Power capacitor protection

    First, the type of failure and protection
    Parallel-compensated power capacitors with voltages of 1kV and above have the following faults and abnormal operation modes:
    (1) The connection line between the power capacitor bank and the circuit breaker is short-circuited.
    (2) The internal fault of the power capacitor and its lead-out line are short-circuited.
    (3) If the power capacitor bank consists of several power capacitors connected in parallel and Shenlian, and each fuse is equipped with a fuse, when a part of the power capacitor is cut off due to failure, the voltage increase on the remaining power capacitors may exceed the allowable value.
    (4) Single-phase grounding of the power capacitor bank.
    Shenlian Power Capacitor is equipped with the following protective devices as required:
    (1) For the short circuit of the connection between the power capacitor bank and the circuit breaker, current protection with no time limit or short time limit shall be installed.
Acting for a trip.
    (2) For the internal fault of the power capacitor and its short-circuit of the lead-out line, one of the following protections can be used:
    1) If the number of power capacitors is large, the power capacitors can be grouped according to the size of the power capacitor and the breaking capacity of the fuse.
Install fuses on each group.
    2) The power capacitors can be divided into two groups, and the lateral differential protection is installed to act on the trip.
    3) In the power capacitor bank, the voltage rises due to the cutting of the individual power capacitors, and the cross-link differential protection or the lateral differential protection using the internal reduction of the power capacitor can be installed. It can be applied to the signal when the allowable value is not exceeded, and should be tripped when the allowable value is exceeded.
    4) For single-phase ground faults of power capacitors, single-phase grounding protection is installed according to specific conditions.
    Second, the general principle
    I. Timing current fast breaking protection
    (1) The setting of the quick-break protection current has sufficient sensitivity coefficient when the end of the power capacitor is faulty. Generally, the setting is 3-5.
Multiple rated current.
    (2) Consider the impact of the transition process of power capacitors. The quick-break protection action time is generally 〖1.
    (3) The sensitivity coefficient of the lead wire at the end of the container is not less than 2.
    2. Overcurrent protection
    (1) Overcurrent protection should be three-stage.
    (2) The overcurrent protection setting should be reliable to avoid the rated current of the power capacitor group. The general setting is 1.5-2 times the declination current.
    (3) The protection action time is generally set to 0.3-1s.
    3. Overvoltage protection
    (1) The setting of overvoltage protection shall be set according to the principle that the voltage of the power capacitor terminal does not exceed 1.1 times the rated voltage of the capacitor for a long time.
    (2) The overvoltage protection action time should be within 1 min.
    (3) Overvoltage protection can be selected to trip or signal according to the actual situation.
    (4) Overvoltage relays should have a higher return factor.
    (5) Overvoltage relays should preferably use voltage relays with inverse time characteristics.
    4. Low voltage protection
    The low voltage setting value should be able to operate reliably after the busbar connected to the power capacitor loses pressure. When the bus voltage returns to normal, it will return reliably. Generally, it is set to 0.3-0.6 times the rated voltage. The protection action time should be the backup protection action time of this side. Cooperation.
    5. Single-star wiring capacitors are designed with open triangular voltage protection
    The voltage setting is cut off or broken down by a part of a single power capacitor (or a small capacitor element in a single power capacitor), so the voltage of the remaining single power capacitors is reduced (or a small capacitor in a single power capacitor) Do not long-term sister over 1. I times the rated voltage principle, at the same time. Should also reliably avoid the unbalanced voltage of the power capacitor group during normal operation. The operating time is generally set to 0.1-0.2s.
    The unbalanced voltage of the power capacitor bank during normal operation shall meet the requirements of the manufacturer and the installation regulations.
    6. Single AL-shaped wiring capacitor group voltage differential protection
    The differential voltage setting is cut off or broken down by a part of a single power capacitor (or a small capacitor element in a single power capacitor), and the voltage of the remaining single power capacitor in the fault phase is not set to exceed 1.1 times the rated voltage for a long time. At the same time, it should also reliably avoid the imbalance voltage between the segments during normal operation of the power capacitor bank. The action time is generally set to . .1~. .25.
    The unbalanced voltage of the power capacitor bank during normal operation shall meet the requirements of the manufacturer and the installation regulations.
    7. Neutral line unbalanced current protection of double star wiring capacitor group
    After the current setting is cut or broken down by a part of a single power capacitor (or a small capacitor element in a single power capacitor), the voltage of the remaining single power capacitor in the fault phase (or the small capacitor component in a single power capacitor) is not long-term. More than 1.1 times the rated voltage principle is set. At the same time, it should also reliably avoid the unbalanced current flowing between the neutral points of the power capacitor group during normal operation. The action time is generally set to 0.1-0.2s.
    The unbalanced current flowing between the neutral points during normal operation of the power capacitor bank shall meet the requirements of the manufacturer and the installation regulations.
Parallel power capacitor protection setting formula is applicable to the internal small component wiring first and last string and no fuse, and the external wiring is also the first and then the power capacitor group, or the internal small component wiring is first and then string and fuse A single intensive power capacitor. For other types of power capacitors, according to the specific situation, according to some single power capacitors (or small capacitors in a single power capacitor) cut or puncture, so the voltage of the remaining single power capacitors of the array ( Or small capacitor components in a single power capacitor) are not set for longer than 1.1 times the rated voltage.
    In order to extend the service life of power capacitors, the power capacitors should be reduced and the power supply multiples and times should be reduced. Therefore, under the condition of avoiding unbalanced current or voltage, the protection setting should be reduced as much as possible according to the formula to obtain a higher sensitivity coefficient.