Table of Contents
The DC Power System
1
1.1 DC Power Overview 1
1.2 Rectifier 7
1.3 Battery 16
1.4 Distribution 27
1.5 Battery Return Bus 31
1.6 Supervisory and System Control 33 1.7 Low Voltage Disconnect Contactor 40
1.8 CEMF Cell 43
1.9 Battery Temperature Compensation 45
1.10DC - DC Converter System 51
1.11DC Power System Integration 54
1.12Inverters/UPS 58
Power System Sizing and Ordering
62
2.1 Calculations 62
2.2 Formulas 65
2.3 Power System Design Example 66 2.4 Ordering Information for Power Systems
and Loose Items 67
Site Engineering for DC Power
69
3.1 Site Layout and Loading 69
3.2 Grounding Network 71
3.3 Surge Protection Devices (SPD’s) 74
3.4 Wiring 76 3.5 Engineering Drawings 80
Initial Installation
81
4.1 Safety Precautions 81 4.2 Tools List 83 4.3 Inspection 844.4 Power System Assembly/Mounting 85
4.5 Battery Installation 86
4.6 Cabling 89
4.7 Power Up Procedure 92
4.8 Battery Initial Charge and Discharge Test. 94
4.9 Documentation 95
Power System Commissioning
97
Retrofit Installation
99
6.1 Precautions 99
6.2 Tools List 100
6.3 Distribution Circuit Addition 100 6.4 Common Ground Bus Addition 100 6.5 Distribution Panel Addition 101
6.6 Rectifier Addition 103
6.7 Shunt Replacement 103
Maintenance and Field Repair
105
7.1 Power System and System Controller 105
7.2 RST Rectifiers 107 7.3 RSM Rectifiers 109 7.4 Pathfinder 24-3kW, 3kW, and 48-10kW Rectifiers 112 7.5 CS and CSM Converters 114 7.6 Vented Batteries 116
7.7 Valve Regulated Lead Acid (VRLA)
Batteries 118
7.8 Battery Failure; Detection, Prevention
and Corrective Action 119
Troubleshooting
121
CHAPTER
The DC Power System
The DC power system is a vital part of the communications network.
M
ost communication equipment, including PBX’s, telephone switches,
microwave transmission, fiber optic transmission, mobile radio, cellular,
etc. are designed to operate from a DC input voltage. A DC source has the
inherent benefit of higher reliability as compared to an AC source. This is
because the battery, which is often used for backup, is directly connected to
the load with no intermediate stage such as an inverter that may fail and
disrupt power to the load. The basic power system consists of a rectifier and
usually a battery, but may include various other components. The various
components are discussed in detail later in this section.
1.1 DC Power Overview
1.1.1
Typical DC voltage and current requirements
The two most common input voltage requirements for
communication equipment are +24V and -48V. The use of -48V is rapidly becoming the most predominate as this is the maximum safe working voltage according to both the National Electrical Code (NEC) and the Canadian Electrical Code (CEC) that has no current limiting requirements. The high voltage reduces the current requirements making fuses/circuit breakers/cables smaller.
+
24V evolved from the mobile radio industry, where equipment was designed to operate from either an automotive (+12V) charging system or a truck (+24V) charging system.-
48V evolved from the telephony world where 48 volts was chosen because it was the maximum voltage that was considered safe as technicians had to make live connections. The negative polarity (positive ground, similar to the old British -6 VDC automotive charging system) was chosen as it reduced the galvanic corrosion that occurred when the lead sheathed telephone twisted pair cables were originally deployed and buried in the earth.L
o
a
d
L
o
a
d
L
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a
d
A C P o w e r O nD
C
D
C
D
C
A C P o w e r O ff B a tt e ry B a tt e ryA
C
A
C
DC PS B0 1A R e c ti fi e r R e c ti fi e r-
+
-
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Lo ad ad LoTable A
Typical Telecom Equipment Voltage and Current Requirements
Application Voltage Current Notes
Mobile Radio Base Station
+12 VDC <50 Amps
Analog Cellular Base Station
+24 VDC 200-800 Amps
Microwave transmission station
+24 VDC <400 Amps
Mobile Radio Base Station
+24 VDC <50 Amps
Digital Cellular Base Station
+24 VDC 100-600 Amps
Digital Cellular Base Station
-48VDC 100-400 Amps
Microwave transmission station
-48VDC <600 Amps
Fiber optic transmission station -48VDC <100 Amps Telephone switching center (pedestal) -48VDC 20-100 Amps Telephone switching center (remote) -48VDC 50-200 Amps Telephone switching center (large) -48VDC 200-10 000 Amps PBX -48VDC <100 Amps
Pay phone coin control +/- 130 VDC < 5 amps History
Fiber in the loop (FITL) + 130 VDC 100 VA per circuit Microwave transmission
traveling wave tubes, etc
Typical AC voltage sources
There are many different voltage sources around the world. Identify the source that you are using and watch the rectifiers to the source. See Table B.
Service Configuration L–L Volts L-N Volts Where used? Notes
120/240V 1 PH 3W
Single Phase 240 VAC 120 VAC USA, Canada
120/208V 3PH 4W
Three Phase Wye
208 VAC 120 VAC USA, Canada 277/480V 3PH
4W
Three Phase Wye
480 VAC 277 VAC USA
347/600V 3PH 4W
Three Phase Wye
600 VAC 347 VAC Canada
208 V 3PH 3W Three Phase Delta
208 VAC N/A USA, Canada
480 V 3 PH 3W Three Phase Delta
480 VAC N/A USA
220/380 V 3PH 4W
Three Phase Wye
380 VAC 220 VAC Europe Asia
South America
Table B
Typical AC Commercial Voltage Sources
Figure 3
Three Phase Delta
1.2 Rectifier
1.2.1
Description
The rectifier is a device that changes an AC (alternating current) input to a regulated and filtered DC (direct current) output. The DC output supplies power to the load (communication equipment) and charges a backup battery if required.
1.2.2
Connection
The rectifier is connected in parallel with both the load and the battery (if applicable). Multiple rectifiers may be connected together in parallel, with their corresponding (+) and (-) leads connected together.
1.2.3
Operation (Float charge mode)
The rectifiers are adjusted to the voltage requirement (float voltage) of the battery and to “share” the load or supply the same output current in systems with more than one rectifier.
AC-ON - The rectifier supplies current to the load and provides a trickle charge current to the battery.
AC-OFF - The rectifier turns off and the battery will supply current to the load until the battery is completely discharged.
AC-ON - The rectifier supplies current to the load, any extra
current available from the rectifier will be used to recharge the battery.
1.2.4
Sizing details
The rectifier size is chosen by determining the most cost-effective means of satisfying the total capacity requirements.
N+1 redundancy should always be considered. N is the number of rectifiers required to satisfy the total capacity requirements of the load and the “1” is an extra rectifier added so that a failure of a rectifier in the system will not jeopardize system integrity.
Correct choice of either positive ground (-48VDC) or negative ground (+24 VDC) is critical. The grounded potential is connected to a common point and the “live” cable is connected through either fuses or circuit breakers. Refer to power system design calculation section.
1.2.5
Features and selection criteria
Low output noise/ripple ensures that the load is unaffected by the rectifier in both battery and more importantly battery-less operation. Note: the battery acts as a filter, but VRLA batteries will fail prematurely when connected to rectifiers with high output ripple voltage.
Tight voltage regulation (line and load) to ensure that the battery is properly charged and the load does not receive
fluctuating voltages.
Modular vs. monolithic configuration; modular rectifiers allow for easy replacement and expansion.
Unity power factor (P.F.>.95) is becoming more important as the utilities move toward increased monitoring of power factor. A poor power factor at your Telecom facility may result in the electrical utility adding a surcharge to your electrical bill. In Europe, unity power factor is a CE requirement for Residential and light commercial applications. North America may soon follow this trend. There are two types of power factor
measurements displacement and true. The displacement component of power factor is the ratio of the active power of the fundamental wave (60 Hz), in watts, to the apparent power of the fundamental wave in volt-amperes. This is the value used by utilities to
determine billing. True power factor is the ratio of the total power input, in watts, to the total volt ampere input, this includes the fundamental wave (60 Hz) and all the harmonics (120, 180, 240, 360, 480 Hz, etc. This value is used for efficiency calculations. Early Argus rectifiers utilize passive power factor correction to achieve reasonable power factor at low cost. The Pathfinder rectifiers offered by Argus have a true power factor of >.99.
Figure 5
Power in an Inductive Circuit
Figure 6
Power Factor Triangle
Low THD (total harmonic distortion) and damaging harmonic currents to meet CE requirements and to eliminate AC generator and transformer overheating and interaction
problems. THD refers to the distortion of the incoming AC voltage or current waveform when the rectifier is connected and is
Three phase AC input - For higher power applications this becomes more important to ensure even balancing of load on a three-phase AC source.
High efficiency as well as having the obvious power savings benefit, reduces the size of the input feeder circuit breaker and input cabling.
Wide AC operating window for both frequency and voltage to tolerate fluctuations without the rectifier shutting down. Argus rectifiers have a wide input tolerance range for both frequency and voltage. This allows uninterrupted operation and also allows universal operation for 208/240V 60Hz operation and 220V 50 Hz operation with no modification or reconfiguration required.
Pathfinder 48-3kW & 24-3kW rectifiers (208/240 VAC I/P) will continue to operate down to 90 VAC (with reduced output)!
Compact and lightweight helps reduce installation, maintenance and shipping costs.
Balanced load sharing should be achieved between units of the same design and with other types of rectifiers. Argus rectifiers accomplish this with a combination of forced sharing
(master/slave) and/or adjustable slope regulation. Adjustable slope allows you to tailor the voltage regulation characteristics of different brands of rectifiers.
• Forced sharing works by the rectifiers electing a master unit (the rectifier with the highest output voltage). The other rectifiers are forced to adjust their output voltage to track the master and therefore share the load.
• Slope Regulation (Output Voltage) allows the user to drop the output voltage of the rectifier a small amount from no load to full load. This is done at a fixed rate. The slope in the voltage regulation of the rectifiers helps to allow the user to set the rectifiers to load share easily and also allows you to tailor the voltage regulation characteristics of different brands of rectifiers.
Figure 7
Output Slope Voltage Regulation and Current Limit
Adjustable current limit restricting output current of the rectifier, in either a discharged battery or overload condition. The rectifier can operate in this condition without damage.Power limit allows the rectifier to supply greater output current when the output voltage of the system is low. This reduces battery recharge time and also provides greater overload capabilities reducing the need for redundant rectifiers.
Figure 9
Power Limit (P 48-3kW) - Current Limit (RSM 48/50)
Comparison
A float/equalize mode selector switch allowing selection of two operating modes:
1. Float mode for normal charging of the battery. 2. Equalize mode for boost charging (at a higher
charging voltage) of batteries when required. This boost charging eliminates any sulfation on the battery plates resulting in cell voltage imbalances and poor performance. This is an important feature for vented lead calcium batteries floated at reduced voltage levels. Typically not required with VRLA batteries under normal operating conditions.
Automatic high voltage shutdown (HVSD) or over-voltage protection (OVP) to switch the rectifier off in case of
a high output voltage condition, preventing damage to the batteries and load. An automatic restart feature should be included in the event that a site temporary abnormality surge as a ground surge resulted in the HVSD.
Soft-start gradually steps each rectifier on-line at power up. This eliminates start-up current surges associated with many rectifiers. The feeder breaker and feeder size requirements are decreased, reducing the installation costs of the rectifier.
Adjustable delay start allows staggered start-up of rectifiers reducing stress on the AC generator and also allows the rectifiers to be started after the site air conditioner compressor (drawing high surge current) has started.
Alarms provide indication of rectifier failure and should be of “fail safe” design. Local indication plus remote relay contacts are required.
Remote sensing leads are connected directly from the battery to the rectifiers via a sense fuse distribution panel located in the supervisory panel. This allows the charger output voltage to be regulated at the battery improving voltage regulation at the battery. This is important with power systems that incorporate separate charge and discharge circuits or power systems where there may be a significant voltage drop in the battery cables. If this feature is not connected, the rectifiers automatically revert to internal sensing, regulating the rectifier output voltage to the rectifier output terminals.
Remote Control and Monitoring allows the rectifiers to be remotely controlled and monitored from a central supervisory and control panel.
Model Voltage Current Features
Pathfinder 24 VDC 18, 50,100 A Convection or fan cooled
RSM 48/10 48 VDC 10, 30, 50, 180 A Modular design
200 kHz resonant converter design
RSM 24 VDC 7.5, 50,100 A Convection or fan cooled
48 VDC 15, 30, 50, 100 A Modular design
100 kHz forward converter design Passive power factor correction
RST 12 VDC 50, 100 A Convection cooled
24 VDC 30, 50, 100 A Monolithic Design
48 VDC 15, 30, 50, 100 A 48 kHz forward converter design Passive power factor correction
1.2.6
Theory of Operation RSM 24/50, 24/100,48/30 and 48/50
Please refer to the power circuit block diagram. The 184-264 VAC 50/60 Hz input is fed through a circuit breaker into a full wave rectifier, which provides a 120 Hz 340 V peak pulse train to an input filter circuit. The input filter provides a nominal 290 volts DC "raw supply" with approximately 30 VP-P 120 Hz ripple to the
transistor switching circuit.
The transistor switching circuit chops the raw supply into
nominally 525VP-P, 100 kHz rectangular waveform with a nominal
66% duty cycle. This waveform is fed into a ferrite power transformer, which steps down and isolates the high frequency switching waveform. A rectifier circuit converts the power
transformer output to a DC pulse train of nominally 136 V peak. A two-stage output filter averages and smoothes this pulse train down to provide the nominal 52 VDC output with low noise. A voltage error amplifier circuit senses the output voltage and compares it with the voltage reference to provide a voltage error signal. Similarly, a current error amplifier senses the output current using a shunt resistor and scaling amplifier to compare the output current to the desired maximum output current to provide a current error signal.
These signals are fed into the pulse width modulator (PWM) via OR-ing circuitry so that either voltage or current regulation is achieved. The pulse width modulator controls the "ON" time of the switching transistors to vary the output as commanded by the error amplifiers. It also senses the switching transistor current on an instantaneous basis to provide cycle-by-cycle protection of the switching transistors. An auxiliary supply, powered via a small 50/60 Hz transformer, and a DC/DC converter power the control circuit and front panel circuitry. The PWM receives the ON/OFF command and clock signal from the front panel circuit and control circuitry.
F ro n t P a n e l C ir c u it M ic ro P ro c e s s o r In p u t R e c ti fi e r In p u t 1 8 5 -2 6 5 V A C 5 0 /6 0 H z 6 0 H z 1 2 0 H z 5 2 5 V 2 5 0 V 1 3 6 V 0 V 5 2 V ( 4 8 V U n it s ) 2 9 0 V D C 1 0 0 k H z + 3 4 0 V -34 0 V O V A u x il ia ry S u p p ly L o c a l C u rr e n t S e n s e O u tp u t V o lt a g e S e n s e O u tp u t C u rr e n t S e n s e P u ls e W id th M o d u la to r (P W M ) In p u t F il te r & S to ra g e C a p a c it o rs T ra n s is to r S w it c h in g C ir c u it O u tp u t R e c ti fi e r Is o la ti o n B o u n d a ry T ra n s is to r D ri v e D C /D C C u rr e n t E rr o r A m p li fi e r V o lt a g e E rr o r A m p li fi e r O u tp u t F il te r S h u n t O r G a te V A IN U X I Ou t V o lt a g e R e fe re n c e C u rr e n t R e fe re n c e - A d ju s tm e n ts - D is p la y - M o n it o ri n g V O u t C o m m u n ic a ti o n O n /O ff C o m m a n d O u tp u t R e m o te S e n s e D C P S H 0 7 A
-+
+
1.3 Battery
1.3.1
Description
The battery is an electro-chemical means of energy storage. When AC power is interrupted to the rectifiers or when there is
insufficient current available from the rectifiers to support the load requirements, the battery will automatically supply current to the load. The battery may be used in combination with a generator to provide back-up power for extended time periods to the load. A battery consists of a series connection of multiple cells. The number of cells in series is determined by the operating voltage of the system and the operating voltage of each cell.
1.3.2
Connection
The battery is connected in parallel with the rectifier and the load.
1.3.3
Operation
As detailed in the rectifier operation section.
Some batteries may require periodic equalization. Equalization is where a higher boost voltage is applied to the battery to ensure the proper cell voltage balance and correct conditioning of the battery cells.
Parameter Valve Regulated Lead Acid Battery (VRLA) Flooded or Vented Battery
One Cell 24 V System 48 V System One Cell 24 V System 48 V System
Nom. V 2 24 48 2 24 48 Float V 2.25 27 54 2.20 26.4 52.8 Equalize V 2.30 27.6 55.2 2.30 27.6 55.2 End V 1.75 21 42 1.75 21 42 Op. Win. V 1.75-2.30 21-27.6 42-55.2 1.75-2.30 21-27.6 42-55.2 # cells 1 12 24 1 12 24
Table D
Typical battery operating parameters
1.3.4
Sizing details
Determine your load profile (i.e. amps per hrs) and select the battery using the manufacturers sizing table (See: Table E). Batteries are rated using the following criteria:
Temperature (25 deg C in North America, 20 deg C in Europe).
Endvoltage (the lowest voltage that the cell is discharged down to). The end voltage used in calculations is usually the minimum voltage that the battery can be discharged down to without damage. A more conservative end voltage will increase the life expectancy of the battery but reduce back up time.
Refer to IEEE battery sizing guidelines for calculating battery size for complex load profiles Evaluate battery charge rate for sizing intercell and inter-tier connectors
Apply temperature performance correction factor for average temperatures below 25 deg. C, (77 deg. F), if applicable (See:
Table F).
Ensure that the battery operating voltage coincides with the acceptable operating voltage window for the equipment connected. Apply the beginning and end of life de-rating factor. This factor is 20% and allows for:
• The battery shipped at less than 100% capacity, typically 90% (Full capacity is achieved after a short period of float service).
Cells that are “tank” formed ship at 100 % capacity.
• Battery end of life considered as 80% of capacity
(See: Figure 11).
Battery capacity is determined by the number & size of the plates, therefore the larger the battery the greater the capacity.
Battery strings may be connected in parallel to obtain additional capacity. Strings should be equal in capacity and interconnecting cables should be of approx. the same size and length to obtain optimum charge and discharge characteristics. The maximum recommended number of parallel strings is three.
Smaller applications commonly use mono-block batteries. Mono blocks are batteries that have more than one cell contained in the assembly (i.e. an automotive battery is a 6 cell 12 VDC mono-bloc).
Average Cell Performance Data
*Discharge rates in amperes.
1.215 SP. GR. ELECTROLYTE AT 77° (25°C), INCLUDING CELL CONNECTORS
TYPE NOM. A.H. CAP. 72 HR. 24 HR. 12 HR. 8 HR. 5 HR. 4 HR. 3 HR. 2 HR. 1.5 HR. 1 HR. 30 MIN. 15 MIN. 1 MIN. TO 1.50 VPC 1 MIN. To 1.75 VPC Final EA-5 230 4.6 11.1 18.8 26.6 44.0 49.9 59 75 87 102 152 197 290 530 EA-7 270 4.8 12.9 23.7 33.3 49.0 58.5 73 98 120 154 226 291 426 790 EA-9 350 6.4 17.2 31.6 44.4 65.3 78.0 97 131 160 205 298 380 548 1010 EA-11 440 8.0 21.5 39.5 55.5 81.7 97.5 122 164 199 257 367 465 685 1270 EA-13 530 9.6 25.8 47.4 66.6 98.0 117 146 197 239 308 435 558 792 1460 EA-15 620 11.2 30.1 55.3 77.7 114 137 171 229 279 359 507 651 924 1700 EA-17 710 12.8 34.4 63.2 88.8 131 156 195 262 319 411 571 728 1010 1870 EA-19 800 14.4 38.7 71.1 99.9 147 176 219 295 359 462 634 801 1100 2030 EA-21 890 16.0 43.0 79.0 111 163 195 244 328 399 513 694 870 1190 2200
*Rates shown depict average values and are subject to IEEE-485
CONSTANT CURRENT DISCHARGE RATINGS AMPERES @ 77°F
Operating Time To End Point Voltage
End Point Volts/ Cell 5 min. 15 min. 30 min. 60 min. 2 hr. 3 hr. 4 hr. 5 hr. 6 hr. 7 hr. 8 hr. 10 hr. 12 hr. 20 hr. 24 hr. 48 hr. 72 hr. 100 hr. 1.75 274 162 105 61.5 34.8 25.0 19.6 16.2 14.0 12.3 11.0 9.08 7.79 5.00 4.19 2.13 1.43 1.04 1.80 240 151 99.0 60.1 34.0 24.2 19.0 15.8 13.6 11.9 10.7 8.80 7.58 4.89 4.10 2.10 1.42 1.03 1.85 203 136 92.0 55.0 31.4 22.8 18.0 15.0 12.9 11.3 10.1 8.44 7.23 4.67 3.92 2.02 1.37 0.99 1.90 156 110 75.0 47.0 28.9 21.0 16.8 14.0 12.0 10.6 9.50 7.90 6.73 4.34 3.65 1.88 1.26 0.91Electrolyte C Temperature F Cell size correction factor -3.9 25 1.520 -1.1 30 1.430 1.7 35 1.350 4.4 40 1.300 7.2 45 1.250 10.0 50 1.190 12.8 55 1.150 15.6 60 1.110 18.3 65 1.080 18.9 66 1.072 19.4 67 1.064 20.0 68 1.056 20.6 69 1.048 21.1 70 1.040 21.7 71 1.034 22.2 72 1.029 22.8 73 1.023 23.4 74 1.017 23.9 75 1.011 24.5 76 1.006 25.0 77 1.000 25.6 78 0.994 26.1 79 0.987 26.7 80 0.980 27.2 81 0.976 27.8 82 0.972 28.3 83 0.968 28.9 84 0.964 29.4 85 0.960 30.0 86 0.956 30.6 87 0.952 31.1 88 0.948 31.6 89 0.944 32.2 90 0.940 35.0 95 0.930 37.8 100 0.910 40.6 105 0.890 43.3 110 0.880 46.1 115 0.870 48.9 120 0.860
Table F
Temperature Performance Correction Factor Table
For further information, please refer to:
• IEEE-485-199 - IEEE recommended practice for sizing large lead-acid batteries for stationary applications.
• IEEE-1184 - IEEE guide for the selection and sizing of batteries for uninterruptible power systems.
• IEEE-1689 - IEEE guide for the selection of valve-regulated lead-acid (VRLA) batteries for stationary applications.
Figure 11
Battery Performance vs. Time
1.3.5
Features and selection criteria
There are three main types of lead acid batteries that are used in telecommunication applications. The three types, based on acid classification, are listed below.
Acid Classification Description Advantages Disadvantages
Flooded Technology free liquid electrolyte, similar to an automotive battery
-proven technology
-flat, tubular, plant options -best life expectancy of lead acid batteries at higher operating temperatures -high maintenance -transportation restrictions VRLA-AGM (Absorbed Glass Mat) Technology
a small quantity of liquid
electrolyte is held in suspension in the fiberglass mat
-low maintenance -minimal vented gasses
-easy installation in any position -easier shipping classification -will not freeze
-difficult to evaluate battery state of health
-rapid reduction of life expectancy when operated at high
temperatures (above 25 deg C)
VRLA-Gel Technology
fumed silica is added to gel the liquid electrolyte
-lasts longer than AGM at high operating temperatures
-performance (AH per kg) is less than AGM battery
Cycling requirement - different cell plate alloys and plate configuration affect the cycling (charge and discharge)
performance of the battery. Determine the cycling requirement of your application (i.e. float with light cycling, float with heavy cycling and full cycle service) and choose the correct battery for the application. Rate of discharge: High < 15 minutes Medium 15 min. - 2 hr. Low 2 hr + Maintenance requirements.
Physical design parameters, ventilation, floor loading, available space.
Cost including life expectancy.
VRLA batteries of both AGM and “gel” type are usually the first choice for backup. Some of the important features to look for in a VRLA battery are:
• Jar material with low water vapor diffusion rate i.e. polypropylene or PVC to prevent dry out.
• Flame retardant jar materials.
• Even compression of plates through a fixed method of jar compression to maintain, plate to microporous separator integrity (AGM).
• Designed to prevent strap corrosion and lug corrosion (AGM).
The Battery may be packaged on a traditional battery stand or be of bolt together self supporting construction. For smaller battery strings the use of relay rack shelves or cabinets is a consideration. There are also AGM batteries available from the manufactures prepackaged for easy installation into a relay rack.
1.3.6
Argus Technologies Solutions
DC PS B0 2A R e c ti fi e r # 2 R e c ti fi e r # 1 C h a rg e ( -) C ir c u it B re a k e r D is tr ib u ti o n B a tt e ry
-
+
-
+
C h a rg e ( + ) S h u n t B a r T e rm in a ti o n P a n e l Lo ad G ro u n d B a r Lo ad1.4 Distribution
1.4.1
Description
Fuses and circuit breakers are used to safely distribute the DC power from the rectifier and battery to the loads. These devices protect the loads and load cables from short circuits, overload conditions and allow easy manual shutoff . This helps to isolate faults between circuits. Circuit breakers and fuses are also used for protecting the battery and battery cables and to allow an easy means of disconnecting the battery from the system for safety, fire prevention and maintenance.
1.4.2
Connection
Primary Distribution
Load fuses or circuit breakers located at the power system are connected in series between the power system and the loads and/or between the power system and the battery.
Secondary Distribution
Large main fuses are installed in the power system to distribute dc power to remote BDFB’s (Battery Distribution Fuse Board’s) or BDCBB’s (Battery Distribution Circuit Breaker Boards). From the BDFB power is distributed to the loads with smaller individual circuit breakers.
1.4.3
Operation
Fuse
Excessive current flowing through the fuse melts the internal link, disconnecting the load from the power system. A guard fuse is connected in parallel with the main fuse and will blow when the main fuse blows. The guard fuse provides a local indication and also will send an external alarm signal via a built-in contact.
Circuit breaker
Excessive current flowing through the circuit breaker causes excessive heat (thermal) or an excessive magnetic field (magnetic) to trip the circuit breaker to the off position. Alarm sending is via breaker auxiliary contacts or electronic trip detection circuitry.
Electronic trip detection circuitry
A 10 000 ohm bypass resistor is connected across the circuit breaker (to limit current) and the output voltage of the circuit breaker is monitored. The benefit of the circuit is that an alarm is indicated only when a breaker is off with a load connected and no connection to the auxiliary contacts is needed.
Breaker ON with no load voltage on breaker output is high no alarm.
Breaker ON with load voltage on breaker output is high no alarm.
Breaker OFF with no load voltage on breaker output is high (due to bypass resistor) no alarm.
Breaker OFF with load voltage on breaker output is low (due to load forcing voltage down to zero V)
alarm is indicated.
Voltage will be measured on the output of a circuit breaker even when the breaker is off, however current flow is limited to a few mA due to the 10,000 ohm resistor.
Sizing
Most communication equipment requires fuses or circuit breakers with short delay curves “fast blow” to provide proper protection Fuses with different curves may be utilized to match specific load requirements.
Load fuses and circuit breakers should be sized 1.25 to 1.5 times the maximum continuous anticipated load on the circuit for reliable operation.
Battery fuse/circuit breaker should be sized at 1.25 times the maximum current rating of all the rectifiers in the system (minimum).
Ensure that the current capacity of the circuit breaker panels is not exceeded by the current draw of the connected loads.
The interrupting capacity (highest fault current that the device is rated to safely interrupt) of the protection device should match the application. Battery protection devices require higher interrupting capacity due to the high short circuit current capability of a battery and the large cables (low impedance).
Features and selection criteria
Remote alarm sending via guard fuse or remote contacts on circuit breaker.
Alarm indicating lamp and an isolating relay. Traditional “bolt-in”, “plug-in” or “snap-in” circuit breakers.
Guard bars to prevent accidental tripping of circuit breakers.
Electronic breaker trip detection circuitry. Various types of fuses and circuit breakers can be combined in different panels to meet load requirements.
Current monitoring via series shunts to ensure circuits
are not overloaded or power consumption monitoring for billing purposes.
Battery protection features:
§ EPO - Emergency Power Off control capability using contactor or shunt trip breaker for locations that require a mandatory emergency power shutdown to meet local fire codes.
§ LVBD - Low Voltage Battery Disconnect control capability to automatically disconnect and
reconnect the battery during an extended ac power outage.
§ Manual battery disconnection - Single string disconnection for maintenance and fault isolation.
Fuses or circuit breakers?
• Fuse advantages - high interrupting capacity,
cost, flexibility, fast speed.
• Circuit breaker advantages - can be reset,
accuracy, low speed.
1.4.4
Argus solutions
Fuse blocks:
Type Rating-Range (block size)
GMT 0-15A
70 Type 1/2A used for indicating purposes
BAF 0-30A
Cartridge 0-30A, 31-60A, 61-100A, 101-200A
TPL 61-800A
Breakers:
Manufacturer Type Rating Interrupting Capacity Usage
Heinemann AM 5 - 100 A 5 or 10kA Load or battery
Heinemann CD 5 - 100 A 10,000A Load or battery
1.5 Battery Return Bus
1.5.1
Description
The battery return bus (BRB), also referred to as the
common ground bus, provides a common return/reference point for the connected loads and the power system. This common reference point is connected to the site ground to provide a low impedance path to ground for transients and noise.
1.5.2
Connection
The ground lead of all DC load inputs, batteries and rectifiers should be connected to this point. This bus must also be connected to the site ground grid (see grounding network section).
1.5.3
Sizing
Ground bars are sized according to load requirements.
1.5.4
Features
• Allowances for termination of two-hole lugs of various sizes should be provided.
• Ground bars must be isolated from the relay rack through glastic insulators so that the power system can be integrated correctly into the site single point ground network.
• Provisions for small cable termination shall also be provided.
• Tin-plated copper construction for corrosion
resistance.
1.5.5
Argus solutions
Various types are available from Argus including flat bars and “U” shaped bars for additional cable termination.
DC PS H0 3A
A
P o w e r S u p e rv is o ry P a n e l G ro u n d B a r C h a rg e ( -) B a tt e ry-
+
-
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C h a rg e ( + ) S h u n t B a r T e rm in a ti o n P a n e l R e c ti fi e r # 2 R e c ti fi e r # 1V
Lo ad S h u n t C ir c u it B re a k e r D is tr ib u ti o n1.6 Supervisory and System Control
1.6.1
Description
In most power systems it is desirable to have a central control and monitoring panel to provide local and remote indication of system operating parameters and alarms and also to provide system control.
1.6.2
Connection
Various connections are made to the supervisory panel from different components so that different parameters and levels may be monitored and controlled.
Shunts can be installed in the grounded or live load, battery or system conductor.
1.6.3
Operation
The battery (charge) and load (discharge) voltage is monitored with a direct connection of the sense leads to the source; battery or load.
The battery (charge) and load (discharge) current is monitored with an external shunt. Shunts are calibrated low resistance resistors designed to provide a specific voltage drop at a specific current (linear relationship). This voltage drop is measured by the ammeter. A typical shunt rating would be 200A, 50mV. Therefore 200 amps of current flowing through this shunt will cause a voltage drop of 50mV.
Calculated values may also be displayed such as total rectifier output current (numerical addition of individual rectifier output currents). In systems where there is no battery shunt an estimation of battery current can be calculated by subtracting the discharge current from the rectifier total output current.
Room and battery temperature can be monitored with temperature probes.
Additional analog parameters can be monitored using available inputs.
Events such as distribution fuse alarm, battery fuse alarm, rectifier failure, converter failure, etc. are monitored by the supervisory panels.
Alarms are based on an analog or digital event. Each alarm has a two to five second delay before extending an alarm. The delay eliminates false triggering due to line transients or false alarms. Analog alarms usually incorporate a hysteresis into the trigger level to prevent oscillation of an alarm condition caused by a level fluctuating around the set point. Alarm functions provide both local (visual and audible (optional)) and remote (relay contact) indicators.
Relay contacts may be configured as form “A” (NO), form “B” (NC), or form ”C” (NO & NC).
Control functions are extended from the supervisory panel to control various other power system components.
Microprocessor based supervisory panels have direct
communications with rectifiers for monitoring and single point control. Communications is via RS-485 connection.
1.6.4
Sizing
Shunts are sized according to load requirements and limit the initial capacity of the power system. Current flowing through a shunt must not exceed 80% of its nominal rating on a continuous basis.
1.6.5
Features (panel dependent)
Typical Alarms
• high/low voltage (1 & 2)
• AC mains high/low/failure
• distribution fuse/breaker
• battery fuse/breaker
• control fuse trip
• rectifier failure alarm minor (one rectifier)
• rectifier failure alarm major (>one rectifier)
• converter failure alarm minor (one converter)
• converter failure alarm major (>one converter)
• high voltage shutdown
• low voltage disconnect
• CEMF (out)
• CEMF (fail)
• rectifier communication lost
• Power system minor alarm (logical “or-ing” of various non critical alarms)
• Power system major alarm (logical “or-ing” of various critical alarms)
• etc.
Controls
Control features are used to control power system devices such as rectifiers and contactors.
Manual equalize - Allows the user to initiate all the rectifiers into the equalize mode with one common switch. Used for maintenance purposes with VRLA batteries, i.e. equalizing cell voltages in a battery string.
Auto-equalize - Common in applications where flooded batteries are deployed. This function initiates the rectifiers into the equalize mode (boost charge) for a preprogrammed amount of time
(duration). It is used with vented batteries floated at low voltages to prevent lead plate sulfation or where a quicker recharge of the battery is required after a power failure. Auto-equalize is initiated in one of three ways:
1. after power failure based on the voltage of the battery;
arm voltage (indicating that a long outage has occurred, rectifiers are off and the batteries have been discharged) and
activate voltage (indicating the battery is nearing full charge and the equalize mode is triggered, rectifiers are on) The rectifiers will remain in the equalize mode for the duration.
2. periodic equalize; where the batteries are equalized at the interval programmed in days.
3. manual initiation using the duration setting to return the rectifiers to float after the duration has expired.
HVSD/OVP - automatically shuts down all the rectifiers when an output DC over-voltage condition is detected.
LVD - controls 1 or more contactors that automatically open when a low battery voltage condition is detected and close when the battery voltage returns to normal. See LVD section.
LVD override control - switch for maintenance.
Battery temperature compensation is used to adjust the rectifier output voltage to ensure that the battery float voltage is correct for the operating temperature of the battery. See battery temperature compensation section.
Charge current control is used to limit the flow of current into the battery when recharging commences after a power failure. It is programmed typically at C/5 (capacity of the battery/5). This ensures that the battery is not charged too quickly, resulting in excess heat generation and possible reduction in battery life. This can be very important for VRLA type batteries.
Battery diagnostics
§ Battery capacity estimation - the capacity of the battery at the current point in time expressed as a percentage of the battery manufacturer's specification. § Battery state of health estimation - a continual measurement of the batteries performance and state of health. It is expressed as a percentage of the
manufacturer's specification. Alarm triggers can be set to alarm when the battery state of health falls below 80%.
§ Battery run time prediction - the algorithm predicts the number of hours that the battery will last, before the battery will be fully discharged or a LVD will occur, at the present discharge rate.
Rectifier group single point adjustment - allows the operator to setup and adjust all the rectifiers at one central location.
CEMF (counter-electro-motive-force) controls 1 or more contactors that automatically close when a high load voltage condition is detected and open when the load voltage returns to normal or is in a low voltage condition. See CEMF section.
1.6.6
Other Features
VAR (Visual alarm reset) - Is used to clear visual alarms.
Lamp test - Illuminates all lamps to verify operation.
Test - Combined with an external power supply, allows the user to test and calibrate the power system while in service (SD series only).
ALCO (Alarm Cutoff) - Is provided to clear the relay contacts and audible alarm associated with each alarm condition this allows extended alarms to be canceled while alarm condition is being resolved by local personnel.
1.6.7
Advanced features (SM series)
• Remote access for control and monitoring, LocalRS232
Remotedial-in Remotedialback
SNMP (Simple Network Management Protocol) alarm reporting over network LAN or WAN
• History and statistics
• Programmable alarm relays
1.6.8
Argus Solutions
SM02
This microprocessor based supervisory panel combines a large LCD display and keypad with optional modem card to provide advanced power system monitoring and control features.
SM03
This microprocessor based supervisory panels provides many of the features of the SM02 (without the remote access) in a smaller, reduced cost package.
SD02 & 04
These discrete component supervisory panels provide comprehensive metering, control and alarm functionality.
SD03 & 05
These discrete component supervisory panels provide basic metering, control and alarm functionality.
DC PS H0 4A
A
P o w e r S u p e rv is o ry P a n e l C h a rg e ( -) B a tt e ry-
+
-
+
C h a rg e ( + ) S h u n t B a rV
Lo ad C ir c u it B re a k e r D is tr ib u ti o n L o w V o lt a g e L o a d D is c o n n e c t G ro u n d B a r T e rm in a ti o n P a n e l R e c ti fi e r # 2 R e c ti fi e r # 1 S h u n t1.7 Low Voltage Disconnect Contactor
1.7.1
Description
The low voltage disconnect (LVD) contactor is used to disconnect either the load from the system (load disconnect) or the battery from the system (battery disconnect) when the battery has been completely discharged in a long duration power outage. There are three reasons for using a LVD:
1. Prevention of load damage due to an under voltage condition. Some communications equipment may be damaged when operated with an excessively low input voltage or draw excessive current that could trip a feeder circuit breaker.
2. Prevention of damage to the battery due to over-discharge. Discharging a battery below the lowest recommended end voltage (see battery section) might permanently damage the battery.
3. Load shedding - to disconnect specific loads in a prioritized sequence to maximize backup time for more critical loads (ex. up to three individually controlled contactors can be used with the SM02).
1.7.2
Connection
The low voltage disconnect can be connected in series with the load (load disconnect) or in series with the battery (battery disconnect).
The LVD is controlled by the supervisory panel.
1.7.3
Operation
The supervisory panel continuously monitors system voltage. After an extended AC outage the batteries will discharge down to the disconnect point. The disconnect point is typically set to the lowest acceptable battery discharge voltage (end voltage). In a Telecom application the end voltage typically used is 1.75 volts per cell (21 VDC in a 24 VDC system and 42 VDC in a 48 VDC
system). When the disconnect point is reached the load or battery will be disconnected from the system.
The load or battery will remain disconnected until AC outage is over. On return of AC a load disconnect and a battery disconnect system function differently (see below).
Load disconnect The rectifiers will pre-charge the batteries for a few minutes until the battery voltage reaches the reconnect point (typically 25 VDC or 50 VDC). When the reconnect point is reached, the load is connected on line at this voltage level.
Battery disconnect Immediately after the reapplication of AC, the load will see a slowly
increasing DC voltage (0-50 VDC over an 8-10 second period, due to the soft start feature in the rectifier). At the 50 VDC point the battery will be connected on line.
A wide voltage differential between the in and out settings (i.e. out 42V, in 50 V in a 48V system) prevents the contactor from oscillation because the battery voltage will naturally rise after the load has been removed from it and reconnection without the rectifiers on-line would not be desirable.
Load vs. battery disconnect - In some cases battery, instead of load, disconnection is desirable. The advantage of this system is that an accidental operation of the LVD will not disrupt power to the load unless the AC is also off. The disadvantage of the battery disconnect that the load will see a slowly increasing input voltage 0-50V as the rectifiers perform the soft start this may cause damage to the load or inadvertent fuse or circuit breaker tripping. Careful evaluation of the load specifications is required to verify that this method of disconnection will not affect the load.
1.7.4
Sizing
Low voltage disconnect contactors are available in various sizes. The rating of the LVD indicates its maximum current
1.7.5
Features and selection criteria
Able to switch high current loads reliably.
1.7.6
Argus solutions
1.8 CEMF Cell
1.8.1
Description
The CEMF cell is a diode array that is connected in series between the power system and the loads. A contactor is installed in parallel with the diodes. The diodes are used to reduce the voltage applied to the loads by a fixed value during normal operation or when the batteries are equalize charged. The contactor automatically bypasses the CEMF when the system is on battery to maintain maximum backup time for the loads.
CEMF cells are rarely used in modern telecommunications systems as they introduce step voltage changes to the load voltage when switched in or out that may affect load operation. It also introduces another single point of failure.
It was historically used with both step by step and crossbar telephone switching offices.
A common alternative to the CEMF cell is to remove one battery cell from the string and lower the rectifier output voltage to reduce the operating voltage of the system; for example: 23 cell system with VRLA batteries 23 x 2.25 V per cell = 51.75V.
1.8.2
Connection
The CEMF cell is connected in series with the load. The supervisory panel controls the CEMF cell.
1.8.3
Operation
The supervisory panel continuously monitors system voltage. There are two scenarios for CEMF use:
1. CEMF cell normally IN to reduce load voltage in the float and equalize mode. The normal system float voltage is above the IN setting of the CEMF cell the CEMF contactor is opened so that current flow is through the CEMF diodes and the load voltage is reduced. When a power failure occurs
and the voltage drops the contactor is closed to increase the voltage at the load to ensure maximum back up time. When power is restored the contactor will open when the voltage returns to normal diverting current through the diodes and reducing the load voltage.
2. CEMF cell normally OUT to reduce load voltage in the equalize mode only. In this system the IN setting of the CEMF is set higher than the float voltage and the contactor normally bypasses the diodes. When equalize mode is selected the voltage rises above the IN setting and the contactor is opened, current flows through the diodes and the voltage at the load is reduced. When the rectifiers are returned to float mode the voltage drops below the out setting and the diodes are again bypassed by the contactor and the load voltage returned to normal.
1.8.4
Sizing
Voltage drop required.
Current required by load.
1.8.5
Features
Monitoring of cell status.
Alarm on failure of cell.
1.8.6
Argus solutions
1.9 Battery Temperature Compensation
1.9.1
Background
Battery performance and life expectancy is directly related to the battery ambient temperature. The optimum temperature for battery operation is 25 deg. C (77 deg. F). Above this temperature, battery life is compromised and below this temperature battery
performance is reduced.
VRLA batteries have a negative characteristic called “thermal runaway”. This occurs when the internal temperature of the battery rises due to overcharge, high ambient temperature or internal fault. The rise in internal ambient temperature causes the battery to draw more float current which in turn elevates the internal battery temperature. This cycle continues until the battery fails. The failure of the battery may be quite dramatic.
1.9.2
Description
Temperature compensation is the process of automatically reducing the charge voltage applied to the battery at high temperature (to increase life and prevent thermal runaway) and increasing the voltage applied to the battery at low temperatures (to increase the battery capacity and to ensure correct charging of the battery).
1.9.3
Connection
Connection is as follows:
1. Traditional rectifiers with non-SM supervisory panels use a temperature compensator module (TCM) connected in series with the rectifier remote sense line input and the battery that requires temperature compensation.
2. Smaller rectifier systems (i.e. RSM 48/7.5 and 48/10) have this feature built in; there are no additional sense/battery connections required.
3. RSM/Pathfinder rectifiers with SM supervisory panels, require no additional sense/battery connections.
Temperature probes (1-4) are mounted directly to either the same battery negative termination post or to multiple negative posts to monitor multiple battery strings.
1.9.4
Operation
Operation is as follows:
1. Non-SM based systems, the TCM adjusts the output sense voltage to the rectifiers based on ambient temperature detected at the battery. The rectifiers will adjust their output voltage according to the sense voltage level detected at their remote sense input. (See Table H & I)
2. Small systems adjust the rectifier output voltage based on ambient temperature detected at the battery. (See Table H & I).
3. SM based systems, the SM will automatically adjust the rectifier float voltage based on the battery temperature detected. It will repeat this process at the interval programmed. The rectifier RS 485 communications link is used for this purpose.
At 25 deg. C (77 deg. F) no voltage compensation will occur. At temperatures below 25 deg. C, the rectifier will increase its output at a fixed rate(ex. -2.5 mV per cell per deg. C change from 25 deg C reference).
At temperatures above 25 deg. C, the rectifier will decrease its output at a fixed rate(ex. -2.5 mV per cell per deg. C change from 25 deg C reference).
To prevent excessive voltage from damaging the load, the battery or causing a high voltage alarm condition; the battery voltage maximum compensation may be limited (lower break point) at a fixed temperature (ex. 0 deg C).
To prevent excessively low voltage from undercharging the battery or discharging the battery; the battery voltage maximum
compensation may be limited (upper break point) at a fixed temperature (ex. 50 deg C).
1.9.5
Sizing
Temperature compensation slope
Match the compensation slope to the recommendations of the battery manufacturer. Default to conservative 2.5 or 3.5 mV if this information is unavailable.
Breakpoint
The selection of the breakpoint is critical. This determines the maximum and minimum voltage that will be applied to the battery and the load. Match the breakpoints to the recommendations of the battery manufacture. Carefully select the lower breakpoint as this determines the maximum voltage applied to the load.
Check load acceptable input voltage operating window; for example: a 4.5 mV slope with a -40 deg C breakpoint in a 48V system will result in 61 volts applied to the load in a low temperature condition.
1.9.6
Features and selection criteria
• Fail detection circuitry.
• Redundant temperature probes for increased safety.
• Automatic turn off if a fault is detected and an alarm extended.
1.9.7
Argus solutions
TCM
This external temperature compensation module can be either relay rack or surface mounted. It will operate with RST (6 max.) and the larger remote sense input equipped RSM rectifiers (6 shelves max.). It will also operate with non-Argus remote sense input equipped rectifiers.
TCM Internal
This feature is available built into Argus non-sense line equipped rectifiers, including RSM 48/7.5, RSM 24/15 and RSM 48/10.
SM System Controllers
Control larger RSM rectifiers and pathfinder rectifiers through the communications link.
Table H
24 Volt Temperature Compensated Battery Float Voltage
These tables are provided as a guideline only. If battery temperature falls between values on the above scale, estimate the voltage setting based on the closest numerical values.
* Refers to ambient temperature at the battery terminal posts.
** BFV refers to “Battery Float Voltage” Check battery manufacturer's recommended settings.
*** Refers to “Nominal Battery Temperature.” This is the optimum temperature for battery operation. No compensation occurs at this temperature (use as a reference point).
TEMPERATURE* BFV**=27.00V BFV**=27.25V BFV**=27.50V °C °F @25°C(77°F) @25°C(77°F) @25°C(77°F) 2.5mV (volts) 3.5mV (volts) 4.5mV (volts) 2.5mV (volts) 3.5mV (volts) 4.5mV (volts) 2.5mV (volts) 3.5mV (volts) 4.5mV (volts) -40 -40 28.95 29.73 30.51 29.20 29.98 30.76 29.45 30.23 31.01 -35 -31 28.80 29.52 30.24 29.05 29.77 30.49 29.30 30.02 30.74 -30 -22 28.65 29.31 29.97 28.90 29.56 30.22 29.15 29.81 30.47 -25 -13 28.50 29.10 29.70 28.75 29.35 29.95 29.00 29.60 30.20 -20 -4 28.35 28.89 29.43 28.60 29.14 29.68 28.85 29.39 29.93 -15 5 28.20 28.68 29.16 28.45 28.93 29.41 28.70 29.18 29.66 -10 14 28.05 28.47 28.89 28.30 28.72 29.14 28.55 28.97 29.39 -5 23 27.90 28.26 28.62 28.15 28.51 28.87 28.40 28.76 29.12 0 32 27.75 28.05 28.35 28.00 28.30 28.60 28.25 28.55 28.85 5 41 27.60 27.84 28.08 28.60 28.09 28.33 28.10 28.34 28.58 10 50 27.45 27.63 27.81 27.70 27.88 28.06 27.95 28.13 28.31 15 59 27.30 27.42 27.54 27.55 27.67 27.79 27.80 27.92 28.04 20 68 27.15 27.21 27.27 27.40 27.46 27.52 27.65 27.71 27.77 25*** 77 27 27 27 27.25 27.25 27.25 27.5 27.5 27.5 30 86 26.85 26.79 26.73 27.10 27.04 26.98 27.35 27.29 27.23 35 95 26.70 26.58 26.46 26.95 26.83 26.71 27.20 27.08 26.96 40 104 26.55 26.37 26.19 26.80 26.62 26.44 27.05 26.87 26.69 45 113 26.40 26.16 25.92 26.65 26.41 26.17 26.90 26.66 26.42 50 122 26.25 25.95 25.65 26.50 26.20 25.90 26.75 26.45 26.15 55 131 26.10 25.74 25.38 26.35 25.99 25.63 26.60 26.24 25.88 60 140 25.95 25.53 25.11 26.20 25.78 25.36 26.45 26.03 25.61 65 149 25.80 25.32 24.84 26.05 25.57 25.09 26.30 25.82 25.34
TEMPERATURE* BFV**=54.00V BFV**=54.50V BFV**=55.00V °C °F @25°C(77°F) @25°C(77°F) @25°C(77°F) 2.5mV (volts) 3.5mV (volts) 4.5mV (volts) 2.5mV (volts) 3.5mV (volts) 4.5mV (volts) 2.5mV (volts) 3.5mV (volts) 4.5mV (volts) -40 -40 57.90 59.46 61.02 58.40 59.96 61.52 58.90 60.46 62.02 -35 -31 57.60 59.04 60.48 58.10 59.54 60.98 58.60 60.04 61.48 -30 -22 57.30 58.62 59.94 57.80 59.12 60.44 58.30 59.62 60.94 -25 -13 57.00 58.20 59.40 57.50 58.70 59.90 58.00 59.20 60.40 -20 -4 56.70 57.78 58.86 57.20 58.28 59.36 57.70 58.78 59.86 -15 5 56.40 57.36 58.32 56.90 57.86 58.82 57.40 58.36 59.32 -10 14 56.10 56.94 57.78 56.60 57.44 58.28 57.10 57.94 58.78 -5 23 55.80 56.52 57.24 56.30 57.02 57.74 56.80 57.52 58.24 0 32 55.50 56.10 56.70 56.00 56.60 57.20 56.50 57.10 57.70 5 41 55.20 55.68 56.16 55.70 56.18 56.66 56.20 56.68 57.16 10 50 54.90 55.26 55.62 55.40 55.76 56.12 55.90 56.26 56.62 15 59 54.60 54.84 55.08 55.10 55.34 55.58 55.60 55.84 56.08 20 68 54.30 54.42 54.54 54.80 54.92 55.04 55.30 55.42 55.54 25*** 77 54 54 54 54.5 54.5 54.5 55 55 55 30 86 53.70 53.58 53.46 54.20 54.08 53.96 54.70 54.58 54.46 35 95 53.40 53.16 52.92 53.90 53.66 53.42 54.40 54.16 53.92 40 104 53.10 52.74 52.38 53.60 53.24 52.88 54.10 53.74 53.38 45 113 52.80 52.32 51.84 53.30 52.82 52.34 53.80 53.32 52.84 50 122 52.50 51.90 51.30 53.00 52.40 51.80 53.50 52.90 52.30 55 131 52.20 51.48 50.76 52.70 51.98 51.26 53.20 52.48 51.76 60 140 51.90 51.06 50.22 52.40 51.56 50.72 52.90 52.06 51.22 65 149 51.60 50.64 49.68 52.10 51.14 50.18 52.60 51.64 50.68
Table I
48 Volt Temperature Compensated Battery Float Voltage
These tables are provided as a guideline only. If battery temperature falls between values on the above scale, estimate the voltage setting based on the closest numerical values.
* Refers to ambient temperature at the battery terminal posts.
** BFV refers to “Battery Float Voltage” Check battery manufacturer's recommended settings.
*** Refers to “Nominal Battery Temperature.” This is the optimum temperature for battery operation. No compensation occurs at this temperature (use as a reference point).
1.10 DC - DC Converter System
1.10.1
Description
A DC-DC converter system takes a DC input voltage and converts it to the same or a different output voltage. The converter system is utilized for any of the following reasons:
• Provide different voltage levels; i.e. -48V to +24V conversion.
• Ground swapping; i.e. +24V to -24V.
• Galvanic or ground isolation; i.e. +24V to +24V, floating ground.
• Voltage regulation for equipment, with a tight input voltage operating window, operated from a battery system.
1.10.2
Connection
The DC-DC converter system is connected in series between the main DC power system and the load.
A converter system consists of single or multiple parallel DC-DC converters and may incorporate many of the features found in the main DC power system including distribution, common ground bus and supervisory.
DC-DC Converters should have dedicated fuse/circuit breaker positions on the main DC power system for protection and isolation.
If converters are located in the same relay rack as the main DC power system, direct connection to the busswork on the input is permissible.
1.10.3
Operation
Since the converter system does not have a battery connected to its output adjustment of the output voltage is less critical and LVD’s, temp comp, etc. are not required. The output voltage of the converters is adjusted to match the requirements of the load and to ensure correct load sharing between parallel converters.
