HIGH CURRENT SWITCHES
Ross Engineering's high current switches have very low contact resistance. They are used for power, RF, capacitor discharge, pulse, transfer, and tap selection. They are used on low and high voltage power loads or with multiple capacitor banks for isolated no-load selection, transfer or grounding. By using non-conductive air or hydraulic lines, no electrical or mechanical ties to contact mechanism are required. Also, when specially built, the units can be used for high current RF applications. Units are built with G-10 epoxy glass laminate insulation for standard applications and G-7 silicone glass insulation for RF applications above 100kHz. Heavy duty contacts, specially designed to minimize corona, are built of highly conductive but weld resistant alloys. Units are able to withstand high shock, vibration, and severe environmental conditions. Simple mechanical design and conservative stress levels result in long life, and trouble-free performance. Additionally, units are built of light-weight material and are of the smallest dimensions possible for full performance within their power ranges. They are easily installed and used in the most compact compartments.
High Contact Closing Force
High contact closing force enables high momentary current. When required, special arcing contacts allow closing capabilities.
Standard Ross high current switches are built with 80 to 120PSI air cylinder actuators. Hydraulic cylinder or motor operated models are also available.
Peak Test Voltage
Ratings are for air at 760 mmHg, 20°C. Derate voltage withstand approx. 3 to 4% per 1000ft above sea level. See IEEE standard. All peak test voltages are 1 minute, 60Hz peak hold voltages unless otherwise noted. The first figure in the model number is the peak test rating between open contacts. If there is only one figure in the model number, the insulation level to ground is the same as that between open contacts. If there is a number following the contact configuration designation, that is the rated peak test voltage to ground. On most nonspherical contacts, transient pulse withstand may be considerably higher than 60Hz test level. Actual flashover values, are at least 10% greater than rated 1 minute peak test hold values for DC & 60Hz, or transients. Corona starts at approximately 2/3 peak test voltage.
Rated voltages should be derated approximately 3 to 4% per 1000ft above sea level. The peak test rating of high current switches should be 1.2 to 5 times the normal circuit operating voltage, depending upon the application. For lower power systems where transients are unlikely or intermittent flashover is of no consequence, a safety factor of 1.2 to 1.5 may be suitable. For medium power systems or where moderate transients are likely, a safety factor of 1.5 to 3 is desirable and 2 to 3 recommended. For higher power systems or where transient over-voltages are expected, a safety factor of 2.5 to 5 should be considered and the factor should be based on the maximum probable transient. The rated peak test voltage to ground should be selected in the same way, as was the contact to contact value. If a value other than the published rating is required, it can normally be supplied as an extra cost option.
Specified current ratings are continuous for 60Hz RMS and DC, but should be derated at higher frequencies as well as approximately 0.5% per 1000ft above sea level. Some units can be used in RF applications at reduced current ratings. At 10kHz, derate current by 50%. Above 10kHz, derate to approximately ½(10/f kHz)-½, (i.e. at 30kHz derate to 29% of 60Hz rating). All RF applications should be submitted to Ross' application engineering department for review. Air or motor actuated high current switches are normally capable of interrupting or making only very low currents depending on type of wave, load, and recovery voltage. HV high current switches are also rated for safety grounding and high current capacitor discharge with special arcing contacts. They have long life and little or no maintenance in most applications.
G-10 epoxy glass laminate is standard insulation on most models. G-7 silicone glass is used in models for RF applications above 100kHz. Most Ross high current switches are available with additional lengths of insulation where the high voltage contacts need to be spaced at a greater distance from the actuator and control circuit.
Oil or Gas Insulation
Voltage withstand value is at least doubled and the interrupt capability is much greater when high current switches are immersed in insulating oil, or SF6 gas. For gas atmospheres no modification is necessary, however oil or fluid immersion requires modification at a slight extra cost. For maximum performance, where high voltage and high current is impressed directly across solid insulation, it may be necessary to increase insulation length to prevent puncture at levels above the test rating in air. Additionally, most Ross high current switches can be mounted in any attitude. Contact the factory's application engineering department for mounting recommendations, and for ratings in gases at higher pressures (see IEEE, IEC, or ANSI standards).
Air type SPDT valves or SPDT 15 amp 450V auxiliary contacts for position indicating or interlocking are available on request on all Ross high current switches.
Specifications are for reference only and are subject to change.
Contact Ross Engineering Corp. for current information.