HRT - 24 & 48 Volt
Reduced-Height Rectifier
Single-Phase, Controlled Ferroresonant, Reduced-Height Rectifiers
for Telecommunications and Utility
The HRT Series
- 24- and 48-volt models
- 15- to 200-ampere output
- Three reduced heights:
12.25, 17.5 and 24.5 inches - Compact design permits more power in the same rack space
- All pc boards and user operating controls accessible through front panel
- Ferroresonant design features voltage regulation, high efficiency, high power factor, low noise levels, current limiting, low maintenance, and low operating costs
- Battery eliminator operation standard
Controlled ferroresonant rectifiers have many inherent advantages, including voltage regulation, short-circuit protection, low operating costs (high efficiency and high power factor), and low maintenance.
HRT float rectifiers combine these inherent advantages with state-of-the-art circuitry , user-oriented packaging, and a compact size. The HRT Series float rectifiers are easily adjusted to meet your special operating requirements. Their quality and craftsmanship provide years of trouble-free service.
Input
All transformers are dual wound for 120-, 208-, and 240-volt, single-phase, 60 Hz operation.
Regulation
DC voltage regulation is maintained within the limits set forth in NEMA PE-7 at any load from no load to full load at:
- ± 1/2 percent regulation over the ambient temperature range of 32F (0C) to 122F (50C).
- One percent (±1/2%) regulation with ac input variations between +6 /-12 percent of nominal input voltage and frequency variations between 57 to 63 Hz while floating/ equalizing the rated number of cells.
Control is accomplished with a single control board for all ratings of chargers and does not require modification for operation of battery.
During operation, the maximum voltage transient does not vary more than five percent of the initial steady state voltage for sudden load changes between 20 percent and 100 percent of rated output. Recovery takes less than 200 milliseconds, and all transient behavior disappears within 500 milliseconds. Operation of the battery is stable within stated limits under all conditions of line and load.
Turn-on under all conditions of line and load has a "soft-start" characteristic without overshoot. The output voltage and current are increased gradually to the rated level over a 10-second interval.
Electrical Noise
Filtered to less than 30 millivolts (rms) with electrical noise less than 22 dBrn with C message weighting on 3A noise measuring set when connected to a battery with an eight-hour capacity rating of four times the charger current rating. Electromagnetic interference (EMI) limits also meet FCC Part 15, Subparagraph J for Class A compliance.
Under rated conditions, the TIF does not exceed 30.
Principles of Controlled Ferroresonant Operation
The controlled ferroresonant transformer has inherently good regulation of output voltage against wide variations of input voltage. Its high reactance also provides protection against overload and short circuit of the output. However, the output does vary with changes in load and frequency. The output winding is on the same leg of the core as the resonant winding, and the resonant capacitor acts to maintain this core section at a high level of saturation, resulting in a fairly constant voltage. To provide a precise constant voltage, it is necessary to control this level of core saturation. This is accomplished in HRT Series rectifiers by shunting the resonant circuit with a switching device in series with an inductor.
As shown in the block diagram, the HRT circuit senses the start of the resonant capacitor charge cycle and switches the thyristor on to interrupt the cycle. The point of interruption is delayed by a signal fed back from the output to allow the voltage to rise to the pre-set level. If the current exceeds a pre-set level, the signal from the ammeter shunt overrides the voltage regulator to limit the current. Thus, precise control of voltage and current is maintained. If a fault occurs, allowing a higher voltage to develop, a sensing circuit causes the ac input breaker to shut down the rectifier.
Current Limiting
Current limiting circuitry is factory set at 105 percent of rated dc output but can be adjusted down to 80 percent. This feature automatically protects the charger even if the output terminals are accidentally shorted.
Float And Equalization Voltages
To accommodate different kinds of batteries, both the float and equalize voltages are continuously adjustable (no taps) over the nominal voltage range of 2 to 2.35 volts per cell. For 24-volt models, the range is 24 to 28.2 volts; for 48-volt models, 48 to 56.4 volts. Float and equalize adjustments are not interactive. They can be set independently.
Circuit Protection
A two-pole, UL-recognized, shunt-trip ac circuit breaker is provided for input protection and rectifier shutdown in the event of a high dc voltage condition. A single-pole, UL-Iisted, dc circuit breaker is provided in the appropriate leg for output protection for telecommunications models.
A summary alarm relay will indicate any combination of high-voltage alarm, low-voltage alarm, no-charge alarm, high-voltage shutdown, or rectifier failure alarm. A dc no-charge alarm typically is set to operate when the output current is less than two percent of the rated current but may be adjusted for other threshold values.
Ambient Operating Temperatures
All HRT rectifiers will operate, at current limiting, continuously in ambient temperatures from 32F (0C) to 122F (50C). These units can be safely stored for up to one year at temperatures from -40F (-40C) to 185F (85C).
Battery Eliminator Operation
HRT rectifiers are provided with standard filtering to reduce ripple to 30 mv rms or less for operation as a battery eliminator. The electrical noise level for battery eliminator operation is less than 32 dBrnc.
Load Sharing
Load sharing is standard on all HRT rectifiers. Units will share the load within five percent of the rating of the largest rectifier and between 10 percent and 100 percent of their combined ratings.
Mechanical Features
- All controls and adjustments are recessed to prevent accidental operation.
- Removable front panel gives access to all service adjustments while providing maximum protection against electrical shock.
- Circuit breakers are mounted in a fixed position, eliminating the need for hinged ac and dc power cables.
- Hinged control panel provides easy access to all operator controls and adjustments.
- All cabinets can be relay rack or wall mounted. Large cabinets also can be floor mounted.
- Cabinets have a baked epoxy powder finish (ANSI-61 gray).