Cathodic Protection

Electrochemical Corrosion is one of the types of corrosion in metals.  Electrochemical corrosion occurs, chiefly, in submerged metallic structures such as pipelines, storage tanks, water circulating systems, ship hulls and off shore platforms.  Electrochemical Corrosion occurs when the potential on the surface of the metal is not uniform.  

This uneven potential on the surface is caused due to impurities in the surface or uneven stress on the surface of metals.  This causes certain parts of the surface to act as an anode while other parts of the surface act like the cathode.  The current which flows between the anodic and the cathodic regions can cause corrosion.

Cathodic protection refers to a method of protection of these metallic structures from electrochemical corrosion.  This is achieved by making the metal to be protected the cathode.  When a material which has a higher electrode potential is kept in the same medium as the object to be protected, it becomes the cathode while the object to be protected becomes the cathode.  A simple electrochemical cell is created.  The electrons move from the anode to the cathode in the medium.  In the process, the anode gets corroded while the cathode is protected from corrosion.  The anode used is called the sacrificial anode. 

The sacrificial anode has to be periodically replaced as it gets eaten away.

Manufacturing Power Transformers

Distilled water in batteries

Distilled water needs to be added periodically to the Lead Acid Batteries to compensate for the water lost during electrolysis.  When a discharged battery is charged with the power from an external charger, the current causes an electrolysis of the water in the electrolyte.  The water dissociates into hydrogen and oxygen.  These gases are released through the vents.  This process results in drop in the level of the electrolyte.  To compensate for this, distilled water is added when the level of electrolyte falls below a particular level. 

Distilled water alone should be used as it is pure water without any impurity.  Tap water should never be used as the chemicals present in tap water can seriously damage the batteries.  Care should be taken that water is not added in excess known as overwatering.  Overwatering will dilute the electrolyte and affect battery performance. 

APC UPS Systems - A Guest Post

UPS or Uninterrupted Power Systems are widely used in offices, hospitals, industries, in telecommunication as a back up against sudden power cuts. Sudden Power cuts can cause disturbances and losses in the form of lost data, interruption to life support systems in hospitals and unpredictable behaviour in industrial systems. A UPS which usually consists of an battery system and an inverter steps in the moment the supply voltage dips beyond a certain value preventing the interruption of supply to critical systems.

The central part of the UPS is the battery which stores power when the supply is available and makes power available when the mains supply is switched off. A UPS system can provide power backup for a time period ranging from a few minutes to many hours. The duration of the back up supply depends on the capacity of the battery. APC is a division of Schneider Electric which deals with UPS and Power back up systems. The company provides a wide range of batteries with different capacities and ratings for the power back up solutions.

Besides their use as sources of back up power, these batteries can also be used to protect critical equipment against sudden dips in the voltage which can electronic equipment to switch off or reset causing unwanted interruption. APC provides a wide range of UPS solutions for Homes, Small Business and for Large Corporations. The UPS provides sine wave output and distinct LED indicators which indicate the state of the battery and the power conditions.

The systems have a Home away switch which charges the batteries while you are away besides a intelligent battery charging system which enables controlled charging of the batteries thus prolonging battery life. All products are backed by a warranty and the wide service network of APC.

You can check out their products in their website http://www.apc.com

About the Author 

Alex from HTBS  is a technology expert who often writes about topics related to batteries and especially regarding the APC Replacement Battery

Stuck breaker protection

Stuck breaker protection is a situation in which a circuit breaker fails to operate even after receiving a tripping signal from a relay or a switch.  Stuck breaker can undermine the protection scheme and can cause damage to machinery and is a danger to personnel.  

Common reasons for a circuit breaker not opening are a disconnection in the trip circuit or a mechanical problem with the circuit breaker.  In these conditions, there needs to be a backup protection device which can interrupt the fault and isolate the system.  In some cases, the entire section of the bus to which the breaker is connected is de-energized to interrupt power. 

A simple Stuck breaker protection schemes functions by sensing the position of the circuit breaker through the limit switches in the circuit breaker.  The protection system waits for the open status from the circuit breaker after the open signal has been given.  If the signal is not received within a preset time, the scheme assumes that the breaker is stuck and initiates backup measures. 

However, this system has its limitations.  The system cannot detect a situation where the current continues to flow despite the breaker having tripped.  This can occur due to situations where the arc has not been quenched (failure of the arc extinction system) and the current flows even though the contacts have mechanically separated. 

To ensure proper feedback of the interruption of the current, advanced stuck breaker schemes sense the current as well as the position contacts of the circuit.  This ensures that an accurate feedback of the breaker status.

Voltage Supervision Relays

The Voltage Supervision Relay is an integral part of any  protection system.  The voltage supervision relay protections systems from undervoltage and overvoltage.  Overvoltage in a system can result in serious damage to insulation and equipment while undervoltage can cause motors to draw more current and reduce the speed of the motors, disturbing the process. 

Besides protecting against overvoltage, the voltage supervision relay can also be used to detect earth faults as the phase to earth voltage is distorted when there is an earth fault in one of the phases.  Voltage supervision relays can generate alarms when the voltage is low or high in only one phase.  This is also known as phase asymmetry. 

In motor circuits, the voltage supervision relay protects against single phasing.  Single phasing can cause serious damage to motors.

A simple auxiliary relay can also be used to generate alarm for undervoltage.  When the voltage drops, the relay can drop off thus generating an alarm or a shutdown.

Trip Circuit Supervision in Circuit Breakers

Trip circuit supervision in Circuit breakers is an vital part of any protection scheme. If the trip relay fails to operate, it may result in upstream tripping or even in damage to equipment.  Trip circuit supervision makes sure that the tripping coil of a circuit breaker is always in the healthy condition.  

The Trip circuit supervision is particularly important in breakers which have only one trip coil.    The Trip circuit supervision relay continually measures the resistance of the trip coil of circuit breakers.  It also measures the control voltage of the trip coil and gives and alarm when the control voltage falls to low levels. 

The Trip circuit supervision relay injects a constant current through the trip coil of the breaker and measures the voltage drop across the coil.  Thus, the relay is able to measure the resistance of the coil.  

The Trip circuit supervision relays can also monitor more than one breaker coil. 

If the Trip circuit supervision Relay detects a fault, it activates the breaker failure logic which can activate a backup breaker if installed or cause the tripping of upstream breakers.