Different Types of Protection for Capacitor Bank Explained

In electrical power circuits, capacitor bank has a very important role. Capacitor Bank is used to produce reactive power and supply where required. Capacitor bank also used to Improve Power Factor. Electrical Transmission and Distribution System, Substations and Engineering Industries everywhere capacitor bank is used. Capacitor banks contain so many capacitors connected in series and parallel combination.

It is must require to give protection internally and externally to a capacitor bank. Internal protection reduces the chances of damaging all capacitors due to damaging a single capacitor whereas external protection is required to protect the whole electrical system from the internal fault of the capacitor bank.

Different types of Internal Fault Protection for Capacitor Bank

Internal fault protection system prevents the whole capacitor from damage due to damaging of any single capacitor. Also, it prevents the capacitor bank from internal short circuits, capacitor failure, internal unbalance, etc.

In a capacitor bank, capacitors are connected in series and parallel combinations. In a three-phase capacitor bank, capacitors are connected in either star or delta connections. So internal protection system designed to disconnect a single capacitor or multiple capacitors from the main circuit when a fault occurs. Every single capacitor in a capacitor bank is called an Element and the multiple capacitors connected in the same way either series or parallel is called the group of elements. So, elements and groups of elements both need to be protected. This arrangement will disconnect a single capacitor or group of some capacitors according to the fault happen.

Element Protection

Every single capacitor is connected to the circuit with a fuse in series. When any fault occurs in that capacitor or it takes more current then the fuse will automatically disconnect that single capacitor from the circuit without any affects the other capacitor. After replacing that Capacitor we can connect a new fuse to restore the system.

Group of Element Protection

Group of element protection disconnects a branch of capacitors from the circuit when any fault occurs or element protection fails. Group of element protection also provided by a fuse. Group of element protection gives protection against the short circuit or any fault in the connection of capacitor rather than the fault in a single capacitor.

Read Also: Which connection is better for Capacitor Bank Star or Delta?

Different types of External Fault Protection for Capacitor Bank

An external fault protection system prevents the whole capacitor bank from any fault in the electrical power system where the capacitor bank is connected. It also prevents the electrical system from any internal fault of the capacitor bank.

Different types of external fault protection are,

• Over Voltage Protection
• Under Voltage and Under Current Protection
• Overload Protection
• Unbalanced Protection
• Power Fluctuation Protection

Over Voltage Protection for Capacitor Bank

Overvoltage can force the capacitor bank to draw more current or it can damage the capacitor bank. So when the overvoltage occurs in a power system, it is good to disconnect the capacitor bank from the power system. So voltage detector used to protect the Capacitor Bank from overvoltage. A time delay protection system also used for this protection which disconnects the capacitor for a certain time duration. Over voltage protection system is very helpful to protect the whole Capacitor bank.

Under Voltage and Undercurrent Protection for Capacitor Bank

Overvoltage issues of a power system can damage the capacitor bank whereas under-voltage or undercurrent issues can damage the circuit breaker and equipment connected with the capacitor bank. When an under-voltage fault occurs in a power system, the system voltage got lower than the capacitor voltage so it causes to flow reverse current. During an under-voltage fault, catastrophic damage may happen with the circuit breaker.

So under-voltage or undercurrent protection also required for capacitor banks.

Read Also: Why Thyristor used in Power Factor Correction Panel?

Overload Protection for Capacitor Bank

When the capacitor bank draws excess current than normal then it is called overload fault caused by the capacitor bank. It may happen due to an internal short circuit in the capacitor bank, insulation failure, dielectric failure, explosion. So when the capacitor bank draws overcurrent it should be disconnect from the system. Overload protection carried out by using CTs, current sensing relays with the circuit breaker. When the electrical system have excessive inductive load then a very high reactive current drawn from the capacitor bank. This also may damage the capacitor bank. This also need to be protected.

Unbalanced Protection for Capacitor Bank

Unbalance protection is must required for three-phase capacitor banks. Because if unbalance fault in the capacitor bank it will make the power system also unbalanced. An unbalanced fault occurs due to loose connection, capacitor failure per phase, neutral fault, etc. Unbalance fault causes to draw unbalance current per phase.

Unbalance current measures by RCCB protections, CTs, etc. When the current sensor senses the unbalance current it will send the signal to the circuit breaker to disconnect the capacitor bank from the system.

Read Also: Working and connection diagram of Single Phasing Preventer.

Power Fluctuation Protection for Capacitor Bank

When the capacitor bank once disconnects from the power system, it can not be again connected immediately to the system due to the trapped charge stored in the capacitor unit. Otherwise, it will cause to flow reverse current or make a catastrophic failure. Power fluctuation means suddenly off and again on in the power supply. So when the capacitor bank once stops consuming current due to power fluctuation it should be disconnect from the power system and after a few times, it should be connected to the power system. This little time required to discharge the capacitor through the internal resistor.

The time delay On/Off protection system helps to protect the capacitor bank during power fluctuation.

Read Also: 

• Why capacitor is connected in parallel not in series for Power Factor improvement?
• Negative Power Factor Causes, Effects, Improvement
• Shunt Capacitor Use, Applications, Advantages
• When Capacitor store more Energy Series or Parallel connection?
• Electrical Shock from Motor Body Causes, Safety, Prevention

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