Common Myths Regarding Power Quality and Compensation-3
Last part of our article regarding Power Quality and Compensation Compensation is as given below. We hope it shall be beneficial…
No contactor failure shall be experienced if we select the block contactor to perform switching in compensation system without reactor as one size larger.
False. Duty of compensation contactor in the compensation system without reactor is to limit the inrush current to be withdrawn from the grid (approximately 100 x In) during initial activation of capacitor and protect the capacitor. Selecting one size larger block contactor shall only strengthen the contact current for a limited amount, therefore it shall increase the nominal current carrying level. However, it shall not be enough for limiting the inrush current arriving at 100 x In levels. Internal structure of compensation contactor.
Compensation contactor has an initial-resistant structure. During shut-off, initially PA contact is closed and capacitor current flows to the capacitor through R resistance and R resistance limits the inrush current flowing to the capacitor at the first moment. Then PP contact is closed and PA contact passes to by-pass position, capacitor continues to feed the stable capacitor through the main contact.
In compensation systems with reactor, inrush current is naturally limited due to internal resistance of the coil serial connected to capacitor and compensation contactor usage is not required. Transformer fixed compensation level is fed from the same point with compensation system.
It is placed in the compensation panel.
False. Directive related with compensation states that transformer fixed compensation level shall be placed at front or back of the main switch. However, the fixed level connected to load side beneath the main switch located at transformer secondary may cause penal situations for the facility.
Transformer fixed compensation connection
Energy meters of power users having individual transformer are generally located at MV side. Distribution transformer has an inductive reactive loss due to its structure and this loss is read by the meter. Transformer fixed compensation level is placed in order to compensate this loss. If the fixed level is connected to load side of the main feeding switch located in transformer secondary, when main feeding switch is left open for a long time for any reasons (feast holiday, facility maintenance period, etc.), meter shall only write transformer inductive reactive loss as transformer fixed capacitor shall not be active and system may encounter with penal situations. Therefore, transformer fixed level is connected to grid side of main feeding switch and continuously remains active independent from position of the main switch and prevent penalties for the system by compensating the transformer loss.
Uğur YAŞA, Güç Kalitesi Müdürü – Aktif Mühendislik