UNIT 6: BATTERIES, UPS AND CABLES

Transcription

1 UNIT 6: BATTERIES, UPS AND CABLES 6.1 Batteries Introduction i. Definition of Batteries: Stores chemical energy in cells and converts them into electrical energy in the form of direct current (D.C); Process is known as electrochemical reaction. ii. Functions of Batteries: Provides a mobile source of power for equipment in places where there is no permanent electrical supply; When connection to a permanent power supply is not practical, e.g torchlights; Temporary back up for permanent electrical systems in the form of UPS (Uninterrupted power supply). Symbol of Battery on Single Line Diagrams 1

2 6.1.2 How Batteries Work i. Battery consists of: Positive electrode (Cathode); Negative electrode (Anode); Electrolyte. ii. Working Process: When wired with a load in a circuit, the negative electrodes will have the tendency to travel to the cathode; In the process, this is stopped by the electrolyte as it contains negative ions; The electrodes are then forced to enter the wiring circuit to enter the cathode. This generates electric current to the load and depletes the positive electrodes; When positive electrodes are depleted, electricity generation stops; Some batteries can be recharged (By replenishing the positive electrodes and reducing negative electrodes). Diagram illustrating the working principle of battery. Diagram illustrating the charging of battery. 6.2 Uninterruptible Power Supply (UPS) Why UPS? i. Essential services are usually connected to a generator electricity supply. ii. In the event of a power failure, the generator will kick in to supply auxiliary power supply for a brief span of time to allow time for main electricity supply to recover. iii. Shortcomings of generator power: Short time interval between power trip and generator to kick in (Usually between 8 10 secs); While this span of time is minimal, there are sensitive systems within the building proper which cannot tolerate this time lapse. iv. Examples of sensitive systems include: Hospital equipment, fire alarm systems, security systems, server equipment, etc. v. UPS helps to bridge this time lapse by continuing to supply electricity to these equipment during a power outage. vi. May operate independently or together with generator power. 2

3 6.2.2 Types of Generator-UPS Configurations i. Static Electronic Converter-Inverter Unit: Connected to batteries. Converts DC current to AC current. A.C power from electric mains for battery charging; ii. Alternator coupled to A.C (Alternating Current) synchronous motor: Connected to two sources of electricity supply (one of which is electricity mains); iii. Alternator coupled to D.C (Direct Current) motor: Connected to electricity mains (via rectifier) and main battery tank; iv. Alternator coupled to diesel generator and A.C synchronous motor (To electricity mains). Generator UPS Set Up Main Components of Static UPS System UPS Single Line Diagram 3

4 Main components of a typical Static UPS: Rectifier/Charger; Inverter; Battery; Static Transfer Switch; Bypass Switch. Provides precise AC Power to Support Equipment and other sensitive systems. a) UPS module: To provide precise AC Power; Houses Rectifier/Charge unit, inverter unit; Other accessories: Control logic, synchronizing equipment, protective devices, etc. 1. Rectifier/Charger Unit: Converts A.C power to D.C power for battery charging; 2. Inverter Unit: Converts D.C power from battery or rectifier/charger unit to A.C Power. Only A.C Power can be used to supply critical load. Rectifier/Charger Unit Inverter Unit b) Battery: Stored energy source; Heavy industry battery for standby power service; Must have sufficient capacity to provide power to inverter to sustain critical load for stated time period. c) Static Transfer Switch: Designed to minimize disruption to critical load by bypassing UPS system immediately should malfunction of UPS system occurs. Normally opened switch; Operates parallel to the mechanical bypass switch; When UPS malfunction occurs, static transfer switch receives signal from UPS module and closes immediately to complete bypassing of UPS system. Industrial Strength Battery Static Transfer Switch d) Battery Disconnect Circuit Breaker: Used to terminate electrical supply to and from battery. Disconnected when: Battery reaches minimum discharge levels; Signaled by UPS module. e) Disconnect Switch for Static Transfer Switch: For disconnecting Static Transfer Switch if it malfunctions. 4

5 6.2.4 How UPS Operates i. Normal Operating Conditions: a) CB1, Input CB, output switch, CB2, disconnect switch for Static Transfer Switch and CB3 are closed; b) Power from input AC power supply flows in one direction to critical load (Red arrow). ii. iii. Failure of AC Power Supply (Power Trip/Failure): Battery supplies power straight to inverter, with no disruption to inverter output supplying critical load (See red arrow); Restoration of AC Power Supply: a) Power supply restored to normal (See (i)); b) Restored AC Power Supply is used to charge batteries with no disturbance to inverter output (See blue arrow). 5

6 iv. UPS Fault a) Monitor of UPS Module: Detects UPS fault, sends signal to static transfer switch; b) Static transfer switch closes instantaneously. CB1 and Input CB will open. Electricity flows via the bypass line through the static transfer switch towards critical load (See Red Arrow); c) Mechanical bypass switch closes, static switch opens. Power supply is then maintained through mechanical bypass switch (See blue arrow) Auxiliary Components of Static UPS System 6

7 i. Reactor: To reduce current ripple acceptable to both battery and inverter. ii. Output filter: To reduce harmonic content (Voltage fluctuation) of inverter output to acceptable levels of critical load. Harmonic Content in Voltage Form iii. Input Harmonic Filter: Installed in rectifier; Ensure distorted harmonic currents do not flow back to the source. Harmonic Content in Current Form Input Harmonic Filter Single Line Diagram Back Up Generator for UPS Systems i. Problem with Static UPS Using Batteries only: Insufficient power to last a long time should power failure be prolonged. ii. For longer duration of power backup, standby generator is required. iii. When standby generator is connected: Once there is power failure, batteries will supply power for a brief period of time to stand in temporarily for the generator; Standby generator will take some time (Possibly 10 secs or more) to kick in. Single Line Diagram showing Genset Connected to Static UPS 7

8 6.2.7 Maintenance of UPS Systems i. Why maintenance? Planned Maintenance: Minimize failure of back up power should the main electrical supply line fail; Corrective Maintenance: Carried out when UPS Systems fail. ii. Maintenance Procedures: 1. Remove all input and output power (i.e Isolating) connection to UPS system; 2. Discharge and ground all capacitors in inverter/charger 3. Inspect parts for overheating and damage; 4. Inspect all terminals for loose connections or burnt insulation; 5. Check for liquid contamination (E.g spilling of battery electrolytes); 6. Inspect and clean all intake and excess openings; 7. Check for liquid continuation in batteries and overall battery condition; 8. Check and calibrate voltage output and efficiency as per manufacturers specification; 9. Connect back to UPS; 10. Check output voltage and frequency under load; 11. Simulate power failure, check for proper system operation. 6.3 Cables i. Definition of Cables: Insulated electrical conductors, held together by a sheath, designed to carry electricity from source to electrical loads. ii. Basic components of cables: Electrical Conductors: Conducts Electricity; Insulation: Protects users from electric shock; Protective Jacket/Sheath: Protects damage to insulation and conductor. iii. Types of Cables: Polyvinyl Chloride (PVC) Cable; Thermosetting/Cross-Setting (XLPE) Cable; Rubber Cable; Fire Resistant (FR) Cable; Low Smoke Zero Halogen (LSOH) Cable; Neoprene Cable. Cross Section of an Armored Cable 8

9 iv. Method of cable installation: Conduit and trunking; Cable Tray; Underground cable trench. PVC Trunking Steel Cable Tray Steel type Galvanized GI Electrical Conduit Laying of Underground Cable in Trench Types of Cable and Insulation i. PVC Insulated Cable: For normal appliance use, e.g connection to power point; Ease of handing for termination and jointing purposes due to the absence of sheath protection; Disadvantage: Restricted by 70 degrees Celsius maximum temperature. This restricts its usage up to only 600V/1000V. Cross Section of a PVC Cable ii. XLPE Insulated Cable: Operates up to 90 degrees Celsius; Application: From 600/1000V to 32kV; Advantages: Better electrical, thermal and thermal properties; Ease of handling for termination and jointing. 9

10 iii. iv. Rubber Cable: Cable protected by outer layer of tough rubble sheath: Operated up to 85 degrees Celsius; Application: For use in applications requiring extreme toughness protection against mechanical hazards; Disadvantage: Rigid and inflexible for installation purposes. Fire Resistant Cable: Made of fire resistant material for conductor, insulator and sheath; Application: For use in locations with extreme fire hazards, e.g oil refineries. Cross Section of a Rubber Cable Cross Section of a Fire Resistant Cable v. Low Smoke Zero Halogen (LSOH) Cable: Used for cable jacketing of cables; Made of thermoplastic or thermoset compounds. Advantages: Emits little smoke and no halogen when exposed to high heat source or fire; Environmentally friendly as it does not release toxic gases under high heat conditions; Lighter, so overall cable system weight is reduced. Applications: Used in locations with poor ventilation, e.g aircrafts; Locations where fire hazard is high and there is high occupancy load, e.g Factories. In these facilities smoke can impede occupants from evacuating buildings. LSOH Cable Jacketing Cross Section of LSOH Cable Jacketing 10

11 vi. Neoprene Cable: Used for cable jacketing of cables; Advantages: Flexibility over wide temperature ranges; High resistance to degradation; High burning point (260 degrees Celsius), giving it fire retardant properties; Flat construction allows for space saving advantages. Applications: Extreme environments, such as shipyards, warehouses, steel mills, etc. Neoprene Flat Cable vii. Armored Cables: Additional steel taper layer/steel wires for mechanical protection of cables. Can serve as return path for earth currents. Applications: Typically for underground installations and cable trenches when installing PVC or XLPE cables. Comes in: DSTA (Double Steel Taped Armored) and SWA (Steel Wire Armored) Types. Cross Section of Steel Wire Armored Cable Cross Section of Double Steeled Tape Wire Armored Cable 11

12 Tutorial Questions 1) Batteries are used in many portable and non-portable devices. i. Briefly define batteries, the function of batteries and the circumstances whereby batteries are used (5 marks). ii. Explain, with the help of a simple diagram, how an ordinary dry cell battery works (15 marks). 2) Generators and UPS systems are typical installations in buildings. i. Explain why generators are used and the shortcomings of generators (4 marks). ii. Explain the shortcoming(s) of the UPS system as a standalone back-up power supply and recommend a solution to overcome the problem (3 marks). iii. Maintenance of UPS systems are viable to the operational quality of these systems. List down the types of maintenance plans which are required (2 marks); List down the maintenance procedures which are typically carried out during the maintenance regime for UPS systems (11 marks). 3) Cables are part and parcel of electrical installation works. i. List the major components of a cable and explain their basic functions (3 marks). ii. List down the propert(ies) of the PVC insulated cable and its application, and the disadvantage(s) of using a PCV insulation cable for cable installation works (3 marks). iii. List down the types of cable installations options available(3 marks). iv. List down the advantages of using the Low Smoke Zero Halogen (LSOH) Cable and its applications (5 marks). v. Briefly explain the use of the neoprene cable and list down the advantages of using neoprene cables for cable installation works. List down the applications of the neoprene cable (6 marks). 12