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Batteries
Chapter 15
Batteries 15.1 INTRODUCTION 15.1.1 Power Sources AC power is often preferred because it is easy to generate, to transmit, and to use. However, in some situations, DC power is preferred because it can be stored in batteries and used if the generating equipment fails.
15.1.2 DC Power Circuits A DC power circuit consists of a battery charger with an AC supply, a battery, and loads. The battery charger converts AC to DC. The resulting DC is used to supply the load and to supply a charge to the battery (float charge). The battery stores DC power and is used to supply power to the load if the AC supply and charger fail; if the demand is high, the battery may also supplement the power supplied by the charger.
15.1.3 Cells and Batteries Cells are devices that store and deliver DC power. A battery is made up of one or more cells connected in series. Each cell of an industrial storage battery provides a specific voltage; the battery voltage depends on the number of cells. The cells are filled with an electrolyte (a solution of acid and water) that activates a chemical reaction and provides a path for current flow. The plates are connected to the appropriate terminal posts (positive or negative, depending on the plate material). Many plates may be connected together to increase the storage capacity of the cell. An outer jar contains the plates and the electrolyte.
15.1.4 Cell Operation Connecting a battery charger to the terminals of a battery starts a chemical reaction, causing electrons to leave one plate and build up on the other. One plate becomes positively charged, and the other is negatively charged. If a load is connected across the terminals, current flows and the stored charge is Practical Power System and Protective Relays Commissioning. DOI: https://doi.org/10.1016/B978-0-12-816858-5.00015-0 © 2019 Elsevier Inc. All rights reserved.
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dissipated. The charge slowly dissipates from charged cells over a period of time. Keeping the cells continuously connected to the charger ensures they will be fully charged at all times.
15.1.5 Safety Considerations The charge stored in the cells can cause shocks, even if the battery has been disconnected. Electrolytes can cause burns. The hydrogen given off by the cells can cause explosions. Battery rooms should be kept clean, wellventilated, and locked. When working on batteries, electricians should wear protective gloves, aprons, boots, goggles, and face shields.
15.1.6 Additional Checks Safety equipment, such as eyewash stations or showers, should be located and checked to ensure proper operation. The temperature of the room should be verified. The battery racks and the floor under the racks should be checked for signs of acid spills. Spills should be reported and cleaned, following facility procedures.
15.1.7 Acid Concentration The initial concentration of acid in a cell is determined by the manufacturer. When a cell is discharged, acid concentration is low; when a cell is charged, acid concentration is high. The concentration of acid in the electrolyte is a good indication of the amount of charge in the cell.
15.1.8 Specific Gravity and Acid Concentration The specific gravity of a liquid indicates how heavy the liquid is when compared with pure water. The specific gravity of electrolyte depends on the concentration of acid. Therefore, the specific gravity can be used to determine the amount of charge in the cell. Specific gravity measurements must be corrected for temperature and level of the electrolyte.
15.1.9 Determining the Condition of a Battery The final determination is usually made by facility engineers or supervisors based on data usually supplied by the electrician. Two measurements are needed: the corrected specific gravity measurement and the direct voltage measurement.
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15.1.10 Taking Measurements A voltmeter may be used to check cell voltage. A hydrometer may be used to measure specific gravity. In general the batteries are used in power stations and substations to supply a DC current for tripping circuits and protection relays and can be found in 110 or 220 V and for communication equipment of 24 or 48 V. An alkaline battery consists of cell container, positive plates, negative plates, and ebonite separators. Lead-acid batteries also exist.
15.2 CHARGING AND DISCHARGING OF A NEW BATTERY To start a new battery, the following steps are required: Clean the surface of the batteries; check all positive and negative connections polarities. Check all tightness of all joints between the battery cells. Open the battery filling caps then fill the battery with the electrolyte with specific gravity between 1.150 and 1.200. Leave the battery about 10 hours for plates to be saturated with electrolyte. Measure the electrolyte level which should be above the plates by 12 15 cm. Connect the battery to battery charger. Start the charging with the charger in fast-charging mode with a current equal to battery Amp hour (Ah), for example, for 400 Ah the charging current will be 40 A for 10 hours. On the beginning of the charge start the charge with 10 A for 30 minutes, and then increase the current to 40 A in steps. When battery reaches 2.35 V/cell, decrease the charging current to 30 A. After 60 hours decrease the charging current to 20 A. When battery reaches 2.6 V/cell stop charging, then restart charging at 10 A until the voltage of cells are stabilized and no changes occur for 2 hours. Put the battery charger in floating mode of charge. Charging or discharging should not be undertaken if the temperature gets to greater than 45 C 55 C. For example, for a 400 Ah 220 V lead battery the following measurements were taken: Lowest cell 5 1.73 V/cell Number of cells in the battery 5 164 cells of lead-acid Highest cell 5 2.6 V/cell Highest temperature: 55 C—hence stop charge or discharge immediately; let the battery temperature decrease over time. Complete the charging cycle of the battery: first charge, discharge, second charge. Start the discharging process
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15.2.1 Discharging of a New Battery G
G
Leave the battery to discharge in an external resistance (water resistance may be used at site) for about 2 hours. For example: The discharge current should start at 66 A for a 400 Ah 220 V battery for 200 ms, then 49 A for 2 hours.
15.3 BATTERY CHARGER A battery charger consists of a rectifier circuit, power circuit, ripple monitoring, control circuit, regulator circuit, and fault detection circuit. This charger can also be used as a DC source for a control and protection circuit of a substation during normal operation, or to charge the battery in floating mode. When there is a problem in the AC system, then the battery supplies the DC loads in a substation. There are two types of charging modes: the first is the fast charging for a new or unused batteries, and the second is the floating charge to charge the batteries in service and supply a load to compensate for the small charge lost by the battery in service. Fig. 15.1 shows a DC system using batteries in a high-voltage substations.
15.4 CHARGER SETTING MODES DURING BATTERY CHARGING Depending upon the cell voltage, the charger can be set in the following modes as seen in Fig. 15.2.
FIGURE 15.1 DC distribution system using batteries in a high-voltage substation.
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FIGURE 15.2 Operating voltage range for battery charger settings for the charging of alkaline batteries.
The boost charging means the commissioning charging mode at the beginning of new battery operation. The floating charge is the charging of the battery at normal service.
15.5 BATTERIES IN HIGH-VOLTAGE SUBSTATIONS For a 400/220/132/33 kV substation, the specifications are: G
G G
G G
G
The minimum ampere-hour ratings of battery for 400 kV switchyard of 400/220/132/33 kV substation and all 400 kV equipment shall be 300 Ah. The voltage rating of an 300 Ah battery shall be 220 6 10% V. For 220, 132, and 33 kV switchyard portion of 400/220/132/33 kV substation and equipment, the minimum Amp-hour rating of battery shall be 400 Ah. The voltage rating of a 400 Ah battery shall be 220 6 10% V. The DC system shall consist of two battery chargers of 220 V, 300 Ah for 400 kV and battery charger of 220 V, 400 Ah for 220/132/33 kV. For 400 kV there shall be two sets of battery with an amp-hour rating of 300 Ah and for all other voltage classes, one battery set with a rating of 400 Ah. For a 220/132/33 kV substation, the specifications are:
G G G
The minimum ampere-hour rating of battery shall be 300 Ah. The voltage rating of a 300 Ah battery shall be 220 6 10% V. Two battery chargers of 300 Ah shall be required. For a 132/33 kV substation, the specifications are:
G G G
The minimum ampere-hour rating of battery shall be 200 Ah. The voltage rating of 200 Ah battery shall be 220 6 10% V. There shall be one battery charger of 200 Ah.
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The trickle charge and quick charge voltage per cell of the above batteries shall be 2.15 2.25 6 0.02 V and 1.85 2.75 V respectively. The range of charging current of the batteries shall be as follows: G G G
For 300 Ah battery: Boost charge 42 21 A and float charge 720 240 mA For 400 Ah battery: Boost charge 56 28 A and float charge 960 320 mA For 200 Ah battery: Boost charge 28 14 A and float charge 480 160 mA The minimum demand load on the chargers are:
G G G
Charger for 300 Ah battery: 24 A Charger for 400 Ah battery: 40 A Charger for 200 Ah battery: 16 A
Batteries 15.1 INTRODUCTION 15.1.1 Power Sources AC power is often preferred because it is easy to generate, to transmit, and to use. However, in some situations, DC power is preferred because it can be stored in batteries and used if the generating equipment fails.
15.1.2 DC Power Circuits A DC power circuit consists of a battery charger with an AC supply, a battery, and loads. The battery charger converts AC to DC. The resulting DC is used to supply the load and to supply a charge to the battery (float charge). The battery stores DC power and is used to supply power to the load if the AC supply and charger fail; if the demand is high, the battery may also supplement the power supplied by the charger.
15.1.3 Cells and Batteries Cells are devices that store and deliver DC power. A battery is made up of one or more cells connected in series. Each cell of an industrial storage battery provides a specific voltage; the battery voltage depends on the number of cells. The cells are filled with an electrolyte (a solution of acid and water) that activates a chemical reaction and provides a path for current flow. The plates are connected to the appropriate terminal posts (positive or negative, depending on the plate material). Many plates may be connected together to increase the storage capacity of the cell. An outer jar contains the plates and the electrolyte.
15.1.4 Cell Operation Connecting a battery charger to the terminals of a battery starts a chemical reaction, causing electrons to leave one plate and build up on the other. One plate becomes positively charged, and the other is negatively charged. If a load is connected across the terminals, current flows and the stored charge is Practical Power System and Protective Relays Commissioning. DOI: https://doi.org/10.1016/B978-0-12-816858-5.00015-0 © 2019 Elsevier Inc. All rights reserved.
157
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dissipated. The charge slowly dissipates from charged cells over a period of time. Keeping the cells continuously connected to the charger ensures they will be fully charged at all times.
15.1.5 Safety Considerations The charge stored in the cells can cause shocks, even if the battery has been disconnected. Electrolytes can cause burns. The hydrogen given off by the cells can cause explosions. Battery rooms should be kept clean, wellventilated, and locked. When working on batteries, electricians should wear protective gloves, aprons, boots, goggles, and face shields.
15.1.6 Additional Checks Safety equipment, such as eyewash stations or showers, should be located and checked to ensure proper operation. The temperature of the room should be verified. The battery racks and the floor under the racks should be checked for signs of acid spills. Spills should be reported and cleaned, following facility procedures.
15.1.7 Acid Concentration The initial concentration of acid in a cell is determined by the manufacturer. When a cell is discharged, acid concentration is low; when a cell is charged, acid concentration is high. The concentration of acid in the electrolyte is a good indication of the amount of charge in the cell.
15.1.8 Specific Gravity and Acid Concentration The specific gravity of a liquid indicates how heavy the liquid is when compared with pure water. The specific gravity of electrolyte depends on the concentration of acid. Therefore, the specific gravity can be used to determine the amount of charge in the cell. Specific gravity measurements must be corrected for temperature and level of the electrolyte.
15.1.9 Determining the Condition of a Battery The final determination is usually made by facility engineers or supervisors based on data usually supplied by the electrician. Two measurements are needed: the corrected specific gravity measurement and the direct voltage measurement.
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15.1.10 Taking Measurements A voltmeter may be used to check cell voltage. A hydrometer may be used to measure specific gravity. In general the batteries are used in power stations and substations to supply a DC current for tripping circuits and protection relays and can be found in 110 or 220 V and for communication equipment of 24 or 48 V. An alkaline battery consists of cell container, positive plates, negative plates, and ebonite separators. Lead-acid batteries also exist.
15.2 CHARGING AND DISCHARGING OF A NEW BATTERY To start a new battery, the following steps are required: Clean the surface of the batteries; check all positive and negative connections polarities. Check all tightness of all joints between the battery cells. Open the battery filling caps then fill the battery with the electrolyte with specific gravity between 1.150 and 1.200. Leave the battery about 10 hours for plates to be saturated with electrolyte. Measure the electrolyte level which should be above the plates by 12 15 cm. Connect the battery to battery charger. Start the charging with the charger in fast-charging mode with a current equal to battery Amp hour (Ah), for example, for 400 Ah the charging current will be 40 A for 10 hours. On the beginning of the charge start the charge with 10 A for 30 minutes, and then increase the current to 40 A in steps. When battery reaches 2.35 V/cell, decrease the charging current to 30 A. After 60 hours decrease the charging current to 20 A. When battery reaches 2.6 V/cell stop charging, then restart charging at 10 A until the voltage of cells are stabilized and no changes occur for 2 hours. Put the battery charger in floating mode of charge. Charging or discharging should not be undertaken if the temperature gets to greater than 45 C 55 C. For example, for a 400 Ah 220 V lead battery the following measurements were taken: Lowest cell 5 1.73 V/cell Number of cells in the battery 5 164 cells of lead-acid Highest cell 5 2.6 V/cell Highest temperature: 55 C—hence stop charge or discharge immediately; let the battery temperature decrease over time. Complete the charging cycle of the battery: first charge, discharge, second charge. Start the discharging process
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15.2.1 Discharging of a New Battery G
G
Leave the battery to discharge in an external resistance (water resistance may be used at site) for about 2 hours. For example: The discharge current should start at 66 A for a 400 Ah 220 V battery for 200 ms, then 49 A for 2 hours.
15.3 BATTERY CHARGER A battery charger consists of a rectifier circuit, power circuit, ripple monitoring, control circuit, regulator circuit, and fault detection circuit. This charger can also be used as a DC source for a control and protection circuit of a substation during normal operation, or to charge the battery in floating mode. When there is a problem in the AC system, then the battery supplies the DC loads in a substation. There are two types of charging modes: the first is the fast charging for a new or unused batteries, and the second is the floating charge to charge the batteries in service and supply a load to compensate for the small charge lost by the battery in service. Fig. 15.1 shows a DC system using batteries in a high-voltage substations.
15.4 CHARGER SETTING MODES DURING BATTERY CHARGING Depending upon the cell voltage, the charger can be set in the following modes as seen in Fig. 15.2.
FIGURE 15.1 DC distribution system using batteries in a high-voltage substation.
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FIGURE 15.2 Operating voltage range for battery charger settings for the charging of alkaline batteries.
The boost charging means the commissioning charging mode at the beginning of new battery operation. The floating charge is the charging of the battery at normal service.
15.5 BATTERIES IN HIGH-VOLTAGE SUBSTATIONS For a 400/220/132/33 kV substation, the specifications are: G
G G
G G
G
The minimum ampere-hour ratings of battery for 400 kV switchyard of 400/220/132/33 kV substation and all 400 kV equipment shall be 300 Ah. The voltage rating of an 300 Ah battery shall be 220 6 10% V. For 220, 132, and 33 kV switchyard portion of 400/220/132/33 kV substation and equipment, the minimum Amp-hour rating of battery shall be 400 Ah. The voltage rating of a 400 Ah battery shall be 220 6 10% V. The DC system shall consist of two battery chargers of 220 V, 300 Ah for 400 kV and battery charger of 220 V, 400 Ah for 220/132/33 kV. For 400 kV there shall be two sets of battery with an amp-hour rating of 300 Ah and for all other voltage classes, one battery set with a rating of 400 Ah. For a 220/132/33 kV substation, the specifications are:
G G G
The minimum ampere-hour rating of battery shall be 300 Ah. The voltage rating of a 300 Ah battery shall be 220 6 10% V. Two battery chargers of 300 Ah shall be required. For a 132/33 kV substation, the specifications are:
G G G
The minimum ampere-hour rating of battery shall be 200 Ah. The voltage rating of 200 Ah battery shall be 220 6 10% V. There shall be one battery charger of 200 Ah.
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The trickle charge and quick charge voltage per cell of the above batteries shall be 2.15 2.25 6 0.02 V and 1.85 2.75 V respectively. The range of charging current of the batteries shall be as follows: G G G
For 300 Ah battery: Boost charge 42 21 A and float charge 720 240 mA For 400 Ah battery: Boost charge 56 28 A and float charge 960 320 mA For 200 Ah battery: Boost charge 28 14 A and float charge 480 160 mA The minimum demand load on the chargers are:
G G G
Charger for 300 Ah battery: 24 A Charger for 400 Ah battery: 40 A Charger for 200 Ah battery: 16 A