Selection Guide

HVL/cc switchgear is an integrated assembly of many components, properly selected and coordinated to provide consistent operation of the overall equipment. Each component has its own ratings defined by its own industry standards (usually ANSI). In the past, these individual component ratings have been emphasized since they often appear to be quite impressive. However, they may be irrelevant to the component’s application.

Integrated ratings of the complete equipment are the natural solution, and Square D brand switchgear is rated in this manner. Integral equipment ratings are readily comparable with the anticipated voltage, short-circuit, and continuous current values obtained when designing a distribution system.

Equipment Ratings without Fusing covers the HVL/cc load interrupter switches when applied without fuses.

Integrated short-circuit current ratings with Square D brand and Mersen CS-3 brand current-limiting fuses are shown in Integrated Ratings for 600 A HVL/cc Switches with Square D brand Current-limiting Fuses and Fuse Rating Table with Fuses in Parallel. Integrated equipment, short-circuit current rating at a given voltage defines the maximum short-circuit current to which the entire equipment may be subjected without damage to the equipment.

Current ANSI standards for metal-enclosed switchgear and the components are rated individually in rms symmetrical amperes. The integrated rating may also be expressed this way (the asymmetrical rating is obtained by multiplying the symmetrical value by 1.6). For convenience, when comparing to older equipment, the integrated rating is also expressed in “MVA.” The MVA ratings are calculated at the nominal system voltage and with the rms symmetrical amperes, for example, MVA = Nominal System Voltage, kV x A rms sym kA x √3.

The integrated equipment rating combines the following ratings:

• Switchgear-momentary and short-time (bus bracing)

• Load Interrupter Switch-momentary, fault-closing and short-time

• Fuses-interrupting and energy let-through characteristics (current-limiting fuses limit the energy during a short circuit, thereby allowing higher integrated ratings than the switches and switchgear would have if unfused)

• Other components that may have limited capabilities

Voltage Ratings: The voltage for a given system is normally expressed in nominal Volts and is operated in a range that fluctuates, based on a number of operating factors. ANSI standards generally recognize a tolerance of ± 5%. For switchgear, do not exceed the maximum design voltage. When operated below this maximum, the equipment withstands the 50 or 60 Hz voltage continuously, the low frequency withstand for one minute, and impulse voltages applied in accordance with ANSI design test procedures.

Continuous Current Rating: The overall continuous current is determined by the component with the smallest capacity–bussing, load interrupter switch, fuses, fuse mountings, and connections. Unfused equipment is normally rated by the main bus, which is available in ratings of 600 or 1200 A continuous. The continuous-current rating of fused equipment is generally determined by the fuses, since the other components have greater current-carrying capacities than the fuses.

HVL/cc Switch Interrupting Current Rating: The HVL/cc switch is designed and tested in accordance with ANSI standards as a “load interrupter” switch, capable of interrupting load currents up to its continuous current rating. However, per ANSI, this switch is not intended to be the main switching device. Load interrupter switches are not designed or tested for interrupting currents above their continuous currents.

Full Load Current Switching Endurance: In accordance with ANSI C37.20.4, the number of full-load current interruptions the switch can make at maximum design voltage is established through tests on “a circuit having a 0.8 power factor lagging,” and “requiring no maintenance for the number of operations stated.”

Short-Circuit Current Ratings: An integrated short-circuit current rating is normally established based on the Momentary, two-second short time, and fault-close capabilities of the equipment as explained in Integrated Equipment Ratings. The most important number is the Integrated Short-Circuit Current Rating, which establishes overall rating for the equipment. This number is normally based on unfused switches. Current-limiting fuses can be used to increase the integrated rating. Use Equipment Ratings with Fuses and Fuse Rating Table with Fuses in Parallel to select the proper fuse and associated integrated short-circuit current rating.

Mechanical Endurance: These numbers represent actual test values to which the given switch rating has been subjected. ANSI C37.20.3 and C37.20.4 do not require a rating, only testing to a specified minimum number of operations without repair, component replacement, or maintenance. In all cases, the switch rating shown has been tested to many more than the minimum number of operations shown here.

Fuses are usually used with the medium-voltage switch to provide overcurrent protection. They are normally mounted vertically below the switch (Application A). When an Application B (inverted) arrangement is used, the fuses are mounted above the switch.

Current-limiting type fuses offer the maximum short-circuit current rating and are most economical in the majority of “E” ratings in which they are available.

Fuses supplied with the equipment provide the following conditions when properly selected:

• Fuse-interrupting capacity is in accordance with the integrated equipment short-circuit current rating.

• Fuse continuous-current E rating is as required up to the maximum continuous-current rating of the fuse.

• Most applications seem to favor fast-acting, current-limiting fuses. These fuses limit the let-through current and minimize the short-circuit damage to a system. They are completely factory-assembled and sealed to keep out dust or foreign material, and they operate without any noise, pressure, or expulsion of gas, flame, and extinguishing material, even at maximum capacity. Boric acid fuses are not available with HVL/cc switchgear.

Current-limiting fuses increase the integrated short-circuit current rating because of their energy-limiting capabilities. To increase the short-circuit current rating of the entire lineup of switchgear, current-limiting fuses must be used in the entrance sections.

Current ratings are shown in rms symmetrical amperes:

• Symmetrical amperes = asymmetrical amperes ÷ 1.6.

• Nominal 3Ø symmetrical MVA rating = system nominal voltage, kV x sym. amperes, kA x √3.

• Ratings are based on an X/R ratio of 16.

E-rated, Square D brand DIN style and Mersen CS-3 style current-limiting fuses function as follows:

• 100E or less – Must melt in 300 seconds (five minutes) on 200–240% of E (A) rating.

• Over 100E – Must melt in 600 seconds (ten minutes) on 220–264% of E (A) rating.

• Refer to Fuse Ranges and Sizes (DIN Style) for available E-ratings.

• Positive extended travel blown fuse indicator pin on Square D brand fuses only (used for the Fuselogic system applications)

• UL listed

• Fast acting to limit available trip-level current stresses on the system and minimize damage to system components

• Fuselogic system automatic fuse tripping requires stored energy mechanism

• Silent, non-venting interruption

• Completely factory-assembled and sealed for consistent characteristics

• High-interrupting capacity

• No refills to replace or parts to clean

• Requires minimal electrical clearance; no exhaust clearance required

• Controlled-arc voltages

• Single- and double-barrel fuse designs; double-barrel fuses increase ratings

• Standard ANSI characteristic curves

• Used for blown fuse indication and blown fuse tripping (Fuselogic system)