What are the Causes of Power Factor Correction and Capacitor Failure?
Date：2013-07-24
Power Factor Correction & Power quality products are somewhat specialised and offer a difficult challenge to general maintenance staff and contractors who may not be fully conversant with their operation and associated dangers, a malfunctioning capacitor bank can manifest a multitude of effects onto the main distribution system from Voltage Multiplication, Nuisance Tripping of Circuits and Unexplained Electrical Failures.
Power Factor Correction, Power Quality products & Harmonic Filters are sometimes vital to a clients operation, malfunction is not always apparent and in most cases only detected months later through higher energy charges and hidden penalties on electricity bills. Planned annual maintenance is recommended to avoid potential failures and detect failures before they become problematic and attract penalties.
PES will ensure efficient and safe operation, enhanced reliability and potential monthly savings are not compromised through our cost effective planned or reactive maintenance scheme to cover all power quality products and associated switchgear irrespective of manufacturer or location
Typical failures of power factor correction capacitors can be attributed to a number of reasons as detailed below:
Reasons for Capacitor Failure
Modern day capacitors are on the whole, manufactured using “self healing, safety disconnect” technology whereby the integrity of the capacitor dielectric is maintained under a minor fault condition by gases released within the capacitor element to effectively weld closed any hole caused by the fault in the dielectric, under major fault conditions, the gas is released with such force that the capacitor disconnects itself from the supply before further damage is caused by raising the top of the preformed canister and mechanically breaking the internal fuses, in some cases when oil filled capacitors are used, the oil can be seen to leak out of the top of the capacitor..
Temperature
Capacitors are both voltage & temperature sensitive and have therefore been categorized for use BKMJ Series are which is the highest performing category, this states that a capacitor is expected to withstand a maximum of 55oC although no higher than 45oC average for 24 hour and 35oC for 1 year, the ideal temperature to ensure trouble free operation would be < 25oC, should you expect temperatures to be above a 25oC ambient, de-rating of the capacitor should be carried out by increasing the dielectric strength from say 415V to 450V or even 525V in arduous applications.
In applications with an expected ambient above a 25oC, forced air ventilation should be employed to move the warm air, avoid potential hot spots and the potential of thermal runaway.
For extremely arduous applications BKMJ series capacitors may be employed
Harmonics and Detuned Capacitors
Detuned capacitors are capacitors complete with harmonic blocking inductors which work in two ways, one to protect the capacitors from harmonic overload and associated high currents, the other is to remove the likelihood of resonance between the capacitors and supply transformer.
Harmonics are a currents or voltages that are a multiple of the fundamental power frequency (50Hz), harmonics are generated by a number of non-linear loads like variable speed drives, Thyristor Drives, Inverters, fluorescent lighting or any plant that draws current as a pulse thus causing a distorted wave form, harmonic overload of a capacitor can result in higher currents flowing into the capacitor creating excessive heating of the element and ultimate failure if not protected by a Detuning Reactor.
Resonance
Resonance is a situation where the capacitors and supply transformer create a low impedance path for the circulating harmonic currents, when this happens the electrical system could tune to the most dominant specific harmonic frequency thus increasing current flow through the electrical system.
Sometimes resonance can be heard as a high frequency vibration, detuned capacitors are installed to combat the resonant situation and also it can occur in any electrical system where harmonic currents are present although the presence of harmonic currents do not necessarily mean that a resonant situation will occur.
Power Factor Correction, Power Quality products & Harmonic Filters are sometimes vital to a clients operation, malfunction is not always apparent and in most cases only detected months later through higher energy charges and hidden penalties on electricity bills. Planned annual maintenance is recommended to avoid potential failures and detect failures before they become problematic and attract penalties.
PES will ensure efficient and safe operation, enhanced reliability and potential monthly savings are not compromised through our cost effective planned or reactive maintenance scheme to cover all power quality products and associated switchgear irrespective of manufacturer or location
Typical failures of power factor correction capacitors can be attributed to a number of reasons as detailed below:
Reasons for Capacitor Failure
Modern day capacitors are on the whole, manufactured using “self healing, safety disconnect” technology whereby the integrity of the capacitor dielectric is maintained under a minor fault condition by gases released within the capacitor element to effectively weld closed any hole caused by the fault in the dielectric, under major fault conditions, the gas is released with such force that the capacitor disconnects itself from the supply before further damage is caused by raising the top of the preformed canister and mechanically breaking the internal fuses, in some cases when oil filled capacitors are used, the oil can be seen to leak out of the top of the capacitor..
Temperature
Capacitors are both voltage & temperature sensitive and have therefore been categorized for use BKMJ Series are which is the highest performing category, this states that a capacitor is expected to withstand a maximum of 55oC although no higher than 45oC average for 24 hour and 35oC for 1 year, the ideal temperature to ensure trouble free operation would be < 25oC, should you expect temperatures to be above a 25oC ambient, de-rating of the capacitor should be carried out by increasing the dielectric strength from say 415V to 450V or even 525V in arduous applications.
In applications with an expected ambient above a 25oC, forced air ventilation should be employed to move the warm air, avoid potential hot spots and the potential of thermal runaway.
For extremely arduous applications BKMJ series capacitors may be employed
Harmonics and Detuned Capacitors
Detuned capacitors are capacitors complete with harmonic blocking inductors which work in two ways, one to protect the capacitors from harmonic overload and associated high currents, the other is to remove the likelihood of resonance between the capacitors and supply transformer.
Harmonics are a currents or voltages that are a multiple of the fundamental power frequency (50Hz), harmonics are generated by a number of non-linear loads like variable speed drives, Thyristor Drives, Inverters, fluorescent lighting or any plant that draws current as a pulse thus causing a distorted wave form, harmonic overload of a capacitor can result in higher currents flowing into the capacitor creating excessive heating of the element and ultimate failure if not protected by a Detuning Reactor.
Resonance
Resonance is a situation where the capacitors and supply transformer create a low impedance path for the circulating harmonic currents, when this happens the electrical system could tune to the most dominant specific harmonic frequency thus increasing current flow through the electrical system.
Sometimes resonance can be heard as a high frequency vibration, detuned capacitors are installed to combat the resonant situation and also it can occur in any electrical system where harmonic currents are present although the presence of harmonic currents do not necessarily mean that a resonant situation will occur.
