Star connection and delta connection are common connection methods for power compensation capacitors. The wiring mode of the capacitor bank should be selected according to the voltage, protection mode and capacity of the capacitor, usually including delta wiring and star wiring. When the rated voltage of the capacitor is consistent with the rated voltage of the network, the delta connection should be used; when the rated voltage of the capacitor is lower than the rated voltage of the network, the star connection can be used, or series and parallel connection, and then the star connection. At present, the commonly used wiring method in enterprises is delta wiring, because it can realize phase-splitting compensation and solve the problem of three-phase unbalance.
First of all, let's make a simple comparison between the delta connection method and the star connection method:
Advantages of delta connection:
①Compensation effect is better.
②The wiring is simple and the cost is low.
③It can reduce the overvoltage operation to a certain extent and reduce the inrush current of the input capacitor bank.
Advantages of star wiring:
① Flexible configuration.
②It is easy to choose a better protection method.
③ When a phase capacitor breaks down, it will not cause a short circuit between phases, and the operation is relatively safe, which can avoid large-scale explosion of the capacitor.
When wiring the capacitor bank according to the actual application, what problems should be paid attention to?
1. There are certain protective devices
It is best to arrange a certain protection device for the capacitor bank. Generally, the transverse differential protection is suitable for the capacitor bank using the double-delta connection method; the zero-sequence current protection is suitable for large-capacity group capacitors; and the neutral line unbalanced current protection is more suitable for double-star Shape connection method, open delta voltage protection is more suitable for single star connection method.
2. Appropriate reactors can be connected in series
Some power grid systems have large harmonics, because appropriate capacitors can be connected in series in front of the capacitors, which can be lower than the influx of harmonic currents to a certain extent, and prevent various problems caused by internal short-circuits of the capacitors.
3. The capacitor must be insulated from ground
When the capacitor is connected to the system, it is necessary to ensure that it is insulated from the ground. For the neutral point ungrounded system, when the short-circuit current protection device cannot reliably protect the ground, and the short-circuit single-phase current is large (over 20A), it is necessary to use a single-phase grounding protection device.
4. Make sure the capacitor is fully discharged
When wiring or overhauling the capacitor bank, it is necessary to ensure that the capacitor is completely discharged to avoid electric shock accidents. If conditions permit, a no-voltage release automatic trip device can be installed, which can avoid the generation of closing inrush current and prevent the capacitor from bulging, oil leakage, explosion and other faults.