test Reports which are listed on page 30-29. The Design Test Reports are available on our web site www.hubbellpowersystems. com or by calling an Ohio Brass representative. The temporary overvoltage capability can be determined from this curve. The prior duty curve of this table is based upon absorption of rated energy immediately preceding application of the overvoltage.