Technical Manual. An Invensys company

Transcription

1 Technical Manual An Invensys company

2 Content Page Application Areas for OPzS Batteries... 1 Cell Design... 2 The Electrolyte... 3 Basic Electrochemical Function of the Lead-Acid Cell... 4 Discharge Properties... 5 Charging Properties... 7 Service Life... 9 Battery Selection Safety EMC Requirements and CE Marking... Flap

3 Application Areas for OPzS Batteries This manual will enable you to select and specify batteries using OPzS lead-acid single cells. OPzS is a range of vented tubular cells designed for stationary battery applications where reliability and long service life are of utmost importance. The cells are designed for a long life expectancy when operated in normal float charge conditions at 20 C. The OPzS has a long proven track record. OPzS batteries in standby power systems for telecommunication, control and safety systems power plants and power distribution applications, emergency lighting installations and photovoltaic solar systems. OPzS batteries are suitable for all stationary applications, that require a safe and reliable battery with long life. Vent Plug Lid Pole post Microporous Separator Container Positive tubular Plate Negative Flat/Plate Sediment Space 1

4 Cell Design OPzS cells have tubular positive plates. The tubular plate design is well proven and is well known for its high reliability and long service life in float charging operation ; it also withstands a high number of charge discharge cycles. Cell Containers and Lids OPzS cell containers are made from fully transparent SAN with clearly marked maximum and minimum levels which enable quick and easy reading of the electrolyte level and visual inspection of the cell. The lids are made from grey coloured ABS. Electrodes The positive tubular plates are made from a special lowantimony selenium alloy. This alloy is characterized by a fine-grain structure and low corrosion rate, a basic property for obtaining long battery service life and high reliability. Due to the low antimony content, the water consumption will stay low and stable during the service life. The negative electrode consists of pasted flat plates where the active material is pressed into the grid structure. Cell Connectors The OPzS standard cell connectors are made from solid copper. They are mounted to the pole post with stainless steel bolts and washers. Cell voltage can be measured through a small hole in the protection above each pole post. Vent Plug The standard vent plug is a flame arrestor plug, which filters the sprayed acid and protects from external ignition of internal charging gasses. A ceramic funnel vent plug (see drawing below) as an option allows topping up of the cell and taking specific gravity readings without removing it from the cell. Cap Separators The separators are made of a special microporous material. The porosity is such that the separator is easily permeable for the ions that take part in the charge and discharge processes but protects from migration of solid particles to the other electrode, i.e. shedded active material. Beside the microporous separators the OPzS cells have a spacer consisting of perforated plastic to provide more space and consequently more acid around the positive plates. Pole posts Lid Explosive gas Water trap Flame arresting porous material MAX acid level MINI Plate edge The design effectively prevents acid leakage and pillar corrosion over the lifetime of the battery. The pole posts have a brass insert which metric thread to which the cell connectors are mounted. On request, these cells are also available with lead calcium alloy for the positive grid (OPzSC). 2

5 The Electrolyte The electrolyte of the OPzS cells consists of dilued sulphuric acid. It is colourless and odourless. The electrolyte is strongly corrosive and it attacks most metals and many organic compounds. The water used for topping up the battery must meet high demands of purity to ensure that the battery function is not impaired. Specifications can be found in the DIN standard part 1-2 and 4. The topping up water must be distilled or deionized. The water is sufficiently pure if its electrical conductivity is less than 10µS/cm. The water should be stored in sealed plastic containers. For filling and commissioning of dry-charged cells, see our installation and Operation Manual. Electrolyte Specific Gravity Fully Charged Cell : ± at 20 C and maximum level at 20 C and minimum level. Topping-Up Interval : Approx 3 years under normal float-charge conditions at 20 c Electrolyte Specific Gravity Temperature Coefficient : per 1 C Electrolyte Freezing Point Fully Charged Cell : 45 C (reference acid specific gravity : 1.240) Electrolyte Freezing Point Fully Discharged Cell : 5 to 10 C (reference acid specific gravity : 1.100) These values of specific gravity and float charging voltage have been selected for the OPzS cells to give the optimum combination of recharge time, low maintenance requirements and life expectancy. 3

6 Basic Electrochemical Function of the Lead-Acid Cell A lead-acid battery consists of a number of cells electrically connected in series and/or in parallel. The basic parts of the lead-acid cell are the positive and the negative electrode immersed in an electrolyte consisting of dilute sulphuric acid. The electrodes consist of a lead structure with the double purpose of giving mechanical strength and conducting electric current. They also contain the active materials which stores the chemical energy. The active material in the charged and the discharged state is shown in the following table : State of Charge Positive Electrode Charged Discharged Lead dioxide PbO 2 Lead Sulfate PbSO 4 The Open Circuit Voltage Active Material Electrolyte Sulphuric acid H 2 SO 4 Water H 2 O Negative Electrode Spongy Lead Pb Lead Sulfate PbSO 4 The open circuit voltage depends on the concentration of the electrolyte. An approximate value for the open circuit voltage Uo can be calculated from the formula : Uo = (acid specific gravity) V An OPzS cell with acid specific gravity 1.24 has an open circuit voltage of = 2.08 V. During charging the cell voltage is higher and during discharge it is lower than the open circuit voltage. Discharge Reactions Positive electrode : PbO 2 + SO H+ + 2e - Negative electrode Pb + SO e - 2PbSO 4 Total reaction : PbSO 4 + 2H 2 O PbO 2 + Pb + 2H 2 SO 4 2PbSO 4 + 2H 2 O From the electrode reaction formulae it is observed that the discharge means release of electrons at the negative electrode and consumption of electrons at the positive electrode. These electrons represent the discharge current in the external discharge circuit connected to the cell. During discharge sulphate ions are taken from the acid and form lead sulphate in both electrodes. In the positive electrode water is formed, which is transferred to the electrolyte. Both the transfer of ions to the plates and the formation of water contribute to a decrease in the acid density during the discharge process. Charging Reactions Positive electrode : PbSO 4 + 2H 2 O + + SO e - PbO 2 + 2H 2 SO 4 Negative electrode : PbSO 4 + 2H + + 2e - Pb + H 2 SO 4 During the charging process sulphuric acid is released from the electrodes. Thus the acid density increases during recharge. During the last part of the charging process hydrogen and oxygen gas is released from the electrodes due to water decomposition. 4

7 Discharge Properties The published performance and other electrical data for the OPzS cells have been established in accordance with the test methods given in the international standard EN Capacity The capacity of a battery is the amount of electricity, expressed in Ampere-hours(Ah), which can be supplied during a discharge with constant current under specified conditions of time, temperature and end of discharge voltage. The available capacity of a fully charged battery depends on the rate of discharge. A low rate discharge the capacity is higher than at a high rate discharge. The nominal capacity C 10 of OPzS batteries is defined at the 10 hour rate of discharge with an initial temperature of 20 C to an end voltage of 1.80 V/cell. Typical characteristics for 10 and 5 hour discharge rates are given in the diagram above. The plate performance diagram is used to determine the cell size needed at discharge rates and end voltages that are not given in the performance tables. The OPzS range consists of four plates sizes : 50, 70, 100 and 125 Ah. The adjacent diagram for the 100 Ah plate defines the current available during a 1h30 min discharge to an end voltage of 1.87 V is 33 A/plate. This means that the cell type 6 OPzS 600, having 6 positive 100 Ah plates, can supply 6 x 33 = 198 A during this period and to this end voltage. Discharge Performance Plate Performance Diagram capacity (Ah/pl) Cell voltage (V) , h 10h 8h 6h 5h 4h 3h % of C 10 2h 1,75V 1,70V 10 1,83V 1,80V 0 1,98 1,95V 1,92V 1,87V 1,85V 1,90V ,5h Discharge Current 5 h 1h 10 h ,5h 0,25h 5

8 Internal Resistance and the Short-Circuit Current The internal resistance and the short-circuit current of a cell depend on several parameters. The values given in the adjacent table have been derived by test on fully charged cells in accordance with the international standard EN For calculation of battery short-circuits current refer to the international standard EN and 2. Coup de fouet (Voltage Dip) During the first few minutes of discharge the battery voltage drops significantly and recovers to a steady value. The voltage drop is called coup de fouet and is caused by a particular phenomenon when the formation of lead sulphate starts on the positive plate. The published performance data of OPzS cell include the voltage drop. The cell voltage will not drop below the specified final voltage. Deep Discharge Deep discharge should be avoided. After a discharge the battery should be recharged as soon as possible. Occasional discharge of the full capacity i.e. 100 % C 10, does not harm the OPzS cells. When discharging and recharging more frequently a maximum of 80 % in each cycle should be discharged. Self-Discharge The self-discharge of fully charged OPzS cells is about 2% per month at 20 C. The rate of self-discharge doubles for each temperature increase of 10 C. Temperature Influence The temperature correction factor of the capacity is 0.6% per C for capacity ratings from 3 to 10 hours in the temperature range C. Cell Type I sc A R i mω /Cell. 4 OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS OPzS

9 Charging Properties Constant Current Charge Charging with constant current is sometimes useful, for commissioning charging or equalizing. The charging current should be limited to maximum 0.05 A/Ah(=0.5x10) when the cell voltage exceeds 2.40 V. Floating Voltage This voltage must be adjusted to the yearly average temperature of the room according to the following table : Yearly average temperature of room Floating voltage Constant Voltage Charge Constant voltage chargers with current limitation are widely used in stationary battery applications. The following diagram shows the voltage and current of a cell being charged. +5 C to 15 C 16 C to 25 C 26 C to 35 C 2.30 V/cell 2.25 V/cell 2.22 V/cell When float charging OPzS cells the battery charging voltage shall be n x 2.23 Vpc ± 1%V, where n is the number of cells connected in series. A 110 V battery with 54 cells shall have a float voltage of 54 x 2.23 = V. The charger should have an output voltage accuracy of ± 1% or better from zero to full load. The individual cell voltage can vary in the range of ± 1% 0.1 Vpc to 0.05 Vpc. A temperature compensation of the float charging voltage between 5 and 40 C is not required. The float charge should be within the specified limits. An increase of the charging voltage by 40mV per cell will increase the float charge current by %. This will increase the water consumption considerably and also reduce the service life of the battery. The float charge current for OPzS cells is ma/ah at 20 C and float voltage 2.23 Vpc. 120 % 100 2,5 100 Charging current I % Cell voltage V Charged Ah Discharged Ah Charging voltage 2.40 V 2 Charging voltage 2.23 V h 8 Charging period t 7

10 Available Capacity Discharge % % of C 10 Charge Time h 2.23 V/Cell Current Limitation 2.40 V/Cell Current Limitation 0.05 x C x C x C x C x C x C x C x C The normal float charge voltage is sufficiently high to recharge the battery and to keep the battery fully charged during standby operation. To reduce the recharge time the charge voltage may be increase to Vpc. However care must be taken that the maximum permissible voltage of the parallel connected system is not exceeded. No limitation of the charging current is necessary from the battery point of view up to an average cell voltage of 2.40 V. The fully state of charge is achieved when the electrolyte density (S.G) and the charge current show constant values during two consecutive reading at an interval of two hours. Charge Efficiciency The charge efficiency is the ratio between the discharged Ampere-hours ( Ah) or Watt-hours ( Wh) and the recharged Ah or Wh, which are required to recharged the battery to fully charge state. The Ah efficiency and the Wh-efficiency depend on the conditions during discharge and recharge. Typical values for a complete discharge-recharge cycle are : ηah 86 % et ηwh 72 % Equalizing Charge Equalizing charge is recommended when individual cells in a battery show deviations from the specific electrolyte density (S.G) or float voltage exceed tolerance value. Boost Charge Boost charge is used when the recharge time must be kept short or in the case of battery discharges being so frequent that normal float charging is not sufficient to bring the battery back to the fully charged state. This may happen where the battery is used in buffer operation or where power outage is frequent. Boost charging should be carried out periodically. Boost charging should be balanced to be sufficient without giving the battery unnecessary overcharge. Unnecessary overcharge gives no advantage but causes increased water consumption and ageing. A charging voltage of V/cell is normally sufficient. The ideal parameters for boost charging must however be calculated during or experimented with in each case. The Wh efficiency is lower than the Ah-efficiency due to the influence of the high recharge voltage and the low discharge voltage. 8

11 Service Life Temperature Influence Higher temperature increases the speed of chemical reactions. This also applies to ageing processes of a battery. A temperature rise of 10 C under constant voltage charging will double the charging current. Accordingly a temperature increase to 30 C from the reference value 20 C will reduce the service life by half the design life. Ripple Current Superimposed ripple current is caused by the charger. Ripple current generates heat and increases the water consumption and should therefore be kept as low as possible. The RMS value of ripple current shall not exceed 5 A/100 Ah during float charging and 10 A/100 Ah during boost charging. Design life % Battery temp C End of Service Life Typically an OPzS battery keeps its capacity virtually constant during % of its service lifetime. A capacity test is recommended to check that the battery is in order. When the battery approaches its end of life, an accelerating loss of capacity will begin. As a general rule the battery should be taken out of service and replaced when a repeated capacity test indicates that the remaining capacity has decreased to 80 % of its nominal value. Endurance in Cycles The endurance in cycles is about 1200 cycles to a depth of discharge of 75 %. 9

12 Battery Selection Parallel Battery Strings OPzS batteries can be used parallel connected in two or more strings. Advantages : One battery string can be disconnected for repair or test while the other(s) still can supply power in an emergency situation. The battery installation may be arranged for a desired degree of redundancy. Smaller and lighter cells to handle during installation. Disadvantages : Higher battery cost. Increased maintenance work More space required. Sizing Against Constant Current Or Constant Power Load. For the selection of a battery type use the OPzS performance tables. The batteries can be sized for constant current or constant current power load. Example 1 Problem : A battery is needed working within the voltage range 220 ± 22 V. In a case of main power outage the battery shall be able to deliver a discharge current of 75 A for a duration of 2 hours. Select the adequate battery type in the OPzS type series. Solution : Step 1 : Determination of the number of cells. To obtain maximum utilisation of the battery capacity, the number of cells should be kept as high as possible. This number of cells is limited upwards by the battery float charging voltage, which should be kept as close to the maximum voltage limit as possible. The float voltage for OPzS is 2.23 V per cell. The number of cells therefore is calculated as : (220+22) / 2.23 = which is rounded off downwards to the closest integer. Thus the number of cells therefore is 108. Step 2 : Selection of cell type from the discharge performance data sheet. The minimum allowed battery voltage during discharge is = 198 V. The battery must be able to carry the load not exceeding minimum cell voltage of : 198 / 108 = 1.83 V Use the table in the data sheet for discharge at current to the end voltage 1.83 V/cell and look in the column for two hours discharge for the current equal to or larger than 75 A. Read the cell type in the left column. It is found that 5 OPzS 250 gives 76.3 A for two hours to an end voltage of 1.83 V/cell. Thus, the battery is 108 cells type 5 OPzS 250. Example 2 Problem : A battery is needed operating within the voltage range 220 ± 22 V and shall be able to supply 17.5 kw for a duration of 3 hours. Solution : In the same way as in example 1, calculate the number of cells to be 108 and the end voltage to be 1.83 V/cell. The requested power per cell / 108 = 162 W/cell. Use the performance table for constant power with an end voltage of 1.83 V/cell and look in the 3 hours column for a power of 162 W or the closest higher. It is found that 5 OPzS 350 gives 166 W. The suitable battery type is 108 cells type 5 OPzS

13 Sizing Against a Load Profile In many cases the battery is expected to perform to a load profile, i.e. a load that varies during the discharge time.the purpose of the battery can be a power supply for : A control and monitoring system calling for constant low power for 2 hours followed by a Circuit breaker tripping for a total of 30 sec.high power. There are number of different methods available for the calculation of the proper battery type to achieve such a combined load profile. The use of these methods relays upon experience as the different methods depend on the shape of the discharge profile. The battery type selection in such cases should be forwarded to Hawker local sales office. To reach an adequate solution it is necessary to specify properly the load profile to be met along with parameters listed below. Use of the following checklist is recommended : Voltage : The highest (charge) and lowest (discharge) permissible battery voltage. Number of cells : Specify if certain number of cells shall be used. Load profile : Where the specified current values represent the total battery load. If there is a requirement for a battery design safety margin for example for a battery ageing or compensation, the load profile should include the correct values accordingly. Temperature : The range of temperature within which the battery shall be able to supply the specified load. Charging Time : Possible limitation on the recharge time available until the discharge in accordance with the load profile can be repeated. Dimensions : Possible dimensional limitation in the battery floor area or weight. Required Service Life : To be given where required Accessibility : Requirements of free space over and around the battery for inspection and water replenishment. Technical Spec. : Possible requirement to follow the customers technical specification. Service Result : Where an existing battery is to be replaced, information about the experience with the old battery can be useful for the selection of the new one. 11

14 Safety General Some risks are present when working with lead-acid batteries : Corrosive electrolyte Explosive gas mix Voltage Weight Battery dismantling and installation work must be carried out with caution to minimize the risk of accidents. Use of adequate safety equipment prevents or limits the damage caused by accident. Electrolyte The electrolyte of fully charges OPzS batteries contains about 32 % by weight of sulphuric acid. The acid attacks many metals and organic materials. All handling of acid must therefore be carried out with caution and with fresh rinsing water available in the vicinity. Splashes of acid on the skin must immediately be rinsed off with plenty of water. If the eyes or mouth is affected, rinse for at least 5 minutes and then see a doctor immediately. Protective equipment, at least protective eye glasses, must be used during all work with a risk of acid splashes. When handling large amounts of acid, e.g. during moving or filling the cells, always use rubber gloves and protective apron. Battery explosion Explosive gas may be present in the cells at any time. A tiny spark is sufficient to ignite the gas. Ignition is likely to result in a cell explosion breaking the cell container into pieces. The risk of transfer of the explosion to the surrounding cells is considerable. Be aware that acid and debris from the cell container can cause personal injury. Avoid making sparks during all work with batteries. Remove finger rings, metal bracelets etc, use insulated tools and never remove connectors while there is a current flow in the battery. Avoid electrostatic charges by wearing clothing made from suitable materials. The risk of static electricity can also be reduced by the use of conductive floor cover material. Use of flame arresting vent plugs gives a high improvement in safety as ignition of gas. Most cases occur outside the cells and then spread into them. Voltage and Short Circuit A filled battery is live. The potential difference between cells far enough apart in the battery can be dangerous to life. The short-circuit current of stationary tubular cells is about 1000 A per 100 Ah nominal capacity. Even a transient inadvertant shortcircuit may cause heavy sparks with the risk of personal injury and/or damage to contact surfaces. ALWAYS USE INSULATED TOOLS WHEN WORKING ON THE BATTERY To reduce the risk of injury a stationary battery must be arranged so that inadvertant touching of live parts with a potential difference of more than 120 V is prevented (EN ). This rule also applies even when the battery is furnished with fully insulated cell connectors. The standard flat copper cell connectors used with OPzS batteries has a protection degree of IP 20. *A prolonged short circuit may cause damage to the pole seal as the pillars become hot. Weight Large stationary cells are heavy. Imprudent handling of them may result in crush injury on hands and feet or back injury. Use proper lifting devices and work carefully. 12

15 Marking of batteries Electrical equipement used within the EES shall meet the general requirements given in the EU EMC Directive (EMC = Electro-Magnetic Compatability) and the Low Voltage Directive. The test methods and specific requirements needed to demonstrate fulfilment of the directives are given in harmonized standards for the different equipment and apparatus. Equipment that has passed the prescribed tests with approved and documented result is marqued with the CE symbol. The EMC Directive Batteries are immune against external electrogmagnetic disturbance and do not, isolated from any other electrical system, create electromagnetical disturbancies. Accordingly the CENELEC Report R states that batteries free from electrical/electronic equipment other than cell connectors are excluded from the EMC directive. Use of the CE mark is then not appropriate. The Low Voltage Directive (LVD) According to the CENELEC Report R all individual cells are excluded from the requirements of the LVD directive, their nominal voltage being less than 75 V. Therefore CE-marking of individual cells is neither appropriate nor permitted. Conclusion The individual OPzS cells must not be marked with the CE symbol. However, the assembled battery, if the nominal voltage exceeds 75 V, together with the electrical system it is a part of, could be such that the EMC and LVD directives apply.

16 Hawker S.A. Rue Alexander Fleming ZI EST BP Arras Cedex France Tel: Fax: Please refer to the website address for details of your nearest Hawker office Hawker Worldwide Marketing Rake Lane Clifton Junction Swinton Manchester M27 8LR, UK Tel: +44 (0) Fax: +44 (0) Ref. DCS 9905G/ Subject to technical modification without prior notice.