Dc Power System


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Dc Power System

  1. 1. DC power system training The purpose of this presentation is to give an introduction to DC power systems and DC power fundamentals. DC Power System
  2. 2. Scope of training <ul><li>Why do we user DC power ? </li></ul><ul><li>DC system – Water analogy </li></ul><ul><li>Definition of electrical terms </li></ul><ul><li>Electrical basic equations </li></ul><ul><li>DC power system – Elements and fundamental operation </li></ul><ul><li>Battery management </li></ul>DC power system
  3. 3. Why DC Power ? <ul><li>Provide a reliable power supply for telecom industry. </li></ul><ul><li>Telecom equipment must operate when AC supply is absent. </li></ul><ul><li>DC energy can be stored on batteries and used when AC power is absent. </li></ul><ul><li>A DC power system is 100% uninterruptible. </li></ul><ul><li>The DC power supply is a filter for noise (EMC, surge etc) that is present on the mains supply. </li></ul>DC power system
  4. 4. Water analogy <ul><li>A dam in a river is a god representation of a battery . The pressure across the dam represents the voltage on the battery . </li></ul><ul><li>A pump that pumps water into the dam is a god representation of a rectifier that pumps current into a battery. </li></ul><ul><li>The water represents the current in an electrical circuit. </li></ul><ul><li>The pipe that the water flows through is a good representation of resistance . </li></ul>DC power system
  5. 5. DC power system PUMP = RECTIFIER DAM = BATTERY Pipe = Resistance Water = Current
  6. 6. Definition of electrical terms DC power system The time rate at which energy is transmitted to the time rate of doing work. Power is measured in Watts (W) Power: The opposition to the flow of current. Resistance is measured in ohms (  ) Resistance: The differences in potential between two points that causes electrical charge to flow. Voltage is measured in Volts (V) Voltage: A flow of electrical charge caused by an potential difference. Current is measured in Amps (A). Current:
  7. 7. DC power system The derivation between the AC current and the AC voltage. Power factor is a number between 0 and 1. The power factor or any equipment should be close to 1. Power Factor: The ratio of the output power to the input power. Usually measured in percentage (%) Efficiency: The ability to do work. Energy is measured in joules (J) Energy:
  8. 8. Electrical basic equations <ul><li>Ohms law : </li></ul><ul><li>Voltage = Current x Resistance </li></ul><ul><li>Power calculation : </li></ul><ul><li>Power = Voltage x Current </li></ul><ul><li>Energy calculation : </li></ul><ul><li>Energy = Power x time </li></ul>DC power system
  10. 10. DC power system The elements in a Power system P rotection against surge and voltage spikes on the AC supply. Surge protection: Circuit breakers for protection of individual rectifiers. AC input protection: The diesel generator is a small power plant that generate AC current. The generator is used as a standby power, that will be connected when mains fail. The generator can be connected manually or automatically. Diesel generator: The AC input to the power system is taken from the switch board AC Switch board:
  11. 11. DC power system Fuses of circuit breakers for distribution of DC power to the telecom equipment. Power distribution The control unit monitors all the essential parameters in the system (voltage, current and alarms). Parameters can also be changed from the unit. Control and monitoring unit: The rectifiers converts AC to DC. Rectifiers: The rectifier system converts the current from AC to DC. The system consist of rectifiers and a control and monitoring unit DC rectifier system: AC DC
  12. 12. DC power system Converts from DC to AC. Used for AC load that require long battery backup. Inverter Converts power from AC to DC and back to AC again. The UPS usually have a small battery bank on the DC side UPS Fuses for protection o f individual battery banks against short circuit. Battery distribution: Low voltage battery disconnect (LVBD) is used for disconnecting the batteries before the y are damaged due to deep discharge. LVBD The batteries stores the energy for use when the AC mains fail Batteries
  13. 13. System operation Current flow in a system – Normal operation <ul><li>MAINS INPUT OK </li></ul><ul><li>LOAD SUPPLIED BY THE RECTIFIER SYSTEM </li></ul><ul><li>BATTERIES ON FLOAT CHARGE. </li></ul>RECTIFIER SYSTEM TELECOM EQUIPMENT BATTERY BANK AC INPUT
  14. 14. System operation Current flow in a system – Mains fail <ul><li>MAINS INPUT FAILED (ABSENT) </li></ul><ul><li>LOAD SUPPLIED BY THE BATTERIES </li></ul><ul><li>BATTERIES ARE DISCHARGING </li></ul>RECTIFIER SYSTEM TELECOM EQUIPMENT BATTERY BANK AC INPUT
  15. 15. System operation Current flow in a system – Mains restored <ul><li>MAINS INPUT OK </li></ul><ul><li>LOAD SUPPLIED BY THE RECTIFIER SYSTEM </li></ul><ul><li>BATTERIES ARE RECHARGING </li></ul>RECTIFIER SYSTEM TELECOM EQUIPMENT BATTERY BANK AC INPUT
  16. 16. System operation U 54.5 43.2 Float charge Battery discharge Battery recharge t - - - w/current limitation Disconnect Voltage Voltage sequence: Mains failure Mains resume
  17. 17. Constant output power <ul><li>Modern telecom equipment behaves as a constant power load </li></ul><ul><li>A constant power rectifier system will regulate the voltage – current ratio to give constant power output . </li></ul><ul><li>Constant power rectifiers will a increased recharge capacity for the batteries ( 15- 20%) . </li></ul>Constant power
  18. 18. Constant power Constant output power rectifier and constant current rectifier.
  19. 19. Battery management Battery management – definitions The nominal capacity referred to a 10 hours discharge rate C 10 Is the electrical energy stored in the battery and is measured in ampere hours (Ah) Capacity A group of battery cells linked in series to produce the operating voltage. Battery string The recommended charge voltage to be applied to a battery under normal conditions Float voltage:
  20. 20. Battery management A technique that change the battery voltage as a function of battery temperature. This technique will increase the lifetime of the batteries and the rate of change is usually specified by the battery manufacturer Temperature compensation Is a voltage higher then the float voltage for fast charging or equalising of batteries Boost voltage A high voltage is applied to the batteries in order to equalise the cell voltage on a string of batteries Equalising batteries:
  21. 21. Battery management - why <ul><li>Ensure long lifetime of batteries . This is done by correct float voltage, temperature compensated charging and temperature controlled environment. </li></ul><ul><li>Prevent batteries form being damaged due to deep discharge . Low voltage battery disconnect is used to prevent deep discharge & damage to the load equipment </li></ul>Battery management
  22. 22. Battery management Open Circuit Voltage in relation to state of charge of the cell. 25 50 75 100 V DC 1.90 Open Circuit Voltage (per cell)l 1.95 2.00 2.05 2.10 2.15 0 State of charge (%)
  23. 23. Battery management Float Voltage versus temperature Temp (ºC) V DC 2.22 Volt per cell 2.24 2.26 2.28 2.30 2.32 2.34 2.36 2.38 -10 0 10 20 30 40
  24. 24. Battery management Battery capacity versus temperature Temp (ºC) V DC 70 Available capacity (%) 75 80 85 90 95 100 105 110 5 10 15 20 25 30