SINGLE-POLE HV VACUUM CONTACTORS / RELAYS
Compared with other devices of the same power interruption range, the Ross contactors and relays are much lighter in weight and more compact in structure. Ross designed these devices especially for installation in indoor open style equipment and metal enclosed switchgear or power supplies of the smallest and lightest configurations. Also, because of the reliable actuator design and Ross Engineering's standard vacuum sealed HV contacts, each unit can operate quietly and efficiently in air, oil, or insulating gas atmospheres.
Long Life Vacuum Interrupters
To insure minimum maintenance and extremely long life, these Ross HV current interrupting contactors and relays are built with sealed vacuum interrupters. These versatile components assure high dielectric strength and rapid recovery after arc extinction. This high dielectric strength exhibits comparatively low arc energy during high current interruption, and thus minimizes contact erosion. The vacuum medium provides a very rapid but controlled arc extinction due to high velocity radial diffusion of vaporized special metal alloy contact surfaces during contact separation, Consequently, this allows the very rapid but controlled recovery of dielectric strength and minimizes over voltages. The interruption capability is not affected by adverse conditions such as altitude, extreme temperature or humidity. Of major importance, the high speed interruption reduces possible fault damage to equipment.
In addition to the extended life characteristics of the vacuum interrupters, the Ross HV vacuum contactors and relays are built with highly moisture resistant G-10 Epoxy glass as standard insulation (special insulation and insulation lengths can be ordered by contacting the factory.)
Variety of Uses
Ross Engineering basic HV contactors and relays with sealed vacuum contacts are available in single pole, two-pole, and three-pole variations. Models include normally open, normally closed, or double throw units. Latching actuators are also available. The Ross contactors and relays are used in many high voltage power supplies for capacitor bank charging and discharging, current transfer, tap or load selection, or sealed arc interruption. The units are excellent for high speed interruption of up to 10 amps DC or up to 28,000 amps AC. They are also very reliable for high speed crobar or fault diversion to protect sensitive electronic devices. These different functions are accomplished with 1 to 4 milliseconds contact closing or parting time when the vacuum contactor is driven byan SCR triggered stored energy driver. This combination, aided by a high speed vacuum power interrupter, can crobar in 2 milliseconds, divert the fault, then interrupt up to its maximum rated current in approximately 3 to 16 milliseconds total, depending on type of system and current zero timing.
High Voltage Protection
OSHA and other safety organizations require high voltage and line to ground current protection. Ross Engineering's lines of HV vacuum contactors and relays help users and manufacturers meet these regulations- In as little as 2 to 16 milliseconds the unit's high speed trip, driven by a Ross relay driver, can close the contact(s) and divert the fault current, or open the contact(s) and interrupt the load current, or both, thus minimizing damage to the controlled equipment. When proper ground fault or leakage current sensing is used, this can be fast enough to reduce injury to personnel from accidental electrocution as a result of contact with one line and ground or voltages developed in the ground circuit from ground current.
Ross Engineering's HV contactors and relays require only a 1/16" to 1/2" contact opening to obtain voltage withstand of 20kV to 70kV PK (or more for series contacts) Operate times of I to 16 milliseconds are easily obtained using the simple reliable Ross operating mechanism to move the lightweight contacts the short travel required.
Contact resistance is consistently very low, usually less than 10 microhms to 1 milliohm, depending on the type of contact used. Higher continuous currents are also available with the use of Ross high current shunting switches with capacities of up to 36,000 amps. The contacts are readily adaptable to series placement for higher voltages, with a maximum operating voltage of 30kV to 45kV PK per contact, enabling withstand voltage capabilities to 300kV or more.
Each unit's vacuum contact mechanical life is generally at least 10,000 operations to several million operations depending on type of unit, speed of operation, and contact opening distance. Contact electrical life is1 to 10 operations at maximum interrupt to several million at lower currents; and is much more dependent on closing current than on interrupt currents up to several times rated load current. Closing bounce and amp-seconds during arcing are the biggest electrical life determining factors.
Ross Engineering's single contact, normally open, normally closed, latching and trip free type HV vacuum contactors and relays are used at 208V RMS to 30,000V PK, and 50 to 1,200 amps continuous. In most standard applications, voltage ratings are raised in multiples of 30kV (operating) above 15kV (operating) by placing contacts in series. For example, two 15kV rated HB type contacts in series per phase are suitable for 45kV, three contacts in series per phase are suitable for 75kV applications.
Continuous current ratings are 50, 200, 400, 600, 900, and 1,200 amps RMS, with up to 36,000 amps RMS continuous with the use of a shunt switch to carry the continuous current while using the vacuum interrupter's capability for the actual interruption. This switchgear has 60Hz interrupt ratings of 2,000 to 28,000 amps, 10 cycle momentary ratings of 5,000 to 60,000 amps and capacitor discharge to 1,00,000 amps Some 50Hz maximum interrupt ratings are derated 10%.
AC/DC Current Interruption
The Ross Engineering single pole HV vacuum contactors and relays can be used on both AC and DC current interruption. The units' DC rated vacuum contacts can normally be used for limited current interruption to -10 amps DC. Some AC rated contacts can interrupt DC at much higher currents with carefully controlled counter pulses to create current zeros, and slow recovery voltage rates similar to those of 60Hz to 400Hz waveforms. Ross utilizes special tungsten contacts for limited DC current interruption. In some cases, the interruption can be carried to as high as 20 to 40 amps DC. When interrupting DC, transient suppression such as non-linear resistance or the proper size of capacitor in series with an 1 ohm per kV inrush limiting resistor should be used in parallel with the Ross vacuum contacts and the load.
For higher DC current interruption, i.e. several hundred to several thousand amps or more at 15kV DC per contact, or 40kV DC for 2 contacts in series, Ross AC rated contactors with copper alloy vacuum contacts can be satisfactory. This is possible if multiple counter-pulses are applied with a carefully controlled rate of recovery voltage that approximates 60Hz current zero and recovery voltage characteristics by means of a resistor/capacitor and switching network or if in combination with an inductive ringing circuit.
For AC interruption, the Ross contacts are designed with copper alloy combinations to limit current chopping to less than a 1 to 8 amp level to minimize switching transients. AC current interruption generally occurs at the first current zero after contact parting. If contacts are not parted sufficiently for the rate of recovery voltage, or arc energy is very high, current may carry over to the second current zero before clearing. At higher contact voltages and currents, care is taken to insure that contacts do not bounce back after opening, thus reducing contact spacing temporarily. Ross mechanisms are designed to be easily checked for contact erosion limits and over travel to insure that proper over travel and positive contact closing are maintained as erosion continues.
Inductive Load Switching
With highly inductive loads, wherever possible, transient suppressing non-linear resistance or protective capacitors should be placed across the line as close to the load equipment terminals as possible. Standard lightning arresters have not been found as effective as a protective capacitor with approximately 2 ohm per kV of inrush damping resistor in series directly connected across the load. This is particularly essential for repeatedly switched inductive loads such as arc furnaces, motors, and many low current, transient generating inductive loads. Most switching devices can create over voltages on switching and Ross Engineering experience has shown that for iron core reactive loads, normal switching over voltages of 2 to 2-1/2 times operating voltage are to be expected with almost any type of interrupter. Dry type transformers and air core inductive loads can generate higher over voltages if there is insufficient shunt capacitance.
Closing and Inrush Currents
When closing-in on transformers and other iron core inductive loads, normal inrush currents of 5 to 10 times rated load current are expected, depending on the degree of magnetic retentivity from the previous interruption. If iron core inductive loads can be re-energized on the opposite polarity from which they were de-energized, then inrush is minimized, otherwise, it is limited primarily by the circuit and winding resistance. Repeated high inrush closing causes great mechanical stress on the transformer windings as well as rapid erosion of the vacuum contact (which can be over 10 times as great on closing as on interrupting even the same current). Therefore, transformers that have marginal insulation and bracing can deteriorate with repeated switching, regardless of type of switch. A much larger number of transformer failures have probably occurred because of these high inrush currents and poor bracing than from over voltages.
Contact erosion and resultant internal vaporized metal deposit distribution generally determines end of electrical life. I/16" to 1/4" of total erosion is generally the limit. With the proper selection of contact material and with currents under 600 to 1,000 amps, erosion should be very small. At currents between 1,000 and 3,500 amps, erosion should be moderate. At currents approaching maximum interruption rating, life may only be 1 to 100 operations. Even at low to moderate currents, closing generally causes 2 to 10 times as much erosion as interrupting the same currents. Thus, for best long-life current closing, the closing current should be limited. Step-start dual closing contactors which use inrush current limiting resistors are available. Voltage zero and current zero sensing devices for closing or opening are under development.
Actuator Types and Contactor Configurations
They are available with line or stored energy driver opening or closing and anti-pump or automatic reset actuators. Normally open, normally closed, double throw and latching type configurations are available. Standard actuator voltages are 115V, 60Hz for smaller units, 230V, 60Hz is recommended for larger, heavy-duty solenoid actuated units. 208V, 480V, 24V, 60Hz, 50Hz, and 24V DC, 100/125V DC, 400Hz, and other voltages are available. Application information should be furnished along with contact configuration requirements. When ordering or requesting recommendations, actuator voltage should be specified as well as the applicable HV contact operating voltage and current, basic impulse level (BIL), insulation level for HV contacts and HV contacts to actuator or ground, maximum RMS current interrupt, 1 cycle (17 milliseconds) momentary RMS current, 10 cycle RMS momentary current, or peak capacitor discharge current and the RC time constant of the current decay to 35% of peak. Other information such as type of load, number of operations per year, maximum current levels on closing and opening, speed of opening and closing, and number and type of auxiliary contacts required is also necessary for the best application recommendation.
Two auxiliary SPDT contacts are standard on each model. Additional contacts can be ordered.
Specifications are for reference only and are subject to change.
Contact Ross Engineering Corp. for current information.