HV VOLTAGE DIVIDERS
DC up to 10MHz
1kV to 1000kV
For best AC accuracy HV clearances should be a radius equal to twice the height of the unshielded divider. HV withstand clearance should be at least 1 inch (2.54cm) for each 5kV to 10kV for DC or peak AC (RMS x 1.414), to nearest HV or ground. Maximum operating voltages are limited by voltage withstand of internal components, external flashover withstand and temperature rise limits of types with resistive components. On lower resistance units, steady state DC and PK AC may be limited to less than the rated peak short time operating voltage. For withstand test purposes, an impulse rating is also given to indicate the safety factor for transients above rated maximum operating PK voltage which could occur unintentionally. Flashovers may destroy attached measuring and display equipment and endanger personnel associated with it. Therefore safety factors must be observed.
If in a confined area with proximity clearances marginal, the AC divider should be calibrated in place or in a simulated area. DC accuracy is not affected unless corona is present.
For best results when working with fast rise time pulses (particularly 10 usec or less) a single, common, system ground plane should be used at the base of the voltage divider. Display or recording equipment, cables attached to the output of the voltage divider, and personnel near the equipment should be isolated from conductive surfaces or leads with a minimum of capacitance to ground to prevent multiple ground returns which can distort the signal. Where output cable is longer than 20ft, or load is low impedance, Ross fiber optic transmission systems or cable driver 50 or 75 ohm matching amplifiers are available.
Versatility, Wideband And High Accuracy
Ross Engineering Corporation’s lightweight, base-mounted high voltage dividers or hand-held probes are designed for use from 1kV to 1000kV with accuracies of 0.01 % to 3% DC, 0.2% to 10% AC with some model bandwidths to over 20MHz, or pulse to 10 nanosecond rise times. They can be used at any attitude and many are self-supporting up to 10G’s shock. They are available in compensated resistance-capacitance types or uncompensated resistive or capacitive types. Applications include use with panel meters, recorders, digital voltmeters, oscilloscopes, or computers for viewing and recording DC, CW (Continuous Wave), AC, pulse, or modulated frequencies. They can also be used as simple, high-accuracy meter multipliers.
High voltage resistances are usually 2 megohms or 4 megohms per kV to minimize heating and voltage coefficients consistent with compact sizes. High Voltage resistances of 50 ohms or less and as high as 1000 megohms or more per kV are available. High voltage capacitance is usually maintained at low picofarad values to minimize circuit effects.
DC and 60Hz calibration is traceable to the N.I.S.T. Units are matched for 1 megohm, 20 to 50pF typical oscilloscope input impedance or other instrumentation impedances as required, with up to 20 feet (please specify length, the shorter the better for optimum frequency response) of RG59 coaxial cable or special Ross Engineering Corporation coaxial cable. For longer wide-band distances, fiber optic or 50 or 75 ohm coaxial transmission can be supplied for up to 1 kilometer or more. Ross's fiber optic transmission systems are ideal for full isolation to eliminate multiple ground paths or pick-up at the instrumentation level. High voltage terminations are designed for minimum corona. For units with ratings at very high voltage, additional corona and grading rings or toroids are utilized, further minimizing corona and maintaining proper voltage distribution. Insulating surfaces are sealed with anti-track, moisture-resistant material for further corona reduction and environmental protection.
Although the Ross voltage dividers can be ordered for use in oil or other atmosphere, the standard models are designed for use indoors or outdoors in air. Each model is hermetically sealed and filled with a non-toxic insulating gas at low pressure to exclude moisture. The high dielectric strength of the gas makes it ideal for use in voltage dividers. More desirable than heavy solid encapsulation, insulating gas minimizes internal corona by eliminating the possibility of isolated voids or bubbles which could occur if internal components were potted in solid material. Gas also eliminates the weight and less stable dielectric constants and losses of oil, other liquids, or solids, and allows easy dismantling for modification or repair if required. Ross can supply a gas refill kit if needed. See brochure B-1010 and B-1012-A for additional use with digital multimeter or digital panel meter. See brochure B-1020-B for fiber optic transmission systems, or B-1020 for coaxial cable drivers, and matching systems.
Standard maximum operating voltages are from 3kV to 1000kV DC or PK AC, and to 1,500kV impulse, in steps of 2kV to 15kV. It should be noted that transient and intermittent single short pulse operating voltage can be 50% or more beyond the low frequency or DC steady-state rating, depending on the type of divider.
Derating for CW RF
With frequencies above 100kHz, steady state CW (Continuous Wave) voltage derating depends on the type of compensating capacitors and the type of insulation. Maximum RF voltage operation is generally limited by dielectric heating of insulation, therefore, units with special insulation are available for CW at these higher frequencies. Please inquire about special insulation if your application may require its use.
Multimeters, Oscilloscopes, Power Quality Recorders, Fiber Optic Transmitters, 50 or 75 Ohm Matching Amplifiers and Instrumentation Systems
Ross Engineering Corporation can supply wide-band DC-1MHz fiber optic, or coaxial transmission DC to over 35MHz and matched recorder or display systems to provide you with a complete measurement or display system. Please see brochures: B-1010, B-1010-A, B-1012-A Digital Multimeters, B-1020 Matching Amplifiers and B-1020-B Fiber Optic Transmission Systems for more information on our transmission, display, and recorder systems.
Accuracy and Stability
Accuracy and stability in standard Ross voltage divider units is generally better than ±0.1% DC, ±0.5% 50/60Hz, and 3% to 10% to 1MHz-10MHz, at better than 30PPM/ºC Temperature coefficient and 0.1 to 0.5PPM/V Voltage coefficient. Accuracies to 0.01% DC at less than 5PPMTC, low voltage coefficients and 0.2% AC or better (over specific frequencies) available on many models. See brochure B-1011-B.
Calibration charts related to N.I.S.T. can be furnished for each 10% or 20% Voltage Point to allow Correction factors to better than 0.1%, or better than 0.01% for the 0.01% types, Frequency charts DC-20MHz are available as well as temperature stability (drift) with warm-up time. Useful frequency response is generally DC to 5MHz (to 10MHz and up to 20MHz on some models) with 250 to 10 nanosecond rise times. Wide-band accuracy is generally better than 3% to 10% over the frequency range, but can be to 0.2% or better at some specific frequencies and with proper proximity or shielding. Phase shift is generally minimal below 100kHz for wide-band types and negligible at 60Hz.
For highest accuracy in high impedance, low input capacitance types, consideration must be given to induced voltage pick-up in leads, contact potential, corona, effective capacitance, and voltage gradient and capacitance shift related to proximity to high voltage sources, ground planes, walls, enclosures, and loads. Preferably the divider should be calibrated with the specific instrument being used and specific proximities if extreme accuracy is required, Greatest accuracy, particularly AC accuracy, is attained with proper ground plane and if maximum clearance to conductive materials, which can cause capacitance variation and corona. If available, user's proximity dimensions will be simulated when calibrating.
Maximum accuracy is centered around two-thirds to three-quarters of the DC or PK AC rating, unless otherwise requested. For higher frequencies, the lower capacitance, lower ratio models with shortest output cables have fewer resonances above 1MHz, but proximity effects are greater and must be considered for best AC accuracy and wave shape transfer. If larger diameters are allowable, special shields are available to eliminate proximity variations for extremely high accuracy AC or pulse wave shape requirements and to provide better voltage grading. Operating temperatures range from -80ºC to +65ºC ambient. Some units can be built to withstand up to +75ºC ambient and vibration and shock of up to 50G's or more.
Ratio and Loading
In the standard 1000/1 or 10,000/1 Ross voltage dividers the low voltage capacitors and resistors are selected to provide correct ratios when shunted by 1 megohm, 20-50pF oscilloscope (or other load), plus 2, 3, 6, 15, or 20 feet (please specify the shortest practicable length) of low capacitance RG59 or special Ross Engineering Corporation coaxial cable unless otherwise required. Standard cable lengths are 3 or 6 feet for 15kV or 30kV dividers, 15 feet for dividers above 30kV, For the compact types, with metal oxide resistors, DC ratio is generally stable within better than 0.1% to 1% in an operating range of over 80 degrees C ambient temperature change for most models, and even better than 3-5 PPM/ºC (0.0003%) for most high accuracy types. In 0.1% dividers with less than 4 megohms per kV, units can drift up to 0.1% - 0.3% as they warm up when used continuously at maximum rating, less at below maximum rating. However, repeatability remains at 0.1% after stabilizing. The actual voltage divider ratio is determined by the following formula:
If the high voltage input resistance is high and the HV capacitance and ratio selected are low, normal external and added load capacitance including coaxial cable and resistance of many display or recording devices can seriously affect the ratios. The relationships in the ratio formula will indicate where and to what extent low frequency response or ratio becomes affected. Special ratios, capacitances, and resistances are available to satisfy most matching problems, however output cable length and instrumentation load must always be considered.
Specifications are for reference only and are subject to change.
Contact Ross Engineering Corp. for current information.