Surface Charge in batteries

Surface charge and surface discharge in batteries refers to the superficial charging and discharging which occurs only on the surface of the electrodes.  A lead acid battery consists of lead oxide anode and a lead cathode.  When discharging, the lead oxide in the anode and the lead in the cathode get converted to lead sulphate.  When charging, the reverse happens.  

Surface charge refers to a condition when the chemical changes mentioned above occur only in the surface of the electrode.  For instance, if only the lead sulphate in the surface of the anode of a discharged battery gets converted into lead oxide, the battery will indicate a full charge when the open circuit voltage is  measured.  However, the charge in the battery will last only for a short time. 

Surface discharge is a condition when the open circuit voltage of the battery wrongly indicates a discharged condition, when the battery is still holding charge.  This too relates to chemical changes which occur superficially on the surface of the electrode. 

The surface charge can be removed by applying a slight load on the battery.  In vehicles, switching on the headlights for a while can help remove the surface charge.

Sulfation in batteries

Sulfation in lead acid batteries refers to a condition when the battery is not able to hold any charge.  It occurs when the plates of a battery get hardened with a layer of lead sulphate. 

Sulfation occurs when the battery is kept unused for long periods of time in the discharged state.  This makes the lead sulfate in the plates to get hardened.  These hardened plates prevent the battery from charging.

The lead acid battery consists of an anode made of lead oxide and a cathode made of lead.  These two electrodes are placed in an electrolyte of sulphuric acid.  When the battery is discharged, the sulphuric acid reacts with the electrodes which are transformed into lead sulphate.  As a result, the sulphuric acid in the electrolyte becomes dilute and almost becomes water.  The specific gravity of the electrolyte thus drops.

When the battery is recharged, the lead sulphate in the cathode and anode is converted into lead and lead oxide respectively.  The sulphate in the electrodes react with water to again form sulphuric acid. 

When the battery is kept unused for long periods of time in the discharged condition.  The lead sulphate which is in the electrodes solidifies into a layer which has high electrical resistance. 

When the battery is recharged using an external supply, this hardened layer of lead sulphate prevents charging.  The electrolyte too, does not become sulphuric acid.  Thus the battery is not able to absorb charge. 

Another reason for sulfation is incomplete charge and discharge, When the battery is not charged capacity and  not discharged completely, a small amount of the sulphate always remains in the electrodes.  This forms a hardened layer and diminishes battery capacity. 

Identifying Sulfation in batteries

If your battery is connected to the charger for a long time and still does not have charge.  Test the specific gravity with a hydrometer.  If the specific gravity is low, the battery probably has the problem of sulfation.

Repairing Sulfated batteries

Sulfated batteries can be repaired by applying a high charging voltage and low charging current from the battery charger. 

When batteries are to be kept unused for long periods, they can be connected to a battery minder, an electronic device which continually monitors the voltage level of the battery and prevents sulfation from occuring by firing electronic pulses into the battery to break any sulphate layer which may have formed. 

Single Phase Pole Mounted Distribution Transformers

Single Phase Pole Mounted Transformers are usually used in rural areas where three phase power may not be required.  These Transformers reduce the voltage from the line voltage 11kV to a single phase voltage usually 230V.

The secondary of the Pole mounted Distribution is usually connected between the two phases of a MV line.  The secondary voltage is a single phase voltage which is fed to the house.  These transformers can be easily installed and do not require extensive mounting Structures.
Pole mounted Transformers come in sizes up to 500 kVA.

These transformers have a fuse to protect against faults inside the transformer.  They are also equipped with an interrupting device.  These Transformers are tested to withstand the impulse of lightning. In the US, The secondary of these transformers has a centre tapping and therefore has three terminals.

The voltage between the end terminal and the centre tapping will provide 120V while the voltage between two end terminals will be 220 volts. These Single Phase Pole Mounted transformers can also be used to provide three phase LV supply.

Three pole mounted transformers are connected in wye or delta to get the desired connection. Besides, small size three phase transformers which can be mounted on poles are also available. Video Showing the Manufacture of Single Phase Transformers

Wireless Switches

Wireless Switches are used in homes, godowns, offices, etc to remotely control an electric appliance such as a lamp or a fan. Wireless switches work by preventing power from flowing through a receiver into the device.

The switch is mounted to the switchboard of the plug. The appliance to be controlled is connected through the device. When the switch is operated, it emits a radio frequency which activates or deactivates the receiver controlling the supply to the device. Wireless Switches can result in energy savings as it is easy to switch off the lights and fans in the room at the press of a single switch from another room.

Wireless switches can also be used to dim lights or reduce the speed of fans. You can adjust the lighting to suit your moods. You can switch on the lights when opening the front door when you return home in the evening. Wireless switches can be used to save energy. Dimmed lights consume less power. You can control your energy consumption while using optimum lighting.

Wireless switches can also be made part of a lighting program. These lighting programs can be activated when you are on a vacation. Lights can be switched on and off at different times of the day. This gives an impression that your house is occupied and can ward potential burglars and thieves.

Here is a video which describes the wireless switch and its function

Distribution Transformers

Distribution Transformers play a vital role in the system which delivers electricity to the end user.   It is the final part of the transmission system from the power plant to the consumer.  Distribution Transformers step down the MV power, usually 11kv into the domestic LV, 440 V supply.

Distribution Transformers are a critical part of the distribution network.  These transformers are always online throughout the year.  Hence, design of the distribution transformer is made considering the high iron losses.  Besides, the transformer is sized to have high efficiency at 70% of the load as the power output varies through the day as per the load cycle. 

Distribution transformer are protected by fuses in the HV side.  They are also designed to withstand unbalanced loading.  They have ONAN cooling (Oil Natural, Air Natural ). 

Distribution Transformer are usually of the vector Dyn11.  While, designers are not particular about any particular vector group , most systems will standardize on one particular vector group, usually the Dyn11.  Some systems also use the Dyn1.  These vector groups have a difference of 30 degrees between the primary and secondary vectors which is unavoidable in delta to star conversion.

B, C and D types in Miniature Circuit Breakers

MCBs (Miniature Circuit Breakers) are categorized into B, C and D types.  These three ratings are determined by the level of overload which causes the MCB to trip. 

B type MCBs operate at an overload of 3 to 5 times the rated current.  Type B MCBs are usually used in domestic installations where the inrush currents and surges are low. 

C type MCBs operate at an overload of 5 to 10 times the rated current.  These MCBs are used in commercial and industrial installations where high inrush current are likely due to motor starting or due to large no of fluorescent lighting. 

D type MCBs are used in special applications such as x-ray machines and transformers which can draw heavy inrush current.

Plante Batteries

Plante Batteries were invented by the French Scientist Gaston Plante in the year 1859.  The Plante Battery was the first rechargable battery.  It is also the first lead acid battery.

As a  lead acid battery, the Plante Battery uses pure lead plates.  The advantage of the Plante battery is that the capacity remains the same throughout its life.  Its grid design enables it to generate high currents and is thus suitable for applications which require high bursts of currents.  The active material in the positive plate is generated and regenerated throughout its lifetime.  Hence, there is  no loss of capacity. 

Each cell typically has a voltage of 2 volts.  Its ampere hour efficiency is 90%. 

The downside of this battery is its large size and high cost.